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New PM-25MV Mill

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shooter123456

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Everything is mounted up and tested. So far so good. The spindle threads aren't straight so the top hat wobbles a little bit. I get a little bit of vibration at 5000 rpm now, but it will do just fine.

I tested the drawbar with a 2 inch face mill doing .75" WOC, .1" DOC at 25 IPM and it didn't pull out at all. That is 1.875 cuin/min I was able to make the belt slip and there was no pull out. Right now, the air cylinder can release the tool just fine at 70 PSI, so I can probably tighten the drawbar even more. I just need to seal some air leaks and it will be good to go.
 

macardoso

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Everything is mounted up and tested. So far so good. The spindle threads aren't straight so the top hat wobbles a little bit. I get a little bit of vibration at 5000 rpm now, but it will do just fine.

I tested the drawbar with a 2 inch face mill doing .75" WOC, .1" DOC at 25 IPM and it didn't pull out at all. That is 1.875 cuin/min I was able to make the belt slip and there was no pull out. Right now, the air cylinder can release the tool just fine at 70 PSI, so I can probably tighten the drawbar even more. I just need to seal some air leaks and it will be good to go.
Awesome job. Can’t wait to get mine finished. That’s a hell of a cut for this mill!
 

shooter123456

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Well that didn't take long... I had the day off on Monday and spent the day working on the mill and I conked out the spindle bearings. This was expected since they aren't meant to be run at 5500 RPM, it was just a matter of time.

I finished 2 parts that had a total spindle time of about an hour each, let the machine rest for about an hour and half while I went to the store and got some lunch, then set up some new tool holders (ordered some TTS holders, these things are nice!) and started the third part, I stopped it before the first cut after the spindle had been on for about 30 seconds (height offset wasn't right) and it went from 5500 to zero in like 2 turns. It was almost immediate. I touched the spindle and it was burning hot and no longer rotating freely. Luckily, I had a set of angular contact bearings ready for just such an occasion.

Swapping the bearings was relatively simple. I made a simple tool to remove the lower bearing nut and just used a pipe wrench on the top nut. The top nut was terribly machined, its a lock nut and the slots that were cut into it are nowhere near straight. Not a huge deal, but its a rotating part that will certainly need to be replaced if I want to get it moving faster. The spindle was tapped out of the housing with a deadblow hammer and came out pretty easily. The bearing cups fell right out as well. They were a bit of a loose fit which I was surprised by. I thought I would need to tap them out. Since the AC bearings are shorter than the tapered rollers, I had to turn 2 spacers, but those went on with no trouble. The reassembly was easy enough. I stuck the spindle in my lathe and used sand paper to clean up the non contact parts just so it looked a little better and I touched up the bearing seats a little to remove any burrs or raised edges. I stuck the spindle in the freezer for a few minutes while I heated the bearings and spacers with a hair dryer. The bottom one slid right on and got screwed in, but the top one had to be forced in with the lock nut. It didn't take much pressure to get it to slide on, but it took more than just hand pressure. I reassembled and put it back on the machine to let the bearings break in a little bit. I used regular automotive bearing grease to grease them. The spindle wasn't noticeably quieter with the new bearings, but the loudest one is the very top one which wasn't replaced. I have started questioning whether that one is really needed anyway, but it doesn't get hot at all so I haven't been worrying about it. After 45 minutes or so of slowly ramping up the speed, I started machining the third part. There was no noticeable loss of rigidity from the spindle and all of the same cuts were handled just fine. After about 2 hours of total spindle run time, the spindle was noticeably cooler than with the tapered rollers (again, to be expected).

Here are the new bearings compared to the old ones. I thought these were surprisingly small since my X2 used the same size lower bearing, but a much larger upper bearing. It may not matter, but I figured they would be larger.


Unfortunately, the third part was scrapped as well. There was an issue with the tool offset and I messed up a tool path in fusion. I need to figure out how to do the automatic tool height offset with LinuxCNC. The first part had no problem at all, but the second part had multiple issues with the offsets not working right. I also found the X axis slowly and consistently drifting to the right. The first operation is a roughing pass all the way around the part to get the stock to the right size, and looking at the right side dead on, you can see each pass is slightly farther over. Since it is consistent, I am guessing it is probably an issue with backlash, so I will need to check that before making more parts. Another issue I need to address is with the air cylinder. After sealing all the leaks at the connection points, I was able to hear a slight hiss from one of the exhaust in the solenoid when the other channel is open. When there is air pressure going to the retract side of the cylinder, the exhaust for the expand side starts leaking. I am guessing that air is escaping where one of the spacers meets the piston since there is no seal there. If it ends up being a problem, I will just take the cylinder apart, use some silicon to seal those areas, and go from there.
 

shooter123456

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I couldn't deal with the chips getting everywhere anymore, so I decided to put a short hold on the tool changer to get going on the enclosure. I originally planned to try to do it with sheet metal, but after trying to make a small simple part without a brake and shears, I decided that just wasn't going to happen. Looks like MDF is the material of choice. I used it on my X2 enclosure and sealed with epoxy paint and that held up fine for a year until the PM25 came and that mill stopped being used.

I am not very good at working with MDF or wood, so this might end up being a bit of a hack job. I plan to use plywood for the base and MDF for the body, acrylic for the windows and aluminum for the doors. I am going to machine a 4 piece frame for each door and they will slide on drawer sliders I used on the X2. I am hoping to just use the sliders on the top away from the chips and then something simple to support the doors on the bottom. I ordered 2 LED floodlights to light it up inside and I am planning to make a fogbuster type coolant system to use for the coming months until I figure out how to handle the flood coolant. I will need to do some waterproofing of the electronics before I can do that. I plan to put a chip drawer under the mill to make clean up easier.

As of now, I have all the MDF pieces cut out and almost all of them assembled. I put a quick coat of paint on it before I fully assembled it while everything was easy to access. This thing is already really heavy, so I might stick it on wheels so it can be moved once the mill is in it. The back panel where the tool changer will go is 2 pieces so that one can be removed when I install the tool changer and then when I need to get to it to work on it. The head will stick out the top a little bit, but that seems to be how all of them are. I am going to relocate the control box on the side of the head to the electronics enclosure in the back. I still need to figure out how to control the spindle directly from the computer.

I also made a tool finger to test before I make more of them. The machine cut it fine, but it is too tight on the tool. I will need to make that fit a little bit looser. I also changed the tool finger design so that it will have a spring and lever to hold the tool in place instead of just gravity. This should keep the tools from sliding out if the machine is vibrating, if the tool changer spins too fast, or when it is being pushed into place and retracted.

I solved 2 of my previous problems as well. The tool height issue was user error. When I set the tool off set or touched off, I did the correct T1 M6 to tell it which tool I have, but I didn't do G43 H1 to tell it to use that tools offset. For the lost motion in the X, it was the stepper coupler being a little bit loose. I was able to turn each of the screws in the coupler a full turn and a half so I am guessing it slipped a little bit when switching directions causing the axis to drift.

Here are some pictures.















 

macardoso

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I couldn't deal with the chips getting everywhere anymore, so I decided to put a short hold on the tool changer to get going on the enclosure. I originally planned to try to do it with sheet metal, but after trying to make a small simple part without a brake and shears, I decided that just wasn't going to happen. Looks like MDF is the material of choice. I used it on my X2 enclosure and sealed with epoxy paint and that held up fine for a year until the PM25 came and that mill stopped being used.

I am not very good at working with MDF or wood, so this might end up being a bit of a hack job. I plan to use plywood for the base and MDF for the body, acrylic for the windows and aluminum for the doors. I am going to machine a 4 piece frame for each door and they will slide on drawer sliders I used on the X2. I am hoping to just use the sliders on the top away from the chips and then something simple to support the doors on the bottom. I ordered 2 LED floodlights to light it up inside and I am planning to make a fogbuster type coolant system to use for the coming months until I figure out how to handle the flood coolant. I will need to do some waterproofing of the electronics before I can do that. I plan to put a chip drawer under the mill to make clean up easier.

As of now, I have all the MDF pieces cut out and almost all of them assembled. I put a quick coat of paint on it before I fully assembled it while everything was easy to access. This thing is already really heavy, so I might stick it on wheels so it can be moved once the mill is in it. The back panel where the tool changer will go is 2 pieces so that one can be removed when I install the tool changer and then when I need to get to it to work on it. The head will stick out the top a little bit, but that seems to be how all of them are. I am going to relocate the control box on the side of the head to the electronics enclosure in the back. I still need to figure out how to control the spindle directly from the computer.

I also made a tool finger to test before I make more of them. The machine cut it fine, but it is too tight on the tool. I will need to make that fit a little bit looser. I also changed the tool finger design so that it will have a spring and lever to hold the tool in place instead of just gravity. This should keep the tools from sliding out if the machine is vibrating, if the tool changer spins too fast, or when it is being pushed into place and retracted.

I solved 2 of my previous problems as well. The tool height issue was user error. When I set the tool off set or touched off, I did the correct T1 M6 to tell it which tool I have, but I didn't do G43 H1 to tell it to use that tools offset. For the lost motion in the X, it was the stepper coupler being a little bit loose. I was able to turn each of the screws in the coupler a full turn and a half so I am guessing it slipped a little bit when switching directions causing the axis to drift.

Here are some pictures.
















That's a nice looking enclosure. Would you be willing to share plans for it?
 

shooter123456

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That's a nice looking enclosure. Would you be willing to share plans for it?
I could do that. All I have is a 3D model, but if you have a way to view it, I would be happy to send it to you. Message me your email address and I can send it right over.
 

shooter123456

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I am just about done with the enclosure now. It has the inside completely painted and waterproofed and the stand has the skeleton done. Getting the enclosure up onto the stand was a bit of a challenge, but it got done. I made the decision to put the machine into the enclosure before making the doors since they would make a ton of chips and I can mostly contain them even without doors. The windows are going to be .093 acrylic sheets, and I am considering going with something a bit thicker for the doors just in case something gets flung like a broken tool or workpiece pulled loose. That way, if it is thrown toward me, hopefully the doors will stop it. I removed the spindle control box and it will be relocated to the electronics box on the back of the machine.

I can control spindle on and off easily with the computer, but I have not yet figured out how to control speed. Since I run it at full speed 95% of the time, for now I will just leave the pot with the box and walk around to the back of the machine to adjust the spindle speed. I am waiting on a cable track for the head so I can wire it up nicely. The track will carry the lines for the air cylinder, the spindle motor wires, and the mist coolant lines.

Here are a few pictures. Unfortunately, the glass on my camera is still broken (Just got a new one, need to get it installed!) so there is some flaring of the light.

Empty enclosure. There is about an inch of clearance on each side for the machine to get in. I did this just because I don't have a way to cut the MDF accurately enough to make it closer. I will use some rubber sheets to fill the area between.


Machine in place. Getting the table in there wasn't easy, but hopefully I won't need to do it again for a while.


Other side.


Here is the naked head. There are lots of holes in it that I would like to fill somehow. I will try to re use some of them to mount the coolant head, but I want to get rid of the rest. I might fill them with body filler and repaint it.


I am still looking for a new spindle motor, but so far that search hasn't yielded any good results. I don't think it is worth it to spend $500 or so for a DMM servo as discussed a little earlier. I have not been able to find an AC motor that would work either. The ones I have found are 56C, which will not fit. I was looking for some smaller motors, but I haven't found anything that looks suitable yet. I am looking for something 1 to 2 HP, 3500 RPM or higher, less than 20 lbs, and hopefully $400 or less for the motor and control. It seems like that is a tall order. If anyone knows of a motor that would fit those points, that would be much appreciated.
 

phazertwo

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Looking pretty good. I am patiently waiting to see how your enclosure turns out... I have been dreaming of a sweet enclosure, but also lack the equipment to make something nice out of sheet metal.

As far as a motor, why can't you use a 56C and just let the face be above the top of the mill? As long as the shaft hangs down low enough.

PZ
 

shooter123456

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Looking pretty good. I am patiently waiting to see how your enclosure turns out... I have been dreaming of a sweet enclosure, but also lack the equipment to make something nice out of sheet metal.

As far as a motor, why can't you use a 56C and just let the face be above the top of the mill? As long as the shaft hangs down low enough.

PZ
Its just one of those things... I could probably invest the time and money and make something really nice, but its a supporting accessory. Something hacked together that looks rough and gets the job done faster and cheaper is fine by me in this case. Now if I bought the mill because I wanted to have a show piece I could be proud of, that would be a different story. But in the end, I want to spend that time and money making parts and adding stuff to the machine.

Referring to the motor, when I imported a 56C model from one of the manufacturers, there was not enough room between the air cylinder and column for the motor to go. With it just clearing the air cylinder, it overhung the back of the head and interfered with the Z axis stepper. The other option was to off set it to the side, but that would require either using 2 belts to route under the air cylinder or redesigning the air cylinder to make it work. Neither of those seemed like ideal solutions if there are smaller motors available. On top of that, the motors I was looking at were 26 lbs, compared to less than 10 for the current motor or some of the servo options. I would like to try to keep the weight of the head down so it can move quickly.
 

shooter123456

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In hopes of figuring out who makes the spindle motor and finding more details about it, I took the sucker apart. In the end, I have learned nothing.

It is a 2500 rpm Nema 34 750w brushless motor, it has a small fan under the top cover, with 8 wires. 5 appear to be for feedback, 3 for power. The feedback wires are marked +, -, W, U, V. The 3 larger wires did not have any visible markings.

The only markings on the circuit board inside the motor are:
L3155-HL
13/3/23
H13938
P46S24027

Unfortunately, google did not yield any results that give me relevant information. I had asked Matt for some more information about the motor and control board and he wasn't able to provide anything for me.

If you have ever wondered what these things look like on the inside, here are some pictures.

Top cover off. You can see the weird fan on the top.


Side view with wire cover removed. It looks like this thing melted at some point. It may have been to seal the motor or support the wires, but it no longer does so.


Fan removed. It is just pressed onto the back of the shaft. I am not sure how it works with the blades not having much room for air flow, but it might be to draw air over the fins on the outside of the motor.


Rear panel removed giving me a decent view of the encoder inside and rear bearing. You can also see the cooling fins pretty well here.


Here it is next to the 1000 oz in nema 34 that will be going on the Z axis at some point. The spindle motor is slightly longer, but the same face size I think.


Closer view of encoder and power wires. Soldering doesn't look all that clean.


Shaft removed. The magnets are in the shaft and the coils are in the motor body. Backwards from a brushed motor as far as I know.


Picture of the shaft. The magnets in this thing are rediculously strong. It took some care to get it back in the motor without crushing my fingers or breaking the encoder.


That's all for now. If anyone can tell me anything about the motor, that would be great. I may repurpose it once I pick a new motor for the machine. Maybe to keep costs low, I will swap the motor with the one on my lathe. The lathe has a 4000 RPM 750w brushed motor. That should give me the higher speeds I want, about 8800 RPM with my current pulley set up. The 2500 RPM motor would change the lathe low speed from 50-1000 to 30-625. That would give the lathe a ton more torque and the mill would get the speed I want. Decisions decisions.
 

shooter123456

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The enclosure is about set now except for the doors. The windows have been installed, they are just .093" acrylic sheet and have 6 holes drilled, then 6 matching holes are drilled into the MDF and screws and nuts are used to secure it in place. I made a few parts with the machine and even without doors, I am containing well over 90% of the chips. There are only a few cuts in a few directions that manage to send chips out the front of the enclosure. I got my LEDs installed and that makes a huge difference. They are cheap ebay units, they cost $10 for the 2 of them. They are wired directly into an AC line and come on when the machine is powered up.

I had an issue with the Z axis driver cutting out and dropping the head, which obviously is not what you want when you are spinning a cutter... I lost a part to that and I am not 100% sure why it happened. The drive wasn't hot, but after leaving the machine off overnight and running it with an extra fan blowing on the electronics, the machine cut for probably 6 hours (spindle time, probably 10 hours total on time) with no problem.

For the spindle draw bar, I wired a button into the box where the chip guard interrupt was. I simply took that out, shorted it so that it assumes the chip guard is always closed, then the hole was the perfect size for a button I had on hand. Just wired it in to the solenoid and now when you press the button, the tool releases, release the button and the tool is secured. I forgot to take a picture of that, but you can see it easily in a few of the other pictures I have.

I am going to need to come up with a better work holding solution, because the vise I have isn't ideal. Using the vise, the max usable Y axis travel is a little over 4". In one direction, the vise runs into the way covers, and in the other direction it leaves 2" unreachable past the front jaw. I am considering either trying to find a vise that doesn't stick out as much in the front or making something suitable instead. There are other methods of workholding, but a simple and effective one that cuts your travels by 40% isn't ideal.

I finished making an encoder mount to give the controller some feedback and hopefully increase the reliability a little bit. I know a lot of people aren't fans of encoders since "properly designed" stepper systems shouldn't need them, but I am not an expert, and this system is far from properly designed. $30 for 3 encoders and a few hours of machine time to prevent lost parts due to stalls, drives overheating, etc is worth it for me.

Up next is some pulleys for the steppers and encoders, some motor covers, making the doors, a control panel, and continuing on the ATC. I have some of the parts machined already, now I need to figure out the air cylinder for it and the sensors. I got an inexpensive 7" usb monitor that I think should suffice for the control panel, along with some buttons and switches. I was looking into a motion controller for the machine, but I wasn't able to find one that would run linuxcnc for a decent price. Instead, I may just try to replace the control computer with something a little better.

Here are the LEDs I got. They are 10w each and are plenty bright.


It makes it nice and bright inside. In this picture you can see the button on the side of the head for actuating the drawbar.


Here is a side view through the window. There is some glare off the LED and the cracked camera glass, but you get the idea. The wiring needs to be cleaned up, but in due time. I plan to fix all of that when I make a new electronics box (Not enough room in the current one) and control panel. Here you can also see the drawbar button. The wires and hoses will need to be run through the cable track once I figure out how I want to mount it.


Here is the little USB monitor. It is only 7", but as you can see that is plenty to see linuxcncs interface.


Here it is working on the encoder mount. It is using a 5/8" 2 flute indexible carbide endmill in a homemade holder. Everything is much easier to see with the lights.


Here that part is after finishing everything but the backside. It is looking pretty good for the most part. There were some issues with chatter doing the corners during a finishing pass and there were some marks left by imperfect backlash compensation.


Shiny.


Backside.


Using super glue work holding for this part. It needs just about every inch of the 7" of travel the machine has (actually more like 6.8" due to an error on my end). The stock is 6.5" long. The first part will be done on the mill, then I will mount it on the lathe to cut the outsides down to size.


I need to work on my Fusion skills, because every program fusion gives to run, something like 30% to 50% of the time it spends just moving around and not cutting anything. On this program, it was 45 minutes in total, and 15 of those, it was just walking around doing random whisper cuts.


Lotsa parts getting made. Some of them need some work on the backside done, but it is coming along. There is some corrosion on a few of the parts because I get my material from a recycling center and sometimes they sit outside for a while before I can rescue them. The discoloration usually comes right off with some sandpaper.
 

shooter123456

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I ran into a snag with the enclosure doors, as tends to be the case. I was planning to re-use the draw slides from my old enclosure for the doors. Unfortunately, they are 18" long, and my smaller door is 14" long. That limits its opening by about half, which isn't going to do. I also didn't plan through how to account for the metal bending after machining, and there is a bit of twist in the door frames. I think I can force it to be relatively straight if I have stronger rails on the top and bottom. Also, I cut the long pieces I needed for the doors out of a big plate on the mill, and that took forever. I should have just ordered the stock in the size I needed and saved the time (at 5x the cost though...)

So right now I am trying to come up with new ideas for mounting the doors. I could try using some cheap round linear rails on the top and bottom, but I may run into space issues, since I didn't build enough in between the Y axis motor and the doors. I think I can slide the whole machine back a little bit to make room. I could also try some aluminum angle stock and make some plastic blocks to slide on those. It won't be as smooth, but I think it would be effective. Another option might be using some skate bearings and making some guide rails using an arrangement similar to how a bandsaw guides its blade.

I have a line on a new spindle motor that I am really excited for. It isn't final yet, but I may be getting a 2 HP 6000 RPM motor for it, and I will bump the speed up to about 7500. If that works out, I am looking into adding an encoder to the current motor and getting a servo drive to use that on a 4th axis/lathe attachment. That would be much better than making 2 4th axis attachments, one with a stepper for indexing and 4th axis cutting, and one with a BLDC for lathe work. If I can't make the spindle motor a servo, I might just forgo a true 4th axis, and instead do what Tormach does with their Rapidturn and have a motor + indexing plate.

Here is how I cut off the stock for the doors.


Then they were held like this to cut them to size and such. I spent probably 15 hours with the spindle running to make the 8 brackets. There must have been better ways, but I made tons of chips and the machine ran well, so it works for me. Also, you can really see the button here. It is almost like that part was made for a power draw bar button.


I didn't take a picture of the finished parts because I wanted to solve the mounting problem first. They are going to need some clean up and a coat of paint though.

I also turned the tool platter on the lathe to remove all the excess material. That part is done now, which I figured would be the most difficult of all the tool changer parts. I have started on the air cylinder for it and I am waiting on stock for the tool fingers.


I could have sworn I took a better picture once this was done, but I don't have it now (anyone else have a galaxy S8+ that has disappearing images?) This is the best I have at the moment.


The machine is coming along! Working out issues as I go seems to be working, and each little upgrade makes the machine (and me) much more productive. Hopefully that continues until it is making parts faster than I can keep up.
 

shooter123456

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Also, I figured it was time to update the total costs so far. I am adding this info since I rarely see it about others machines which makes it hard to tell what you will spend to get a certain result. Hopefully this way, if someone else is researching the way I was and trying to figure out what it will cost for a machine like this, they will see this and get a much clearer idea. If it isn't useful to anyone else, at the very least, it can help keep me organized in case something breaks and I can't remember what it was when I go to replace it. If anyone wants links to the parts I used and where I got them, let me know.

I figured I would break it down by area so it isn't one huge list. All costs include shipping.

General Machine Parts:
PM-25 mill - $1649
4 inch mill vise - $100
4 TTS holders +1 ER20 collet - $126
6 TTS knock offs (non atc collar) - $90
5 Homemade TTS holders - $30
Total: $1995

CNC Conversion Parts:
2 400 oz in Nema 23 steppers - $67
1 1000 oz in Nema 34 stepper - $69.79
2 DM542T stepper drivers - $67.90
1 DM860T stepper driver - $53.95
1 550 mm SFU1605 ballscrew - $65
1 750mm DFU1605 ballscrew - $0 (Details below)
1 350mm DFU1605 ballscrew - $0 (Details below)
6 7001 AC bearings - $15.54
3 flexible couplers - $15
350 watt power supply - $30
240 watt power supply - $20
Break out board - $10
Aluminum stock - $10
Total: $424.18

Enclosure:
2 48x96x.75 MDF Sheets - $72
5 2x4s - $15
1 box of screws - $9
3 Acrylic Sheets - $36
2 can of Epoxy Paint - $30
2x 10 watt LEDs - $11
Total: $173

Automatic Tool Changer:
Air Cylinder Stock - $50
Air Cylinder Seals - $20
Air Cylinder Connectors - $5
5 Way Pneumatic Solenoid - $20
Fasteners - $30
400 oz in Nema 23 - $33
6205 Ball Bearing - $3.11
Linear Guides and Bearings - $34
Aluminum stock - $25
Total: $220.11

Grand Total - $2812.29
 

shooter123456

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I realized I mentioned I would document the deal with the ballscrews, then forgot and never did.

I ordered a pair of double nut ballscrews from linearmotionbearings2008 on ebay. I was quoted $100 for the 2 screws and 2 double nuts, shipped to me, machined to my specifications. I knew that price was low, but others had reported good experiences and received a good product, so I said what the hell, and took a shot. They were made and shipped, I received them about 2 weeks after I placed the order. First thing that was a problem was the packaging. It was packaged in a flimsy cardboard box, and the ballscrews were wrapped in bubble wrap. There was nothing to protect them from being bent.

The second problem was pretty obvious from the picture below.


He had sent single nuts, not double nuts. Oh well, it happens. I contacted him and he apologized and sent a pair of double nuts the same day. I received those about a week later. In the mean time, I inspected the screws. They were indeed not straight, with the long one being much worse than the short one. The actual bend wasn't so bad, it was probably around .05" for the long one, and .03" for the short one. The real issue was the end machining. First, none of my stuff fit. The bearing journals were oversized (by about .01") so it took a lot of sanding to get the bearings to fit. That is where I found just how straight the end machining was. When I chucked it up in the lathe, holding one end in the 3 jaw and the other end in the steady, while both ends had runout less than .005", the middle was wiggling at .375", if not .5". It was way off.

Then the double nuts came.
The first thing I saw was the grinding job done to make the screws and keys sit flush. Looks like someone just put them together and used a bench grinder to grind it flat. In the process, taking the head off the screw making it very difficult to remove. When I tried to thread them onto the screws, neither one would thread past the first nut.




Removing the screws was rather difficult, because they were soft, and had almost no head left. I eventually did get them removed and put them on the ballscrews. Then it was pretty clear why I couldn't get it to thread on. With the keys removed, this is where the two nuts met, with no pressure added.


Taken apart all the way for further inspection found that the key ways were not milled straight and they weren't on center. The faces that met each other also were not ground, and there were some nasty burrs. Both were also full of grinder dust.


A closer look at the screws showed some of the threads were stripped out. I got some replacements which showed that 3 of the 4 holes were not tapped straight.


All of these issues meant the screws and nuts were basically unusable without significant work.

I told the seller about my concerns, and the response was very unprofessional. I won't go into detail, but he said that was the first complaint, these screws and nuts are actually very high quality, the double nuts are precision adjusted for backlash under .0006", and he has already lost money on the transaction because he had to send the double nuts that they messed up the first time. After some back and forth, he tried to get me to send them back to him on my dime, I refused because that cost was huge, and it was their problem to fix. Then they offered to remake the screws if I paid the $46 shipping, I again refused stating that I did not want to pay extra to get what I was promised the first time. Then they offered a full refund asking me to ship them back if the cost isn't too great so they can check them and try to improve. The cheapest quote I got for the slowest shipping option was $296. I have no idea how he was shipping them here so cheap, but I did not send them back.

It took a lot of work trying to get the preload set somewhat well, but these screws are still very rough and because of the bend and poor end machining, there is some oscillation as the axis moves. As a note, the nuts and screws were significantly lower quality than the ones I got for the X2, and even after I spent a lot of time trying to get them preloaded, the backlash is still about the same as with single nuts. So I am using these screws for now while I look for replacements. I check ebay often looking for some ground options I can afford. Some have come up that are close, but nothing is just right.
 

macardoso

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I realized I mentioned I would document the deal with the ballscrews, then forgot and never did.
Sorry to hear about your experiences. I originally purchased Roton screws, but wasn't the most pleased with the backlash and lead error (although the screw and nut quality was quite good). Really this isn't their fault as they are commercial "transport" grade screws, not precision ground units. I had looked at your supplier for screws and was still actively considering them, however based on your experiences I may pass them over. Unfortunately there aren't many offerings for low cost precision screws for us hobbyists.
 

shooter123456

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Sorry to hear about your experiences. I originally purchased Roton screws, but wasn't the most pleased with the backlash and lead error (although the screw and nut quality was quite good). Really this isn't their fault as they are commercial "transport" grade screws, not precision ground units. I had looked at your supplier for screws and was still actively considering them, however based on your experiences I may pass them over. Unfortunately there aren't many offerings for low cost precision screws for us hobbyists.
Given the price I was quoted, I went in expecting them to be crap, hoping they would surprise me. They did not surprise me though so I got a decent deal and some day, I might try to fix them. I have thought about pressing a sleeve onto the bearing journal and threads that are off, then trying to machine it in line with the ball races and stepping up to the next size AC bearings. At the very least, I don't think I could make it any worse.

You are right about the screws. The options are few and far between unfortunately. I found another place that sells ballscrews that look a lot nicer, but they are priced accordingly. Anahiem automation is the site, and they have 1605 and 1610 DFU screws available for $236 for 1000mm max length screws. But they are still rolled and C7 accuracy. As soon as you step up to ground, the cheapest I have found start around $485 each. For 3 axes, that costs almost as much as the entire mill, which just doesn't make sense.
 

macardoso

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Anahiem automation is the site
I've looked at their products and have been impressed. They seem to have quality products at less-than-industry prices, but still higher than a hobby machine deserves. Another thought would be to work with Automation Technologies to get the screws you need. I'm pretty sure they come from the same place as your screws, but as a US based company, you can probably have a little more luck with making sure your screws come straight and concentric. Worth a call at least.
 

GunsOfNavarone

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I have had the chance to play with the mill a bit more and get started on the CNC parts. I forgot just how much fun it was turning handles and how fast simple operations can be.

I modeled up the conversion parts I will be using. I am going to need to make 15 total parts. I am currently shopping for a new X axis ballscrew with double nuts and a nema 34 for the Z axis.
View attachment 256296

The machine is very capable and leaves a very nice finish in aluminum. It has been able to hold .001" without much effort on my part. If I tried a little harder, it would certainly do better.
View attachment 256297

A couple of weird things I have experienced so far:
1. When I lock the X axis gibs, the Y axis tightens up and becomes harder to turn. The only thing I can think of that would cause that is the saddle distorting when the gibs are tightened.
2. There is a point on the X axis where it starts chattering a bit in deep cuts. It is only about half an inch that it happens so I figure it must be something with the leadscrew, or maybe a low spot in the ways.
3. There is a slight delay from the spindle motor when you start a cut. When the cut starts, it pauses for maybe half a second while the RPMs drop, then it jacks up the torque and gets the spindle back up to speed. It takes way longer for this motor to respond than the brushed motors I have used.
hey shooter, now that you have many pounds under your belt on the pm-25, do you have any regrets not going with the PM-727? I am right on the edge of ordering the 727 (my first mill) but is the 25 capable enough? I assume that since you purchased it to immediately upgrade it to CNC, ( and your parts look great!) The 25 must be a pretty strong contender for a first mill?
 

shooter123456

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hey shooter, now that you have many pounds under your belt on the pm-25, do you have any regrets not going with the PM-727? I am right on the edge of ordering the 727 (my first mill) but is the 25 capable enough? I assume that since you purchased it to immediately upgrade it to CNC, ( and your parts look great!) The 25 must be a pretty strong contender for a first mill?
When I was looking at a new mill, the PM-727M was also one that I considered. For me, the PM-25 won for a few reasons.
1. Factory belt drive with the spindle going to 2500 RPM. The PM-727M uses gears and a single speed motor, which meant it would be a little less flexible, and speeding up the spindle would take a lot more work. The PM-727V has a 1.5 HP BLDC motor, but still had the gear head and was $600 more than the PM-25. Bumping up the PM-25 spindle only required making 2 new pulleys. The 727 would probably need to have the head taken apart, the gears removed, potentially draining the oil, then redesigning the motor mount, maybe replacing the motor (not sure if it can be run variably with a VFD), buying a VFD to get variable speeds, then making the new parts. Just a lot more work.
2. The extra X axis travel. The PM-727M and the PM-25 have the same table (I think, not 100% sure, but same size) but the PM-25 has 20.5" X travel while the PM-727M has only 15:. This means that the 727 will have a stronger table since the saddle is longer and supports an additional 5.5", but having only 1 milling machine, that extra travel was worth the loss in strength.
3. Being similar to the G0704 meant that there would be more info related to the CNC conversion out there. That meant less design work from scratch for me.

While I don't doubt that the 727 is a stronger and more capable machine, I don't regret my choice at all. The PM-25 is more flexible (and I mean that like being adaptable, not flexible like flimsy) in my opinion which is what I needed. I can say for sure that the machine is strong and capable, and very well made. So far, the limiting factor in terms of heavy cuts has been the spindle motor. It usually starts struggling before rigidity in the machine becomes a problem. So far, the heaviest cut I have taken is 1.25" wide, .05" deep, at 52 IPM. It was with my 2" 4 flute face mill, which gave me an MRR of 3.25 in^3/min. I think the motor still had some strength left, but the belt started slipping when I went higher.

I hope that helps make your decision! If you have any specific questions, I would be more than happy to try to answer them.
 

macardoso

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hey shooter, now that you have many pounds under your belt on the pm-25, do you have any regrets not going with the PM-727? I am right on the edge of ordering the 727 (my first mill) but is the 25 capable enough? I assume that since you purchased it to immediately upgrade it to CNC, ( and your parts look great!) The 25 must be a pretty strong contender for a first mill?
I also wrestled with the mill size question. I purchased my G0704 from Grizzly when I was just starting out in the hobby and had outgrown my Sherline "mini mill" (micro). The machine out of the box was really quite nice, and I did eventually CNC it because it was a fun project. Today, (5 years later) I am feeling like I am just running out of space and power on the machine. I would love a larger machine (RF45 or larger) and will probably upgrade. That being said, I think it all about the kind of parts you want to make, how much you want to spend, and how capable you are to design your own CNC conversion (if you choose to do so).

I will say that the extra 1.5" of Y travel on the 727 would go a long way as that is where I am the most limited on the G0704. I rarely need the full 18" of travel in X. The 727 also weighs quite a bit more would would likely lead to better rigidity (the biggest issue with all <2000lb machines). In the end, you will have a great time with either machine, just understand everything will have its limitations.
 

GunsOfNavarone

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I also wrestled with the mill size question. I purchased my G0704 from Grizzly when I was just starting out in the hobby and had outgrown my Sherline "mini mill" (micro). The machine out of the box was really quite nice, and I did eventually CNC it because it was a fun project. Today, (5 years later) I am feeling like I am just running out of space and power on the machine. I would love a larger machine (RF45 or larger) and will probably upgrade. That being said, I think it all about the kind of parts you want to make, how much you want to spend, and how capable you are to design your own CNC conversion (if you choose to do so).

I will say that the extra 1.5" of Y travel on the 727 would go a long way as that is where I am the most limited on the G0704. I rarely need the full 18" of travel in X. The 727 also weighs quite a bit more would would likely lead to better rigidity (the biggest issue with all <2000lb machines). In the end, you will have a great time with either machine, just understand everything will have its limitations.
That really leans me towards 727 again. All good points as well. I would love CNC, but the expense! I wouldn’t even know what software to control it. It would have to be a premade kit as I don’t think I have the attention span to wing that over months. I have seen kits for $2500 and up, right now that sounds crazy, one day I know I’ll be chomping at that bit. Is the 727 just out of the question for CNC?
Thanks everyone for the help, my apologies if I hijacked this thread...
 

macardoso

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one day I know I’ll be chomping at that bit. Is the 727 just out of the question for CNC?
So take anything I say with the understanding that I have done a few CNC conversions and feel pretty comfortable with the process. Basically all hobby CNC conversions are: design a few motor mounts/bearing blocks, machine ballscrews, hook up motors to control electronics, and plug into a PC. You can take it to any extreme that you want but you could probably do the whole thing for <$1000 on a budget. You will need some design abilities, machining capabilities (you can use your shiny new mill to make most of the parts, but if you need to modify the machine itself, then you need another tool), and comfort with basic wiring. The big question is, do you really need it? Many of the components I make actually could be done on a manual machine in less time than writing a program or jogging the machine. But there are certainly others which absolutely need CNC to be made.

My thoughts in short, think what kind of work you want to do on it (a manual machine is very capable by itself). If you want a CNC, and are comfortable designing and making your own conversion, either mill works fine. If you will enjoy the building of the CNC then it can be a ton of fun to do just that (and save money), but if you need to have a machine working as fast as possible, buying a kit accomplishes that.
 

GunsOfNavarone

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You know, that brings up a really good question and I have been pondering for weeks.....haven't gotten up the nerve to ask yet. What if you need to mill something let's say 5/8" thick and let's say at one end it comes to a taper. That is, say the Y measurement is 3" but tapers down slowly, at a 4 5 degree angle to 1/2" along the Y. This requires the X and Y to be turned at a specific ratio to one another. How would you do this w/o CNC....this is why I KNOW I will need CNC....unless there is a common way to do this that I am unaware because.....well, I haven't learned that among many things right now.
 

macardoso

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How would you do this w/o CNC
Use a swivel milling vise. Set the vise at 90* square, mill your one side, the loosen the vise, set to whatever degree your wedge requires, then cut the second side. Gets tricky, but there were probably a hundred years of people machining stuff w/o cnc.


The other way (if the part can’t be held in a vise) is to clamp it to your mill table with hold down clamps and use an indicator to set the angle. Basically you do some trig to say that over a distance of 4” you should have a change in Y of something. Use the handwheels and a test indicator to measure where you are at and tap it into alignment with a mallet. Tedious but perfectly doable.
 

GunsOfNavarone

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Yeah, I thought that about life before CNC, the “old timers” probably did this without batting an eye. Your first technique sound doable, the 2nd sounds tricky as hell!
 

mksj

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Nice conversion on the PM-25, your saga with the ball screws is similar to others posted experiences with the least expensive options. There are some reputable sources from China, usually a bit more cost but sometimes spending a bit more, one ends up with not having unusable products. What always is shocking to me is that you can buy these parts from China have them shipped to you for far less than just the cost of shipping it back to China if there is an issue. I am glad at least you got a refund. On some items, Chinese sellers just send you a new part because of the cost of returning the item. The positive side of buying through say eBay is at least you have some recourse if the product is defective or not as described. I pretty much have stopped buying anything direct from China because of the issues mentioned, along with long delivery times and very poor packing which often results damaged parts.

There needs to be some consideration if CNC conversion is a dream that it would be nice, vs. buying a mill with the intent to convert to CNC. Also the scope and type of work, along with the build budget. Almost every CNC conversion with smaller mills, individuals will mention that it would be nice to have more travel. When one looks at the machine footprint/floor space, once you build an enclosed cabinet, there might be 25% difference between what you would need for say a PM-25 vs. PM-932. Just mentioning this, because table travel becomes a significant factor. If your intent is to mill, then the PM-927MV would be a good choice with limited floor space, if your intent is to do a CNC conversion down the line, the PM-30MV would be my first choice due to the increased travel and 2Hp motor vs. the PM-25MV.
 

shooter123456

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That really leans me towards 727 again. All good points as well. I would love CNC, but the expense! I wouldn’t even know what software to control it. It would have to be a premade kit as I don’t think I have the attention span to wing that over months. I have seen kits for $2500 and up, right now that sounds crazy, one day I know I’ll be chomping at that bit. Is the 727 just out of the question for CNC?
Thanks everyone for the help, my apologies if I hijacked this thread...
Everything is a trade off, you just need to decide what you can live with trading away and what you really need. I have converted 2 machines to CNC and sort of built a CNC lathe from scratch (its mostly done, just back burnered for now) and you really can do it for as much or as little as you want. I don't think I would ever spend $2500 on a conversion kit, that just seems silly to me. Some motors, electronics, and ballscrews is really all you need to get it going. I typically upgrade along the way as is needed, but a lot of the cheap stuff I get at first has never needed to be upgraded. I prefer to make mounts just because they are so simple and easy to do.

The 727 is absolutely not out of the question for CNC. There were just a few specific things I wanted that the 727 would have been more difficult and expensive to accomplish. Mainly related to the spindle and spindle motor. I have no doubt that the 727 would make a fine CNC mill.

Also, you didn't hijack the thread. This is right on topic in my opinion.
 
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