9x20 Lathe CNC conversion

Do you have any further info on what you did for a spindle pickup? Did you used a single tang mounted inside the headstock or a wheel mounted on the exterior at the rear?

Also, I noticed you did away with the floating bearing mount on the z axis and now just have the motor mount and coupler supporting the screw. You found it wasn't needed? Will this change when you mount a ballscrew? Do you plan on covering the ballscrew at all with guarding?

I have heard the turn version of Mach3 is far from polished. It's unfortunate there isn't the support for it. I have been leaning toward going with a Dynomotion KFLOP/KSTEP setup for my builds.

Thanks again for the great documentation of your build and for answering my questions. There are not many recent 9x20 documented builds out there.
 
the bearing at the coupling end was causing a problem in the cutter pattern because of the leadscrew being poor quality ( warped ). removing the front bearing stopped the screw from moving the apron up and down with screw deflection and made no difference in backlash because the endbearing is a thrust bearing. I will probably install the ballscrew the same way it adds a bit of flex without backlash and makes screw alignment very easy.
i am on the email list for dynomotion forum posts on the kflop/kstep on site and decided to not use one because of all the hand coding and problems i have read in posts for the initial setup. it looks to be a great product but requires a lot of coding knowledge. so i went with the uc100 on my mill but do not use a uc100 on the lathe yet it has a problem with spindle sync at this time and will not thread. i have been beta testing for them almost daily by email from hungary but there are still problems to work out. a lathe will work fine with just parallel and dont really need more than 50ipm for anything i can think of.
as far as the spindle pickup i use a infared sensor and reflective tape it is sending a perfect square wave. i purchased a slotted wheel sensor and buffer prior to using the oscilliscope but now i know i dont have to install it. the problem i was having was with the uc100 so i now run parallel port it is real time sync.
there is a cover above the screw that keeps all the swarf off the leadscrew it moves along with the apron retracting in and out of the belt cover. its hard to notice
steve
 
sure that would be an option instead of the gender changer. the option came up when using a uc100 or not with the same parallel cable. i have had good luck with everything i have purchased off of ebay as far as working but you have to be careful about the power supplies not being big enough (amps) or too low of a voltage. you really have to read the add and not just go for the cheapest. the seperate drivers and power supplies work better than the tb6560 boards with everything built into one, i have 2 tb6560 boards running, one on a sherline mill and one on a sherline lathe and they are good for that. anything bigger and they go poof too often. i have never owned geoko drives so i know no comparison. but what i do know is these guys are really competitive on ebay and to make the kits sound better they will fudge a bit on the specs. they may say the motor will be 880 oz/in but the power supply you get will never get that kind of power out of the motor because it is too small. or the motor is high power high speed but that requires twice the amperage your controller is rated at so you never get to wire it to get those results.thats the problem i'm having threading on my lathe. the motor drops in power rapidly as the rpms go up, so to move fast to thread i need a faster lead screw pitch and a bigger motor to get those speed or drop the spindle rpm really slow resulting in a poor finish on the thread. the ideal in cold roll i have found is to thread at about 600 rpm but that requires over 30upm feed to do 20tpi (not exact math) i start to falter above 20ipm right now so i have to drop the spindle rpms conciderably on course threads. if i wasnt threading the lathe works really well.
steve

I forgot to mention I am mostly referring to your mill with 3 axes.

OK. I was just wondering if the power supply sold at keling like 60v - 20 amp would handle the loads a little better. Most of the time you are just running 1 or 2 axes so having that much reserve power might be benificial rather than having 3 separately wired supplies.

(still referring to your 3 axis mill) Another option may be wiring 3 of the ebay power supplies in parallel. I would think that running 1 or 2 axes on one 18 amp circuit would be better than running 1 or 2 axes on 1 each - 6 amp each supplies. Of course if you run all 3 axes at the same time you would be getting the same amount of power to each axis as having them wired separate but you would have the advantage of 3 power supplies running only 1 or 2 axes when not.

I don't know if any of the above makes much sense to you or if you have already done it or considered it?

Edit: I just realized that your z axis is a much larger motor with it's own power supply built together with the driver. I guess we would just be talking about 2 supplies. One for your x and one for your y. I guess the same question applies for 2.
 
the motors and power supplies were a package deal and they work great the way they are
a big power supply costs more than 3 smaller ones (i have 4 axis on the mill ) and allows me to shut one off when not using the 4th axis.
and z is bigger for the 4200 motor
steve
 
Steve, with tax return in hand, I am spec-ing out what parts I need for my HF 9x20 conversion. I like the way you have gone with your conversion and would like to duplicate much of it. There are some changes: motor mounts, ball screws, etc., but I would like to use your design as a base line for my effort.

Would you be willing to put together a short list of dimensions, materials, approaches that you used?

* What size lead screws did you use (Z & X)
* What thickness of stock for the motor mounts
* What size and grade screws, nuts, bolts
* Size and source for the bearings
* Dimensions of the X motor assembly and how it effected your X travel distance
* Sizes of your motors
* Size and source of your power supply
* Where did you get that case? Did you make it yourself with sheet metal (I like it)
* Any drawings you might have
* How you determined mounting height for the Z screw (I figured I would make the end mounts vertically adjustable)

I have some Keling NEMA 34 460 oz/in steppers that I was going to use. A NEMA 34 motor seems a bit large (physically) for the X drive. Did you find any problems with that?

I'm interested in the sheet metal brake you have. Could you post a picture? I would like to get one myself, but have no idea where to start. My last use of a brake was 60" brake in middle school shop class - doubt I would find one like that cheap. A 36" would be nice though.

-Freeman
 
hi freeman
thats a lot of questions lol
what i'm using for motors now are nema 34 880 oz/in
i have the parts now to change the z axis to 1605 ballscrew and a nema34 1600 motor, I want more speed for threading at higher spindle rpms
there was plenty of room for the nema 34 motors (and the 1600 will fit )and once the lower half of the apron was removed mounting the ballnut is easy with plenty of room. the best these 880 motors would do on the 10tpi screw is 30ipm and that is even less in mach3 while running in spindle sync more, as low as 20 so to thread a course thread i had to run the spindle under 150rpm. thats not a problem at 16tpi but at 8tpi the motor would have to run at less that 100rpm and mach3 spindle tach wont work under 100 rpm. so you can see my need for speed. the x axis motor mount is a single block milled out to fit and there is a ridgid coupling turning the original screw from the back. it has worked very well with the 880 motor and no changes are needed there. the only thing is the alignment of the motor, screw and nut have to be exact or there will be binding and premature wear of the nut. i made a tool to align everything then install the motor with screw attached.
if you dont plan on threading smaller motors will work but i mainly wanted the cnc lathe for threading without changing gears. I would not build one with smaller motors and be happy with it.
I made the enclosure and tried to match its shape to the original covers, the 30in box brake shear came from harbor freight and it is 400 if you dont get a discount or coupon. it is a really nice tool that works great for 20 gauge.
I didnt draw anything i just cutout the parts and fit them together. i measured the existing bolt holes in the fron of the bed and used them to locate my cnc parts. the only alteration to the lathe was threaded holes in the back of the cross slide to mount the motor on the back for x. the lathe could be returned to original in about a half hours time.
I think there is a parts list in the beginning of the thread for the motors and electronics, it is really basic nothing fancy just 2 axis. i control coolant and spindle manually.
steve
 
Thanks Steve for responding.

The only real surprise was the size of the motors. I've never seen numbers for response time mentioned in motor specs. Do stronger motors equate to faster motors, or does it have to do the with overall inductance in the motor itself? Do you need 1600s on both axis or just the Z axis to address the threading issue? I wouldn't expect to need much more than I have for the X axis.

Is the brake this one from HF?

http://www.harborfreight.com/30-inch-shear-press-brake-and-slip-roll-5907.html
 
your motor would work with x fine with a ballscrew but not with a 20 tpi screw
the x axis really does not need the power that much but when you are contouring the axis's move in conjunction with each other. so a really slow x and with a 20 pitch screw has to turn twice as many rpm to match the same amount of z movement. when contouring the slowest axis determines the fastest movements available and everything slows down to its speed. the slower a stepper motor turns is when its at it's highest power. thats why they give you a ratings for motors at holding torgue. the faster it pulses by microstepping or higher speed the less power it has. if you think about a fine pitch screw compared to a course pitched screw the fine pitch is easier to turn but because it causes a stepper to turn faster you are loosing power at a faster rate than the torgue you would gain in a finer pitch. so a high pitch screw with a stepper gives more power. by making it a ballscrew you remove most of the friction a course thread would have and then most of the torque is now available for movement not overcoming friction caused by the higher pitch. it took me forever to understand all this it all seems backwards but stepper motors are totaly different in function they look to be rotating smoothly but really they are jumping a step at a time to the next location with a pause in between each jump. the electric stored in the winding takes time to drop before the next pulse comes, if it gets there before the last pulse has dropped to nothing they work against each other. also it takes a certain amount of time for the coil to charge so to make that faster the voltage to the controller is raised to force the coil to charge faster. steppers run at up to 10 times their rated voltage because of this time needed. the motors coil never reaches that 48 volts your power supply may be putting out before discharging. the extra voltage makes it reach its rated voltage faster making the motor more powerful at higher speeds. electric is not instant it takes time to move and the pulse is so short at higher rpm the voltage got high enough to produce any power.
thats probably way more than you wanted to know. but its why you want the biggest strongest motor that will fit you can afford if you dont want to compromise somewhere else like not getting to microstep and running rough and loud.
yes that is the brake it works really well, it has a poor finish rough castings but what counts works perfect. northern tool asks about 600/700 for it i think and the same one from wholesale tool is about the same, they are identical.
you can put small motors on a cnc but to really get one to be a machine to produce, you need power. a friend has one that is so underpowered it will only make .005 passes at best in aluminum it takes all day to make a part. granted it gets it done it's not worth spending the money to accomplish that little amout of production unless its to just play with it like a toy. i have sherline cnc and they were great for learning, cost about 3500 new and my zx45 mill cost less than 5000 to build 4 axis, will snap a 1/2 4 flute mill like nothing if you make a wrong move. it does not care if its in steel or aluminum it just keeps cutting.
steve
 
Thanks Steve, this was exactly the level of detail I wanted. I think I understand what you are getting at.

So, I should be fine with the Keling 460 oz/in motors for both Z and X as long as I use ball screws. I'm planning on a 1605 ballscrew for the Z and I have a smaller diameter ballscrew for the X. I'm using Gecko 203V with a 72v 20A power supply.

What thickness stock are you using for your motor mounts? It looks like 5/8".

I saw your comments on Mach 3 Turn and Mach 4. I'm now a bit nervous about the conversion until Mach4 comes out. Maybe purchasing a fully functional manual lathe would be a better option at the moment. What is your opinion?
 
the z motor mount and thrust bearing mounts are the same distance out from the bed so 1/2 will work, i just used scrap i had and it is probably close to 5/8. the thrust bearing thick section is 1" and there are 2 thrust bearings in there. center bore is a loose fit to allow the shaft to self center, nothing precision it just maintains backlash and the screw is actually floating with no endplay. that keeps the motion of the screw turning from affecting the finish. the screw i used was not very straight and a ridgid mount showed it up in the finish when everything was too tight. so thats why the front bearing at the motor end was removed and the thrust end left to float. i have no backlash and it worked really well for being so unorthodox.
as far as mach3 i start with i'm a novice at lathe cnc and I would not use my comments as advice i'm hoping someone straightens me out and puts me on the right track lol
if i had to do a big run of parts i'd figure out how to do it and tweek everything until i got what i needed it to be but there are other factors involved like cutter deflection so it will always take some fine adjustments. the mill is live tooling and a lot more predictable than a lathe operation just because you dial in a .010 pass does not mean your going to get a .010 pass exactly on any of my lathes there is always little differences. these are things i have to learn yet.
steve
 
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