Another obligatory New PM-833TV and PM-1340GT Ordered!

[Christianstark]

This recently came up in another posting, they are not parallel to each other, it makes no difference as long as you use the same method/position to measure if there is any bed twist. I prefer to use 123 blocks on the flats of the ways, in particular when using a longer level that will not fit on the cross slide.

New PM-1236T Lathe has arrived

It is probably alright for most lathe work. But I have a milling vise that I want to use on the lathe as a backup milling option. I can't do accurate milling with a vise that runs downhill with respect to the spindle. I have reached out to P.M. for a solution. They are contacting the factory. I...

www.hobby-machinist.com

I have been doing some reading on the cross slide not being perpendicular to the spindle as well past few hours. The one thing that troubles me is that most have said that the lathes are set up to give a slight concave or dish to facing cuts to make faced parts fit tighter. I get that. What I am seeing is I will be getting about .004" over about 7" CONVEX cuts when I align my head stock again.I guess hobby machining is a balancing act of compromise, huh?

 

[mksj]

I would go back and read the full thread, I am not aware of any manufacturer where that would be intentionally the case. I would start over when you get a precision level, then check the headstock alignment using Dollie's dads method to start with and then you can do a light skim cut on some 2" diameter aluminum stock say out to 6-8" or do a two ring test. You can do some final tweaking if needed. A skim cut facing a disc should measure the same across the face, there is no dishing in the cut. I am not sure why your test bar is so far off, but your headstock alignment would appear to be way out of alignment at this point.

Cross slide not square to spindle

Hi Guys, I have a 10” Atlas lathe will a milling attachment. I had a fly cutter in the spindle, when taking a standard flat cut across a piece of metal in the vice I noticed the back rotation of the tool was taking a significant trailing cut. The tool was set at about a 3” diameter. From this I...

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Take a look at this old post, this is how we checked the headstock alignment on an Acra 1640TE

NEW ACRA 1640TE

Come on Paco, spin the chuck by hand, we need to see chips. lol There's always a couple of little glitches when you dive into a project like this. Greg

www.hobby-machinist.com

 

[Christianstark]

Have you put an indicator on the carriage - reaching out about 10" and down to the bedways, and run the carriage back and forth? I have seen situations where a badly adjusted gib on the back of the carriage or the handwheel that engages the rack along from front of the bedway casting has caused the carriage to lift. And have you checked the bedways for flatness with a straight edge and feeler gages to ensure it isn't shaped like a banana?

So I checked this out just now. Mag base on flat side and DTI on flat side, No runout. Stayed 0 the entire run. Mag base and DTI on prismatic side, sweeping top of prismatic 0 runout. Mag on peak and DTI reaching across to flat. 0 run out.

but...

Mag on flat side of carriage, and reaching across to the top of the peak, I can measure .001" over the closest 12" to the headstock. This could be contributing to the taper closer to the head stock for sure. Would account for some of the .004" diameter discrepancy. About half I recon. Another factor could be deflection. The unsupported tail stock side is larger in diameter than the cut at the chuck.

Here's a question regarding twist. If I discover twist close to the head stock (Where the machine is most rigid I assume) would I make small adjustments to the head stock side (4 bolts on that side to level) to try to cant the headstock to force correct the bed? I feel like if I adjusted at the tail side, I would need to move the bed significantly to correct a one thou issue in the last 12 inches of travel to the head stock.

@davidpbest and @mksj Just wanted to pause for a moment and thank you for all your input here. Above and beyond.

 

[jaek]

Do you have a set of instructions for lathe alignment that you are following? A methodical approach helps immensely with this kind of thing - measure and adjust one thing at a time.

It's possible to measure twist in the lathe bed directly without a precision level if you have a straight-edge and a v-block. Put the v-block on your prismatic ways at one end of the bed and a 1-2-3 block on the flat ways at the other end of the bed, span them with a straightedge, and measure the height of a point on that straightedge. Then flip everything around so the straightedge goes diagonal the other way and measure the height of the same point. If the bed is not twisted, the height will be the same. If the heights differ, you can shim or level the appropriate feet.

The pictures are measuring the tailstock ways but you should measure the carriage ways. Should probably also use a dowel pin on the v-block vs a random chunk of aluminum, use an adjustable parallel to make the v-block and 1-2-3 block the same height, and use a straightedge with a nicer surface finish.

 

[Christianstark]

Just a side note, something I have thought about while leveling the lathe the first time around, and then this most recent time. I kinda wish the lathe was HEAVIER. I find that adjusting the feet will occasionally lift other load point to where it is not touching. Say like jacking up the front tail side I will sometimes find the rear tail side is lifted off its pad.

If I had this to do over again, I would drill and anchor studs into my slab, and then make the adjustments on those studs, with a nut above and a nut below the stand so I can (once very close) force the bed to do what I want it to do, even if gravity is too weak to do it. The current system now, where the stand is threaded for adjustments, and then a locking nut is beneath the stand itself is a mid of a PITA. I wonder if I put the Jam-nut on the wrong side of the equation now. trying to lock the adjustment actually lifts that point due to slop in the threads. and each threaded point is slightly different. Therefore you spend hours making slight adjustments to level the lathe and minimize twist, and when you finally get the Bubble where you want it and try to lock it down with the Jam nut, you move the lathe.

I may make this change before I start this whole process again. If nothing else, I imagine it would help with rigidity overall.

 

[mksj]

A new lathe you should not have bed twist, if you are forcing it into a pretzel by anchoring it then you are doing something wrong. The main times I see the need to twist the bed has more to do with wear and/or the lathe was previously not leveled correctly and took a set. Leveling is a simple process, I use the inside 4 legs to level the machine and then bring down the two outer legs at the headstock. If there appears to be some set to the bed causing it to twist, adjust the feet and let it settle. You have a small lathe, it is new, you should have no bed twist nor require it to cut true. Setting up a lathe one needs to follow a step wise sequential approach, determine if there is any issues and fix them by determining the root of the problem. Seems like you are in a loop and just compounding the problem, possible this is an issue with the measurement devices you are using. Bottom line is you should not need to twist the bed to cut straight on a new lathe.

 

[davidpbest]

Just a side note, something I have thought about while leveling the lathe the first time around, and then this most recent time. I kinda wish the lathe was HEAVIER. I find that adjusting the feet will occasionally lift other load point to where it is not touching. Say like jacking up the front tail side I will sometimes find the rear tail side is lifted off its pad.

If I had this to do over again, I would drill and anchor studs into my slab, and then make the adjustments on those studs, with a nut above and a nut below the stand so I can (once very close) force the bed to do what I want it to do, even if gravity is too weak to do it. The current system now, where the stand is threaded for adjustments, and then a locking nut is beneath the stand itself is a mid of a PITA. I wonder if I put the Jam-nut on the wrong side of the equation now. trying to lock the adjustment actually lifts that point due to slop in the threads. and each threaded point is slightly different. Therefore you spend hours making slight adjustments to level the lathe and minimize twist, and when you finally get the Bubble where you want it and try to lock it down with the Jam nut, you move the lathe.

I may make this change before I start this whole process again. If nothing else, I imagine it would help with rigidity overall.

This flexi-stand behavior would drive me absolutely crazy. Makes me really thankful I built my own stand, and in the process made it heavy and rigid (with substantial drawer cabinets), and brought the leveling points up to waist height.

 

[Christianstark]

A new lathe you should not have bed twist, if you are forcing it into a pretzel by anchoring it then you are doing something wrong. The main times I see the need to twist the bed has more to do with wear and/or the lathe was previously not leveled correctly and took a set. Leveling is a simple process, I use the inside 4 legs to level the machine and then bring down the two outer legs at the headstock. If there appears to be some set to the bed causing it to twist, adjust the feet and let it settle. You have a small lathe, it is new, you should have no bed twist nor require it to cut true. Setting up a lathe one needs to follow a step wise sequential approach, determine if there is any issues and fix them by determining the root of the problem. Seems like you are in a loop and just compounding the problem, possible this is an issue with the measurement devices you are using. Bottom line is you should not need to twist the bed to cut straight on a new lathe.

Agreed. I am mainly just thinking philosophically about having it anchored to a floor instead of sitting on rough castings and bolts that cant be locked in place without additional wrangling.

I think a bad instrument started my loop, but moving forward I want to do things in a way that are methodical and as close to bullet-proof as I can so I can rest assured I never need to do it again, or at least not have to do it again for a good long time, and have it result in a more rigid platform to boot.

 

[davidpbest]

Agreed. I am mainly just thinking philosophically about having it anchored to a floor instead of sitting on rough castings and bolts that cant be locked in place without additional wrangling.

I think a bad instrument started my loop, but moving forward I want to do things in a way that are methodical and as close to bullet-proof as I can so I can rest assured I never need to do it again, or at least not have to do it again for a good long time, and have it result in a more rigid platform to boot.

Several on this forum have bolted their lathe to the concrete slab. I'm not sure if you got the sheet-metal stand or the cast iron version, but you might want to have a look at this thread. The vibration issues were a motivating factor in PM coming up with the cast iron stand a few years after this post.

How Are You Mounting Your Pm1340gt Lathe?

I want to hear from the owners of the PM1340GT lathe, how are you setting your lathe on the floor? There are several possibilities using the standard stand supplied with the lathe. The factory designed the stand with 4 threaded holes and supplied bolts to be used to level the lathe and then use...

www.hobby-machinist.com

 

[Christianstark]

So I decided th just do my idea. Took a couple of hours but first indication trying to shake the lathe and it’s much more rigid. These are 5/8 x 6” wedge anchors. The bottom nut and washer tightens up the stud, and the lathe stand (unthreaded part) is sandwiched in place with a nut and washer below, and one above. My back is killing me, but I got it in roughly. I raised the head side doing alternate hjacking and blocking of the inner and outer leveling feet, and just lifted the tail side with a Jack. Rested both sides on a 2.5’ length of solid 6160 3”x 5” bar, lubed with way oil. I could then slide the lathe out of the way to drill holes and hammer in the anchors, and cleared the top of the studs by about 1/2” then I lowered each side down onto the anchors, and topped off with another washer and nut.

Old way. Lathe rocked and shimmied pretty easily. Not heavy enough for 6 jack points.

New way. I can already tell this is rock solid. If vibration becomes an issue I can mount some hard rubber or other dampening material, but I don't think I will need to.

Left the top nuts loose. Will level it tomorrow with a Starrett 98, and then fine tune it Saturday with the VIS Master Precision. After that I am headed up to the lake for Christmas. Maybe my back and leg muscles will have recovered by New Year!

Several on this forum have bolted their lathe to the concrete slab. I'm not sure if you got the sheet-metal stand or the cast iron version, but you might want to have a look at this thread. The vibration issues were a motivating factor in PM coming up with the cast iron stand a few years after this post.

How Are You Mounting Your Pm1340gt Lathe?

I want to hear from the owners of the PM1340GT lathe, how are you setting your lathe on the floor? There are several possibilities using the standard stand supplied with the lathe. The factory designed the stand with 4 threaded holes and supplied bolts to be used to level the lathe and then use...

www.hobby-machinist.com