Problem Parting Off On A 101.28980 Lathe

[wa5cab]

Well, let me sleep on it. Or maybe someone else will come along with an idea. In the meantime, carefully measure the spindle register diameter. The register is the unthreaded portion of the spindle nose between the threads and the shoulder to the left of it. According to some texts, it also includes the shoulder. But that shouldn't be in question. According to Clausing, the diameter should be 1.5000"/1.4995". I don't have the figures for the chucks but would guess no more than 1.5005". The register, not the threads, is what centers the chuck to the spindle. Also check the runout on the spindle register. Hopefully no more than 0.0003". Run a bar through the spindle bore and with your dial indicator set up against the spindle register, pull toward you and push away from you.

Check (loosen and reset) the spindle bearing preload. Download the Atlas Technical Bulletin on the late 12" headstock for instructions. Instructions for using DOWNLOADS are in the Sticky area at the top of this Forum.

I also am not sure or didn't understand what you were saying about the wear on the bed, carriage dovetail and cross slide.

And another possible suspect might be the QCTP that you have. I don't believe that I've ever seen one like that.

 

[ericc]

Have you taken a look at the bearings? Or are you sure that it is the chuck thread? This is serious. Any bit of wobbling will cause trouble. Did you do the lift test on the spindle (pry up with wood stick and measure deflection)?

 

[westsailpat]

Hi AM , how wide is the parting tool ? On my little machine a Craftsman 6 inch , parting off is avoided but when necessary a 1/32 blade is the widest I go . Also it might help to modify your tool feed , try feed in about .020 then back out clear any chips and re oil then repeat till done . Hope that helps . Mark .

 

[AMDtrucking]

Looks to me like you're doing everything right, AM. If the work is climbing on top of the blade then there has to be clearance somewhere to allow that, which makes the spindle bearings suspect or excessive slop in the saddle/compound gibs. Another possibility is that the tool holder is moving in your tool post. Try eliminating these things first.

Thanks Mike, I will check all those things.

 

[AMDtrucking]

Well, let me sleep on it. Or maybe someone else will come along with an idea. In the meantime, carefully measure the spindle register diameter. The register is the unthreaded portion of the spindle nose between the threads and the shoulder to the left of it. According to some texts, it also includes the shoulder. But that shouldn't be in question. According to Clausing, the diameter should be 1.5000"/1.4995". I don't have the figures for the chucks but would guess no more than 1.5005". The register, not the threads, is what centers the chuck to the spindle. Also check the runout on the spindle register. Hopefully no more than 0.0003". Run a bar through the spindle bore and with your dial indicator set up against the spindle register, pull toward you and push away from you.

Check (loosen and reset) the spindle bearing preload. Download the Atlas Technical Bulletin on the late 12" headstock for instructions. Instructions for using DOWNLOADS are in the Sticky area at the top of this Forum.

I also am not sure or didn't understand what you were saying about the wear on the bed, carriage dovetail and cross slide.

And another possible suspect might be the QCTP that you have. I don't believe that I've ever seen one like that.

I just came home from work, driving a big rig car hauler. I will take some measurements tomorrow and let you know. As far as my QCTP, It is KDK. Very expensive and supposed to be good.

It was there, when I bought my lathe, I just kept adding more tool holders for it from eBay.

 

[AMDtrucking]

Have you taken a look at the bearings? Or are you sure that it is the chuck thread? This is serious. Any bit of wobbling will cause trouble. Did you do the lift test on the spindle (pry up with wood stick and measure deflection)?

I looked at the beadings when I replaced the belts, they looked OK. THe chuck threads are correct, I think it is 1- 1/2" by 8 TPI. Under normal operation, when I am not trying to part off, it doesn't wobble at all, I showed video, few post back. I will try to do the lift test tomorrow.

 

[AMDtrucking]

Hi AM , how wide is the parting tool ? On my little machine a Craftsman 6 inch , parting off is avoided but when necessary a 1/32 blade is the widest I go . Also it might help to modify your tool feed , try feed in about .020 then back out clear any chips and re oil then repeat till done . Hope that helps . Mark .

I use ISCAR HSS blade with 2 mm wide insert. Sorry, I grew up in USSR and metric is my thing.

 

[wa5cab]

OK. That's 0.0787" which is roughly 5/64". 1/32" is roughly 0.8 mm. For years on my Atlas 3996 I've used ThinBit grooving tool inserts, normally in .0625" width (1/16"). They work well. However, the difference between 1/16" and 5/64" isn't enough to matter. The fact that all of your chucks visibly wobble after an event I'm more inclined to think indicates that the problem is in the fit of the spindle nose to the various chucks.

The KDK tool post and holders certainly seem sturdy enough. I wouldn't think that they are any part of the problem.

 

[AMDtrucking]

OK. That's 0.0787" which is roughly 5/64". 1/32" is roughly 0.8 mm. For years on my Atlas 3996 I've used ThinBit grooving tool inserts, normally in .0625" width (1/16"). They work well. However, the difference between 1/16" and 5/64" isn't enough to matter. The fact that all of your chucks visibly wobble after an event I'm more inclined to think indicates that the problem is in the fit of the spindle nose to the various chucks.

The KDK tool post and holders certainly seem sturdy enough. I wouldn't think that they are any part of the problem.

OK, I took some measurement and some picture:
My spindle threads look good to me. The wear on the ways is visible but I cannot feel it and it is uniformed on the entire length of the bed, well almost on entire. I placed a MT-3 dead center, inserted it into my head stock spindle, put a big wrench on it, extended the handle with a 4 foot pipe and tried to move it up-and-down and left-and-right. I pulled hard, my entire lathe and its cabinet were moving on cement floor. The play I saw, was 0.001" to 0.002". I also shot a tiny video to show, that my spindle, with no load, has virtually no wobble. I am becoming more and more convinced, that rather then my spindle jumps on top of my work, my tool takes a dive under it. Am I wrong?

 

[wa5cab]

AM,

You measured the spindle nose thread major diameter, not the register diameter. The actual thread diameter isn't particularly critical. Your first photo appears to be made up from three photos. What you need to measure is the unthreaded area to the left of the threads as shown in the lower right corner of your first photo. And the inside diameter of the unthreaded area before the threads start as shown in the lower left corner if the first photo. As I wrote earlier, the register diameter should be 1.5000"/1.4995".