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Problem Parting Off On A 101.28980 Lathe

AMDtrucking

Iron
Registered Member
#1
Hello gentleman, I'm new here and need some help.
I also have Craftsman Commercial 101.28980 The bed is 42" long and the cross slide, travels about 6" Is it a 12" lathe or 6"?
There is visible wear on the X-Slide, mostly on the front rail and my cross slide Y-Slide, gets tighter as it goes dipper in away from me. Obviously it is worn on the front. But I've learned to deal with it and not complaining.
However, the biggest problem I have is when I'm parting off a piece. I use KDK tool holders and ISCAR parting blade with inserts and 5C collet chuck, as well as 5" six-jaw Buck chuck. Needless to say, that I have my tool aligned exactly in the center, perpendicular to the work, 50% speed, and plenty of cutting oil. When I'm parting, my work, sometimes jumps on top of my blade and breaks it. When I free the blade and spin the chuck - it seems to wobble, although it wasn't wobbling before. I would unscrew the chuck and screw it back again, then it quits wobbling, until the next parting off accident. Correct me if I am wrong: There could only be two reasons for that. It's either my tool holder is not sturdy enough and it dives under the work, or my spindle bearings are gone. I tightened all the gibbs but it didn't help. The last time I looked at the bearings, was when I replaced the belts and they looked OK to me. Please advise, what am I missing? It only happens under a lot of pressure, when parting. It never happens when I'm turning, even under a lot of pressure.
UPDATE: I forgot to ask: It seems like every time, I move my tail stock, it gets off center. The question is: Do I loosen the nut, that's holding the tail stock, before I start adjusting my screws (one on the front, one on the back), or I could adjust my tail stock, while it's holding my work tight?
 
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wa5cab

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#2
To answer your last question first, loosen the clamp nut, then adjust the tailstock gib screws.

Back to the first question, if you live in the US or US territories, it's a 12". US practice is to class the machine by the maximum diameter of work piece that can be swung over the ways. If you live in Britain or a (former?) Commonwealth country, it is a 6". British practice was to class the machine size by the nominal distance from the inner corners of the ways to the spindle axis. Elsewhere, your guess is as good as mine. In US practice, it would be called a 12x24.

When the parting off problem happens, does the part seem to wobble or the chuck body?
 

AMDtrucking

Iron
Registered Member
#3
To answer your last question first, loosen the clamp nut, then adjust the tailstock gib screws.

Back to the first question, if you live in the US or US territories, it's a 12". US practice is to class the machine by the maximum diameter of work piece that can be swung over the ways. If you live in Britain or a (former?) Commonwealth country, it is a 6". British practice was to class the machine size by the nominal distance from the inner corners of the ways to the spindle axis. Elsewhere, your guess is as good as mine. In US practice, it would be called a 12x24.

When the parting off problem happens, does the part seem to wobble or the chuck body?
Thanks for my first two questions answered very clear.

When I'm parting off, neither the part or the chuck wobble at all. Only after it breaks the tool, then it starts wobbling. If I remove the chuck and put it back, it doesn't wobble any more.
 
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Mwmx54

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#4
I could be wrong, but it sounds like the threads in the chuck, or the threads on the spindle are loose enough that it's allowing the chuck to come loose, skip a thread is the best way I can describe what I would call it. How tightly do the threads fit on the chuck and spindle.
 

AMDtrucking

Iron
Registered Member
#5
I could be wrong, but it sounds like the threads in the chuck, or the threads on the spindle are loose enough that it's allowing the chuck to come loose, skip a thread is the best way I can describe what I would call it. How tightly do the threads fit on the chuck and spindle.
The threads in the chuck are brand-new and the threads on the spindle look OK. I use a a truck oil filter remover tool to grab around the chuck and tighten it, followed by few knocks of hammer on the handle. It's tight to the point, that I can switch in reverse and the chuck doesn't come loose. :) I don't think it is that. Maybe the problem is that I just can't part off on a lathe? I don't know what to think. :sorry: I'm so scared to part off, when it is not brass, aluminum or delrin that I grab a hack saw and cut it off with it, especially when it is stainless steel, although I stick to 303 and 304 instead of 316. :)
 
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Mwmx54

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#6
You're not parting off with an upside down tool and the lathe in reverse right? Don't make any cuts were the lathe has to be in reverse, without doing research into how it can kill you. Sorry I'm not much help. Just reminded me of what stripping threads out feels like. Tightens up nice and tight, then you think just a little more.. click too far and the threads are dickered.
 

wa5cab

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#7
MW's idea is one of three or four that occurred to me. But you (AM) did not answer my question. So I will repeat and add some more that I did not get into my previous because the doorbell rang about that time indicating that our dinner was here.

1) Has this ever happened when you were using the 5" chuck, or only with the 5C collet chuck?
2) After it happens, does it look as though the chuck (and work piece) is wobbling or only the work piece?
3) You said that loosening and then re-tightening the chuck removes the wobble. Do you loosen the collet as well or does it remain tight?
4) How much of the work piece extends up into the spindle (if any)?
5) Approximately how far away from the collet nose is the parting tool?
6) At approximately what diameter does the jump occur?

I will also add that it is not necessary and is in fact undesirable to tighten the chuck to the spindle with anything other than inertia. When you screw a chuck onto a threaded spindle, tighten it by hand until it is about 1/8 of a turn (45 degrees) shy of being tight. Then grasp the chuck jaws or the collet chuck nose with your right hand and with your wrist and elbow smartly or rapidly twist it home. You should hear a snap or a ringing noise as the rear face of the chuck hits the shoulder part of the register (solid flange on the nose of the spindle).
 

AMDtrucking

Iron
Registered Member
#8
MW's idea is one of three or four that occurred to me. But you (AM) did not answer my question. So I will repeat and add some more that I did not get into my previous because the doorbell rang about that time indicating that our dinner was here.

1) Has this ever happened when you were using the 5" chuck, or only with the 5C collet chuck?
2) After it happens, does it look as though the chuck (and work piece) is wobbling or only the work piece?
3) You said that loosening and then re-tightening the chuck removes the wobble. Do you loosen the collet as well or does it remain tight?
4) How much of the work piece extends up into the spindle (if any)?
5) Approximately how far away from the collet nose is the parting tool?
6) At approximately what diameter does the jump occur?

I will also add that it is not necessary and is in fact undesirable to tighten the chuck to the spindle with anything other than inertia. When you screw a chuck onto a threaded spindle, tighten it by hand until it is about 1/8 of a turn (45 degrees) shy of being tight. Then grasp the chuck jaws or the collet chuck nose with your right hand and with your wrist and elbow smartly or rapidly twist it home. You should hear a snap or a ringing noise as the rear face of the chuck hits the shoulder part of the register (solid flange on the nose of the spindle).
I'm sorry, I guess I didn't understand your question the first time around. I apologize for that. I'll try to answer them in order:

1) It happens with every chuck I own: 5" 6-jaws Buck chuck, 4'" 4-jaw no name chuck and my brand-spanking-new chinese collet chuck.

2) The work piece was still being held tightly, by the chuck and wobbled together with it.

3) If I remember correctly, I unscrewed the chuck to see if my spindle threads were damaged. The threads were fine and I screwed the chuck back on the spindle. Then I noticed, that it doesn't wobble anymore. My work piece was still in the chuck.

4) Since I was parting off 3 inches of a foot long rod, 9 inches were inside the head stock bore.

5) So close, that it left a mark on my collet.
6) the rod was 1/2". It "drove" onto my tool and broke it, when I was half way trough. So, I'm going to say: 0.25"

I will definitely take a note of your suggestion on how to tighten the threaded chuck and will use it in the future. Thank you. I honestly did not know that.

At first, it was parting just fine. I liked those nice looking little rolls of chips coming out. I even thought of engaging my cross slide auto feed.
And all of a sudden - kaboom!
My $10.00 Iscar insert is gone and the $78.00 blade is bent. The chuck jammed and stopped turning.
 
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mikey

Active User
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#10
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.
 

wa5cab

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#11
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

Active User
Active Member
#12
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

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#13
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

Iron
Registered Member
#14
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

Iron
Registered Member
#15
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.
 
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AMDtrucking

Iron
Registered Member
#16
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

Iron
Registered Member
#17
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

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#18
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

Iron
Registered Member
#19
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

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#20
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".
 

AMDtrucking

Iron
Registered Member
#21
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".
Got it. Here it is. My Soviet micrometer's jaws grabbed some of the threads, that's why I double-checked with thin jaw calipers.
 

wa5cab

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#22
I assume that in the 4th decimal place, your digital caliper only displays 0 or 5. But in any case, the spindle register is fine. And it is unlikely that three different chucks are over-size in the register area. I would re-set the spindle bearing preload, tighten the compound and cross slide gibs, and re-check that the parting off tool holder is perpendicular to the spindle axis.

I note that your micrometer is reading about 1.50027" but that could as you said be due to catching the thread.

I would suggest also switching to the ThinBit holder and cutters. At the very least, if it happens again, you won't damage the holder. I don't know what the ThinBit cutters cost today as it has probably been a decade at least since I last had to buy any. But not damaging the cutter holder will save considerable.
 

Silverbullet

Active Member
Active Member
#23
What your going to find is the machine is flexing or moving as the force of the cutoff blades pushing down bending the cross slide and tool post . Many LATHES just aren't strong enough to use a cut off tool. Mines one too an 11" Logan. The only way I can do it is to mount a solid block with extra support across the ways and snug under the tool itself . I've watched the whole carriage twist under the pressure. I know others will say different so try and see. Make you own observation have your machine video taped from different angles. Do your cutoff routine and watch the machine bend and flex .
 

bobl

Active Member
Active Member
#24
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.
Sounds about right but also is your parting tool at the correct height re the centre just a small amount below to much will give this problem also as I know from experience also chip buildup


Sent from my iPod touch using Tapatalk
 

wa5cab

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#25
Right. I would strongly recommend getting one of the relatively inexpensive bubble-level centering tools. Eyeball on center often isn't good enough.