Parting off!!!

[Josh Bowman]

I have a fit parting off! I tighten my gibs down on the cross slide and compound. I even lock the saddle. I try to have very little protrusion with the tool and be close to the chuck. I insure the tool is on center. I put oil on the cut and push in and out with the cross slide to clear chips. All will work fine then all of a sudden the belt (thank goodness) will squeal and all stops! Each time there is a chip that peels out of the kerf but doesn't cut free. What am I doing wrong, I'm afraid if this keeps up I'll break something? The tool is 3/16"x1/2".
Pictures 1-3 show the chip, 3 shows it after I use my hand to rotate the chuck backwards, not an easy task. Picture 4 shows how the slides are set up, trying not to over hang and that the gibs and saddle lock is tight. Picture 5 shows the amount of tool protrusion.

[David G Baker]

I use 3/8" tooling and grind a small cutter on the end of the tool. I think that the cutting part is around/8" or less wide and tapered on each side. I run my lathe at a slow RPM and hand feed the cutter that is set a fraction above center. I also use MoMax tooling. I have had problems in the past using the standard over the counter parting tools. I also hone the cutting edge prior to making the cut to make sure that it is nice and sharp and flood the area with cutting oil.

[Bruce Page]

Josh, parting off should not be that hard. What is the material? What is the RPM you are running? Are you using a standard HS parting blade? Are you feeding by hand? Pic3 makes it look like there is a bevel grind on the top of the parting tool, is that the case?

My gut feeling without more info is that you are running it too slow.

[Josh Bowman]

I'm running a 300 rpm, on cold roll steel with a HSS 1/2" x 3/16 blade. The top does have a kind of peak. I'm feeding by hand slowly and backing out to clear chips. I tried feeding fast but had the same problem.


Josh, parting off should not be that hard. What is the material? What is the RPM you are running? Are you using a standard HS parting blade? Are you feeding by hand? Pic3 makes it look like there is a bevel grind on the top of the parting tool, is that the case?

My gut feeling without more info is that you are running it too slow.

[Josh Bowman]

Below is attached what I think I've learned. I'm going to make another stab at it tonight. Hope to not break my lathe:o

[ray hampton]

I understand how you feel, when I use a cut-off I will advance the tool then back-off then move the cutting tool to take a wide cut so that the cut-off do not seize because of the heat

[Bruce Page]

It looks like your setup is as rigid as you can get it. Cold roll steel is gummy by nature and will cause fits with a loose setup.
Here’s what I would do:
1. Increase your RPM to 400-500
2. Grind the top of the blade flat - loose the bevel. Be careful not to overheat.
3. Grind the rake at 14° to 15°. What you are showing in your sketch is fine for aluminum but to much rake for steel.
4. Make sure the tool is set parallel with the feed direction.
5. Set your tool at center line or no more than a few thousandths below.
6. I will typically use an acid brush to apply the cutting oil with my right hand and feed with my left.
5. Feed the cutter in by hand a little, pause to let the chip clear, repeat.

I’ve included pics of one of my parting tools for reference. It has cut a lot of steel. My parting tool of choice is a Bear carbide insert tool that cuts like butter.

[George Carlson]

Is it really 3/16"? That sounds too wide for a light weight machine. Try using a 3/32" tool, the tool pressure will be decreased and the machine will not tend to back-off from the cut. For small machines those 3/32" carbide insert tools from Iscar (and others) work well. They're not cheap, but they're still worth every penny. I use HSS tooling when cutting soft material like PTFE. You can make the HSS tooling razor sharp if you need to.

[Josh Bowman]

Well I went back out it again with your suggestions. And thanks all for the help.
1) Sharpened tools, a T 1/8" and tapered 3/32"
2) I put a back cut in the top of both which took the peak off the 3/32"
3) I made sure they were plumb in the holder, either with a shim or eyeing.
4) I used a parallel to ensure the tool was aligned with the chuck face.
5) Made sure I was at center line (found if I stared a tad high, the tool would quit cutting, so I'd lower it until it cut through and removed the "tit".
6) Found my thread cutting oil and used lots of it.
7) Cut raised the rpm from 300 to 500 rpm.
8) Gritted my teeth and ran the tool in fairly fast to produce a curl of a chip and kept brushing on the oil.
9) I'd stop and reoil and went at it again.
The below results show my progress. I only had one belt squalling, lathe stopping moment and that was at the first.
10) resharpened often.
The curls of metal are totally different from last nights. I may need to work more on the chip breaker shape, since some of the curls seemed a little long.
I found little difference in the 1/8" to the 3/32", but felt the 3/32" would chatter less.

[george wilson]

That looks like a pretty old S.B.9" lathe. How good are your spindle bearings? Most trouble from cutting off,IF everything else is correct,is from the lathe being too light. I had trouble with my first lathe,a 12" Craftsman. Just not heavy and rigid enough. No trouble at all when I got my first Jet 10" bench lathe,or beyond.

Your spindle bearings could be too loose and helping the bit to grab,stalling out the lathe. Have you put any gripping stuff on your flat belt? I use Belt Traction. That flat belt isn't a real powerful means of running the spindle. You could try grinding up some rosin and carefully applying it.

[Josh Bowman]

I did a total tear down of the 9A and put a serpentine belt on it. I'll look into the Belt Traction. I haven't had any troubles since all the advice. I even did several cutoffs under power cross feed. Now that is slick! I'm still a little edgy that I could break something, but getting the blade perpendicular to the work and the beveled blade not leaning in the straight holder along with feeding a little more aggressively with lots of cutting oil, seems to have stopped the problem. I'll post some before after pictures of the lathe in another post. It was a lot of fun cleaning the thing up and repainting it. Thanks for the help.

[ray hampton]

If you give me this lathe , I will try to teach you how to operate it
of course I mite be stretching the truth

[Josh Bowman]

Ray you are so kind to offer, but I hate to put you to that trouble.;)

[ray hampton]

Ray you are so kind to offer, but I hate to put you to that trouble.;)

you are so right , using a good lathe would be trouble