Technique for cut off tool

zargnut · Sep 10, 2017

Hi,

I am having trouble getting a cut-off tool to work when trying to cut off even relatively soft metals like mild steel.

I have tried both the carbide insert cutoff tools and 3/32 HSS blades - freshly sharpened.
I am using a slow speed ? 60-100 rpm and placing the cutting tool even with the center

I am getting very small chips and a ton of resistance, that results in the whole tool holder rotating clockwise, and then binding.

I experienced the same think on a junk lathe, but when I experience with my new 10k, I realized it was bad technique...

How am I supposed to successfully use these tools?

thanks
dan

DMF_TomB · Sep 10, 2017

zargnut said:
Hi,

I am having trouble getting a cut-off tool to work when trying to cut off even relatively soft metals like mild steel.

I have tried both the carbide insert cutoff tools and 3/32 HSS blades - freshly sharpened.
I am using a slow speed ? 60-100 rpm and placing the cutting tool even with the center

I am getting very small chips and a ton of resistance, that results in the whole tool holder rotating clockwise, and then binding.

I experienced the same think on a junk lathe, but when I experience with my new 10k, I realized it was bad technique...

How am I supposed to successfully use these tools?

thanks
dan

making sure tool not too high or above center. normally if deep i go in so far back out, shift side ways .005 and go back in deeper. by shifting sideways or cutting wider than blade you get less blade side rubbing

Davis In SC · Sep 10, 2017

Depending on the material, you may be work-hardening the cutting area. Letting the tool dwell will harden the surface, and make it difficult to cut. Keep the tool feeding, or back out a few thou..

zargnut · Sep 10, 2017

Thanks. I will try this.

CalG · Sep 10, 2017

What ever you can do to add stiffness to your set up can only help. I've been known to wedge a "jack" under the tool holder that spans down to the cross slide.

newtonsapple · Sep 10, 2017

zargnut said:
Hi,

I have tried both the carbide insert cutoff tools and 3/32 HSS blades - freshly sharpened.
I am using a slow speed ? 60-100 rpm and placing the cutting tool even with the center

I am getting very small chips and a ton of resistance, that results in the whole tool holder rotating clockwise, and then binding.

dan

Are you cutting off from the back or maybe it's a typo, but what is going on the tool holder is rotating clockwise? Excessive cutting force would rotate it counter clockwise.

Typically people underfeed a cutoff tool getting rubbing and hardening. You need be steady with the feed, on it or get out. As you initially feed in you will get a small amount of chatter, which should go away as you get enough feed and good chips develop. Practice that step with shallow cuts and then go deep. Keep the extension to the minimum and make sure your gibs are tight, slop is no good.

What are you cutting specifically in term of diamter/material. RPM is slow, but I only make tiny stuff.

zargnut · Sep 10, 2017

not cutting from the back. You are right... it is rotating CC looking - top down.

I am hesitating, likely hardening the work.
I am cutting about 1" diam mild steel., Not sure actual alloy.
I also use stainless a bunch and struggle with that even more. That is the hardest stuff I work with.

Is it ok to drop the top of the cutting tool to below the midline a bit... ~1mm to ensure I am not above it?

CalG · Sep 10, 2017

zargnut said:
not cutting from the back. You are right... it is rotating CC looking - top down.

I am hesitating, likely hardening the work.
I am cutting about 1" diam mild steel., Not sure actual alloy.
I also use stainless a bunch and struggle with that even more. That is the hardest stuff I work with.

Is it ok to drop the top of the cutting tool to below the midline a bit... ~1mm to ensure I am not above it?

No, That is NOT OK.

What are you doing for top rake?

Cut off can happen with the tool at any azimuthal orientation, But the cutting edge must meet the work with appropriate geometry.
Back RAKE can help a lot at reducing cutting forces. As can appropriate application of sulphured cutting oil. I prefer Canola oil, It smells good, But dries to make a miserable mess. ;-)

JLarsson · Sep 10, 2017

How much stick-out on your parting blade?

SeaMoss · Sep 10, 2017

DMF_TomB said:
making sure tool not too high or above center.

I actually like it a tiny bit above center. That's a tiny bit. That way under pressure the blade deflects down to be on center.

Agreed, below center is bad. Bad bad bad. A bit above cernter you can compensate for by grinding more top rake and front rake into the tool but below center has no fix.

rons · Sep 10, 2017

60-100 RPM is slow. Depends on what the cut is into but cutting oil in a squirt bottle is what I use. If the material is stainless (like 303, 304) you could be work hardening the material if you are moving in too slow. The method for widening the cut (backing out and moving to one side, then plunge in again) is used in wood turning.

Blob · Sep 10, 2017

Use a narrow (1/16") blade with a fairly aggressive positive rake. Feed the tool faster than you think you should. You should be peeling off chips in a fairly continuous ribbon - if you're not, increase the feed. HSS is probably a better choice than carbide inserts which can have a negative rake angle, not good for these light duty lathes. Keep trying, you'll figure it out - I did. :-)

Davis In SC · Sep 10, 2017

I keep a cutoff tool on my Hardinge.. 3/32 wide ISCAR, I have learned that more cutoff tools get wrecked by UNDERFEEDING, than overfeeding.. Touch off and get moving.. I have some tightly wound chip coils the size of a nickel...

newtonsapple · Sep 10, 2017

Do some practice parts, brace yourself and try to over feed, I think you will be surprised, I was when I was learning (still am). As you go from underfeed to the correct feed it is like going from all hell breaking loose to a purr and chips curling.

MattiJ · Sep 10, 2017

SeaMoss said:
I actually like it a tiny bit above center. That's a tiny bit. That way under pressure the blade deflects down to be on center.

Agreed, below center is bad. Bad bad bad. A bit above cernter you can compensate for by grinding more top rake and front rake into the tool but below center has no fix.

I set the tool pretty high if I am parting any bigger diameter pipe. For 2" pipe maybe 0.7mm high. 2mm carbide insert tooling, 1500rpm for 2" stock.

zargnut · Sep 11, 2017

I was using a commercial cutoff blade.
Cupped on the top edge - looks like the holder has about 2.5 deg top rake
Tapered so the top is wider than the bottom.

I was sharpening vertically on a grinding wheel, so there is a concave end relief angle

I just played around...
I was able to knock thorough aluminum 1/2 in a single approach
I tried 1" mild steel and it would bog down as I advanced, it was digging in, and would bind, requiring me to turn lathe off and release the chuck to get the piece out. I was running it slowly using back gear for torque.

I tried 2' brass, and I could not get it to cut... really weird. TCMT tools were cutting fine,

If anyone lives in Baltimore, Buy you lunch at Miss Shirleys if you would care to swing by and show me what I am doing wrong.

CalG · Sep 11, 2017

OK

If your machine "bogs down" in 1 inch steel, You are screwed.

Not enough machine!

You will need to work with geometry and a cutting edge that is so sharp it will cut your eyeballs looking at it. That and copious cutting fluid.

Or else, just keep dick'n around breaking stuff.

LKeithR · Sep 11, 2017

CalG said:
OK

If your machine "bogs down" in 1 inch steel, You are screwed.

Not enough machine!

Yeah, I think that's the biggest problem. If your settings are right and you can't make it work with a good 1/8" wide insert parting
tool then you probably just don't have a rigid enough machine...

Adwcali · Sep 11, 2017

I run a lot of parts from .750 cold roll 1018. I part with a hss tooli in an Aloris tool. 800 rpm and feed with the power feed. This is on an 11" Logan lathe. Lots of cutting oil and feed it hard enough to peel off a continuous ribbon. To slow and bad things happen.

SeaMoss · Sep 11, 2017

zargnut said:
I tried 1" mild steel and it would bog down as I advanced, it was digging in, and would bind, requiring me to turn lathe off and release the chuck to get the piece out. I was running it slowly using back gear for torque.

Back gear ? NO ! WAAAAY too slow ! you don't need torque, it's only a 1/8" wide cut !

For 1" I'd personally kick that thing into top but you may not be ready for that ... but ... South Bend ? Try the lowest or second-lowest pulley in top and when you first get into the cut, give it a little extra oomph to get started. Then just feed it in to keep a nice curl going.

The trouble with an engine lathe and cutoff is that you want it to go faster as diameter decreases. Going too slow will give you more trouble than going too fast. Most people aren't brave enough to go too fast because when the blade snaps, it can be scary. Or annoying when the damn inserts are several bucks apiece. Definitely always wear eye protection when doing partoff.

I tried 2' brass, and I could not get it to cut...

Tell me how you got that in the lathe and I'll tell you how to get it to cut

If anyone lives in Baltimore, Buy you lunch at Miss Shirleys if you would care to swing by and show me what I am doing wrong.

Do they have hamburglers ?

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