Broke a parting tool

[ARC-170]

I broke my brand new parting tool blade. I bought two; a thin kerf one (0.040") and the normal kerf one (0.062"), both 1/2" high by about 3" long, US made. I was using the thin one to part off a small piece of steel rod, type unknown (probably CRS), but it wasn't anything fancy, since I got it from the school shop where I work.

Here's a picture of the broken blade:


I think I was feeding it too fast, but how would I know? I switched over to the thicker kerf and that worked, but I fed it VERY slowly. The machine (Atlas Craftsman 101) chattered/groaned/vibrated a bit whenever I engaged the blade, only stopping when I got to a smaller diameter. It made noise whenever I engaged it and at any feed speed. I was on the 2nd lowest spindle speed. I used cutting oil. I also used the tail stock and that seemed to help a bit.I also cut the slot a little wider than the blade, backing out the bade, moving over 0.005", then making another cut, etc.

Here's a picture of the setup that worked. When I broke the blade, there was no tail stock and the blade was only extended out as much as I needed.


Anyone have any insights as to what I did wrong? Is there a technique to parting?

Thanks!

 

[T Bredehoft]

You were using a cut off tool for its intended purpose, breaking. Happens to everyone. Yes there is a technique. It must be learned, cannot be taught.
Sharpen your tool and try again. Maybe practice with the 1/16 tool until you're comfortable, then try the thin one.

 

[benmychree]

Feeding very slow tends to increase chatter, and very slow speeds may not be helpful either. I would not use a parting tool less than 3/32 wide, personally. An Atlas lathe ( I am guessing is a 6"?) is certainly not the best platform for parting. I use TapMagic for parting, and most other machine work as well, it tends to make the tools cut more freely which lessens the tendency for the chips to pile up on the top of the tool and cause galling and subsequent tool breakage. I see that you have a QCTP, On my 9" Monarch, which is in excellent shape, I have the same situation; if you have the TP pretty much centered in the compound's T slot, the parting tool is hung over the left side of the cross slide , and the tool tends to lean to the left when parting and twists the blade and binds on the partially parted slot, either stalling the machine or breaking the tool; if the TP is moved to the right in the slot so that the tool is not overhung, the tendency goes away and parting can be done without problems.

 

[mickri]

I have had lots of issues with parting with my craftsman 12x36. Rigidity is the key. When I need to part something I tighten everything down except for what I am using to advance the parting tool. And it still doesn't go that well. On my last attempt at parting I inadvertently ground the parting tool at a very slight angle. This actually seemed to help a little bit.

Parting on the backside is just not doable with our lathes. Running in reverse with the parting tool upside down is fraught with the danger of the chuck coming off. In another thread that I had on parting issues it was suggested to use a draw bar through the spindle to tighten a keeper (probably wrong term) against the chuck. Theory was that as long as there were different TPI on the drawbar verses the chuck the two different threads would work against each and the chuck could not unscrew when running in reverse. Haven't made the keeper yet so no experience with this idea.

 

[BGHansen]

Parting is probably the toughest operation on a lathe (or bump knurling), so expect some troubles and a learning curve. I've parted well over 1000 times (closer to 10,000) on the lathe while turning stainless steel, aluminum, brass, CRS, Delrin (plastic), O-1 tool steel, 4140, etc. and still snap a carbide insert (I used GTN-3 or GTN-4) on occasion. Just snapped an insert a week ago parting aluminum of all things.

Tom Griffin (Google Tom's Techniques) has a nice video tutorial on parting with a HSS blade. He has a great tip of sharpening the blade before every use. I tend to use the HSS T-shaped or double-tapered blades which give some side clearance. I'm comfortable with open spindle speeds like 500 RPM+ with the HSS. I tend to go to back gear when using carbide (though you'll likely see posts that carbide likes to run fast).

Biggest thing is to stay safe and don't get discouraged. EVERY one on this forum has likely had a problem parting on the lathe at one point or another.

Bruce

 

[Aukai]

Exactly perpendicular, and exactly on height, I'm going at 250-300 rpm, and using the cross feed at the slowest advance, with lots of lube. It will scream, and make noise if it's not right, just my experience. I'm totally new at this, and I used to set tool height by the point of the dead center in the tail stock. The blade on the chuck, or a 1 2 3 block on the tool holder, and chuck for perpendicular. The closer it is to perfect, the less noise there is, also just my experience. I have a T type blade for now, you can't just slap it in, and go, setup is number one. If you look, there are some different ways guys do it.

 

[ddickey]

Upside down blade on the back side I bet would work much better.

 

[Aukai]

I ran one upside down yesterday from the front, but hand fed, my height was off, it climbed the nub at the end. Not sure where the play came from on that.

 

[mattthemuppet2]

slow speed, high feed. If it screams it's because it's rubbing - either due to too high rpm or too gentle feed. Slow it down and RAM it into the work (well, almost). If you're getting shavings, feed harder until you get little curls rolling off the top of the tool.

 

[mickri]

Jeff has a craftsman lathe. Virtually impossible to have a holder on the backside. He is pretty much limited to the front side. Mikey has educated me on the forces involved and how everything flexes that makes parting on a craftsman lathe difficult. To have any chance of success you need your setup as rigid as possible with a properly sharpened blade exactly on center.

When parting on the front side the carriage, cross slide and compound all want to lift on the outside and press down at the work. This flexing is what causes the blade to go below center line and into the work resulting in the work riding over the top of the blade. There are gooseneck tool holders designed to compensate for this flexing



I bought some but they were too big to use on my lathe. So I have not used them and can not attest to how well they work. I have seen pictures online of gooseneck tool holders for a QCTP. I have thought about making one.

Jeff you just have to keep experimenting until you get a setup that works for you.