Am I the only one who can't part off on the lathe to save his life?

[dado5]

I have really been enjoying my new hobby. Just finished a set of v blocks (not to nearly the tolerances of the youtube video stars, but I'm pleased) and hope to harden them tomorrow. Today I started my next project a fly cutter. I cut too much off my blank and needed to trim off a 1/4". I figured since I already had it in my lathe I would just part it off. It is 2" round steel. I sharpen the tool, hone it, make sure it is dead on center and perpendicular to the piece and all I get is chatter and fine little shavings coming off. I slowed my speed down with my back gears to around 160 and used oil. Any advice? My next project may be a tool post grinder so I can put a cut off wheel in it!!!!

 

[markba633csi]

Parting off can be tough without a brontosaurus lathe, although some do it well with small machines; I dislike doing it myself. I reach for the hacksaw.
Mark

 

[Chipper5783]

Nope. Challenges with parting off are a very common question. I had a hard time with it too. There are several threads on the topic - basically one has to fuss with it. I have no trouble at all now, and I'm really not doing things much differently - just after a while you're able to sort it out.

Make sure you pull all your slides in, keep the work as short as possible. I really like the carbide insert part off tools (they work great in the CXA style post). I find a fairly narrow tool is best (0.125). Keep at it, you'll get it sorted too.

I set up a rear tool post. It works great - but the QC tool also works fine and is faster to set up. It will also depend you what the material is. Quite often, I'll add some tailstock support (just for the first bit of the cut - don't try to finish a part off task with the tailstock supporting the outer end).

 

[Ed ke6bnl]

if your lathe chuck is NOT threaded on, you might try parting with the blade upside down squared and centered, this is now how I leave the tool on the tool holder, just works better for me on a smaller 11 in lathe.

 

[pdentrem]

Most points involving parting on the lathe

Square to tool to the work and on center line.
Tighten your gibs.
Sharp, very sharp, extremely sharp, did I say sharp, Tool!
Work held as close to chuck as possible.
Thin tool is better as a parting tool is taking a heavy cut like a form tool. Only have enough tool sticking out to reach just past the center of the cut. Too much overhang means a squirmy tool.
Cutting oil.
Very rigid tool holder, here the lantern is second best to most tool holders.
RPM is machine dependent, on the Atlas back gears is the highest I had success with. On heavier more stable machines even normal turning speeds are possible.
Feed the tool in as too light a cut will cause issues. When I hand feed, it is about 0.001” or more per revolution.
Pierre

 

[paws-fixit-shop]

I'm a learn as I go hobby guy to, and I recently cut my spindle speed way down for parting. My lathe is an Atlas 10F, and I part with it in back gears and the next to slowest setting which I think is about 45 rpm. I find that by taking just about .005 per revolution (on 1" or smaller stuff) it works a LOT better now. I'm using an HSS cutoff tool in an AXA tool holder and lots of oil.

 

[benmychree]

In addition to the above responses, I add that a tool holder that causes the tool to overhang the cross slide to the side can also cause trouble with the tool trying to twist counterclockwise and dig in and chatter. I think the lantern tool post is better in this respect, especially if the rocker ring is done away with and a new washer is made for under to tool holder of such a thickness that brings it on center. I did this with a 1916 vintage American High Duty lathe that I had years ago, and enjoyed much less parting tool breakage.
You might also look at headstock spindle bearing adjustment,; if a bit loose it would induce chatter; sometimes good also to run a center in the part until it is nearly cut off to reduce chatter. I use Tap Magic for parting off with HSS, and water based coolant for carbide insert parting.

 

[higgite]

... I sharpen the tool, hone it, make sure it is dead on center and perpendicular to the piece and all I get is chatter and fine little shavings coming off.....

Since everything else seems to be up to snuff (cutting edge centered, etc), your parting tool may not have enough front relief and you're getting rubbing instead of cutting. And please don't take this the wrong way, but the spindle isn't turning the wrong way is it? (Somebody had to ask. )

Tom

 

[Technical Ted]

I have really been enjoying my new hobby. Just finished a set of v blocks (not to nearly the tolerances of the youtube video stars, but I'm pleased) and hope to harden them tomorrow. Today I started my next project a fly cutter. I cut too much off my blank and needed to trim off a 1/4". I figured since I already had it in my lathe I would just part it off. It is 2" round steel. I sharpen the tool, hone it, make sure it is dead on center and perpendicular to the piece and all I get is chatter and fine little shavings coming off. I slowed my speed down with my back gears to around 160 and used oil. Any advice? My next project may be a tool post grinder so I can put a cut off wheel in it!!!!

Parting can be one of the biggest challenges on a lathe... the smaller and less rigid the machine the worse it gets. There are a lot of variables at work here, so I'm just going to throw out some random thoughts. Sometimes, little twists can make a big difference. YMMV depending on your setup, equipment, material, experience, etc..

1- This is a big one here. If I only needed to remove 1/4" I would not have parted it off... I would have just faced it off. Much safer and in the long run, much quicker. Or, since it was 2" diameter, if I had more to remove that 1/4" I most likely would have taken it off and put it on my band saw. For me parting small diameters is pretty easy/safe, but larger diameters, especially on smaller lathes, I would only part as a last resort.
2- I usually will have my parting tool above center to help keep the work piece from climbing over the top and breaking my tool. As you get closer to center the tool will stop cutting because it is too high and at that point I will back the tool out, lower it down a little and continue parting doing this at many times as it takes. You can tell when it stops cutting because you will feel it while hand feeding.
3- I've had my best results will only grinding ~5 degree clearance on my HSS parting tools. More seems to cause more chatter.
4- Part as close to the chuck as possible. If out a ways, lightly put a center in the end if you can. Don't apply much pressure or, if you do, back it off before you break through. This will help stabilize and help keep the part from climbing over you parting tool and breaking it.
5- Keep you parting tool as short as possible. On deep parts start with it out only a small amount and stop when you run out of length and lengthen your tool. The shorter you can keep it as you go, the better.
6- Use a good grade of cutting oil. Don't be bashful with it.... slop it on good. You want those chips to flow out easily and not get hung up. If they do, you're in trouble.
7- Here's a tricky part... sometimes when you get chatter you have to feed in harder to get a good chip started and stop the chatter. Of course if you feed in too hard you're in trouble. This can only be learned by experience and it is still a risky maneuver. It takes some finesse!
8- Run the lathe as fast as you can without chatter and from burning up your cutting tool. If you run it very slowly, and sometimes you just have to, it can be very difficult to feed it in by hand at a nice, gradual, steady pace. It's very easy to feed too fast and then you're in trouble.
9- Make sure your tool is exactly perpendicular to your work.
10- I usually grind my tool at an angle so the piece drops off leaving the burr on my stock. But, this angled grind can cause the tool to want to walk off sideways so only use a very slight angle or none at all.
11- The narrower the blade, then less likely to chatter. But, the more likely to break because it is weaker.
12- Lock your carriage in place.
13- Take the slop out of your compound slide.

There's my 5 minute brain dump!

Did you notice how many times I said you could get into trouble?

YMMV and I'm sure others have suggestions and may very well disagree with some of what I've said, but these are things that I have tried over the years with some success.

Good luck,
Ted

 

[eeler1]

What they all said. I find that even after executing all of those suggestions, some materials just resist being parted off on the lathe. I have a couple feet of mystery steel rod, I don’t know what it is, just that it hates being parted. Grab, chatter, etc, I get all possible parting ills trying to cut this heinous material.

Maybe practice on delrin or something similar to get your confidence up, then part something tougher.