Proper chip formation

[refinery mike]

I read lately what Harold V said about stringy chips and multiple stitches. I would like to hear more on that subject. what is the best chips to produce and how do you get them. what are dangerous chips and how do you avoid them, I would like to avoid the stitches. Thank you Harold for bringing this up.

[BadDog]

The long "ribbon" chips are the worst. And the longer they get, the worse they are, often getting wrapped up on work/chuck and whipping around violently. If possible, NEVER mess with chips while the lathe is running. And again, the longer the chips, the more the danger. If you can't get it to break a chip any other way, then stop/start the feed (except for final finish pass(es).

The sole exception to "don't mess with chips while the lathe is running" is for those materials that just won't break a chip (annealed 4340, some stainless, etc), and where finish is paramount. Here, much caution is required. I have a long cheap POS screw driver (~14" or so?) I got somewhere along the way. Almost dead soft chinese crap, worthless as a screw driver, and the flat blade was twisted somewhat screw-like. I straightened the end, and bent it to a shallow hook just past 90*. I use that while standing well clear to rake and/or direct problem ribbons. The screw driver handle is quite useful in this application. You can obviously make something like this from common bar/key stock. But if you do, be aware that there will be times (like finishing cuts) when you will be pretty much forced to use it with the lathe running. So design it with a "handle" that you can hold but won't hold onto you should it get grabbed and wound up in the chuck!

You (or at least I) also often get cuts clearing the accumulations/nests/balls/wads with the machine off. Don't use your hands here. Often when you grab a hand full that is apparently clear, one loop gone unobserved hangs the chuck/cutter/handle/something and it pulls back. Usually this is accompanied by a "zip" sensation followed by stinging, warm sticky wetness, and shortly afterward the air turns blue. So I *usually* (until I get careless) use the hook, or a LONG set of forceps like tongs to clear the nests.

But the chips you want are heavy short curled chips. Folks call them "6's and 9's (among other things). The pile up like fine gravel, easily cleared, generally the ideal state. Next up you get short tight curls, often like a cork screw, maybe a couple of inches long. Still quite dense, easily managed, and reasonably safe. With the right bit (including integral or secondary chip control) you can usually manage one of these results. But it often takes more feed, speed, and/or DoC than many HSMs are comfortable with to achieve the desired result (or the machine may not be capable). If you are sure of your tooling (takes time), then playing with the 3 primary variables usually gets you where you want to be on all but final finish/size pass, and there you sometimes just have to learn to deal with it.

Mostly I run speed pretty close to recommended ranges, so that's the last thing I tend to play with (as long as chip color is ok). DoC is often gaged to get me into consistent results hitting some target in a certain number of steps. It is also tied to the tool profile/size. Sometimes you just feel that changing DoC will get you where you want to be, but I tend to leave that alone to start with in favor of feed. Machine size/rigidity, power, tool profile, and material govern your options with feed, but in general, if you can manage it, faster feed is the most likely to give you nice manageable chips. But again, that assumes you have a tool profile conducive to breaking chips for the material/speed/feed/doc in question (or a secondary chip breaker in some cases). The wrong bit profile leaves you mostly SOL on problem materials.

[Fender]

These chips would be dangerous.

[Bruce_Mowbray]

And these are twice as dangerous....

100" Niles wheel lathe reprofiling trailing truck wheels

[Harold_V]

And these are twice as dangerous....

Talk about a bad need for a chip breaker!
What's the depth of cut? Feed rate looks rather aggressive, too.

Harold

[oldbrock]

One machinist was machining 316 stainless and had cuttings, long strings, all over the shop floor, another machinist wearing running shoes stepped into them and tried to get rid of them by kicking at them. He succeeded in severing his achiles tendon clean through. Doctors had a devil of a time re attaching it. Be careful out there, Peter

[Harold_V]

One machinist was machining 316 stainless and had cuttings, long strings, all over the shop floor, another machinist wearing running shoes stepped into them and tried to get rid of them by kicking at them. He succeeded in severing his achiles tendon clean through. Doctors had a devil of a time re attaching it. Be careful out there, Peter

That concerned me so much that I wore engineer's boots as a younger guy, then switched to Wellingtons as I aged, always with steel toes. Ankle protection is very desirable in the machine shop.

I can't think of any chips worse than those created by machining stainless. Sharp as a razor, and tough to break in most instances.

Harold

edit: corrected punctuation

[oldbrock]

WELLINGTONS? You a displaced limey too Harold?

[Harold_V]

WELLINGTONS? You a displaced limey too Harold?

Uhhhhh----no!
While born in the US, my father immigrated from Greece, as did my mother's parents.

Harold

[Bruce_Mowbray]

And these are twice as dangerous....

Talk about a bad need for a chip breaker!
What's the depth of cut? Feed rate looks rather aggressive, too.

Harold

The tool (roughing is actually just a 1 1/2" diameter slug of high performance HSS held in a steel "pocket" holder.
The depth of cut is 3/16" and the 1/4" per revolution at 3 RPM.

[Fender]

Bruce,
I thought you were making coil springs for a Chevrolet!

[Harold_V]

The tool (roughing is actually just a 1 1/2" diameter slug of high performance HSS held in a steel "pocket" holder.
The depth of cut is 3/16" and the 1/4" per revolution at 3 RPM.

Blink! Blink!
Astonishing!

The HSS you speak of----is it magnetic? Makes me wonder if, maybe, it is Stellite, or something similar. Generally HSS won't hold up long if it's making blue chips, which those appear to be.

One of the most fierce cuts I heard of (I saw the chip) was a 1" deep (per side) with .065" feed. There's nothing quite like being able to move metal when required to do so.

Thanks!

Harold