Parting off in a Lathe

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liveaboard
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Re: Parting off in a Lathe

Post by liveaboard »

I use a hand spray bottle from a garden shop for coolant.
Allows one hand operation.
The pumps don't like suds much; they die after a few months, but the cost is low.
Spray pumps from nasty stuff like kitchen cleaners or anti-fungal spray work great, but the bottles aren't meant to last and they're always high and narrow to look large on the supermarket shelf, which helps them fall off my shop shelf.

You can set the spray to shoot a narrow stream, handy for squirting into a bore.
When parting, I dribble from above into the groove.
shootnride
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Re: Parting off in a Lathe

Post by shootnride »

BDD & Harold,

Thanks to both of you for your input.
BDD's comment about using the same speed/feed I would typically use for facing just doesn't compute well for me because for me, I consider facing just a clean-up operation to square the face of a part. My typical facing operation would be .005 to .025 DOC with a fairly fast feed rate. I think I'm pretty good at following the stated practices of squaring the tool with the work, setting tool height and keeping the tool sharp and my lathe is robust enough to deal with the work I do. As a general rule, I typically machine aluminum with HSS and everything else with carbide, but I don't own a carbide parting tool.
Harold's comment about a starting point of .003 feed rate is good info for me. I will do some experimenting and use that as a starting point. I assume that when you say "with a somewhat reduced spindle speed", you mean reduced from the speed that I would have been using to machine that particular piece of material.
Another question concerning parting is, do you ever change the speed/feed rate as the diameter of the cut is reduced as you get deeper into the material. For instance, I was recently parting a piece of 2" OD, 300 series SS and the thought did occur to me that I could probably stop for a minute and change to a higher spindle speed after I was about half way through the cut, but I didn't.
Anyway, I could probably ramble for quite a while on this subject, and I really do appreciate your help.
Thanks again.
Ted
Some people raise the IQ of the room when they enter.........others when they leave.
John Hasler
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Re: Parting off in a Lathe

Post by John Hasler »

I increase speed as the diameter decreases but that's because I have a variable speed drive. I probably wouldn't bother otherwise.
earlgo
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Re: Parting off in a Lathe

Post by earlgo »

Increasing the speed as the diameter gets smaller reminds me of another life (1986/7) when I was programming a larger Cincinnati Milicron CNC lathe, and the particular part was about 3/4" diameter. I set the constant surface speed to the recommended for that material and the feed at about .008 or .010" per rev. The operator punched the button and the ops started and when it came to the cutoff the part just disappeared. :D The operator was astonished to say the least. I stopped by later and noted that he had turned off the CSS feature and the feel was edited to about .001" per rev. I guess the operator wanted to see where the part went after cutoff.
Fun times, but programming the CM T10 horizontal mill with the 90 tool chain and pallet changer was more fun.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.
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Harold_V
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Re: Parting off in a Lathe

Post by Harold_V »

It's never a good idea to interrupt a cut, as that has the tendency to leave undercuts, or other witness marks, but if the parting cut is not a finish cut, or the resulting surface blemishes are not a problem, sure, stopping to increase surface speed is often a good idea, especially if you're parting a material like stainless, which normally responds to light feed and exaggerated positive rake far better than it does to little or no rake, and high feed rates. In a case where you're using fine feeds, the cutting is so slow that the increased speed is of benefit, especially on large diameter cuts.

Owning a machine like a Monarch EE makes changing speed real easy, but few are so fortunate as to have such a machine (I don't have one, unfortunately). Most home shop machines are either belt driven or geared head, and do not offer the opportunity to make changes on the fly. I can make changes (on the fly) with my Graziano, but it's in graduated steps, not a nice, uniform increase like one gets from a vari-drive.

Interesting comment about parting 2" diameter 300 series stainless. Unless it was 302 0r 303, that's no easy feat. If you can part that size and do it with success, you're certainly doing something right. Well done!

H
Wise people talk because they have something to say. Fools talk because they have to say something.
shootnride
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Re: Parting off in a Lathe

Post by shootnride »

Harold_V wrote: Mon Nov 30, 2020 5:30 pm
"like stainless, which normally responds to light feed and exaggerated positive rake far better than it does to little or no rake, and high feed rates"

"Interesting comment about parting 2" diameter 300 series stainless. Unless it was 302 0r 303, that's no easy feat. If you can part that size and do it with success, you're certainly doing something right. Well done!"
H
I will definitely try the "exaggerated positive rake" suggestion next time I part some stainless steel. When I was parting that 2" SS, I was running at 40 RPM and feeding by hand at a rate just aggressive enough to try to keep a continuous curl coming off. I have to confess that I am making an assumption (ya, I know what they say about assuming) that the SS I was machining was 300 series simply because it is non-magnetic. I'm no expert, so I suppose there are other possibilities for the alloy. I do know that it is some pretty tough stuff. I turned two tapers about 4 1/2" long on two sections just feeding by hand using the compound and was running at 140 RPM at .015 DOC and it was producing straw colored curls.
Anyway, thanks again Harold for the guidance.
Ted
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GlennW
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Re: Parting off in a Lathe

Post by GlennW »

shootnride wrote: Tue Dec 01, 2020 9:08 am I turned two tapers about 4 1/2" long on two sections just feeding by hand using the compound and was running at 140 RPM at .015 DOC and it was producing straw colored curls.
Anyway, thanks again Harold for the guidance.
Machining dry?
Glenn

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Harold_V
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Re: Parting off in a Lathe

Post by Harold_V »

If chips coming from stainless are discoloring to straw, you may be running too fast. Stainless is far less likely to change color unless it is well overheated. That said, if you're running HSS and not experiencing any cutting edge issues (short lifespan), no problem. You did good!

A comment about exaggerated positive rake and stainless. One of the pitfalls of too much positive rake is hogging, or self feeding. You can help manage that problem by reducing front relief to a minimal amount. The geometry tends to defy logic, and you're most likely not to find any of this in any texts you may read. I was fortunate to have this information disclosed to me when I was a young lad. The fellow who talked to me about the subject was just in his mid 20's, but his input was invaluable, in spite of my having first doubted his thoughts.

I've used his guidance for turning the corners off square stainless plate by tailstock pressure holding the piece in a lathe. By plunging straight in, the corners simply evaporate without issue. A lesson I've never forgotten.

H
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BadDog
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Re: Parting off in a Lathe

Post by BadDog »

Harold_V wrote: Sat Nov 28, 2020 4:36 amYou should be generating a ribbon, and, with luck, it will coil in the generated cut. You end up with a "watch spring", tightly coiled, for lack of a better description. That is likely not true if you're using insert carbide tools, however. They most likely do not generate such a chip. Hand ground tools can and will. The material being parted plays a huge role in this, too (my comments about mild steel, above, as an example).
That's the opposite of my limited experience. My proficiency for hand ground parting tools was never sufficient, though I've gotten quite proficient with normal turning/facing tools. That long slender finger to keep straight and all reliefs in order to control the chip well. My efforts in that area are now mostly limited to truncated versions for snap rings. HSS blades were my go to back then. And in both, I experimented with a divot behind the edge attempting better chip control, and ideally producing clock springs. Sometimes better or worse, but the tiniest deviation produced chips that wanted to turn into one or the other wall, and if I got deeper, bad things...

I didn't produce consistent clock springs in a range of steels until I started using the Sandvik insert blades. And since thin, VERY near 100% on steel from junk HR and "sucker rod" to pre-hard medium carbon steels (at the moment I don't recall ever parting high carbon hard?). But with that cutting tool, there is no effort, no concern, it just works as desired every time. For the first while, I liked to keep the clock spring chips as I found them appealing to look at, so precise and consistent, like some sort of art. I got over that pretty fast, and now they just go with the rest of the chips. And I generally use the straight variety, but have inserts that throw left and right to leave a nicer finish on the side of choice. I don't have many of them (never use them), but they also make inserts for snap rings and o-rings.

But for whatever the reason, my experience with insert parting tools appear to be very different from yours. Even on my old Rockwell 11, that insert parting tool has been one of the best investments I have made in tooling. No way it's the right decision for less rigid machines, but contenders with that Rockwell 11 are not at all unusual in home shops these days.
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BadDog
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Re: Parting off in a Lathe

Post by BadDog »

shootnride wrote: Mon Nov 30, 2020 9:31 amAnother question concerning parting is, do you ever change the speed/feed rate as the diameter of the cut is reduced as you get deeper into the material.
With my old Rockwell 11, which had a Reeves variable speed drive, I did crank up the speed as it got closer to the center, but there is inevitably a point where surface speed rapidly approaches zero. With my current gear head, I can't really change speed while running, so I start at or near the maximum speed for the initial OD cut, and let it run till it's done.

Lots of folks have various tricks for delivering lubricant (or coolant) into the cut. I prefer the lab "wash down" bottles as they can generate a very consistent very fine stream right to the cutting edge even when deep in the cut. But if you use carbide, be very wary of intermittent application of lubricant, and particularly coolant. If you let the carbide edge heat up, which happens fast, hitting it after starting can shatter the edge.
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Harold_V
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Re: Parting off in a Lathe

Post by Harold_V »

Frankly, your report of the nature of the chip you generate with your insert tooling is quite unlike what I had expected. Reason is, my lathe does not allow a tool shank greater than ½", and I have less than good memories of using commercial parting tools in the "old days". I've been tied to my Graziano since 1967, and it's the only machine I know, although I have spent a small amount of time on a couple other lathes, just not in my shop. For that reason, I am not the least bit familiar with modern parting tools, so I should have mentioned that I have NO experience with them. I was not aware that they might generate such a chip as I described, assuming that they had a tendency to alter chip configuration so it would be narrower than the developed groove. I thank you for the information.

A divot (chip breaker) on a parting tool isn't a good choice. I've hand ground parting tools since I've been able to grind HSS, and I never use that type of geometry. Too many issues when it's not exactly right, a condition not easy to achieve freehand, plus it spells doom for the tool when re-sharpening is required. Life expectancy is greatly reduced as compared to the grind I prefer. What I do is use the periphery of the wheel to grind a sweeping relief on the top of the tool. The objective is to create minimal positive rake, and to add to the relief of the tool. Such a grind will produce a wonderful cut, and do it time and again. I confess, it may be a little troublesome with mild steel, however, but that's attributed to the nature of the material, which is troublesome for most cuts. Because of the nature of the grind, the parting tool can be sharpened numerous times, extending the useful life of the tool tremendously. It loses center, but that's not a problem with modern posts, as you know.

I do have one very nice memory of parting tool that defied all logic, and it goes hand in hand with the concept of extreme positive rake. I've posted on this before, but in a nutshell, the bearing housings for the stable platform of the guidance system of the missile were made in-house (as was the entire guidance system). The housings were made from a magnetic grade of stainless, and were heat treated. I do not recall the alloy. These housings were machined from bar stock (about 3¼" diameter) on a large W&S turret lathe. The material was issued from stores in bar form, not individual pieces, with the housings parted after machining the first side. Standard parting tools were troublesome, and had created more problems than they had solved, often shattering in the cut. It was clear that a different method of parting the housings was required, as parting was taking far more time than machining, and the housings were made by the hundreds (eight pieces were used per guidance system).

Keeping in mind that carbide was still in its infancy, and that brazed carbide was in abundant use, the company brought in a rather strange looking parting tool, built by Manchester. The parting tool was brazed carbide with a tip about ½" long, well brazed to a steel shank that had a V configuration on the bottom. The holding tool offered a female groove in which the parting tool was inserted and clamped, and provided considerable support, including at the brazed tip. The most unusual feature of this tool was that it had the ability to rotate on its center, so rake was adjustable. With a positive rake setting that was about 18°, a somewhat light feed was used to part this material, at a rather rapid surface speed. The problems with parting the housings evaporated. The chip from this tool was a long, slender ribbon. Needless to say, flood coolant was used.

H
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shootnride
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Re: Parting off in a Lathe

Post by shootnride »

GlennW wrote: Tue Dec 01, 2020 9:56 am
shootnride wrote: Tue Dec 01, 2020 9:08 am I turned two tapers about 4 1/2" long on two sections just feeding by hand using the compound and was running at 140 RPM at .015 DOC and it was producing straw colored curls.
Anyway, thanks again Harold for the guidance.
Machining dry?
Glenn,

I experimented with using cutting oil both by brush application and flood. Neither method seemed to produce any benefit and the light brush coat just caused a lot of smoke. Ultimately, my best results were machining dry using a Kennametal TNMG insert.

Ted
Some people raise the IQ of the room when they enter.........others when they leave.
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