Parting off in a Lathe

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shootnride
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Re: Parting off in a Lathe

Post by shootnride »

Harold_V wrote: Tue Dec 01, 2020 4:07 pm 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
Harold,
This is pretty interesting. What type of tool are you using to do this ?
Ted
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John Hasler
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Re: Parting off in a Lathe

Post by John Hasler »

On a casual look for parting inserts in some on-line catalogs I see a lot of positive rake (also lots of complex geometry).

Example: https://www.travers.com/iscar-tag-tang- ... tname=SITE
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BadDog
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Re: Parting off in a Lathe

Post by BadDog »

Here is a link to an image of a tool similar to what I use. My inserts are single edged and much shorter than those Kennametals, with a cutting edge more similar to that shown in the link posted by John above, but the rest of the cutting geometry appears about the same, and it shows chips like I routinely experience.

I thought I maybe had a curl in my chip tray as it's not been all that long since I used it, but sadly, it appears I was too successful in keeping that tray (more like bin) cleaned out.

And my tool post blocks are CXA with a max of 3/4" bit holding capability. The blade holder has a 1/2" block/tongue that fits full length of the CXA block, and allows use of a 1" blade insert holder. I've got another that is a 1-1/4" blade and allows a substantially longer deeper parting capability.

Image

And this is the adapter like I've got.

Image
Russ
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shootnride
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Re: Parting off in a Lathe

Post by shootnride »

Those are some pretty interesting profiles. I keep reading so much positive feedback about these carbide parting tools that I think I'm going to have to get one. Time to start doing my homework.
Thanks for the input gentlemen.
Ted
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BadDog
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Re: Parting off in a Lathe

Post by BadDog »

I would suggest that only if you have a relatively robust machine, and power feed. While you may achieve success, they are not cheap, and hand feeding can easily damage inserts, or the pricey blades.
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GlennW
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Re: Parting off in a Lathe

Post by GlennW »

BadDog wrote: Thu Dec 03, 2020 1:27 pmI would suggest that only if you have a relatively robust machine, and power feed.
If I'm not mistaken, it's a Graziano SAG 20.
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Harold_V
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Re: Parting off in a Lathe

Post by Harold_V »

shootnride wrote: Wed Dec 02, 2020 9:03 am
Harold_V wrote: Tue Dec 01, 2020 4:07 pm 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
Harold,
This is pretty interesting. What type of tool are you using to do this ?
Ted
Imagine a HSS right hand turning tool, or a tool ground such that it can be mounted so the end cuts, much like a parting tool. The right hand tool would be mounted parallel to the spindle, while the end cutting tool would be mounted @ 90° to the spindle. Either one would work equally well. The difference being you don't create a slot, but machine the width of the plate in one pass. My experience was with plate about 1/8" thick, and was about 5" square. If one has wider plate, two or more cuts may be required, but the process would work equally well.

The tool is ground with extreme positive rake by grinding a chip breaker that is deep and wide. It is important that the chips flow easily. The breaker isn't intended to break the chip, and it most likely will not. If it does, it may be too narrow. The cutting edge may be in the neighborhood of an 18° angle, and appears to be fragile. The feed rate (it should be used with power feed) is quite slow---something like .0015/.003". Surface speed can be surprisingly fast (considering the alloy) because the shearing action, along with the light feed, produces far less heat than one would generate using a coarse feed with less rake. The light feed, accompanied by the high rake, reduces cutting pressure, almost totally eliminating any hammering of the cut. The cutting edge does undergo degradation, but it appears to continue to cut reasonably well.

I had the opportunity to see the difference because I had started the project with conventional tools, and was beating the tool mercilessly. I was almost offended by the suggestion to use high rake and to plunge, but I was to the point where I'd try just about anything, as I was struggling getting the corners off.

I have used this method on my Graziano on occasion. It's a medium duty machine, 12".

H
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shootnride
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Re: Parting off in a Lathe

Post by shootnride »

GlennW wrote: Thu Dec 03, 2020 2:17 pm
BadDog wrote: Thu Dec 03, 2020 1:27 pmI would suggest that only if you have a relatively robust machine, and power feed.
If I'm not mistaken, it's a Graziano SAG 20.
Not quite that big Glenn. It's a SAG 14, but it does seem to be a pretty rigid machine. But, I'm impressed that you even knew that it was a Graziano. I guess that must have been mentioned sometime in the distant past and it's obvious that your memory is much better than mine.

Ted
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shootnride
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Re: Parting off in a Lathe

Post by shootnride »

Harold,
Thank you for that description of the process for cutting the corners off of a plate. I wish I had known about this process about a year ago. I had occasion to cut a couple of circles about 4" OD from an odd shaped piece of 3/8", 316 SS plate. But, I'm sure there will be more opportunities. I've gotten a lot of useful information about parting on this thread. Enough that I'm going to save a link to it for future reference.
Thanks again.
Ted
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Harold_V
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Re: Parting off in a Lathe

Post by Harold_V »

You're welcome, Ted. I hope that there's something of value included that might be helpful when you're faced with machining tough materials.
Funny thing about stainless is it's rarely hard--it just doesn't like to be horsed. The 300 series, in particular, simply do not respond well to high feed rates and little rake (excluding the free machining grades). A light feed with excessive rake tends to defy logic, but it works, and works far better than I'd have ever imagined.

There are times when one will discover that the norms of machining aren't carved in stone. This appears to be one of them. It's hard to refute the results, but for those who have struggled with interrupted cuts in either 304 or 316 (other grades can be included, although they are not as likely to be encountered), it becomes immediately obvious that the approach discussed is the solution. For all I know, it may work with carbide, too. I've tried only HSS. The thin edge in carbide looks to me to be too fragile, but who knows?

One more thing. If you can find Stellite, it will out-perform HSS by a generous margin. It deals with heat much better. TanTung is similar. A quick check is to see if the tool is magnetic. Stellite and TanTung are not.

H
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BadDog
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Re: Parting off in a Lathe

Post by BadDog »

That method for rounding square plate is new to me too. I'll be putting that to use, and wish I knew it sooner. As always, thanks!
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liveaboard
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Re: Parting off in a Lathe

Post by liveaboard »

I did part on power feed today; it was quite exciting.
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