How to use round indexible lathe tool?

abstruse · Aug 18, 2020

I've been using indexible carbide tools for decades, but I just got my first round one (RNMG) with the idea that round cutters are good for heavy stock removal.

I can't get it to work. On aluminum barstock, it cuts very roughly and the turned shaft size varies greatly. I've tried various heights obove center line, makes no difference

I must be missing something simple. Any ideas? Thanx.

DDoug · Aug 18, 2020

abstruse said:
I've been using indexible carbide tools for decades, but I just got my first round one (RNMG) with the idea that round cutters are good for heavy stock removal.

I can't get it to work. On aluminum barstock, it cuts very roughly and the turned shaft size varies greatly. I've tried various heights obove center line, makes no difference

I must be missing something simple. Any ideas? Thanx.

I'm pretty sure it's a negative rake tool.

Try it below centerline, it sounds like your rubbing the tool.

However, aluminum usually uses positive rake carbide tooling.

Hardplates · Aug 18, 2020

I have very little experience with round turning tools. The only time I've used them is ceramics in very difficult turning with fairly light cuts. Something tells me there is way too much contact area and push off for it to be an effective roughing tool unless maybe on a super rigid machine and heavy workpiece.

No sure why you would even consider them for aluminum unless your just playing around. Try them on something hard.

eKretz · Aug 19, 2020

Yeah I had access to these at lots of places... Normally there were only two situations where I actually wanted to use one.

First, the obvious, when I needed a radius of the same size or larger than the insert. Second, for heavy roughing in fairly hard material, like chilled cast iron or hardened stainless, etc. They don't work very well in small lightweight machines, not rigid enough. And yeah, RNMG is a negative insert, you do not want it above centerline.

Bill D · Aug 19, 2020

I suppose the theory is you have an infinite number of new cutting faces so the insert will last forever.
Bil lD

DDoug · Aug 19, 2020

Bill D said:
I suppose the theory is you have an infinite number of new cutting faces so the insert will last forever.
Bil lD

There was a manuf that made ones that rotated during the cut.....

dian · Aug 19, 2020

i use a round hss tool for finishing. works well.

EmGo · Aug 19, 2020

Hardplates said:
I have very little experience with round turning tools. The only time I've used them is ceramics in very difficult turning with fairly light cuts. Something tells me there is way too much contact area and push off for it to be an effective roughing tool unless maybe on a super rigid machine and heavy workpiece.

No sure why you would even consider them for aluminum unless your just playing around. Try them on something hard.

Did lots of motorcycle wheel hubs with round inserts. They should have been positive rake but might have been neutral, not sure they had positive rake rounds then. About 1/2" diameter Sandvik.

The reason was, you can cut both ways and go around corners and even do a slight bit of negative taper on the flanges. Don't need to change between left and right and you can plunge into narrow slots. They chatter easy though so you have to run them hard.

Mount the blank on a mandrel, pour the coals to it, bury the insert, 30 hp motor running consistently at 120% load, off comes the aluminum. 2024 bar stock, starting at about 6" diameter, ended up weighing a couple pounds in a short time.

They can work okay on the right part.

Limy Sami · Aug 19, 2020

'' How to use round indexible lathe tool?''

In short :- only when you have to :eek:

TeachMePlease · Aug 19, 2020

digger doug said:
There was a manuf that made ones that rotated during the cut.....

SHARS?

I don't think theirs do it on purpose, though.

DDoug · Aug 19, 2020

TeachMePlease said:
SHARS?

I don't think theirs do it on purpose, though.

Naw...these had bearings under the seat, made in Kalifornia IIRC.

CarbideBob · Aug 19, 2020

digger doug said:
Naw...these had bearings under the seat, made in Kalifornia IIRC.

Yes and the bearing a pain. The milling cutters using it were more popular but would turn out to be not so economical in use.

RNMG not a good AL insert on a lathe unless you have big parts, big machine, heavy feed rate and high pressure coolant.
The forces all wrong, unground side, not enough heel clear, honed edge, and not enough top rake.
Basically everything wrong. Chatter city and does not want to hold size.
Grind the top off the tool to get a sharp edge, drop below C/L to get the clear, lots of lube or WD-40 and you can sort of make it work.
You are not doing anything wrong, the tool and holder not designed to do this.
RNGG or RNGP if in an AL type holder better but these rare ducks.
Bob

EmGo · Aug 21, 2020

CarbideBob said:
Yes and the bearing a pain. The milling cutters using it were more popular but would turn out to be not so economical in use.

Remember the ones for milling, had a single insert in a full-round body, the inserts were laid way over and sharpened oddly, positive rake ? Those used to work super for finishing. But they didn't spin, just clamped down solid.

RNMG not a good AL insert on a lathe unless you have big parts, big machine, heavy feed rate and high pressure coolant.

Agree with everything you say (except don't need high pressure coolant) but when faced with a part like this

they worked pretty well for roughing out the center section. Needle in the red and chips everywhere. I love the howl of a motor working hard

Yeah you can plunge in at an angle, use left and rights, blend the bump at the bottom where they meet but ... a 1/2" round with a brawndo lathe was faster and worked (I think) better. Cut in both directions, plunge go plunge go plunge go, fast. If you want to get fancy you can arc-plunge, which helps a tad with the chatter when you change directions.

Finished with a 6mm positive rake round on an extended holder, just a light fast skim cut across the entire surface, came out nice except you're right, that bastard really wanted to chatter.

Still think it's the best way to make that part tho. Either that or forgings

eKretz · Aug 22, 2020

Yep they work pretty good for roughing, but definitely can not let the tool dwell. Positive rake circles are a bit better about chattering but still way worse than a tool with less area in contact at once.

DDoug · Aug 22, 2020

EmanuelGoldstein said:
Remember the ones for milling, had a single insert in a full-round body, the inserts were laid way over and sharpened oddly, positive rake ? Those used to work super for finishing. But they didn't spin, just clamped down solid.

Same company, different cutter.
Here it is in "BIG PRINT" so even YOU can read it..... :nutter:

Innovative Rotating Inserts | Rotary Technologies Corporation
“Innovators of the Insert that Rotates
as it Cuts“

ratbldr427 · Aug 22, 2020

I have a Sandvick tool that I used to make two 4 groove A=B type steel 8" pulleys.Using a manual lathe it worked fine didn't have any chatter,finish fine.Managed to do v grooves, od and face with only a few position changes.So in my case it was a good tool for the job.I think it was a 1/4" od insert.

john.k · Aug 22, 2020

I bought a 1/2 dia holdr and ten boxes of inserts,all Carboloy....Cheap ,very ,because they have never been any use on a 24 x 72 Swift lathe ,4 jaw chuck must weigh 500lbs .....So maybe heavier is needed to avoid chatter. I thought maybe the inserts might be usable as little rollers.

EmGo · Aug 22, 2020

digger doug said:
Same company, different cutter.
Here it is in "BIG PRINT" so even YOU can read it.....

What's your problem, doug ? Someone shit in your cheerios ? This topic is about inserts, for some reason you feel compelled to be an asshole ?

trevj · Aug 22, 2020

EmanuelGoldstein said:
What's your problem, doug ? Someone shit in your cheerios ? This topic is about inserts, for some reason you feel compelled to be an asshole ?

And what part of the "inserts" criteria did he fail at there?

'Cause, the video I looked at, was about an insert!

One that rotated as it was working, even.

Milland · Aug 22, 2020

I'd swear that I remember reading about the rotating insert round cutter back in the early 2000's, maybe even 1990's? I think the idea goes back a ways, but the obvious factor of keeping a bearing alive isn't trivial for this use.

I watched two videos, one OD and one boring, can't say that they overwhelmed me with "gotta have it"...

How to use round indexible lathe tool?

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