I need help

All discussion about lathes including but not limited to: South Bend, Hardinge, Logan, Monarch, Clausing and other HSM lathes, including imports

Moderators: GlennW, Harold_V

KellyJones
Posts: 189
Joined: Mon Nov 29, 2010 10:10 pm
Location: Snohomish, WA

I need help

Post by KellyJones »

...and beyond the obvious, i could use some help with a boring project.

I am boring an approximately 4.0 inch diameter hole in a 3/8 inch thick ring made from mild steel. I am turning at 80 RPM, taking .020" to .025" depth of cut, and the feed is about .010" per revolution. I am using an indexable carbide insert boring bar. The bar has the rake angle set up already, so no adjustment is possible, and when loaded into the quick release tool folder, the rake is about 10 degrees. I took special care to set the point of the insert right at the height of a dead center mounted in the tail stock.

But I keep breaking inserts. The cut starts out all right, but about .050" deep into the bore it breaks and the work tries to come out of the chuck.

Any ideas what I''m doing wrong?

thanks
Attachments
image2.jpeg
image1.jpeg
image0.jpeg
Kelly Jones, PE
A life spent making mistakes is not only more honorable, but more useful than a life spent doing nothing.
George Bernard Shaw
(1856-1950)
User avatar
GlennW
Posts: 7284
Joined: Sun Apr 15, 2007 9:23 am
Location: Florida

Re: I need help

Post by GlennW »

The feed rate looks a bit high for 80 rpm. Try slowing it down.

Carbide likes spindle speed to keep it cutting rather than digging in and chipping the edge.

May need a harder grade insert as well.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: I need help

Post by pete »

Ditto on Glenn's points. But is the insert itself breaking or just chipping the tips off? Industry lists hardness grades from C2 up to I think C12? I've had some offshore one's that were decidedly soft and crumbly so maybe a poor composition. One reason I no longer buy the cheap ones. If yours are more brand name, then maybe harder or softer? It's also not unknown to have inclusions in the metal. Is it happening always at the same depth? I've read posts where some have mentioned finding even broken pieces of carbide embedded in the metal. Rare maybe, but still possible.
User avatar
Bill Shields
Posts: 10460
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

Re: I need help

Post by Bill Shields »

I could do that with a HSS bit at the correct speeds.

Other things that can destroy carbide is vibration...it IS a ceramic and the tips like pressure not light vibrating cuts.

Your tool setup looks reasonable from what we can see, but have no idea of how the work is held.. the ring might be ringing...


When you say BREAKING INSERTS...how many have you broken?
Too many things going on to bother listing them.
jcfx
Posts: 713
Joined: Sun Aug 09, 2009 1:24 pm
Location: NY

Re: I need help

Post by jcfx »

Maybe I'm missing something, 80 RPM is kinda slow, no ?

I also don't undertand how the insert is held in the holder, it doesn't look like the one's I normally see where the
insert is screwed down from the top with a torx screw. Could it be that the insert is wobbling in the holder seat ?
User avatar
GlennW
Posts: 7284
Joined: Sun Apr 15, 2007 9:23 am
Location: Florida

Re: I need help

Post by GlennW »

jcfx wrote: Wed Jan 19, 2022 6:30 pmMaybe I'm missing something, 80 RPM is kinda slow, no ?
Way too slow.

Should be three times that speed for carbide, but I have no idea what machine is being used. A small bench lathe like an Atlas or SB isn't going to like something that diameter turning at very much speed for rigidity reasons.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
jcfx
Posts: 713
Joined: Sun Aug 09, 2009 1:24 pm
Location: NY

Re: I need help

Post by jcfx »

KellyJones wrote: Wed Jan 19, 2022 4:56 pm
..... The cut starts out all right, but about .050" deep into the bore it breaks and the work tries to come out of the chuck.
I missed that part of your post, can you post a picture of your setup ?

If your insert breaks your work shouldn't come out of the chuck, are you using a independent 4 jaw chuck ?
Round stock is never round if you get my meaning, if you haven't turned the OD of the ring to be concentric
a standard chucks jaws aren't going to grip the work evenly, you would have to use a soft metal to shim the grip
or a indepenent 4 jaw chuck.
But it's all moot since the hole your boring wouldn't be center to the OD, it would be close but not dead nuts
with a indi 4 jaw..
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: I need help

Post by Harold_V »

Kelly,
What is the wall thickness of the ring?
Have you tried using HSS instead of carbide? In my experience, positive rake inserts aren't fond of feed rates that you are using. You most likely would enjoy better success if you ran around four thou, and less for a good finish.
Do you have soft jaw capability? What parameters are you trying to hold? Tight tolerance? Is finish critical?

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Russ Hanscom
Posts: 1955
Joined: Wed Mar 15, 2006 11:10 pm
Location: Farmington, NM

Re: I need help

Post by Russ Hanscom »

Is this by chance a torch cut ring?
jmanatee
Posts: 32
Joined: Mon Mar 09, 2015 12:17 pm

Re: I need help

Post by jmanatee »

Or Plasma cut?
KellyJones
Posts: 189
Joined: Mon Nov 29, 2010 10:10 pm
Location: Snohomish, WA

Re: I need help

Post by KellyJones »

Thanks for all the replies.
I'm getting the message that the sped and feed are wrong. I used the 80 RPM because much faster than that, the chips come off hotter than blue blazes and i keep getting burned by the flying chips.
I am using a Grizzly 4003 lathe, which is 12 X 36. While not a paragon of stiffness, it should be able to handle his job.
I have broken about 5 different carbide inserts. Three on the indexable tool I shared in the last post, and at least two brazed boring bars. I though I had the boring bars at the wrong rake angle, so I switched to the indexable tool since the rake was built in. I don't have any HSS boring tools.
I cut the stock out of plate with a band saw, then used the lathe to make the OD true and round. I then switched to chucking on the OD to finish turning the bore.
The project is an experiment to see if I can cut an internal ring gear on the lathe, so the concentricity to the OD isn't critical. The ID does need to be true, round and sized to about .002" to get the project to work.

Attached is a view of the set up. I haven't cleaned up all the swarf yet. You can see on the OD where the work started spinning in the chuck.
Attachments
image0.jpeg
Kelly Jones, PE
A life spent making mistakes is not only more honorable, but more useful than a life spent doing nothing.
George Bernard Shaw
(1856-1950)
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: I need help

Post by Harold_V »

That's not likely to work under most circumstances. The ring is too thin to grip securely and would distort beyond your two thou requirement if you tried. The tool chipping is most likely due to movement of the ring, exacerbated by the rapid feed rate.

This is a classic example of the need for soft jaws. Pie jaws, in fact. I suspect that if you support the ring better (much better) what you're trying to achieve is doable. In any event, I'd still suggest you lower the feed rate unless you are roughing only.

If you have the ability to make and use pie jaws (two-piece chuck jaws are pretty much mandatory), make sure that you machine a register (a shoulder) so the ring is supported in regards to perpendicularity. That way the part won't move under pressure, and the large area of contact, machined to the proper diameter, will prevent distortion, while allowing greater chucking pressure.

If you don't have soft jaw capabilities, I strongly encourage you to make a holder. Bore an aluminum plate, one thicker than the piece you intend to hold. The cavity would be a few thou shallower than the ring, so screws can be used to retain the ring in the cavity. If you choose socket head cap screws, they can pick up the outer edge and hold the part securely without distorting. The holder would be rigid enough to chuck firmly. If the holder is made from a plate considerably larger than the part, you should be able to bore through (smaller than the shoulder diameter but providing relief for future machining in forming the internal gear).

H
Edit: Surely you have some HSS blanks? You can EASILY fashion a boring tool, especially for the shallow depth required. It would look similar to this:
Attachments
Boring tool1.jpg
Boring tool2.jpg
Wise people talk because they have something to say. Fools talk because they have to say something.
Post Reply