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Carbide Inserts Breaking Immediately

BoxcarPete

Stainless
Joined
Nov 30, 2018
Location
Michigan, USA
I've been using TPG 322 inserts in a boring bar for the lathe for a little over a year now, and they've been solid and reliable for all that time. I don't do all that much machining, so in that time I only went through three inserts. When I went to replace the third one, I dropped the spacer from the boring bar holder right into the damn chip pan. Searched for a while and finally gave up on finding it because the chip pan was pretty full. As I recall, it was only a little triangle of steel slightly smaller than the insert meant to pinch the insert into the holder, so I made a new one.

Now, the next three inserts have broken within seconds of starting a cut on all three corners. Doesn't matter if I baby it, if I do I might get a dozen seconds rather than a couple. Since I changed the insert at the same time as I lost the spacer, I don't have the experience to know if I am just unlucky three times in a row, or if there really is a difference in the way my new spacer holds the tool that's causing them to crumble once I get them within an inch of a workpiece.

For what it's worth, the boring bar is marked "FIRTHITE FS 810F" and I was unable to get any hits on a quick search. Am I SOL and in need of a new boring bar?
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
Shim seats can be had but I don't know what your holder needs
Are the breaking inserts out of the same box?
Inserts can have different clearance angles
I think TPG should have 11* clearance, better check that if a different box of inserts.

I like to hold my boring bar up to something of the same hole and eyeball that the heal won't rub.
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
Yep, sounds like perhaps your shim/seat isn't flat. The originals are carbide and they are ground. How did you make your replacement?

It also occurs to me that you could be talking about a piece on top of the insert - that would usually be a chipbreaker, but also made of carbide, not steel. You weren't very clear about what exactly you've lost...
 
Joined
Nov 19, 2007
Location
marysville ohio
I've been using TPG 322 inserts in a boring bar for the lathe for a little over a year now, and they've been solid and reliable for all that time. I don't do all that much machining, so in that time I only went through three inserts. When I went to replace the third one, I dropped the spacer from the boring bar holder right into the damn chip pan. Searched for a while and finally gave up on finding it because the chip pan was pretty full. As I recall, it was only a little triangle of steel slightly smaller than the insert meant to pinch the insert into the holder, so I made a new one.

Now, the next three inserts have broken within seconds of starting a cut on all three corners. Doesn't matter if I baby it, if I do I might get a dozen seconds rather than a couple. Since I changed the insert at the same time as I lost the spacer, I don't have the experience to know if I am just unlucky three times in a row, or if there really is a difference in the way my new spacer holds the tool that's causing them to crumble once I get them within an inch of a workpiece.

For what it's worth, the boring bar is marked "FIRTHITE FS 810F" and I was unable to get any hits on a quick search. Am I SOL and in need of a new boring bar?
Must be a POS tool, any real tool has a separate fastener for the "spacer" as you call it. junk it and get a Kennametal, Iscar or some other quality tool.
 

atex57

Hot Rolled
Joined
Sep 6, 2006
Location
SW Wisconsin
In a pinch you can grind two sides of a TPG to make it sit farther back and it can be your new seat "spacer". You may have to adjust the height.

Ed.
 

sfriedberg

Diamond
Joined
Oct 14, 2010
Location
Oregon, USA
Shim seats for the common insert sizes (TPG32x is a common one) are fairly standard, with industry standard nomenclature. If you can't dig your old seat out of the chip pan, you can probably buy a new one at an industrial supplier and try it. It's not guaranteed to fit, especially on smallish boring bars, but it's likely to fit.
 

BoxcarPete

Stainless
Joined
Nov 30, 2018
Location
Michigan, USA
I'd keep looking if I were you...

I looked as much as I was ever going to right at first, grabbed the rats nests of razor wire, shook them out, then swept everything else off to one side and grabbed it handful by handful over to the other. Looking isn't an option any longer.

Yeah, you need to find the original spacer. I'll bet there's enough geometric difference between what you made and the original such that the carbide inserts (super brittle) aren't being supported correctly, and the loads are snapping it.

Pretty much what I was afraid of...

Yep, sounds like perhaps your shim/seat isn't flat. The originals are carbide and they are ground. How did you make your replacement?

It also occurs to me that you could be talking about a piece on top of the insert - that would usually be a chipbreaker, but also made of carbide, not steel. You weren't very clear about what exactly you've lost...

The replacement is A2, cut on the mill and then dusted off on the surface grinder (on the bottom side, the top is not ground). It sat between the insert (on top) and the holder, and the original did break chips as well. Picture of the replacement attached.

In a pinch you can grind two sides of a TPG to make it sit farther back and it can be your new seat "spacer". You may have to adjust the height.

Ed.

Tried that too, no luck. Didn't adjust the height though, the inserts are .125" and as close as I can figure the original spacer was .090 or so, probably 3/32" which is how I made my replacement. I don't have a good wheel to use on carbide for the surface grinder, so I don't know that thinning it out is going to be worth trying.
 

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michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
The shim seat has to be the same thickness or it may make the insert higher than desirable for your boring bar. It has to be small enough IC or it may rub.

I see no reason the steel one would not work, but the steel one will not protect your boring bore pocket as the carbide one is designed to do.

Is it a hold-down top clamp boring bar, and does the clamp set correctly on the inset so as not to tip the insert up-angle so off the seat,

If there is any space under the inset when clamped the insert will chatter, if so you may need to resurface the pocket bottom, to blue in to the clamped insert/shimseat.
 
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BoxcarPete

Stainless
Joined
Nov 30, 2018
Location
Michigan, USA
The shim seat has to be the same thickness or it may make the insert higher than desirable for your boring bar. It has to be small enough IC or it may rub.

I see no reason the steel one would not work, but the steel one will not protect your boring bore pocket as the carbide one is designed to do.

Is it a hold-down top clamp boring bar, and does the clamp set correctly on the inset so as not to tip the insert up-angle so off the seat,

The hold down does appear to clamp correctly, if you look at the picture you can see there is a notch in the front edge, which is a triangular pressure foot which has meat under it all the way down. I can't get shim stock under the insert either so I don't think it's tilted up.
 

Joe Henderson

Aluminum
Joined
May 21, 2006
Location
Blooming Grove, Texas
Well it's a fact the thing is laying around there somewhere. Probably where you least expect to find it. The problem with toolholders is they get replaced with newer better. Planned obsolescence.
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
Are you sure the clamp comes down tight enough on the insert?
You might grind up a mock insert or just the end of a piece of steel .010 smaller than your insert assembly to be sure your clamp is coming down hard. Perhaps use a JoBlock minus .010.

Also, be sure that no part of your boring bar is bumping the part bore..

And that taping the boring bar with a small hammer it feels solid, and with minimum vibration.
 
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BoxcarPete

Stainless
Joined
Nov 30, 2018
Location
Michigan, USA
Are you sure the clamp comes down tight enough on the insert?
You might grind up a mock insert or just the end of a piece of steel .010 smaller than your insert assembly to be sure your clamp is coming down hard. Perhaps use a JoBlock minus .010.

Also, be sure that no part of your boring bar is bumping the part bore..

I can tighten it down with just the insert in the pocket and the home-made spacer bumps into the clamp, looks to be about .010-.015" interference.
 

dian

Titanium
Joined
Feb 22, 2010
Location
ch
i think whats going on might be this: the top of your spacer is not ground. by very firmly tightening you crack the insert. it then breaks right away. you might try tightening loosely to see if it will hold up for a while lke that.
 

BoxcarPete

Stainless
Joined
Nov 30, 2018
Location
Michigan, USA
OK, resolution for anyone who still cares:

Measured the tool in the holder, found some angles were a little off (0.2° or so from what you'd expect) so I took a closer look and also found the holder was tilting just a bit when it came down. There was some caked-on crud in the back that I scraped out, which allowed the holder sit flat on the actual pocket at the "heel" side. After that, I found according to Buck's instructions that it was no longer tight, but essentially a slip fit with my home made insert spacer.

What I suspect was the issue was that the holder "toe" was not tight unless the "heel" tilted the whole thing forward when it was sitting on the crud in the back. This made everything look tight from the front, but it was essentially edge-contact instead of face-contact and the looseness in the back end of the insert made it poorly supported enough to break.

So, one more piece of A2 later (hardened, tempered to blue, and ground on BOTH sides this time) and a bit thicker, we are back in business! The first insert crunched a little bit, but I kept pushing because I figured there were some embedded chunks from previous insert destruction. It made the rest of the cuts with no complaint, so I think I'm all set! Thanks all!
 

Turretturn

Plastic
Joined
May 16, 2015
Glad you sorted it.

Sometimes it's just easier and more cost effective to replace the tool holder, if you can't get a replacement seat or there's some damage where the seat sits.

One of my pet hates is when someone damages a tool holder and then attempts to repair it, with a bit of welding and regrinding, the seat and tips never sit the same and it causes more breakages.
 

4GSR

Diamond
Joined
Jan 25, 2005
Location
Victoria, Texas, USA
That particular boring bar does not have a shim seat under the insert. It only has a chip breaker on top of the insert. I used to have like that one but a little smaller. Was always losing the chip breaker when changing the insert. You can't clamp down the insert without it. This should fit and work in your boring bar, a CBT-12F. Make sure it has the "F" at the end of the part number. Here's a eBay listing for one https://www.ebay.com/itm/163908570959?hash=item2629b64f4f:g:38QAAOSwhA9eK3FQ

Ken
 








 
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