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pntrbl
06-26-2008, 01:40 AM
I don't know how long these brazed carbide bits I've been using lately are supposed to last, but you could measure how long they last for me in a matter of a few hours! What happens is I get what I think is called "cratering" right at the corner of the radius. The damage is visible to the naked eye but you really need an eye loupe to see the crater itself. Not big but .....

There's never a snap or other noise to alert me. Just all of a sudden, usually right at my final cuts naturally, it starts the buck and rub routine.

My typical usage is HRS. Got a piece of 4140 up at the moment but the cheap stuff is good enough for most of what I do. Dry because it's carbide. 1" dia. or less most of the time. 550 rpm unless threading or doing large dia work. .007 feed and I usually buy the 015 radius. Light cuts and I mean .025's big for me. It's just an 11" Logan and I've given up on ripping anything big off. I got time. LOL!

So is it normal for a machinist to sharpen up every hour or so or is there something yours truly is doing wrong?

Thanx for any advice.

SP

wierdscience
06-26-2008, 01:52 AM
Well it's not normal to sharpen up period anymore,inserts rule!:D

Back off on the sfpm would be the first thing I would try.

Fasttrack
06-26-2008, 01:55 AM
I've recently been running my carbide at .100 DOC and .035 feed and 380 rpm on a piece of 2" dia rod. It turns beautifully, a nice mirror like finish and the carbide has already outlasted the duplicate carbide that I run on my Smithy.

They always say carbide likes heavy cuts, but I didn't really figure it matter until recently. I had the same problem you did on my smithy, but with these pacemakers I can really use carbide to its fullest extent.

If I were you, I'd get some HSS. It will last longer than a few hours.

Anyway, I'm no pro - as you know - so it'll be interesting to hear some other opinions.

pntrbl
06-26-2008, 02:15 AM
Well it's not normal to sharpen up period anymore,inserts rule!:D

So far I've tried "one" insert. A TCMT and it seemed to cut nice until I managed to "operator error" the corners off! They seem bit brittle for the likes of me but I've got some more to experiment with.

SP

pntrbl
06-26-2008, 02:25 AM
I've recently been running my carbide at .100 DOC and .035 feed and 380 rpm on a piece of 2" dia rod.

Wow! That must be a stout machine! My Logan OTOH weighs in at 550lbs. Not likely huh? LOL!

SP

MickeyD
06-26-2008, 02:31 AM
From my personal experience, if your machine feels like the flexible flyer carbide is not going to work. It can't take the shock of chatter, and it is easy to make it chatter on a final sneak up cut if your tool is the tiniest bit dull or shock pitted. If you have a big stiff lathe carbide is terrific, and can really give a good finish and last a long time. If you have a light or well worn lathe, HSS will give a better finish because it will hold a sharper edge and can take a lot more abuse.

MickeyD
06-26-2008, 02:34 AM
If you are using a Logan, you will be a lot happier with HSS.

pntrbl
06-26-2008, 02:53 AM
MickeyD, that's certainly some food for thought. This latest incident featured some high frequency squealing at about the time the bit went bad. Nothing visible in the way of chatter but I heard something squeaking away.

Right now what HSS grinding I'm doing is on a no table 8" bench model with a welded bearing where it spun a groove on the shaft! LOL! Well at least it was free.

There's an HF Carbide Grinder waiting to take it's spot, but I can't live without the wire wheel on the old 8". The plan is to repair the shaft for new bearings and then mount the 8" on a post with a cement filled wheel rim for a base ..... and I better move that project up the list. :)

SP

J Tiers
06-26-2008, 09:25 AM
Early cratering is one sign of the WRONG carbide grade. At least in production situations. That is why there are more than one of the grades.

A Logan will be PERFECTLY HAPPY with carbide. Don't mistake it for an Atlas.

I use carbide when I need to and it works fine. yes I have broken off tips, but that has been from totally other causes, not chatter and not flex. I have broken off HSS from the same causes.

The consideration is NOT so much the machine name, I find the major consideration is the motor type.

If you use a single phase motor, especially if you use flat belts, you won't have any luck with carbide unless your machine is the original rock of Gibraltar. Single phase chatters too much, and slips belts etc. You can't get any power through a flat belt on single phase.

Three phase will double your power (at the driven pulley) and will avoid the screaming, roaring, bouncing chatter that you can get with single phase.

When I switched over, I found that the chatter virtually disappeared, I could part off easily, and I got FAR MORE POWER through the flat belt.

torker
06-26-2008, 10:45 AM
Any chatter issues aside.. the grade of carbide makes a HUGE difference.
I bought one of the big sets of brazed tip boring bars from KBC. I was astounded at how crappy they where. Was boring a hole in some mild steel and ground most of the tips off two bars on that one project. I phoned KBC and complained.
They had me send them back but told me to wait two weeks as they where going to try a different mfg.
The new ones they sent are light years better than the first set.
I'm about 3 years(?) with this set now and seldom have to sharpen any of them. I'll maybe chip a corner off when hitting a weld or something but overall...these things are bullet proof.
I also have some cheapie brazed bits that came with my lathe. HOLA...notice I didn't say carbide. I think these have brazed lead tips on them ;)
Russ

Forrest Addy
06-26-2008, 11:08 AM
Here's reality: general purpose tooling should last from an hour to a shift of axtural time in the cut. Any less and the cost of early replacement work against you. Any more and you're not working the tool hard enough. That's general purpose tooling. Ground to shape form tooling is generally babied to preserve its expensive form. Some tooling is used to break scale and is expected to have a short working life.

Precision replacible inserts make tooling changes a snap. Brazed-on tools are in the same category. When they poop out you have to replace the whole tool not just the insert.

The preceding is just to lend a little perspective. In the end all tooling is perishable. It has a certain life and then it's dull and has to be re-sharpened or replaced.

So if you having trouble with cratering or chipping, that's a routime problem addressed with changing feeds, speeds, or grade. I suggest you consult a trouble shooting chart. There used to be scads fo them. I'll see if I can find one on-line.

Fasttrack
06-26-2008, 11:21 AM
Wow! That must be a stout machine! My Logan OTOH weighs in at 550lbs. Not likely huh? LOL!

SP


Well it does weigh 8200 lbs ... :D

lane
06-26-2008, 11:29 PM
One thing I did not see any one say is . Chinese carbide Don`t know what you are using but the crap from China is no good . Bough t boxes full and after trying 2 or 3 pieces threw them in the trash . Went back to Kenmetal only.

Carld
06-26-2008, 11:52 PM
I had a 10" Logan with a lantern post and it used 1/4" tools. I had a set of holders for HSS and Carbide. There is a difference and if your using carbide in a HSS tool holder you will have problems.

What size tool bit are you using and are you using a lantern post or QC post?

I used HSS and Cobalt cutter bits most the time with the Logan.

wierdscience
06-27-2008, 12:28 AM
One thing I did not see any one say is . Chinese carbide Don`t know what you are using but the crap from China is no good . Bough t boxes full and after trying 2 or 3 pieces threw them in the trash . Went back to Kenmetal only.

I thought that went without saying?:rolleyes:

The only Non-Kennametal I run are cheap boring bars and TPG 322's since they are like napkins anyway:D

pntrbl
06-27-2008, 02:25 AM
Thanx for the replies guys. This place is the best on the net ...

Some answers. AXA sized Phase II toolpost. 1/2" shanks most of the time but I've put the hurt on some 3/8" too. I'm getting the bits from McMaster and buying the C6 grade. McMaster "says" they're comparable to Kennemetal K21.

3 Phase power. VFD driven. The original flat belt setup was upgraded to V-belts from the Logan 19xx line at sometime during the 50 years it's been alive. Got a poly link type belt on it right now.

I realize now I had a vibration cut waiting to squeal when the last bit cratered out. What I'm making is an 8x1.25mm bolt from 4140 1/2" hex stock that my Logan thinks is a 5/16x20 tpi, shhh, don't tell, :D , but it's 8 1/4" long. It's up on a dead center and could probably use a follow rest but unfortunately I don't own one. Being that long, thin, and unsupported perhaps I shouldn't have been surprised....

So Thanx again guys. I'll keep listening and learning.

SP