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lbhsbz
02-24-2011, 01:13 AM
I've been using the typical 5 piece set that uses tcmt 32.52 inserts....they've been working. I'm looking through catalogs of tons of different holders that use tons of different inserts. Under what circumstances would I want to to use something different?

I've got a boring bar that uses ccmt inserts, but see other bars that use triangle inserts......why would someone use one over the other?

mechanicalmagic
02-24-2011, 01:55 AM
I'm looking through catalogs of tons of different holders that use tons of different inserts. Under what circumstances would I want to to use something different?
Higher production rates, better finish.
Modern Carbide tooling can be very specific. Suppose you need to turn the same exact part in 4 different materials, Stressproof steel, cast iron, Aluminum, and a stringy SS. Each one of these have different needs, Stressproof might need a negative top rake holder, Aluminum a positive rake, cast zero rake, and the SS requires a chip breaker. Potentially four different insert holders, with different inserts or grade of insert. Now add different lead angles, as needed to get to a shoulder, add more holders.
Remember, in a high production environment, a few seconds faster per part can mean profit or going under.

Then again, in a home shop one $7 chunk of Mo-Max with Cobalt can be ground to do all those jobs, but will cut 3x slower.
DJ

PixMan
02-24-2011, 07:48 AM
You would choose "something different" when you have a different job for it to do.

As mechanicalmagic points out, there's little advantage to using carbide insert tooling on a home shop lathe. You can rarely get the speeds on your typical home shop lathe that carbide needs to begin being a cost-effective tool. Moreover, the light cuts used in most home-shop applications are better-served by high positive rake grinds that you learn to do by grinding your own HSS and HSS-Co tools.

That said...I sure like carbide insert tooling. Having used it at work for the last 30 years, I didn't think twice about tooling up my dad's new shop with it. When I got him the lathe about 5 or 6 years ago, it came with a Dorian D40CA QCTP and some holders. I just keep adding to it.

You choose carbide grades to match the material and cutting conditions. By that I mean classes of materials (P steels, M stainless, K cast irons, N non-ferrous, S supperalloys, H hardened) can be matched to their respective carbide grades. Some carbide grades have more cobalt binder to resist chipping in interrupted cuts or scale, others less cobalt to run at higher speeds in smooth cuts. The coatings applied aid in tool life by creating a barrier to keep the material from sticking the the carbide (among other tasks) at various cutting speeds.

You can also select different tool nose radii on the inserts. You use TCMT32.52 inserts. That's a 1/32" radius tip. You might need a smaller radius, so you look for a TCMT (or TCGT) 32.51 (1/64" radius), or 32.50.5 and so on. You might look for a more "general purpose" grade that you can use at lower speeds in a wider variety of materials. You might also desire different chipbreaker designs, such as one for heavier cuts (roughing) and a tight, upsharp one for finishing. While you choose inserts to match grade to the materials and cutting speed, you choose a tool nose radius based upon part requirements and surface finish, and a chipbreaker based upon depth of cut and feedrate with a given material.

The most common error I see with carbide tooling, bar none, is using the wrong inserts in a given holder. The better holders have standard nomenclature stamped or etched onto it that tells us what insert it takes. Those cheap 5-to-7 tool Chinese sets have nothing, and often ship with the wrong inserts in them. I've seen it.

I can help with any of that if you need it, as I am well-versed about the subject. I'm no expert and I don't make inserts, but I do use them extensively and have educated myself. (OK, I had some formal training too.)

http://img.photobucket.com/albums/v466/kenm10759/Dads%20shop/2011-02-08_21-19-11_504.jpg

PixMan
02-24-2011, 08:38 AM
I've got a boring bar that uses ccmt inserts, but see other bars that use triangle inserts......why would someone use one over the other?


Forgot to address your last question:

An 80 included angle of the CCMT/CCGT insert is just a bit stronger than the 60 included angle of a triangle insert, and that's probably the primary reason to choose it. I have both styles, and don't see a lot of difference in performance. I do know that the triangle inserts have been around longer, so I have broken more of those. :D

With a few boring bar brands, the CCMT/CCGT insert bar can get into a smaller minimum bore diameter than a TCMT/TCGT of the same I.C. size for a given bar diameter. All else being equal, the triangular insert offers 50% more cutting edges than the parallelogram for about the same money. Used carefully, they can be a better value. A rare few boring bars can use the obtuse angle corners of the CCMT insert for roughing a through-bore.

http://img.photobucket.com/albums/v466/kenm10759/Dads%20shop/2011-02-08_21-20-01_844.jpg

RussZHC
02-24-2011, 06:04 PM
Pixman:

PM sent

Russ