Carbide Inserts

C

clevinski

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Hi, All,

One of the items from a recent retired tool and die-maker purchase was 36 C-5 TPG 322 Triangular Carbide Inserts. They measure 5/8 inch on an edge, and they have no hole in them. The only tool that was included that could hold them is a boring bar (home-made, I think) with a slot in it and a set screw to hold the insert in place. I know almost nothing about carbide inserts, and was hoping to get a little input on them. Where and on what material would I most likely use these with my 7 x 14, assuming I can find or make an appropriate holder? I was particularly interest/concerned about the fact that they seem to have no top rake.

Thanks... I appreciate any input!
 
Most (not all) of the insert holders made for inserts without a center hole are pretty big; usually 3/4" to 1" at least. That type of insert requires a holder with a clamping mechanism to hold the insert in place. That clamping mechanism takes-up real estate and thus, is reserved for use on larger holders. A lot of my face mills take that kind of insert.

Have a look at this... http://www.ebay.com/itm/NEW-TPG-322...OOL-HOLDER-KENNAMETAL-KTFR-163C-/350581147587 I don't think it will fit in your lathe...

Also, I don't view carbide as being as useful in a mini lathe as, carbide is really designed for high removal rates -whereas a mini lahte is not.

I'm sure people can (and do) use carbide in smaller lathes -but I'm not quite sure why... I think HSS is a far more appropriate cutter for that size lathe.

Ray
 
Ray C said:
Most (not all) of the insert holders made for inserts without a center hole are pretty big; usually 3/4" to 1" at least. That type of insert requires a holder with a clamping mechanism to hold the insert in place. That clamping mechanism takes-up real estate and thus, is reserved for use on larger holders. A lot of my face mills take that kind of insert.

Have a look at this... http://www.ebay.com/itm/NEW-TPG-322...OOL-HOLDER-KENNAMETAL-KTFR-163C-/350581147587 I don't think it will fit in your lathe...

Also, I don't view carbide as being as useful in a mini lathe as, carbide is really designed for high removal rates -whereas a mini lahte is not.

I'm sure people can (and do) use carbide in smaller lathes -but I'm not quite sure why... I think HSS is a far more appropriate cutter for that size lathe.

Ray
Click to expand...

Hi, Ray,

Thanks for the information. The only time I have ever used carbide in the past is in those small boring bars. I know some people do use them in mini-lathes (http://littlemachineshop.com/products/product_view.php?ProductID=2286&category=) but the inserts are the smaller types with a central hole.

I have been thinking about getting a face mill for my mini-mill, though I don't know if this is the right sized insert for one that would fit the mini-mill. Maybe that's a good use for them. If I can't find a good use, I guess I'll sell them.
 
I have a holder for that type of insert that I got with my lathe (it looks just like Ray described). I also have a insert end mill that types the same (or similar) type. It's not uncommon for carbide inserts to not have back rake. In fact, the most common types have no relief ("neutral" inserts) and have a relief introduced by the holder by tilting the insert tip down. Back rake may be added if you get an insert with a chipbreaker ground in. If the type you have is beveled on the edges (ei, it's not at 90 degrees), then it was likely intended to be introduced to the work "flat".

When I had my 7x14, I had a small carbide set. It was useful at times, but I switched back and forth between carbide and HSS. The set I had was much smaller (1/4" IC), and I found that only the really acute inserts (the "V" type diamond inserts) worked well. The triangular inserts might work OK, I didn't have those in my set. I also found that to get a decent finish I had to crank the speed way up and take pretty light cuts.

If I were you, I'd keep that insert as a curiosity unless you got a whole mess of them (or use it in the boring bar, but the min bore size is going to be pretty large). If you want to try out inserts on the minilathe, I would recommend something smaller.

- - - Updated - - -

The insert end mill I have is from LMS. It didn't work particularly well on my mini mill. It works OK on the knee mill, but even then, it can't take very deep cuts (I rarely go over 0.040, and finish is not great). For the mini, you might take a look at a fly cutter, I had better luck with the one I made.
 
I'm with Ray on this too. Our small lathes lack the rigidity and power to really capitalize on the high surface speeds and high removal rates that carbide tooling enables. Carbide tooling really excels in a production environment where metal removal rates have to be extremely high to make a profit. On the other hand if you do happen to have some carbide tipped tooling they do a wonderfull job making a nice clean surface with a moderate pass. I however would tend to stay away from carbide and learn to hand grind HSS bits and you will find that you can get excellent finishes and very good removal rates with them at a huge savings in tooling dollars. I buy a handful of HSS planks for 5 or 6 dollars and I can literally sharpen them to a nub over a long long period of time. I can even change the profile of the cutter to suit a project or specific need. That is something carbide will never allow you to do. And a properly sharpened HSS bit will keep up with a carbide cutter in our small lathes and generally last longer with just the occasional brush up on the grinder or with a diamond hone. Hope this helps,

Bob
 
Thanks, Bob and DMS, for your comments.

I have only been doing this about 18 months, but have always used HSS except for some small boring jobs, and then only because I had purchased a boring bar set with brazed carbide inserts. I have 36 of these inserts, brand new, 3 full packs of 10 and a partial of 6, so I thought I might be able to do something with them, but that's sounding less beneficial as I read your posts. I guess I'll sell them and move on...

I am not very good at grinding HSS tools freehand; I always end up with facets, though the tools work fine. I have a couple dozen blanks of different sizes (plus a few in cobalt), and about 40-50 tools that others have ground for a variety of functions. I agree that the HSS does a really fine job and I'm not really looking for production-like speeds anyway.

Thanks again for your input!
 
I agree that most machines at home do not have the Hp to really take advantage of Carbide.
...But I also remember a few smaller machines I had, like a Sherline, and even my Atlas 618 (which had back-gears!) really needed to keep the spindle speed higher to work efficiently, or the spindle speed just didn't go low enough- and carbide made a difference at some times, to keep the available SFM within a usable range on the machine.

I am not saying this is the "right way", but I remember being happy I had the option.

Bernie
 
itsme_Bernie said:
I agree that most machines at home do not have the Hp to really take advantage of Carbide.
...But I also remember a few smaller machines I had, like a Sherline, and even my Atlas 618 (which had back-gears!) really needed to keep the spindle speed higher to work efficiently, or the spindle speed just didn't go low enough- and carbide made a difference at some times, to keep the available SFM within a usable range on the machine.

I am not saying this is the "right way", but I remember being happy I had the option.

Bernie
Click to expand...

Cool... It's always good to have options, I suppose!

I'm looking forward to Saturday!
 
Pretty sure we've talked about this before but for newcomers... SFM's for carbide are usually 2-3 times higher than for HSS (and HSS-variants such as M2 etc). Also, on mild steel, the minimum cut is around 10 thou DoC otherwise, you get a very rough finish because the pressure is too low. So, if you have a mini-machine that can do it, (which is aided by having a larger diameter piece where SFMs are easy to obtain) sure... it should work fine. I'm not too familiar with mini-lathes but the ones I've seen have lower HP motors so, my natural inclination was to think that HSS will produce more joy than carbide... The next thing to overcome is to find insert holder that accommodate 1/4" IC yet still fit in the tool holder. That's out of my realm and hopefully others have some ideas. You could make your own but, it's surprisingly difficult to get the angles right...


Ray



Ray
clevinski said:
Cool... It's always good to have options, I suppose!

I'm looking forward to Saturday!
Click to expand...
 
Two of my boring bars use TPG 322 inserts. I will take some pics in the morning. I have a smaller one the takes TPG 222.

"Billy G"
 
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