View Full Version : Best kind of indexable cutting tool

02-27-2005, 10:23 PM
I have been using the standard carbide tool bits on the lathe, but don't have a grinder for them. (The HF thread is what made me think of this.)

What do you think of the indexable tooling? Is there a more-or-less "standard" 3/8 or 1/2 size that uses common (and therefore reasonable) inserts, that I can sort of standardise on?


02-27-2005, 10:58 PM

Everyone has their own "favorite". My most-used toolholder in a TMX Pafana:


3/4" shank is the smallest, so I used a solid carbide end mill and removed material from the bottom of shank until it was 1/2". It uses CNMG 432 inserts which are pretty common & inexpensive ($3 retail, as low as $.50 on eBay). There are lots of coating grades and chipbreaker styles available.

At the same time I bought boring bars that use the same insert:


These bars (and the toolholder) are Polish, very high quality. About 70% less than Valenite. My second favorite toolholder uses WNMG 432, another popular insert:


This profile will get into places the CNMG cannot, also give you six cutters/insert.

I have no affiliation with Penn Tool Co, its subsidiaries, or the CIA/FDA/USDA/AA.....

Barry Milton

Spin Doctor
02-28-2005, 07:45 AM
The least expensive option is of course the common TNXX=XXX inserts in various size, chip breakers and coatings. These are the common triangular negative rake inserts. Next up is the CNXX-XXX which is the 80D diamond profile. The W series or Trigon as some manufactures call them has many of the beneifts of the previous two. 6 cutting edges like the TNs versus 4 on the CNs. A much stonger tip like the CNs versus the TNs. Next down the list are the D series and V series inserts that feature much narrower included angles which while allowing you to reach into tighter areas they also sacrifice tip strength. But a great deal also depends on the size of the lathe and horsepower available at the tool itself. On small machines in my experience negative rake inserts don't work well at all. The machines lack the rigidity and power needed to truely utilize the inserts tools. However negative rake inserts that have a positive top profile like these as an example


offer many of the benifits of both sides of the question. Good cutting ability and strength. An other factor to consider is tip radius. the larger the radius the more horsepower the machine needs to properly utilize the tool. Larger radii neeed heavier feeds, heavier feeds need more horsepower and so on. Another factor is tool post type. Carbide inserts tools are not meant to be used in lantern type tool posts. It is almost impossible to really get the tool in the proper orientantion to the work for it to preform properly.

02-28-2005, 09:50 AM
My machine is a 12" Atlas with a 1hp motor. I use a Phase II piston type tool holder.

I have access to a set like this: http://img.photobucket.com/albums/v226/elbryant/Lathetoolssets.bmp

but there are no inserts with them. Since I have to get inserts, I was concerned I would spend a lot of money there whent he tools themselves aren't worth it.

Advantages/disadvantages of this kind of tool holder?

02-28-2005, 03:33 PM

I have one of those sets also, and sometimes use that shape insert for certain jobs. They use the common TNMG insert (a search on eBay produced 61 listings just now). That's the insert SpinDoc suggests in his first paragraph.

If you mount each those toolholders in your Phase II QC blocks, you'll have a good start.

02-28-2005, 04:06 PM
Is there an easy way to identify which insert goes with which size bar? For example, if I have 1/2" toolholders, which of the TNMG inserts will fit?


02-28-2005, 04:40 PM
The inserts for those toolholders are probably TCMT, positive rake, screw hold down. TNMG inserts go into holders with hold down clamps.

The size is measured by the size of the inscribed circle that just fits within the triangle, along with a thickness spec.

www.carbidedepot.com (http://www.carbidedepot.com) has lots of good reference information with carbide grades, insert designations, etc.

Incidentally, some toolholders can be had in more than one insert types but the same shank sizes. I think the SCLC holders are one example of this. You can get them with a 21.5x (x is nose radius) or 32.5x size insert in a 1/2" shank.

Inserts can get real tricky as ferrous / non-ferrous, light finishing vs heavy roughing cuts, chipbreaker types, etc. all enter into the insert selection. I try to keep it down to some for non-ferrous, the rest for steel/stainless and some for general roughing while others only touch finishing cuts.