Hello and wisdom needed

[MattAG]

Hello all. This is my first post here. I meant for my first post to be just a general hello. But in the meantime, the inserts for the bars for my boring head finally arrived. Cool. I can use it now (I have a set of 1/2" bars but this 1/2" head is bored for 12mm). Problem is, the inserts specified by the seller don't fit and I can't for the life of me figure out which inserts are correct. The seller indicated TCMT21.51. Which I ordered. You can see in the picture that every dimension of these alleged TCMT21.51 is too large. In addition, when I look in various charts for insert designation, these inserts don't appear to be TCMT2. They are .095 thick, so the TCMTx1.5 is correct. (But too thick for these bars.) According to more than 1 chart, TCMT2 is a diamond shape inscribed in a 1/4" circle. As close as I can determine, the inscribing circle for these inserts is somewhere close to .450 (7/16). At least at it's widest. The back (minus the relief "flare"?) is in the neighborhood of .375. The inscribe for the insert I need is approx .350 (widest). Although it's hard to measure the negative space. The boring bar is marked D12- (12mm shank dia) TCMT09-55 (55mm long). I'm wondering if 09 indicates a 9mm inscribe. Which is almost exactly .350? It's close to .375 so a TCMT3xxx? But the 3 is listed as larger than the TCMT2xxx I have now that is way too big? I measure the recess depth as 2mm (.0785) so the thickness I need is a TCMTx1.2. I think. Are the inserts I received as TCMT21.51 mislabeled? I don't want to end up with more unusable inserts.

Anyway, can anyone point out what I'm misunderstanding? Thanks for reading and in advance for your help.

[GlennW]

TCMT09 (on the shank) is the insert style needed.

Looks like possibly proprietary inserts from Sandvik, so they won't be inexpensive!

Here's the "Grade" chart which basically determines what the insert is designed to machine.
https://www.industrialmill.com/images/d ... g?sfvrsn=0

Here is the "Chip Breaker" chart which determines whether the insert is for finishing or roughing, etc.
https://www.mscdirect.com/basicsof/chipbreaker-inserts

So, these would be a medium machining insert for Steel, Stainless, and Cast Iron.
https://www.ebay.com/i/223551116440?chn ... kYQAvD_BwE

[MattAG]

Hey GlennW! Thanks for the quick reply. I thought I had tried just searching "TCMT 09". Apparently not. There seems to be plenty of those Sandvik new-old stock inserts on ebay for no more (less) than I paid for the Chinese inserts I have now.

Do you think the inserts I have are actually TCMT21.5? They seem to be much larger than the charts say they should be.

[GlennW]

As long as you can find them on eBay they might not be too bad. If you have to buy them new from a supplier they will be pretty expensive.

I may have some TCMT21. inserts I can measure tomorrow.

[MattAG]

All of the Sandvik 09 inserts on ebay I've looked at have large tip radii. Too large for a boring bar. As you said, appropriate 09 inserts from Sandvik new are price prohibitive. I think I'm farther ahead to buy a set of 12mm bars that take a common insert. Thanks again Glenn.

[Harold_V]

can anyone point out what I'm misunderstanding?

One thing troubles me. In your picture you are measuring across the tips of the triangle. The inscribed circle for inserts should be measured across the flats. A faced piece of stock of the appropriate size can be used.

If, by chance, that was addressed and I missed it, I apologize.

H