Will these inserts work???

[Al Slitter]

Hello All;
I am thinking about buying a boring bar, the boring tool in question uses TCMT 1102 (TCMT 21.51) inserts!
I just so happen to have a few TCMT21.50.5-24 inserts in my home and I am wondering if they will work as well and give a nice finish.
From what I have been able to glean, is that the TCMT21.50.5-24 inserts have a slightly smaller radius versus the TCMT 21.51 inserts.
So prior to buying the boring bar I thought I would ask the fine people here for their opinions.

Thank you in advance

Al

 

[kd4gij]

Have you seen this site. Lots of good info. http://www.carbidedepot.com/formulas-insert-d.htm
You should be fine. The larger the raidus the smother the finish, the smaller the raidus the deeper you can cut. .008 v .016 shouldn't make alot of differnce.

 

[Al Slitter]

Have you seen this site. Lots of good info. http://www.carbidedepot.com/formulas-insert-d.htm
You should be fine. The larger the raidus the smother the finish, the smaller the raidus the deeper you can cut. .008 v .016 shouldn't make alot of differnce.

That is my impression as well, thank you for the confirmation.

Al

 

[4GSR]

..... The larger the raidus the smother the finish, the smaller the raidus the deeper you can cut. .008 v .016 shouldn't make alot of differnce.

Oh you don't say....

I get a better finish with the smaller radius insert than with the bigger radius. Also you can take deeper cuts with higher feed with the larger nose radius insert than with smaller radius insert.

 

[mattthemuppet2]

Doesn't that depend on machine power and the rigidity/ stick out of the boring bar though? For small machines a smaller nose radius reduces cutting forces for the same depth of cut and HSMers hardly need to worry about nose breakdown the way production shops do (main reason for large nose radius roughers, right?). Same deal for boring - if you try and take a deep cut with on overly large nose radius, it'll just push the tip out of the cut and leave a taper unless you're using a thick and/ or carbide bar.

Similarly, a large nose radius, small DOC and fine feed gives a beautifully smooth finish.

 

[Wreck™Wreck]

Doesn't that depend on machine power and the rigidity/ stick out of the boring bar though? For small machines a smaller nose radius reduces cutting forces for the same depth of cut and HSMers hardly need to worry about nose breakdown the way production shops do (main reason for large nose radius roughers, right?). Same deal for boring - if you try and take a deep cut with on overly large nose radius, it'll just push the tip out of the cut and leave a taper unless you're using a thick and/ or carbide bar.

Similarly, a large nose radius, small DOC and fine feed gives a beautifully smooth finish.

Bingo, use a D.O.C. larger then the nose radius of the tool when possible, otherwise all bets are off when it comes to surface finish.

 

[mikey]

Al, for boring, the nose radius of the insert is one of the key parameters influencing cutting forces. Boring isn't about roughing ugly with deep cuts and then sneaking up on final size with a fine cut. Rather, it is a planned approach to a precision result. Controlled roughing cuts will produce changes in ID that are fairly reproducible. Likewise, controlled finishing cuts will produce a change in ID that lets you plan an approach to final size. Much of this is influenced by the NR of the cutter.

As a general guideline, a roughing cut would be NR + 0.005-0.010" deep or thereabouts. This allows full support of the nose to reduce radial and tangential forces, thereby reducing chatter. For finishing, a cut of 1/3-1/2 the NR usually produces acceptable results. So, an acceptable roughing depth of cut with an insert having a NR of 0.008" would be 0.013-0.018" deep in steel. You can go deeper in softer materials like aluminum but should not rough shallower than the NR if possible. Cutting with less than the NR greatly increases both tangential and radial forces but when finishing we generally are feeding slower and, in my mind at least, are able to remove surface irregularities that occur so it works.

All of that suggests that there is a very big difference between a 0.008" NR and a 0.016" NR. For general use, a 0.008" insert will work better for most of us hobby guys with hobby lathes in non-production situations, at least in my opinion. Of course, as you know boring bar and insert geometry also factor into the equation but, in general, the above should apply.