Internal threading tool Question

[benmychree]

We are talking about boring bars here and I am saying if the tool's cutting edge is forward of center then it is, in effect, negative rake.

I am saying that if set on center, it is not forward of center, that is what my eye is seeing. The top of the insert is parallel with the bar's seating surface.

 

[bakrch]

I admit that I basically ignore negative rake boring bars as they are not useful to me as a hobby guy but can you tell me which bar and insert you're referring to? There are turning tools that can be configured this way but with the deflection a boring bar sees I haven't seen such a combination and it might be interesting to have a look at the geometry.

Quite a rabbit hole here as we have very little context.

I'll limit to 80 and 55 degree inserts, since they would be ideal for relatively high cutting forces.

CNGP-K/DNGP-K work well on lighter duty machines as they are sharp, and have aggressive chip breaker that is designed to break at a lighter IPR. You can shave tenths of a diameter off 60HRC stainless confidently, as well as medium machining a variety of common (annealed) material.

With that said, using a regular CNMG(Dormer/Pramet w/ NM? chip breaker) I can get a .100 radial cut @.006 IPR 3" diameter in 316ss with a standard kenloc 1-1/4" shank boring bar (2:1 stick out) on a 2HP 12x36 lathe.

Definitely not the ideal insert choice for the obvious reasons, but quite useful for a myriad of operations.

I haven't found an equivalent WNMG, unfortunately.

 

[mikey]

Okay, thanks, I'll look into this a bit more.

 

[fishingreg]

Thank you all for your input, since I am so new at this I think my brain melted. I did not understand positive, negative and neutral rake but now at least I think I understand that and I can see how a negative rake would make it easier for the tool to be pushed away from the metal. I had heard the terms but thought it had to do the a different angle on the cutting tool. Here is a picture of the boring bar and based on your comments it looks like it has a negative rake. The picture is tough to take but the bar is as it would sit in a tool holder.

Thanks again, I am learning a lot from your comments.