Boring Head- Minimum ID

[rwm]

I have a Criterion boring head DBL 202 with a Mesa insert holder. This exact setup:

Mesa claims the minimum ID for this is .925 using a CCMT 32.51 insert.
The problem is when I uses this for holes less than 1.5" I am dragging the heel of the insert. I believe these inserts have a 7 deg relief? This can be figured out trigonometrically for someone smarter than me. Is Mesa incorrect or am I doing something wrong? Have you seen this issue? Could I get an insert with greater relief?

 

[DavidR8]

I assume the tooling has a flat that prevents it from rotating in the boring head?
Otherwise, I'd just clock around a degree or so to gain a bit more relief.

 

[rwm]

It has a flat. Also that would make it into a negative rake cutter.

 

[DavidR8]

Maybe give Mesa a call?

 

[rwm]

I did. They said 0.925.

 

[DavidR8]

Could be that their .925 info is not accurate.

 

[ChazzC]

Have you tried moving the tool into the center location?

 

[rwm]

Have you tried moving the tool into the center location?

Yes. Same issue.

 

[ChazzC]

Yes. Same issue.

Other than the tool holder not being made correctly, I’m out of ideas.

 

[rwm]

Here is the question diagrammatically:

Assuming a 7 deg relief angle, what is the minimum radius of a circle before the heel contacts the work?
There is a SIN, COS, TAN in there somewhere!
Edit: SIN 7 x .1563 tells you that the heel is recessed by 0.019