MetalworkingFun Forum

Ed is correct.

In a case like that Darren, the inclination angle of the insert varies on boring bars as (in the case of a CCGT) the 7º side clearance angle may not be enough to avoid rubbing the bottom edge of the insert within a bore. Of course tipping the insert reduces the effective top clearance angle (a.k.a. rake) of the insert's chibreaker, so many insert makers offer boring-specific insert geometry. For turning tools, the standard 7º front and side clearance angles are more than enough so inserts sit flat in the turning holders.

hth

That does help. I was aware of the clearance issue but wondered if there were other issues.

Given that this doesn't seem to be the case, it would appear that ensuring the top flat is perfectly parallel is not warranted and that close enough is good enough.

Keeping in mind Darren that you still need to get centre height right, and in a small bore a change in centre height will change a number of things including for example the effect of a move in the x axis of 0.010" won't take out 0.20" if the tip is substantially below or above centre height, this is a small issue, but in addition to the rake and clearance angles being confused, why take the chance, I would investigate just how hard the holders are and either drill and fit a widget as you have described, or do as I do and set up the boring bar using a square, with the stock sitting on the side of the holder and the blade holding the top of the bar in the correct orientation, Easy peasy. No cost or effort required, I would like to take credit for this method but I can't, it was a standard method used in a CNC lathe I was trained on back in the eighties.
Regards
Rick