One of my old mentors would say ;- Drilled holes are great, ............as long as you're not fussy as to their postion, straightness, roundness or size
Another thought ;- have you been machining cast iron? .......it can produce very fine airborn particles can rust other stuff easily, which would be an addition to any acids you have
What about a heat shrink fit? ............... less stress in the actual fitting, and if heated gentley and uniformly, should keep distortion to an absolute minimum.
Faced with that situation I do this.
Turn up a ''tube'' to bore of which is a sliding fit - (as in with no chance of snagging) but not loose, with the end machined true to the bore, ..and use that as a pushing sleeve - preferably against the face needing to be true.
After they've off shored production to China or Vietnam, pushed prices up and up, ripped the guts out of the company, sold off any viable assets while at the same time taking massive ''management fees''
Not much of a future.
They're straights Terry, I meant down cut like these https://www.onsrud.com/Series/SolidCarbide1-2FluteDowncutPlastic.asp
Only in a home freezer but it being summer and the fixture plate Alu, it made next to no difference
In short it's a PITA material to m/c
I used YG uncoated HSS (they're almost ''wear gloves to change'' sharp) with a degree of success, but found Onsrud down cut router cutters better.
I stuck the parts down with double sided scotch tape, and didn't cut through - left about 10 - 15 thou and...
I've never done a drill collar but have done a fair amount of HT etc steel repairs ** with stick, and the only successful method was lots of pre heat - let it really soak in, and a slow cool.
** Lemken laminated plough mouldboards were fun - I used to do them in batches by building a fire...
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