My drilling project

[Aukai]

My project today, that is in "what I did today thread", caused me a problem. My OEM clutch Z bar had to be adjusted, with a relocated hole. I used my calculator for RPM used a 140* pilot, 3/8" CL shorty bit, and just polished the hole. If I'm going to burn a bit, I changed to a jobber Erwin. It screeched, and made all kinds of noise,I started just pulling hard, and then it just started cutting. I adjusted speed RPM up, and down from the calculated RPM, but I think the OEM steel is harder than what I was using as an input, and my machine will not run the RPM indicated 3056, ( if I calculated it right). Wondering what I was doing wrong...input......RPM....or bit type. Thank you

 

[mikey]

I always thought they used mild steel for those bellcranks. I know some off road vehicles had forged steel bellcranks but I didn't think Chevy used them. Did you check the metal with a file? If it cuts then it should drill fine.

Assuming it is some mild steel then I would try a pilot drill, maybe about 1/8", then the 3/8" drill. I would run the 3/8" drill much slower (maybe 250-300 rpm) and use higher drilling pressure. This should allow the drill to cut instead of burnish. I probably drill wrong and tend to go slower than recommended but with higher feed pressures. For me, the drill cuts better and cooler.

 

[Aukai]

Thanks Mike, It does not scratch easily, and I burned the teeth off of a Bosch jig saw blade. I ended up using a cut off wheel. I tried going at 90, 600, and higher with the drill, I would lean into it, back off for several tries keeping it lubed, and then it just started cutting. I should have verified RPM with a known source too.

 

[mikey]

Huh, must be some kind of high carbon steel that got work hardened. I hope you got the hole drilled by now. I would have suggested a carbide drill that works at much higher speeds but probably too late now.

 

[Aukai]

Thank you, yes it's done, once it finally started cutting there was no problem, just like mild steel. I dunno