Drilling out of square

[Brian Jackson]

The attached photo is of a practice mock-up from scrap material that I'm very glad I did. I spent a great deal of time accurately center-punching and in preparation of through-drilling. I treated this part as if it were my actual keel. Thankfully it was sacrificial, being a practice piece.

I scored the inside wall. That's a no-no and instantly trashes the part without question, which is why I'm practicing on scrap tubing.

This being the "Builder's Corner" section of the Rotary Forum, what process did successful gyro builders use to drill close-clearance holes through square tubing?

This is certainly an area where much can be learned by many. I know I would be grateful.

Thanks,
Brian Jackson

[Brian Jackson]

I stand corrected. Having reexamined the interior of the tube in better light this morning, I did not score the walls. What appeared as scoring last night was in fact only the micro-abrasions caused by the spiral-shaped cuttings that rubbed against the inside wall when penetrating the opposing side of the tube. Clearances are still .015".

However, the lesson I've learned here is to NOT do precision drilling without adequate light. Besides, my wife was trying to sleep :eek: . She wasn't too happy with me this morning.

Thanks,
Brian Jackson

[Doug Riley]

Brian, you'd have to be a real butcher to score the walls using the hole locations called out in Ralph's plans. Ralph provides for either 1/64 or 1/32 (forget which) of nominal clearance between the inside edge of the tube and the O.D. of the hole. As fussy as you're being with all of this, I imagine you're doing a very precise job placing holes.

OTOH, Bensen gave us .003 as the maximum clearance (less than the aluminum industry's tolerance for wall thickness)! Bensen's material specs for the square/rect. tubing DID require the wall thickness tolerance to be 1/2 of industry spec, for obvious reasons. Not a lot of leeway.