Clearance Drill For 10-32

[T Bredehoft]

I've begun setting up tubes (that R8 collets came in) to hold taps, tap drills and clearance drills. I find I have starter, plug and bottom taps, also spiral flute taps between 8-32 and 7/16. Quite an assembly of boxes/tubes. I've seen pictures (here, lately) of a rack, a piece of aluminum, with holes drilled for each of the taps and drills, for each size. Probably better than my tubes, where stuff can rattle together.

 

[Wobbles]

Considerations on screw clearance should go beyond the physical dimensions of a single screw. If your pattern contained, say for instance 25 screws, then you might wish to go .030" greater knowing that by the time all 25 screws were started there would be zero free play. This because the tolerances allow some holes to the north, some to the east, etc, etc.

The only way around this in a hobby situation is to drill thru both mating parts clamped together with the tap drill. Then go back on the individual parts and add the clearance or threads as needed.

One other bit of minutia for hobby machinist to realize is that a tapped hole will kick up a small mound of material right at the mouth of the tapped hole. Under magnification, this looks like a gopher hole. A larger clearance hole in the mating part will step over this mound. Otherwise you need to finish your tapped part with a countersink or stone to get your flat mating surface back.

Just some random thoughts.