updrilling

[onex28]

Am I wasting time and energy by updrilling to #40 and then to #30 or should I go right to #30? AND - would updrilling procedure apply to both sheet and pieces .125 and thicker?

Thanks for the input.

David

[Andy Walker]

You need to drill pilot holes, as it will make your hole placement more accurate, and your 1/8" final holes will be smoother if you drill pilot holes. Depending on what you're doing, you may or may not need to deburr the #40s before updrilling to #30s.

[XenosTed]

Andy is exactly right. Funny thing about drill bits - my engineer son demo-ed this to me one day - the usual drill cuts a triangular hole (don't ask - doubters should try it on scrap). By "sneaking up on the correct size" the final hole is MUCH more round in shape. Try it, you will like it. Most short cuts seem scary at 8,000 feet. Do it right.
Xenos Ted
flying high and smiling

[XenosTed]

http://www3.sympatico.ca/fhofmann/art_round_hole.html
I do not personally know this gentleman, but, as the British would say, his observations and suggestions are spot on.
Also, I debur everthing before riveting. As Andy says, no need to debur most intermediate holes.
Xenos Ted