round holes

tshort · Post by **tshort** » Fri May 12, 2006 9:36 am

Any tips?
I've found that most larger holes I drill are not perfectly round - i.e. #12 holes on the z-brackets, etc. I always try to drill into something (like wood behind the part). The only way I have been able to get good round holes is either with a unibit or reamer. I'm getting ready to drill the tank screw holes and would like them to be as round as possible; any tips?

Thomas
-8 wings

prestwich · Post by **prestwich** » Fri May 12, 2006 10:34 am

The only way to get a round hole is with a boring bar on a mill. Failing that, go with the reamer! You say you've had good luck with that in the past -- is there a reason you can't use one on the tank holes?

jim_geo · Post by **jim_geo** » Fri May 12, 2006 12:59 pm

The "Standard Aircraft Handbook" that you can get from Vans for 13 bucks goes into some detail about drilling holes and and just about anything else concerned with the hardware used in aircraft. Hints would be, sharp drills, proper drill tip angle (pointy as opposed to flat) and high enough speed.

cjensen · Post by **cjensen** » Fri May 12, 2006 1:24 pm

I guess I need to get a new unibit. I have yet to see a round hole with that thing! I don't like using mine...

TomNativeNewYorker · Post by **TomNativeNewYorker** » Fri May 12, 2006 5:13 pm

Sharp bits is usually a good place to start.

Pilot holes, and then taking the hole up to final size using a piloted reamer or core drill would be better yet. Example, start with a #40 pilot hole, and then use a reamer or core drill size .189" that has a .098" pilot or any combination of step drilling to get you from whatever your pilot holes size is up to your final hole diameter is called out for.

Drill bushings and drill bushing fixture of some sort will most certainly help you drill straighter and will work for step drilling/reaming as well.