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?
It's nearly impossible to get truly round holes with a drill bit. You'll almost always get a triangular hole. If you really want it to be round, use a reamer. There aren't a whole lot of holes in the kit that perfectly round really matters all that much, though.
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John Coloccia www.ballofshame.com
Former builder, but still lurking 'cause you're a pretty cool bunch...
I found the best holes with a normal bit are at high speed and small increments. For the z-brackets I stepped up a size at a time to get the correct hole size. But of course a reemer or unibit are always the first choice.
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Sid Lambert
RV-7 Sold
RV-4 - Flying - O-320 Fixed Pitch - Red over Yellow
Sometimes the unibit is kind of hard to center perfectly accurate (particularly since it starts at 1/4" if it's the standard one that comes with most of the tool kits). Thus, I'd encourage the use of the reamer. I think standard practice is that you drill the hole undersized by 1/32" with a regular bit, then use a reamer of the desired finished side. A 3/16" reamer from Avery's is only $6.00 I think, so it's well worth having in your toolbox for these types of occasions. You'll use it a lot as you get into the fuselage. Incidentally, I had the same experience as you when I first started drilling those tank attach bracket holes. Hope this helps.
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Steve M.
Ellensburg WA
RV-9 Flying, 0-320, Catto
Donation reminder: Jan. 2021
Thomas. Make yourself a drill jig kinda like this out of aluminum or steel and clamp it to your work. All it needs to be is about 1/4" thick and and it positively locate the drill bit and eliminate chatter when it is passing through the undrilled material. It will also put the hole exactly where you see looking through the hole in the block.
Keep It Simple Stupid is what I always sick with. You can make fixtures, use a mill, have a reamer for every size hole and you can also spend years building your RV. If you want to drill a hole ?? or larger just use a step drill. You can drill a pilot hole with a smaller drill.
Sorry boys, but some of you would never make any money working in a shop. I agree there is more than one way to drill a hole ,but?.KISS!
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Roger Ping
KDVT Phoenix Deer Valley
RV-9, O-320, 160HP, C/S
Drilling round holes
Keep It Simple Stupid is what I always sick with. You can make fixtures, use a mill, have a reamer for every size hole and you can also spend years building your RV. If you want to drill a hole ?? or larger just use a step drill. You can drill a pilot hole with a smaller drill. 
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