If your part has final size holes but the part it attaches to has no holes, is it best to match drill using an undersized bit to create the virgin holes, then use a reamer to upsize? Or do you just use the final size bit and drill once? I want to minimize possible damage to the existing final size hole and putting one bit through it vs two seems like the safer option.
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Drilling Through a Final Size Hole
- Thread starter gbaser47
- Start date
JonJay
Well Known Member
Agreed, if you have a hole to start with. If you don’t, like the OP, you still need a centered hole in the part with no hole, if that makes sense.
If the part with the hole is a casting, thick spar material, or something that has critical tolerances, use a drill bushing, then finish the hole with a reamer or double margin drill. Still the same effort. .
If it is just a hole in sheet and will get a rivet, don’t overthink it. Just drill through the piece with the hole final size into the piece you’re trying to drill.
Use a quality split point. It won’t be as nice, and clean as a reamer or double margin drill, but…..
PaulvS
Well Known Member
It depends on the size of the hole. If it is small e.g. 3/32 or #40 then drill once.
If the hole is bigger e.g. #30 and important, or 3/16 or larger, then I would mark the centre and drill smaller first.
The smaller hole should be centred using a drill guide, as mentioned above. The guide can be as simple as a 1/8 steel pop rivet that has the mandrel knocked out. For 3/16" holes, I use a short length of tubing that has this outside diameter and a 5/32" inside diameter for the pilot hole. Same principle for 1/4" holes. Or you can invest in some commercial drill guides.
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wirejock
Well Known Member
Drill bushing.
Easy to make one. Buy one of each size 12" long brass tube. Cut a piece off each a tad shorter than the shortest bit you plan to use. #41 is a good choice. Debur them square on the wheel. Stack them up so the biggest fits the parent hole. Drill #41.
Handy bugger.
Easy to make one. Buy one of each size 12" long brass tube. Cut a piece off each a tad shorter than the shortest bit you plan to use. #41 is a good choice. Debur them square on the wheel. Stack them up so the biggest fits the parent hole. Drill #41.
Handy bugger.
I’m getting ready to drill the longerons (match drill) in my tailcone. I was searching for double margin drills and can only find them at Pan American Tool who requires a minimum purchase of 12. Does anyone know of a vendor that doesn’t require a bulk purchase? I was going to get a several, but I don’t think I need 12.
PaulvS
Well Known Member
Tr
Try yardstore.com for individual double margin drill bits.
