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Drill for 1/4

nohoflyer

Well Known Member
Patron
Hey I know this should be easy but of course it’s not (for me at least). I’m drilling the hole in the flap rib for the rod bearing and it calls for a 1/4 hole. Can someone help with what numbered drill I need?

Thx.
 
Have you read the Instruction Manual? 1/4 is an Imperial measurement of 1/4 inch. Drills are fractional, typically 1/64" increments through 1" (for our purposes), numbered, or lettered. Number or letter drills are typically used as tap drills prior to cutting tapped holes.
 
For a 1/4 inch hole, there isn’t a numbered drill for that size. You would use a 1/4 inch drill bit! Easy, right? Except don’t use a regular drill bit. You want a “step drill”, as a regular twist bit will make a sloppy hole in thin sheet metal. Start with a 40, then #30 or 1/8 would work too, then step up with a step drill
 
For a 1/4 inch hole, there isn’t a numbered drill for that size. You would use a 1/4 inch drill bit! Easy, right? Except don’t use a regular drill bit. You want a “step drill”, as a regular twist bit will make a sloppy hole in thin sheet metal. Start with a 40, then #30 or 1/8 would work too, then step up with a step drill

Thank you.
 
A reamer is the best way to get a round hole.

Drill undersized, ream for final size.
 
What I do

Do you have "letter" drills? if so, step your way up to a "D" (approx .247"), then finish with a .250" reamer. If you make sure to run the step cut drills all the way past the flutes the hole will stay pretty round.
 
If…

If you use a step drill, be aware that it can and will walk if you are not holding it perpendicular to your work, and you will end up with more of a slot.

Many people use a 1/4” drill bit, which works just fine.

A reamer works really well, too…
 
Not cheap, but they work well

Annular cutters make very nice holes in sheet metal. You do need to be careful with the larger sizes as they will walk.
 
Reamer fan here. As Mike said, slightly undersized pilot hole, finish with reamer. Less deburring needed usually, as a side benefit.
 
Step drill

In case it's not clear what a step drill is, here's a link:

https://www.panamericantool.com/step-drills-set-pat.html


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One other tip that might be obvious: when drilling aluminum use the "high" RPM/speed setting on your drill, and don't push too hard. With hard metal, like steel, it's the opposite - set the drill RPMs to as slow as possible with a lot of force. And use oil.
 
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