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Drilling thinner material and larger bits (eg #19)

Ender

Active Member
I have found, when enlarging prepunched holes (typ. #40) to sizes like #19 for nutplates, it’s very difficult to not end up mangling the hole.

I’ve tried backing it up with wood.
Pressing hard and soft
Air drill and electric (fast and slow)
Starting from #40, and opening it up as close to #19 as I can with a unibit.

These are brand new, colbalt jobber bits from Cleveland.

The bit always seems to bite really hard and then get stuck. This invariably mangles the material a bit. To salvage I usually have to reverse the drill, to get rid of the attached curls, then spin forward again.

On a drill press, sometimes it’s fine, but if it’s a smaller piece, I’ve had the bit get stuck and spin the whole piece.

So far I’ve been lucky and not cracked a skin, and if the hole was a little larger, it’s still just for a nut plate, so no huge deal ... but I’d like to know how to do it right as I’m sure there are a lot more of these.

Thanks!
 
Reamers

Try reamers. I usually use a drill bit up to one size below then finish with a reamer.
 
Step drill

Be careful using a step drill as it is easy for it to wander ending up with a hole that isn’t where you want it or an oblong hole...
 
Pilot drill, say #40. Then step drill. Put some tape on the step drill to prevent inadvertently going up to the next "step".

Works a Treat!
 
fast and light

With aluminum, I make sure that the drill bit is spinning fast, and I use very light pressure. With steel, the opposite.

The holes I struggled with were the stainless steel firewall penetrations. Got'em done, but it was a lot of work and time. Next time, I'll buy a punch!
 
One more trick I've tried with some success is to sandwich the thin layer of metal between two layers of wood tightly clamped together. Still "step up" from smaller to larger size - final size with a reamer....
 
Didn't see a reference to the "Basics."

Kinda like a "checklist", in this case a "pre-drill checklist"

What drill and rake angle?

(Don't ask me why I started using checklists - it'll probably prompt another senior moment and I haven't invented a checklist for that one!)
 
The other thing to watch when using step drills is the final size. I had used some from harbor freight and found that the stated size was not the hole size...

It’s worth getting the genuine Irwin unibits. Or at least a clone with a single flute. The two fluted clones are cheap but don’t make as nice of a hole and tend to drill oversize triangular holes like a regular drill bit. And yeah, I’ve found some stuff at hf labeled in imperial but are actually metric. 19mm is usually close enough to 3/4 for woodworking but not for metal.
 
Thanks everyone for their replies.

I have a few unibits (step drills), it non of them are #19, do such bits exist?

Same question with reamers, 1) where to ge my then and 2) does everyone really have that variety of reamers? I have the 30/40, plus the others called out for specific reaming.

I did the step up to it idea first, 40 to step drill, then the #19 bit. Almost seemed worse because it was easy for drill to bite in, get stuck, and yank itself crooked.

Also, on the inbrd wing ribs, you can’t use a unit it because the three layers are too thick. I actually tried the step drill first, but could only go in so far.
 
Step up

Thanks everyone for their replies.

I have a few unibits (step drills), it non of them are #19, do such bits exist?

Same question with reamers, 1) where to ge my then and 2) does everyone really have that variety of reamers? I have the 30/40, plus the others called out for specific reaming.

I did the step up to it idea first, 40 to step drill, then the #19 bit. Almost seemed worse because it was easy for drill to bite in, get stuck, and yank itself crooked.

Also, on the inbrd wing ribs, you can’t use a unit it because the three layers are too thick. I actually tried the step drill first, but could only go in so far.

If you step up 40 to 19 is quite a jump. Maybe 40,30,19.
I get my reamers from wherever the price is best. 40,30,19,12, 3/16", 1/4".
I don't care for step drills.
 
Sorry Larry, I meant to say I did that.

I’ve done a 40-30-19. I’ve also done 40->unibit->19.

Seems like if it’s thin, the reamer is the way to go, unless I can find a numbered unibit.
 
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