Forstner bit equivalent?

[dgjessing]

What's the least expensive solution for drilling shallow flat-bottom holes in aluminum or brass? (for mounting ball bearings in a plate frame) All I've got is a 1/2" capacity drill press. I don't need great precision - I'm not above a little epoxy glue to hold things in place .

 

[Omnimill]

What diameter holes x depth do you need? I've re-ground twist drills to cut flat bottom holes before up to 1/2" dia. Start off with a standard drill of the same size then switch to the flat bottom one.

Vic.

 

[kustomkb]

Like vic said;

 

[Omnimill]

Like vic said;

Yep, spot on Kevin!

Vic.

 

[mklotz]

Besides regrinding drills...

Center cutting end mills will make (nearly) flat bottom holes. Drill chucks may have difficulty gripping an end mill because, unlike a drill bit, the shank is hard. Make a split bushing to get a better grip.

I've reground spade drills to bring holes roughed out with end mills to final size. Shorten the shanks to cut down on the tendency to vibrate.

Use your Forstner bits. Most aluminums can be cut with woodworking tools. Keep the speed down.

 

[dgjessing]

Thanks all - I'll try some of your suggestions. The bearings are .866" OD (roller blade bearings - $2 for 16 at the Goodwill store ).

Maybe just sacrificing a forstner bit is the way to go... I'll try that first.

I could not find any end mills on line this big with a 1/2" shank. Plus they ain't cheap!

 

[mklotz]

Maybe a cheap router bit?

 

[Hilmar]

Fly Cut the OD first to size and then mill out the inner part.
Hilmar

 

[Ed T]

The trick with using a Forstner bit or a router bit will be finding one that happens to be .886" As suggested above, you could regrind a spade bit to do the job and you don't need ant special tools to do it. Even a file would work if you have the patience. If going the spade bit route, there would be some benefit in putting a round piece of ,say 3/8 stock on over the little pointy end. Then drill a 3/8 hole first and use that to pilot the bit. Otherwise it's likely to dance around a lot and not give you the shape or size you were hoping for. If using this aprroach make the bit as short as possible and run it very slowly with some lube (wd-40). The adjustable fly cutter suggested above is also an approach that would alow you to adjust the hole diameter 'til you get what you want. It will cut a groove. so you'll have to clean out the middle but that's not dimensionally too critical so you could even do it with a dremel or similar. A carbide router bit smaller than the hole could also be used with a circlular template, They work pretty well for aluminum. One potential advantage of the spade bit or the flycutter appraoch is that, if you're doing two plates, you can clamp them together and drill the pilot holes in both at once That way, at least the plates will be the same which is often more important than correctness. Despite the "score" on the bearings you might also want to consider just using flanged oilites thay just go into a through hole in the plate. A bit more friction than the ball bearings but a whole lot simpler to do.

 

[dgjessing]

I tried a forstner bit today, and it would probably work. I used a rather worn 3/4" one just to see it it was within the realm of possibility, and I'd say yes; however I was using my little drill press which won't go as slow as needed, and which stalled a couple times from the effort. I'll bet it would work with the big drill press (which can go slower and has a lot more power). A sharp bit would help too I first drilled an 1/8" pilot hole for the little brad point on the bit to follow.

I'm thinking maybe the fly cutter and mill out the middle might be the better route though, as that would make it so I could get the diameter just right and not need to do any shimming. But my "milling machine" consists of the big drill press, a cheap x-y milling table, and a couple small end mills somebody gave me.

I might try modifying a spade bit, just for grins.

Thanks, everybody!

 

[mklotz]

Are you aware of the safety concerns of milling on a drill press?

 

[dgjessing]

Are you aware of the safety concerns of milling on a drill press?

Apparently not... (?)