Drillium Tips?
 

I drilled decorative holes in some aluminum bicycle cranks tonight. As the holes got larger - about 1/2" - It was hard to get a smooth round hole. The bit chattered and tried to make polygonal shapes.

The end result was okay - this is just a $35 set of BMX cranks for my son's bike - but jeez I'd be unhappy if these were Campagnolo.

What is the secret to:

- Drilling perfectly round holes of diameter up to 1/2".

- Chamfering the edges of those holes, with a sharp bevel shape.

- Cutting through slots with parallel sides and semi-round ends.

- Cutting half-blind slots (i.e. recesses) with polished sides and bottoms.

Assume the material is softish aluminum, and the tools available are a Dremel and a drill press.

You'll get better results in a home environment with one of these.

Klein 59003 Unibit 1/4" To 3/4" Hole 362-105

This is a very common problem. I went through it while drilling holes of various sizes in a sheet of steel last year when I made my tube amp.

pilot hole ?
1/8 then 1/4 then 1/2

The crank isn't going to crack?

the secret is kerosene!











also, your speeds & feeds

Unibit - interesting! I have never seen such a bit.

Crack - nah, it is a BMX crank, way overbuilt for jumps and thrashing and racing by big kids and adults. He's a 12 y/o kid who won't be (hopefully) jumping this old ten-speed.

It seems that the unibit is for drilling holes in conduit boxes, but works quite well for other metal applications. You can find them at HD.

You probably used normal bits to drill the holes. If so, even in a drill press, the bits will wander and flex.

I got the unibit because I needed to drill 1" holes and I could not find a big enough bit. :D It drilled pretty clean big holes so I touched up the smaller ones as well with it.

This and rigidity. Chuck the drill up as short as possible. Clamp the part firmly so that it can not move relative to the drill. ( it is okay to chuck on the flutes , you can even use a cutoff wheel on the dremel to shorten the drill if it is a issue)

What is the secret to:

- Drilling perfectly round holes of diameter up to 1/2". covered

- Chamfering the edges of those holes, with a sharp bevel shape. use a single flute counter sink

- Cutting through slots with parallel sides and semi-round ends. milling machine or
drill the ends then saw and carefully file to make the slot

- Cutting half-blind slots (i.e. recesses) with polished sides and bottoms. milling machine

I was going to mention this, but you also sacrifice a bit. Not that that is a bad thing, but it does slow projects down when you forget and two months later grab the 3/4" bit only to be reminded that it no longer can be used to drill a deep hole because it has been "modified". :D