co-axial holes with drill press

[brybot]

I am working on a project at home, and the only tools I have at my disposal are a drill press and a hack saw. My objective is to drill two co-axial holes in aluminum scrap to adapt a 1/4" shaft to a 2mm shaft. The issue I am having is that my holes are misaligned by a degree or two, which is enough to cause the rest of my system to seize up.

Here's my procedure:
1) Cut a ~15mm section of 1/2" aluminum rod stock with a hack saw (apologies for mixing units)
2) Clamp the stock into my drill press. Adjust it so that it's close to vertical with a square. This isn't super critical for me, as long as the holes are properly co-axial
3) Adjust the drill press table so that I can drill my 5/64" hole all the way through, and step up to 1/4" half way through. This way I won't have to adjust the table between presses
4) Start a hole for the 5/64" bit so it doesn't wander around too much. Here's what I've tried
a) Center punch
b) Starting a 1/8" hole
c) Starting a 1/4" hole, a bit deeper
d) Make sure that the 5/64" bit is as far up in the chuck as possible.
5) Slowly drill the 5/64" all the way through, adding a little bit of tap magic lubricant
6) Switch the bit, and step my way up to 1/4", drilling only half way into the stock
My drill bits are cobalt HSS jobbers.

The final result always has a degree to a few in axial misalignment.

My guesses:
1) The 5/64" bit is bending and wandering off axis as I drill.
2) The bit changes are introducing an axial offset. It's a relatively cheap drill press. Perhaps the chuck doesn't have good tolerances.
3) The hacksaw surface of the aluminum is relatively planar, but is not square, which definitely doesn't help the drill bit stay on track

Suggestions or advice would be appreciated. Thanks!

 

[francist]

You might try drilling the larger of the two holes to depth first, the run through with the smaller bit after that. It's maybe a bit counter-intuitive, but you may find the smaller bit stays on track better. Also have a look at the cutting edges on your drill bits -- if one flute is damaged it can cause the bit to pull one way or the other.

-frank

 

[Reddinr]

I would drill the 1/4" hole part way through and use the conical indentation at the bottom of the 1/4" hole to center the 2mm drill. If you think things are shifting around, use a light / magnifier to peer into the hole to align the small bit by eye. The key I think is to make sure the small bit is exactly centered by the prior operation. If bent one way or the other when started, it may tend to keep going that way.

...oops francist beat me to it...

 

[magicniner]

Smallest hole all the way through first, larger holes will follow smaller ones but smaller ones will not reliably centre accurately in a larger blind hole.
Peck drilling is essential for straighter holes.
Do you know the trick with a centre point on the drill press table to drill converging holes from two ends of a part?

- Nick

 

[benmychree]

Nick (above) said it all !

 

[brybot]

Thanks for the suggestions. I tried the 1/4" first with a 1/8th pilot, and followed up with the 5/64". It came out dead on! I also switched to a square rod which gave me a flat surface to work with.

@magicniner I believe I was following your suggestion originally with my 5/64" and then going up to 1/4". I was using a peck drilling technique. However, I'm not familiar with the converging hole center point trick. Would you point me to it?

Thanks

 

[ezduzit]

...It's a relatively cheap drill press...

Here's one of your problems.

 

[Firstram]

Do you know the trick with a centre point on the drill press table to drill converging holes from two ends of a part? - Nick

I give, what's the trick?

 

[larry4406]

I give up as well. What is the trick?

 

[magicniner]

Use a lathe dead centre in the table, align it with the tip of your drill bit, mark two sides of a part and with one mark on the centre the drill will be cutting towards it.