[sdiy] DB25 hole

[Stewart Pye]

Hi David,

I've done it many times. I've always had the advantage of having a 
template (a scrap of a panel that was actually cut out by a CNC machine 
for a "D" hole) but the same principle applies....

Mark out the centre line, nut holes and outline.
The final drill size you will use will be about 2mm smaller than the 
width of the slot. If you're not confident make the hole size a bit 
smaller to allow for error.
Centre punch along the centre line so that the final hole size doesn't 
quite go out either end, but each hole will overlap a bit (like the Audi 
symbol).
Drill a 1/8" hole where each punch mark is.
Drill a 1/4" hole where each punch mark is.
If you're game drill the final hole size (or a bit smaller) but don't 
drill right through the first hole. Get into each hole a bit then go for 
another round. Keep doing this until you get through all of them (or 
until you slice your hand open). A slightly blunt drill bit will help in 
this situation. You have to be really careful as the holes meet up.
You should have an opening all the way across the slot, and not too much 
to file off. Use a medium sized flat bastard file to get the bulk off, 
and triangle and small round files to shape up the end.

This method is a bit dangerous so do whatever you have to to make sure 
you don't get injured. Secure the job in a vice, and I wouldn't do this 
without a drill press.
I find this a lot quicker than drilling lots of tiny holes around the 
perimeter, in which case you often have trouble getting the unwanted 
piece out if there's a gap between the holes.

Cheers,
Stew.






David Moylan wrote:
> Anyone made a DB25 shaped hole in a cast aluminum box?  Favorite 
> methods or tools?
>
> Thanks.
>
> Dave
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