[Lost81]

Hi guys,

Anyone got pointers for drilling the holes to mount the transistors?

I will be using WD-40 for lubricant.

I don't have a bench vise, nor a drill press.
Shall I go borrow one?

thanks,

benny

[blizzard]

Hi Benny,
  You don't need a bench vice or a drill press.  Just borrow your neighbor's laser plasma vaporizer.  That ought to get some real nice holes.  And, as an added bonus you won't have to remove any burrs.
  Just kidding.  You don't need a vice or a press.  You should clamp the sink to something to secure it while you're drilling though.  And, for aluminum, I think you're supposed to use kerosene as a lubricant -- not oil (WD-40).  Don't go too high with the speed of the drill.  I would go about 1/2 to 3/4 full speed.  And, don't push too hard with the drill.  Let the bit do the work.   Start with a very small bit.  Then, keep increasing the bit size until you reach the desired diameter.  Even though Aluminum drills pretty easy, don't try and make too big a hole in one shot.  Finally, try to stay as perpendicular to the surface as possible.
     Good luck,
        Steve

[bubba966]

Might add to Steve's suggestions to make sure you've got a good high quality sharp drill bit. A lot of cheaper bits aren't straight & wobble when using them. I've got some nice cobalt coated bits from Makita that are still sharp after 7 years. And still perfectly straight. I've also got a few Titanium coated bits brom Bosch that are also very good, but not quite as sharp as the Makita's.

It's much easier to drill the holes right the first time with a good bit, than it is to try & fix them after after using a poor quality bit. Investing in a good bit up front is cheaper than repairing later.

[cmscott6]

I used the Bosch titanium bits too, and they worked great.  Also making a starting point with a center punch helped keep the bits from "wandering".

[PSP]

If you can find one, buy a pin vise.... this is a hand-held chuck, about the size of a fat ballpoint pen, and it takes very small drill bits.  When I want to drill a hole in a very precisely located position I measure with a caliper or steel ruler and mark the spot with crossed lines (x mm from the left edge, ymm from the bottom edge, the lines cross at the point I want the hole).  Then I use the pin vise to drill a small pilot hole, not very deep, just by spinning the pin vise with my fingers (it takes less than a minute, even in steel). This little hole has the same function as the depression you get from a center punch, but you can locate the hole much more accurately with a pin vise.  

Then I drill a small pilot hole (say with a 1/32 or 3/64 inch bit) all the way through, and then drill the actual hole with the actual bit... the final desired diameter.

Lots of fooling around, I know... but I've never drilled a hole in the wrong spot, either.  I bought my pin vise at RadioShack.com, but they don't sell it anymore... I tried to buy one for a friend for Christmas, but no cigar.

By the way, a pin vise is absolutely perfect for making a pcb hole a little larger, removing a bit of solder in the hole etc... extremely handy tool.

And all of the advise above about drill bits... yup!!

good luck,
Peter

[Lost81]

Thanks for the tips, guys.

How large a hole did you guys drill for the transistors (100W)?
I am assuming 1/8" diameter?

Thanks,

benny

[RobDe]

I don't know the exact size drill bit I used for drilling my heat sinks (100W).  I picked a size from the set that just fits through the transistor mounting hole.  I have a drill press at home but that is not required here. An electric hand drill will do just fine.  I use WD40 all the time even though I have access to aluminum tapping fluid from a machine shop.  I just marked the spot to drill with a Sharpe marker followed with a center punch.  Just start slow applying light pressure to keep the bit from wandering even after using a center punch.  I have cobalt and high speed steel bits. If you have trouble finding cobalt or titanium bits, high speed steel  bits work just fine on aluminum.

 Rob

[John H]

You can buy a pin vise online in the U.S. for $8, including shipping, from www.greenway products.com/buy_tool_drills.htm.