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Old 9th December 2010, 03:41 AM   #11
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Hi Ken,

I don't think there is enough meat on the Conrad heatsinks to drill a blind hole and tap it easily (by me that is). I would suggest you drill and tap through the base of the heatsink, but grind the ends the bolts so they are flat and flush, then paint them black.

If your holes are inboard from the edges you probably won't notice the tops of the bolts in the shadow of the fins.

The Conrad heatsink are cast which makes tapping a little more difficult I believe. I have always used Conrad heatsinks and find I have to clean the tap 2 or 3 times during the tapping process. Half way through tapping it starts to bind and I need to remove the tap and remove the swarf with a toothbrush and kero. Once I have tapped through the base I blow the swarf off before removing the tap.

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Old 9th December 2010, 03:46 AM   #12
frags is offline frags  Canada
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I made blind holes with 6-32 threads in 10mm aluminum board using regular tap with the tip ground off. No problem at all to make 8mm deep holes.
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Old 9th December 2010, 07:29 AM   #13
ZUM911 is offline ZUM911  Australia
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I'm wondering if the quality of the taps might play a part? I've used the Conrad sinks on 4 amps now and had no problems. I do have some good quality 3-tap sets with the bottoming tap. Using tapping oil, I just make a full rotation with the tap and then back it off half a turn to break the chip, repeating until I hit the bottom. There seems to be plenty of meat there to get more than enough torque without having to go through the side of the sink.

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Old 9th December 2010, 11:51 AM   #14
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Thanks, all. One more simple question (and I think I already know the responses I'll get....). At one time I had planned on mounting my amp boards only with the tabs of the MOSFETs, into drilled/tapped holes in the heatsinks. (I thought this might be adequate, due to the light weight, and relatively small size, of the amp boards.) Having said that, my amp boards are drilled for four mounting points (one in each corner of each board). For reasons of "good construction", should I use all six mounting points for each board (2 MOSFETs + 4 on the board itself). I'm guessing you'all are going to tell me to drill/tap all six.

Probalby a dumb question, but I wasn't able to tell if there is a preferred approach by looking at the F5 pics posted to the forum..... Thanks, in advance....

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Old 9th December 2010, 12:07 PM   #15
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It sounds like I am just not trying hard enough.

I must find my plug tap and give it a try.

Greg Erskine
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Old 9th December 2010, 06:31 PM   #16
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Originally Posted by CanAm Man View Post

Thanks for the great advice. Probaby will go the McMaster-Carr route, and chucking it in my drill press to keep alignment true. Thanks, too--for the tip about "required depth" to give me a satifactory fastening. Re: "buy a couple because you'll probalby break one or two......" Oh, boy--something else to look forward to....!
For what its worth, I eye balled mine and drilled them with a hand held cordless drill. Worked perfect!

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Old 9th December 2010, 08:04 PM   #17
westend is offline westend  United States
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Tap magic is good cutting oil for these. I dilled device mounting holes deep and used a conventional tap in a 3/8" heatsink base. Removing the swarf is the trick, occasionally blowing out the hole with air does it for me but I've also heard that using wax or grease in the hoile moves the swarf out. Even if you through drilled the heatsinks, the holes should be unnoticeable to any but the most intrusive inspector. Of course, you'll always know. The through holes could also be backfilled and paint retouched, if you end up going that route.

BTW, don't break a tap, it is a PITA to the whole project. There is really no worry about threading aluminum with a quality tap, if done by hand.
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Old 9th December 2010, 08:09 PM   #18
frags is offline frags  Canada
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In the past I used pork lard as tap lubricant and it worked really great (no kidding).
So if you have a piece of bacon in your fridge you can try it.
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Old 9th December 2010, 08:10 PM   #19
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BTW, don't break a tap, it is a PITA to the whole project. There is really no worry about threading aluminum with a quality tap, if done by hand.[/QUOTE]

Dont forget you need cutting oil on the tap otherwise it will break quite easily.

Tap in a turn or so then back it off before going forward again.
Murton-Pike Systems PCBCAD51 pcb design software. http://www.murtonpikesystems.co.uk
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Old 9th December 2010, 10:20 PM   #20
Magura is offline Magura  Denmark
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Ok, this topic seems to have taken the usual detour

A few simple guidelines about threading aluminum:

1) Alcohol is by far the best cutting liquid for aluminum.
Anything else "made for aluminum cutting", is made due to the issue of the fire hazard of alcohol, as the industry does not like flammable liquids in free air.

2) Never use a tap or die, that has been used for cutting anything besides aluminum, as such tap will be wast inferior to one that is used for aluminum only.

3) Stay clear of el-cheapo taps. A good quality tap this small, can be had for like 15us$, and is well worth every cent. The cheap ones are almost always either brittle or too soft, and frequently both.

4) get a small straight angle, and measure that you have managed to tap straight. This will lower the stress on your tap significantly.

5) For short blind holes, use a spiral flute tap.

If you stick to these simple guidelines, tapping heatsinks is a walk in the park.

Everything is possible....to do the impossible just takes a little while longer.
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