The 600W amplifier is struggling to take shape. The PSU is built, the main board is populated and I have tested the bias circuitry. It seems to deliver the needed voltages. But the drilling and tapping of the copper heat spreader is not going well.
I'm usually very good at the mechanical aspects of my projects. I can cut holes in panels, mount switches etc. But I have not worked with copper before. And to be honest, I have not tapped a hole since I was in school about 25 years ago.
So far I have broken two drill bits, which are now lodged in the piece of copper for posterity. Advice on the internet suggests welding something to the broken piece to remove them. Well, that seems to hard. I located the board 5mm over and started drilling the holes again. This time I used WD40 (actually it was a can of bicycle lubricant, but websites suggested WD40) and the holes cut much easier. I also drilled for a second, then removed the bit from the hole to clear debris, then drilled some more. After 5 or so one second cuts, I added another squirt of lubricant. That seemed to do the trick.
With drilling solved, I moved on to tapping, again using lubricant. Well, as you would expect, I now have a broken tap in one of the holes needed to mount a transistor. I'm so frustrated. I was very careful, put the tap in and out many times to clear debris, but it caught and snapped as I was removing it.
So now what. The hole is blocked. I have not way to remove the tap. I guess I could move all of the holes over yet again, but that is too frustrating for words. Also I usually pride my self in the look of my finished pieces and this is starting to look very bad. Ideally I would buy another piece of copper, but the plate was nearly $100, with copper prices at record highs.
I think I will abandon tapping the holes. If I counter sink then, then I can screw through from the other side and the bolts will still be flush with the heatsink. I will just need to order the appropriate bolts from Mouser first.
Enter Comments Here:
| On: 11/10/19 19:19 Kiwi2 said: |
Hi, I know that this is rather late. Check out EDM sometimes called spark erosion. Most decent machine shops can remove broken drills and taps by arcing through the broken part. Other wise use a carbide drill bit and drill through the broken item. Regards, Brian ZL1UXB |
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