Metalwork for the linear amp is going GREAT. First I drilled the wrong hole sizes for the heat sink, then broke two 4-40 taps. Will figure out how to extract these then try a thread forming tap instead of a cutting tap.

#hamradio #amateuradio #electronics

@jmorris FYI: If you boil in alum solution to dissolve the taps as I have, make sure to submerge the whole part — I ended up with a permanent line at the interface of the boiling water that I didn't succeed in polishing out when I dissolved one tap out of a piece of 6160.

@mcdanlj I hadn't heard of that method, interesting!

@jmorris Here's one reference. Can't remember where I first learned the trick though...

https://bbs.homeshopmachinist.net/forum/general/1927244-broken-tap-removal-with-alum

It's potentially an all-day process.

Also, besides thread forming taps, have you tried spiral flute taps? I've had good luck with them, particularly ones with polished flutes expressly made for aluminum. Mine are from YG-1.

@mcdanlj I'd read that spiral flute taps are weaker and more likely to break for small taps, so I haven't tried them yet. Thanks for the pointers!

RE: https://social.makerforums.info/users/mcdanlj/statuses/111060149655556379

@jmorris I guess maybe less likely to break from chip packing? They readily evacuate a long string chip out the top. The cheapest ones are still cheap of course. I use tap magic most of the time for tapping, too.

I'm trying to remember the smallest I've done. I own an M2 spiral flute tap and it's not broken, but I do so little that's smaller than M3. And the M2 spiral flute tap I own isn't the highest quality.

But yeah, spiral tip should be stronger than spiral flute, and eject the chip ahead of it as long as you aren't tapping a blind hole. (I do plenty of blind taps which is part of why spiral flute taps are my go-to one-and-done.)

@jmorris Oh, #4-40 is only .155mm smaller diameter than M3, so maybe my good experience with M3 carries over...

I do almost always use a tap follower or some other effective guide. I think the spiral flute taps are not at all forgiving of misalignment. But I'm usually doing it on mill or lathe where I have a good normal reference.

I did also make 3D printed jigs for tapping openbuilds v-slot with M5, where I can't typically use either mill or lathe to get that normal reference.

@mcdanlj a mill would be great but I currently have no room for one. Btw, I ended up brute force drilling the broken taps out with a solid tungsten carbide bit (which broke twice), then I was able to drill & tap for 6-32. There was enough slack in the copper spreader to handle some misalignment. The rest of the 4-40 were done very carefully with a form tap and tap magic. I’ll try the spiral flute next.

@jmorris Glad you got it working!

Tap guides are a reasonable form of vertical reference; mill not required. That's why I mentioned what I do for tapping v-slot. They keep the taps straight enough that I've (touch wood) had 100% success power tapping with a drill and a spiral flute tap.

Also, not trying to talk you out of form taps. I want to go in the opposite direction and start using form taps where appropriate.☺

@mcdanlj I’ve tried a YG-1 spiral flute tap here now and it is working well. It seems to need much lower torque than regular or form taps. I think the form tap is more precise and will provide more strength, but this is not critical in my application.