What are these screws called?

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Try reading what I said. Look closer. Thats not a backed out screw. The first hole is the start, the screw was not in yet, it was just started. I did that to show you what the screw did with the waste, it ejects it like a drill bit. The screw that's in went straight in with no back out. Why dont you try it?

So your point is that when self drilling screws are first started, and not yet tapping threads, they will self clean? And from this you conclude self tapping screws will self clean into any thickness?
 
They are used in securing output transistors on heatsinks. They seem much more user friendly
I have to add that self-tapping screws are possibly not good for securing powerful output transistors to heatsink because I always thought they are only suite for thin sheet metal. But output transistors need more secure fastening. It is possible (I think) only with a usual screws because they have an appropriately short (small/frequent) thread (carving ?).
Self-tapping screws have too large thread (carving) step. That is my thoughts.
Thats why I use a tap (2.5 mm or 3.0 mm). I use it with a battery screwdriver. I fail about one of 12-20 threads.
 
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Wrong. Thats exactly what there made for. Its a driil bit on the end of the screw. 1/8 inch aluminum, could have been a lot thicker. Look at the start of the hole where the aluminum is beeing drilled out. You dont have too back out to clean it.

Is that about a #8 screw? I won't ask why you're screwing holes into a level.:confused:

I'm guessing that this type of self tapping screw has a purpose, and might come in handy, maybe on a construction site? But for amplifier assembly, it's sorta like building fine furniture with nails and a hammer.

jeff
 
No idea what you are working on, but I have a concern. Are the transistors not going to be insulated from the sink? I got concerned when you said the holes were larger than #8 screws. On something like a TO220 the screw is often smaller than the hole because it uses a plastic step washer to keep the screw from making electrical contact with the transistor.

For TO3, we usually insulate the body with a mica sheet, the sink hole is larger than the screw so the screw can center and not touch. Often there is a socket with plastic shapes to provide the centering. Or a step washer and smaller screw can be used on them as well.
 
Why don't you just learn how to tap aluminum for machine screws. Those self tapping sheet metal screws aren't the answer for thick aluminum. They will bind in the hole and snap off, and then you'll be really angry.

If you bugger a threaded hole, you can fix it with a thread repair kit.

jeff

Did a couple of years ago. It was a PIA, instead of screws, (had 32 holes to tap) I had 2 tapping tools break on me. Those holes were in a straight line too, so it ruined the whole line....
 
The photo I show is of a commercial well known amplifier maker (Sonance), thats the screw they use to secure the T-O3P devices on to the heatsink. They have extra holes there that are un-used (for a different model perhaps) so I took one the existing screws from one of the OP devices, and handscrewed it into the un-used hole, it went in nicely without any fuss or any tapping. It was NOT pre-tapped, it was anodized, so it was just a drilled hole. Kenwood and other manufacturers also use the same thread style. This is why I was asking in this August body of experts... Tapping 32 more holes will be another PIA.
 
You’ll need to drill the holes to an exact size as specified by the manufacturer of the screws regardless of the process, and use a decent cutting fluid.
Most of the issues with manual tapping blind holes is from not maintaining perpendicularlity while tapping.
If you were to make a simple fixture on a drill press, that should help greatly. Then go a half turn at a time and back the tap out to clear out the metal chips. The trick is then to not approach the end of the hole if you’re not experienced. That fixture could be a chunk of wood with a hole in it.

Honesty the thread cutting screws have the same risks with starting crooked and failing.
 
Tapping aluminium is super easy and very consistent after a little practice. Just make sure to use the right size drill, then wind the tap in and out, brushing the excess from the channels in the tap and using cutting/tapping fluid (or olive/canola oil) while doing so

After a while you can freehand both the drilling and tapping with a cordless drill

With self tapping screws you are entirely dependent on the quality of screw to both easily tap the hole and not snap off
 
Rookie question, what is the percentage of success with or without cutting oil?
There is no need at all to work (to tap) without some lubricant (I use an alcohol or an oil for aluminium), because it became harder and quality may go out of your control.
I don't like oil (because it is oily :) ) so I use an alcohol with an aluminium - it leaves no oily trace. (I use the same liquid as for cleaning the PCB - a mixture of an isopropil alcohol and a clean gas/gasoline).
There is of cause some difference between an oil and an alcohole but for DIY-tap it works about the same.
 
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