Just don't use self-tapping screws. They leave metal shards all over the place and those shards tend to get into places where you don't want them.
Tom
Tom
For me, when using 4-40 taps, a light weight T-handle for small taps is the best holder. The 4-40 taps are so small in diameter, and brittle, that a small sideways bump is enough to snap them. I know that from experience. So, if the tap holder has some mass, extra careful handling is required.
There are taps specified for "blind holes"
Rayma on 4-40's -- I haven't busted any recently (and they are PIA when it happens) but those I got from McMaster a while back have proven up to the task.
+1 for the taps from McMaster-Carr. I have some spiral flute, TiN coated, M3x0.5 mm, bottom taps from there. They've lasted at least a decade by now and do see regular use.
Tom
Tom
There have always been bottoming taps. But if you want to tap right to the bottom of the hole, you have to grind them back a little.
jeff
I got a pair of M3 bottoming taps from McMaster also and the corresponding drill bit. Seems to work fine.
For TO220 devices I like to drill a 2.5 mm hole then tap it with M3 tap, then use a nylon screw to mount the device instead of using a plastic bushing with a metal screw. With the bushing I get no free play at all if the hole is maybe off by 1mm. With no bushing and nylon screw I can be off by as much as 1mm with the hole and still get the device mounted and leads aligned with the board. The Wiggle room is very helpful. The nylon screw insures no shorting of the device to the heatsink.
It depends on the fin spacing on the opposite side of the heat sink. Rarely can you get a nut to fit between fins. Tapping is infinitely easier because your hole can even go down through a fin if it has to and you just tap through the fin, no problem, nuts are nearly impossible with fins unless the fins are 12mm apart or so, even then you'd have to plan your board so the hole winds up in the center between two fins to fit a nut down through there.
I was just looking at McMaster-Carr's nylon 4-40 screws. They are only rated up to 140°F. Not saying that's what you are using but MC stuff is usually top-notch.
Good point. I have so far used them on voltage regulators and mosfets and bipolar devices where I tend to use overrated parts and big heatsinks (just me). For exam0le I routinely use LD1084 5A regulator even if the draw will be just 100ma.
But I see PVDF screws can withstand up to 300F (over the boiling point of water). Does anyone have a supplier of PVDF m3 screws? I have not had issues with nylon, but you're right check how hot it's gonna get first.
here we go...
https://accu-components.com/us/cheese-head-screws/496646-SFE-M3-10-PVDF
10mm m3 is the shortest I could find, depending on the insulator thickness you'd be left with maybe 4-6 mm, if you need shorter m3 aluminum washers under the cap would shorten it and conduct some heat off the top of the TO220 tab as well.
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Nylon 140F
PVDF 300F
PEEK 500F
Wow it looks like PEEK M3 screws go to 500F, McMaster has them:
https://www.mcmaster.com/products/peek-bolts/
PVDF 300F
PEEK 500F
Wow it looks like PEEK M3 screws go to 500F, McMaster has them:
https://www.mcmaster.com/products/peek-bolts/
You talking about PEM nuts? I've mashed them in using a vise. An actual press with some sort of die/holder would be preferably though.
Nylon is not a good material for mounting devices to a heat sink. It tends to stretch over time resulting in a poor thermal connection between the device and the heat sink. It also goes brittle with time. You're better off with shoulder washers and metal screws. The shoulder washers are not expensive as long as you buy more than one at a time.
Tom
Nylon is not a good material for mounting devices to a heat sink. It tends to stretch over time resulting in a poor thermal connection between the device and the heat sink. It also goes brittle with time. You're better off with shoulder washers and metal screws. The shoulder washers are not expensive as long as you buy more than one at a time.
Tom
The peek screw listed do not have a hardness nor tensile strength rating. What seemed like a good idea for me at first glance may not inspire confidence for me.
My oldest son got me a Marson Thread-Sert tool kit (Aircraft Spruce?) For 6-32 minimum material thickness is 3/32 inch (0.093). Of course, before he gifted it, he used it to fix the dishwasher.