Socket Head Screws for Heatsinks?

[luvdunhill]

I'm wanting to get away from standard / Philips screws for securing devices to heatsinks... they just don't work so well. So, any recommendations?

I have to place an order at www.fastener-express.com anyways, so now's a good time (hopefully I can place it today!)

The base of my heatsink is 3/8" and I'll be attaching TO-220 devices.

 

[HeadSh0T]

Not sure if you thought of this already, but I found good hex drive socket screws in the hardware section at Home Depot! Used them in my Aleph 30 amp to screw the front plate to the heat sinks.

 

[luvdunhill]

ah, well, I figured I'm placing an order there anyways... I'm thinking about some 4-40 x 1/4 Socket Head Cap Screw Stainless Steel (versus Alloy Steel). I'm not sure I can larger than 4-40 and I don't know if 1/4" is too deep or not... but if I don't get any other replies, I'll probably go with these

 

[Chucko]

Always use a hardened washer under a socket head cap screw! Especially with soft metals like aluminum or copper heat sinks.

 

[Conrad Hoffman]

With anything that changes temperature, you should use a lockwasher. I prefer split ring types. Avoid button head cap screws, as they tend to strip out easily. If that happens, slot it with a cutoff wheel and remove it with a standard screwdriver.

 

[jackinnj]

How does your vendor compare with McMaster for fasteners. My son and I order from McMaster about every other week.

 

[head_spaz]

I use these Black Oxide Button Heads for just about everything. I love 'em! I use a lot of 6x32x1/4, and have never had one strip. (use QUALITY allen wrenches / hex keys and you won't have a problem).
I don't use lockwashers either. These tend to snug up tight and stay that way. You get a distinctive SNAP whenever you try to loosen them. Can't really explain it... but they really work well.

The link is to Nutty Fasteners, who have always provided good service in the past, but their pricing has gone exponential lately. Or perhaps the dollar is crashing exponentially.

I will probably go with MSC or McMaster-Carr on my next order.
McMaster-Carr is one of my favorite toy stores. They have a huge inventory, they ship quick for cheap, and they've never screwed up on my orders. Competence like that is rare these days.

 

[dangus]

If you're in a reasonably large city, there's probably a place that deals in specialty fasteners (Pacific Fastener in Vancouver, for example). If you're near a large body of water, marine suppliers carry a range of stainless fasteners.

 

[luvdunhill]

thanks everyone!

I went ahead and got the lock washers, but since I'm going to need to use a shoulder washer to isolate the devices, where does the lock washer go? I wasn't really sure how the length was calculated with the socket head, so I went for some extra length, assuming that the quoted length includes the total length, not the length of the thread

once they get here, I'll report back

 

[hifimaker]

I used black Hex cap screws to great effect on my A30 to fasten the heatsinks to the chassis and hex head screws to fasten the to-247 irf144 FETs. They were purchased at Orchard Supply Hardware here in San Jose.

Here's a link to a thread with the picture.

The heatsink uses 1/4" by 5/16" and the fets are #6 at 1/2".

http://www.diyaudio.com/forums/showthread.php?postid=870719#post870719

-David

 

[jackinnj]

thanks everyone!

I went ahead and got the lock washers, but since I'm going to need to use a shoulder washer to isolate the devices, where does the lock washer go?

Here's an illustration from Keystone Electronics:

http://www.keyelco.com/pdfs/M55p103.pdf

 

[luvdunhill]

Here's an illustration from Keystone Electronics:

http://www.keyelco.com/pdfs/M55p103.pdf

right, but I will be tapping the heatsink with a blind hole to secure the transistors... Seems that I won't be able to use much other than the shoulder washer ...

 

[Conrad Hoffman]

Ahh, blind tapped holes in chewing-gum grade aluminum. Some time back a machinist friend introduced me to forming taps. Since then I've never wasted money on anything else. Get yourself a few Balax thread forming taps. They cost, but you'll never wear them out, and likely never break one. You'll never have to pull chips out of blind holes because there aren't any. The threads are stronger because the metal is formed and work hardened. The only downsides are that the tap drill sizes are different and the really clumsy can more easily cross-thread things if they start the screw wrong. These work on anything up to mild stainless steel (with moly oil), but not hard steels. For aluminum and brass, they can't be beat. They also do a better job with sheet metal because you get a bit of a rise and more usable thread.

 

[luvdunhill]

Conrad:

these look great! I'm going to use 4-40 screws, so I just need to find a place to purchase one of these critters. Thanks!

 

[Conrad Hoffman]

Forming taps have become much more mainstream in the last year or two, and most of the tool suppliers like Travers and MSC carry them. I've used various brands, and the Balax seem to work best- smoother and lower torque than the others. Amazingly, a forming tap often turns easier than a cutting tap.