I'm trying to find a vendor of #4 conical, sometimes called compression or "Belleville", washers. My hardware supplier could not find them. I thought to get clever and contact Key Bellevilles directly but they don't make anything that small.
Does anyone have a lead to a US vendor of such things?
Small Parts Inc,
Kind of pricey, though.
-Chuck Harris
Mike Rocket J. Squirrel Elliott wrote:
$17.10 each in the .125'' size. Yikes!
Duh. Thanks!
-- Mike "Rocket J Squirrel" Elliott
71 VW Type 2 -- the Wonderbus (AKA the Saunabus in summer)
Nah, that's $17.10 for 10 washers. Just a mere $1.70 each.
Some of the stuff that Small Parts has is very attractively priced, but... sometimes it isn't.
-Chuck Harris
Oh yeah. That's right.
Anyone have a pointer to how to stack Belleville (conical) washers to achieve higher clamping force. The best .125 i.d. / .25 o.d. washer I can find has a force of 49lbs when tightened fully flat. What if I want three times that?
Mike,
You're supposed to be able to stiffen the spring constant by stacking them so their conical sides fit together. Stack in an opposing manner to reduce the spring constant.
--Mike
Thanks, Mike. I've found that stacking them in parallel (all pointing in the same direction) allows you to sum spring (clamping) force. Stacking them in opposition keeps the force the same but increases the deflection range.
My application has some of those itty-bitty Caddock TO220 power resistors mounted to a big heatsink, and I'll be dissipating up to 50W from the parts. So I need to clamp these parts are mighty good.
I don't know where I read about these washers. Someone (Motorola? National?) has on a data sheet somewhere that a good mounting technique for TO220 devices is to use these washers as part of the hardware. They specify how much pressure (150lbs, need three .125 i.d. conical/Belleville washers in parallel to achieve this) and how much torque to use to tighten the bolt. A torque screwdriver is specified. Torque screwdrivers are not inexpensive, as I've found. Anyone want to sell one?
Mike,
Humm, opposing stacking will lower the spring constant, but I guess the bottom out point is the same because it travelled twice as far.
I'd just tighten until it feels like it's bottomed out and then enough of an extra twist so that it just feels like something is just about to cold-flow. I hope this isn't for anything life critical like a pacemaker.
--Mike
Turns out that the mounting spec comes from Caddock's data sheet for their MP850 TO-220 power resistors. It's a full-body plastic package, not just a metal tab and they write, "Mounting torque to avoid package damage is 8 in-lbs (0.90 N-m)."
Perhaps you have calibrated fingers -- I don't. Hate to crack the package. I'll get the torque driver.
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