OT? Seeking conical washer for heatsinking

[Mike Rocket J. Squirrel Elliott]

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?

 

[Chuck Harris]

Small Parts Inc, http://www.smallparts.com has stainless steel
Bellville spring washers in the following sizes:

3/32",1/8", #6, #8, 3/16" 1/4" 5/16" 3/4"

Kind of pricey, though.

-Chuck Harris

 

[Sporkman]

www.mcmaster.com

 

[Mike Rocket J. Squirrel Elliott]

Small Parts Inc, http://www.smallparts.com has stainless steel
Bellville spring washers in the following sizes:

3/32",1/8", #6, #8, 3/16" 1/4" 5/16" 3/4"

Kind of pricey, though.

$17.10 each in the .125'' size. Yikes!

 

[Mike Rocket J. Squirrel Elliott]

www.mcmaster.com

Duh. Thanks!

 

[Chuck Harris]

$17.10 each in the .125'' size. Yikes!

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

 

[Mike Rocket J. Squirrel Elliott]

Nah, that's $17.10 for 10 washers. Just a mere $1.70 each.

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 Engelhardt]

Mike,

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?

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

 

[Mike Rocket J. Squirrel Elliott]

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.

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 Engelhardt]

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.

Humm, opposing stacking will lower the spring constant, but I guess the
bottom out point is the same because it travelled twice as far.

... A torque screwdriver is specified...

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

 

[Mike Rocket J. Squirrel Elliott]

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.

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.

 

[Jim Adney]

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.

I think at this size you'll find that the limiting thing will be the
strength of the screw that you can put thru that hole. If you want
stronger Belleville washers try the SP series from Rolex. They are not
as precise as some, but they are perfect for stuff like this.

For the all-plastic package, put a steel washer UNDER the Belleville
to help spread the force out over a larger plastic surface area.

-

 

[Mike Rocket J. Squirrel Elliott]

I think at this size you'll find that the limiting thing will be the
strength of the screw that you can put thru that hole. If you want
stronger Belleville washers try the SP series from Rolex. They are not
as precise as some, but they are perfect for stuff like this.

For the all-plastic package, put a steel washer UNDER the Belleville
to help spread the force out over a larger plastic surface area.

Good suggestion on the flat washer to spread the force.

Regaring Rolex washers: I'm a pretty good Google jockey but have struck
out on this one. A Flash animation of a seedy-looking guy did pop up and
he offered me some Rolex washers, but I'm pretty sure they were only
counterfeit. Can you point me to a vendor for these parts?

 

[Jim Adney]

Regaring Rolex washers: I'm a pretty good Google jockey but have struck
out on this one. A Flash animation of a seedy-looking guy did pop up and
he offered me some Rolex washers, but I'm pretty sure they were only
counterfeit. Can you point me to a vendor for these parts?

I'll check my catalog on monday.

-

 

[Mike Rocket J. Squirrel Elliott]

I'll check my catalog on monday.

Much appreciated!