Author Topic: Custom Belleville (conical) washers  (Read 550 times)

Offline bent

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Custom Belleville (conical) washers
« on: July 26, 2019, 11:21:52 PM »
Haven't had time to post here much, because ... life.  So, I work as an engineer for a living.  An assembly that I inherited many years ago, from a colleague, uses a stack of Belleville washers to preload some parts on a shaft.  The Bellevilles were chosen from a large national shop that had something in stock that was "close enough".  Except they aren't/weren't - when you do the tolerance stack analysis, you end up needing to put either 3 or 4 of them in an assembly, which requires a lot of futzing around in the production shop.  And recently, the Belleville shop had a problem getting the parts heat treated, and so the parts have been delayed, for over a month now, which is holding up an order.

So, I spent some time looking for alternatives.  Doing the math from the Roark's formulas, we want a stainless washer, somewhere between 0.03 and 0.04 thick, with a 1.53 i.d. and a 2.1 to 2.4 o.d. with about a .120 overall height.  And we don't really need to heat treat them, standard 300 series stainless should work.  But regardless, these new design springs are going to be custom, because nobody makes them in anything close to those sizes.  And the tooling charges, plus minimum order quantities, puts the cost up over $1500 for 50 to 100 pieces (roughly a 1 year supply for us).

So, yesterday and today, I spent some lathe time making a stamping die.  Found a scrap chunk of 4140 that was big enough, and cut a 15 degree cone on the mating faces (photos 1 and 2 below), which ended up being too shallow.  A second try at 25 degree cone angle ended up giving slightly more dish than we wanted when I stamped a blank I hand-punched out of some .031 full hard 302ss shim stock.  But then a quick load test with the arbor press (using a cylinder and pressure gage as a load cell) showed a load profile pretty close to what we wanted - the washer flattened out a bit to end up right in the target dish height, and its gives the right load profile.  Success!  Now we need to get our local waterjet shop to cut the blanks for us, and we can get back to making shipments.

I think I credit this forum, and its clever engineers and machinists, for inspiring me to give this a try.  Hope somebody can make use of the information someday, but bottom line: stamping a Belleville washer is pretty easy, you might make a couple of iterations to get the cone angle right, but then you are in business.


Offline cnr6400

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Re: Custom Belleville (conical) washers
« Reply #1 on: July 27, 2019, 12:15:43 AM »
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :cheers:

Offline b.lindsey

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Re: Custom Belleville (conical) washers
« Reply #2 on: July 27, 2019, 01:04:18 AM »
Nice looking die bent!! With the water jet blanks you will be good to go  :ThumbsUp:

Bill

Offline Zephyrin

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Re: Custom Belleville (conical) washers
« Reply #3 on: July 27, 2019, 09:57:25 AM »
nice results with these washers!
the point I found difficult is to determine the internal diameter, as the die stamping increase this diameter then the loading on the axle reduces it.

Offline Ye-Ole Steam Dude

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Re: Custom Belleville (conical) washers
« Reply #4 on: July 27, 2019, 01:07:33 PM »
Hello Bent,

Very nice work :ThumbsUp:

Have a great day,
Thomas

Offline bent

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Re: Custom Belleville (conical) washers
« Reply #5 on: July 29, 2019, 04:29:22 PM »
Thanks all. ^-^


Offline Roger B

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Re: Custom Belleville (conical) washers
« Reply #6 on: July 29, 2019, 08:00:37 PM »
Excellent  :praise2:  :praise2:  :wine1:
Best regards

Roger

Offline bent

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Re: Custom Belleville (conical) washers
« Reply #7 on: July 30, 2019, 08:45:30 PM »
Update:  We shipped the delayed assembly yesterday using 4 more emergency prototype spring washers that I fabricated.  The assembly tested perfectly.    :wine1:

The national shop we have been buying from has been telling us that our order for more (old style) washers are "shipping today or tomorrow" for the last several weeks, and our shipment had been delayed more than a month, so I got to be a hero.  Local waterjet shop is going to cut some .040 thick blanks, hoping for a little higher preload to hold under worst case conditions...though it may mean one more tweak to the stamping die.  Who knows, if the old shop delays a couple more weeks, we may have a successful replacement part, and tell them to pound sand with their order.  The cost for a small batch of 40 blank pieces is the same as for 100 of the heat treated parts, so we are okay with local short run methods, and the price will only go down if we order larger quantities some day and find a washer stamping shop to run the blanks.

Funny thing, when I was parting the piece of 4140 to make the die, I was noticing that the parting tool seemed awful dull.  Stopped, and found the HSS parting blade had chipped and dulled, so went to resharpen it.  Then, decided to take a quick look in Machinery' Handbook for recommended speeds and feeds for the cut...and realized I was using a speed more appropriate for carbide.   ::)

Chunked the old Rockwell into back gear, and eyeballed the recommended 90 rpm (really need to get an rpm gage for that beast, the mechanical one was broken when we got it) - and made the parting cut in one pass.