Shim Washers

[mwessel]

Looking for aerospace quality shim washers for an application similar to a double shear joint, like a clevis lug connection. Anyone happen to know of any NAS... MS... spec which has a selection of CRES, maybe A286 washers? Looking for some to work with a shoulder bolt. Thanks

 

[tbuelna]

Take a look at this document:

http://everyspec.com/COMML_ITEM_DESC/A-A-59000_A-A-59999/download.php?spec=A-A-59561.036553.pdf

 

[WKTaylor]

Mwessel... also

Laminated metallic shim [peel ply W/WO solid thick plies]
AMS-DTL-22499/3 SHIM STOCK, LAMINATED, CRES
[AMS-DTL-22499 procurement spec]
AMS5500 Steel, Corrosion-Resistant, Laminated, Sheet Surface Bonded

Here is how to make 'round shims' any ID/OD combination....

Cut shim stock into squares larger than OD required by at least 0.2" [5-mm]. May chamfer corners, to minimize machining; but must retain 0.2" OD machining margin across corners.

NOTE. several shims, same size must be made at one time using this method. Experience suggests that total stack depth must be at least 0.8-inch [2-cm]

Drill/ream a hole in middle of squares to match ID. May use tooling to stabalize the shim stock.

Stack shim-stock on a lathe mandrel/shaft with a shouler on one-end and a threaded-tip opp. Shaft OD must match shim ID very closely [undersize 0.0010--0.0020] to allow shims to slide down shaft but still have a tight fit.

Stack shims against the mandrel shoulder. Thread on a nut/washer to tightly clamp [almost crush] the stack-up. CAUTION; nut/washer must have smaller-OD than shim stock will be machined. NUT may be a round/thin-wall nut with internal threading, W/WO any spanner-wrench notches or cross-spiral hatching for hand--tightening.

Lathe-turn the OD of the stacked shims to attain required shim OD.

WARNINGS.
STACK-UP MUST BE VERY TIGHT or all h*ll will break loose at this point.
Bits-n-pieces of sharp CRES foil may be liberated and fly-off in various directions.

Disassemble the mandrel/shim stack. Deburr shims IF/AS required.

Peel-off shim laminations A/R to attain exact thickness required.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[tbuelna]

"WARNINGS...STACK-UP MUST BE VERY TIGHT or all h*ll will break loose at this point...

I love the disclaimer! Especially since I have personally seen something similar happen when attempting to mill a shim profile from this exact MIL-DTL cres material. The material stack must definitely be clamped tightly right at the trim line between two pieces of (sacrificial) material so that the upper/lower laminate edges do not peel back and wrinkle. You can order the material half solid and half laminate which is easier to work with if you need to machine a profile shape.

For the shoulder bolt application noted I can see advantages/disadvantages for both shim washers and peel shim. The shim washers are standard components, but you will need a supply of washers in a range of thicknesses so you can stack them up to fill the gap. The shim washer kit might need 8 or 10 different thicknesses depending on the min/max limit of the gap and how close the shim fit must be.

The peel shim washer may likely be a custom part, but it will only require using a single piece which makes assembly easier. Preparing the peel shim takes a bit of practice to cleanly peel back the edge of a single thin ply. And if a large number of plies must be removed it can take a bit of time and patience removing them one by one.

 

[Sparweb]

Having briefly experimented with peel-shims, and hence discovered its drawbacks, and having also used standard shim washers (on shaft bearings) I'd strongly recommend using the standard thickness washers if at all possible. I would rather make a washer out of solid CRES than try peel shim. If this is a production environment, one could consider stamping a series of thicknesses for a kit (as tbuelna already suggested).

How much clamping and/or rotation will the shim be exposed to in the joint?

STF

 

[tbuelna]

It can be difficult to position a stack of 4 or 5 thin shim washers into the gap between a clevis lug and a bearing face if you have fat sausage fingers. Especially if you can't clearly see the location of the hardware.

 

[rselby7]

Not sure about the size of your shoulder bolt, but if it is 1/4" or less, try NAS620 washers. Regular thickness is .032(1/32") and thin version is .016(1/64") Depending on the resolution you want from your shim, this may work.

 

[Compositepro]

http://www.mcmaster.com/#shoulder-bolt-shims/=wfwd4g