Brass Shim Washer

I have an ancient key duplicator ( “Micrometric Precision” ) that I need to shim. Specifically, the cutting wheel has to be shimmed to the precise location so the key notches won’t be offset. Right now, it’s almost there - needs to move over about ten
Amazon yielded up a package of various thicknesses of brass shim stock. I need to cut this thin brass into a washer. I have a 3018 CNC router. It’s a nice stiff machine, and has an upgraded 500W 48V spindle.

How to clamp the shim stock? I’m thinking to glue it to something thicker that can be clamped - or maybe just gluing it to the spoil board. Super glue and masking tape?

       - Jerryk

I’d super glue it to sacrificial stock, then release it with acetone afterward, probably wishing that I had pure nitromethane instead, since I haven’t yet ordered a quart for $60:

I think I’d try it on MDF first so that acetone could soak through from the other side to release it without bending.

Also, because it’s brass, you may have to be careful about which mill you use. Dunno whether you have milled brass and know how “grabby” it is.

Stefan Gotteswinter put up this video a couple months ago that might be worthwhile:

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Whats are the specifications of the washer needed?

Once upon a time, I was working on my largest FDM printer and discovered the guy who developed the whole thing overlooked shims for the Bearings. This mattered because the Nuts and washers being used applied pressure to both the inner and outer rings causing friction. So what i needed was something thin enough to create a shim. I know I am actually forgetting a piece of that story. But the net result is that I found I could get these thin washers at a hobby store, and if I recall they were sold as shims. -I am not sure if that will be of use to your application.

When it comes to brass and copper, I have often used fine sand paper and file to polish.

Never needed to do anything more exact. However if you do. I second @mcdanlj in that you can glue a face of the washer to stock. Now mill down the washer. Release with a solvent. Polish both sides. -Note if not already obvious, making sure your washer shim is as smooth and flat as possible with help make sure it does not break free in machining. The same for the stock. Super glue depends on surface tension to work. -Also to additionally in sure success, a machine with z axis micro stepping will be in your best interest, or maybe a Bridgeport. Otherwise you wont ever get the nice clean steps at 0.001mm, and you might always over shoot your reduction.

Pure Nitro is one I have not yet added to the tests. :frowning: Though it should in theory work exactly the same as UNDO6020.

After you posted that question I went searching and found a bunch of machinists saying that their shops bought pure nitromethane for superglue removal. Pretty sure I saw references to buying it by the 55 gallon drum! :open_mouth:

Another possibility is to sandwich the brass. You could make a sandwich with masonite, smooth faces in, supergluing the stock to both sides, then soaking the stack. That should reduce the possibility of tearing and grabbing, especially if you don’t have an end mill with the best geometry for brass.

I’ve never done this, but… I’d consider clamping that sandwich and milling the center hole in one op, then with it still clamped screw through the hole into the spoilboard, then plunge with a downcut and cut the outer edge in a single pass with slow feed. That way I would expect a clean edge without grabbing.

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