Making SS Shims on EDM
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  1. #1
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    Default Making SS Shims on EDM

    Here is a thought I am having. We need to make specialty shims for fuel nozzles. We want the shims to be in .001" increments starting at .020" up to .032" thicknesses. My thought was to machine the ID and OD of 347SS bar stock to size using 6" longs chunks. Then slice the shims off using WEDM. We want to hold +/-.00025 thickness tolerance. OD = 0.390" +-0.005 ID = 0.2705" +-0.0025

    I have very minimal experience with WEDM so I am not sure if this would be a feasible way of doing this, or if it would take too long.

    This method would replace our purchased shims and would allow us to have less inventory, more control, and versatility.

    For those with more experience than I.....what do you think?

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    Me thinks you would be far far better served using laminated shim stock and cut your parts out of that.
    They do come in .001 thick laminations, and they are available in 347 or 321 (AMS 5512 or AMS 5510, mostly the same chit ... )

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    The problem is that this is for aircraft parts, both military and commercial OEM. I doubt they would go for the laminated.

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    Hi MikRin:
    Do I understand correctly that these will be glorified washers and that you hope to slice them off a tube like baloney slices?

    If so you will have several problems to deal with.

    First, if you need exquisite precision, you must make several passes over the surfaces.
    Once you slice the part off, you cannot hang onto it anymore, so you cannot make those additional passes unless you can find a way to hold the skinny washers accurately.

    Second, your problem is compounded by the fact that the first cut will leave a crescent shaped cutoff stub at one end.

    Third, the slices will curl as you cut them off, so you'll have a bunch of potato chips, not a bunch of plates.
    Attached is a picture of what I mean.

    If it was me, I'd explore having these precision lapped to thickness the same way skinny gauge blocks are lapped.
    It's fast, accurate, and totally automated, lending itself well to batch processing and easily capable of holding your tolerances.

    Cheers

    Marcus
    www.implant-mechanix.com
    www.vancouverwireedm.com
    Attached Thumbnails Attached Thumbnails dscn5007.jpg  

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    Quote Originally Posted by MikRIn View Post
    I doubt they would go for the laminated.
    For clarity, when Seymore says 'laminated', I have to believe he's telling you to buy shim stock in the thicknesses you require, stack 'em, hole pop the stack, then cut your diameters. some folks will tell you to weld the edges together, but I'd start with metal binder clips, from the office supply store.

    This is BY FAR easier than trying to get the thicknesses you require, AND will take less cutting time, AND you'll easily hold the diameter sizes - just don't go crazy with the height of the stack, unless you want to add skim cuts.

    I'd add that a slugless cut would likely be best for the ID, so you don't have to chase a bajillion little slugs out of the stack and/or out of your work tank.

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    Quote Originally Posted by MikRIn View Post
    Here is a thought I am having. We need to make specialty shims for fuel nozzles. We want the shims to be in .001" increments starting at .020" up to .032" thicknesses. My thought was to machine the ID and OD of 347SS bar stock to size using 6" longs chunks. Then slice the shims off using WEDM. We want to hold +/-.00025 thickness tolerance. OD = 0.390" +-0.005 ID = 0.2705" +-0.0025

    I have very minimal experience with WEDM so I am not sure if this would be a feasible way of doing this, or if it would take too long.

    This method would replace our purchased shims and would allow us to have less inventory, more control, and versatility.

    For those with more experience than I.....what do you think?
    Do you have a grinder? Slice them off and dust them. We do it often. You can get fairly close in one pass if your cut and material are stable, just leave a little to dust in to tolerance. Tricky part is being SS for the grinder but it can be done.

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    We make a lot of precision shims by stacking precision shim stock and wire EDMing the inside and / or outside shape. Absolutely 100% agree with Marcus, slicing off will not get you precision shims. 30 years experience with wire EDM, it won't work to those tolerances. Get the sizing done on thickness first , then wire EDM the shape. Or fine blank it if there is enough quantity.

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    Quote Originally Posted by MikRIn View Post
    The problem is that this is for aircraft parts, both military and commercial OEM. I doubt they would go for the laminated.
    Aircraft? Do you/need approval for using a wedm to make these? Alot of aerospace parts don't allow edm.

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    What is your AMS spec?
    Those laminated shims are very very often used for aerospace applications, in fact to date Aero is ALL I've ever made them for.

    In any case, if that's not allowed, then yes, stacks of individual shims of various thicknesses is the way to go.
    As far as the EDM allowance .... yeah, well .... you're at the mercy of the engineer who drew it up, but even if it isn't allowed, it is still a shitton easier to wire cut
    to leave .004 on ID and OD and then finish grind.

    If your spec is AMS 5646, then you have a problem and will need to ask for variance approval.
    If you don't get it ( some places are thickheaded pigs ), then you are stuck with the slice option, but like Marcus said, you will NOT be able to finish cut them!
    No friggin' way will they be accurate or flat.
    So, you will be cutting oversize by a shot and then double disc grind and final double side lap the discs.

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    Unfortunately you all are telling me everything I feared. The problem I have is that I have limited equipment and limited resources. (We don't have a lot of skill in house by way of machining) We have always done very little machining and we would buy all of our details and work the parts up from there. We are just now starting to get into making things ourselves. I have the most experience to deal with this, but my expertise is strongly in CNC machining Mill/Lathe.

    But, what I am seeing is that no matter what, this is not an easy undertaking. These are parts we are going to have to produce a lot of, in various thicknesses and sizes. I was really hoping for an "easier" method. In aerospace, there doesn't seem to be an "easy" way to do anything.

    Thank you all of you for your input. I'm really going to have to take into consideration everything you have said.

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    If it was me, I'd explore having these precision lapped to thickness the same way skinny gauge blocks are lapped.
    It's fast, accurate, and totally automated, lending itself well to batch processing and easily capable of holding your tolerances.
    I was thinking about this method as well, but not sure how it is done. I was looking at metallurgical lapping machines, but they aren't really setup to do what I need as far as I can tell.

    Do you happen to have an example of the type of equipment?

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    Hi again MikRin:
    Do a quick Google search for "Lapmaster" or "Wolters"
    They are producers of double disk grinding and precision lapping machines.
    Lapping machines come up on Ebay once in a while, so no need to spend a pile.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    It would be less expensive and quicker to buy 13 spools of 1/2" wide feeler gage stock ranging from .020 to .032" in .001 increments.

    The required fabrication equipment then consists of a precision press and a punch and die set with a .39" OD and .2705" ID. Maybe several punch and die sets to handle the range in shim thickness.

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    If the quantity is not large enough to justify stamping them, I used to make various thicknesses of internally splined shims by stamping out circles from shim stock, then making a closed-at-one-end tube that fit the o.d. Drop the shims in, set a plug in the top, put it in the press, squarsh down tight and weld the plug in. Now machine the stack-in-a-tube just as if it were a solid. (In this case, drill it and pull a broach through, no distortion at all.)

    Works very well, pretty simple and cheap.

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    I'd agree completely with the approach of finding the material in the thicknesses you require, build up the "stack" (I always did it with relatively thick sacrificial plates top and bottom), and in this case... no-core the center. After that's done, make a couple of small stepped washers and clamp the stack through the hole you've completed. Then wire the outside.

    Needless to say, the stack will need to be just a bit above Z=0 so you can put the bottom stepped washer in there without violating Z.

    I'd keep the entire stack height (including plates), under 2", maybe even 1.5". Oh... fwiw: I would always put the stack in a hydraulic press, squeeze the heck out of it, then weld small pieces of steel connecting the sacrificial plates. I avoided welding on the shims.

    In my wire edm days, I made tons of custom washers and shims of all different shapes, sizes and thicknesses, and that method worked the best for me.

    PM


    1.jpg

    2.jpg

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    Nothing better to do tried cutting a few
    From seamless tubing. Worked ok but
    My machine is old doubt it would do
    Tolerance required and I have no way to
    check anyway. Better machine,better fixturing
    could probably be done but expensive.
    Bob
    Attached Thumbnails Attached Thumbnails img_20210519_0535128.jpg  

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    Why go to all that when you can probably purchase them?

    Shims | Boker's, Inc.

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    Rule #1 in manufacturing: "If you can buy it, don't build it".

    Then there's the weird stuff though... that always lends itself to making in stacks via wire edm:

    1.jpg

    2.jpg

    3.jpg

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    The USAF uses laminated shim stock

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    I think it would be tough to beat catalog stuff when you can find it.
    Making them out of catalog material might be good.

    Back when I was a broach bar builder we had 1" wide and 6" precision shim in rolls. Mostly in steel but thay also sols SS, copper, and brass...and plastic. I forgot the brand names but we had a number of brands.


    But I don' know beans about WEDM


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