holding small flat brass parts for surface grinding
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  1. #1
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    Default holding small flat brass parts for surface grinding

    I have four brass parts which need to be ground to the same thickness within 0.001". They are about 3/16" tall. Can I just block them in on the mag chuck with ground flat 1/8" parallels, or should I superglue them to a single parallel or use double sided tape or what is actually the current best practice?

    metalmagpie

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    As long as your temp remains low while grinding a cyanoacrilate adhesive shoud be fine. An old machinist told me he used double sided tape and swore by it. I don't know what tolerances he was holding though. If you can find a tape that is of good quality (uniform thickness) that would due to.
    On hint on the super glue; spend a little more and avoid the 20 pack / $1 stuff. I use stuper glue frequently on my drones and R/C helicopters. You find a big difference in quality as the price goes up. No need for for the $40/bottle Loctite stuff, a good hobby brand should suit you fine.

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    I grind brass & bronze, sometimes aluminum or non-magntice stainless from time to time.
    With one or 2 parts, i use the traditional hold-down combs, one on each side. Most combs are about 1/8" thick or less, so you should clear if they are sucked down almost flat. (Needs some angle to grip). I also have sections of chopped up handsaw blades to use similarly, for thinner material; usually only on one side, holding the part to a rail or parallel.

    Holding 4 parts at once is more than a little risky.
    Like assuming you could hold them all snug for milling lined up in a vice for one go, without paper.

    It is possible to mill snug pockets in a magnetic parallel or even just soft steel block. Or between 2 blocks that you squeeze together while activating the magnet. Dirt, burrs or non-parallel surface can shoot the .001 tolerance in a pocket, though.

    Lastly, toolmakers vise & parallels. Again, only a couple at a time. Though if your vise is wide and accurate enough, 4 across could be held with paper against the moving jaw. Trust your gut - if it seems iffy, it probably is.

    Part in pix is aprox 18" long, 1/4" thick.






    smt

    PS: you really did not give much to go by AFA dimensions.
    Thin long parts or very wide parts may be tricky both to hold and due to heat distortion.
    I always grind stuff like this (except when held in a vise) on auto with slight infeed (.005"-ish) per reversal, & coolant.
    Last edited by stephen thomas; 10-01-2021 at 10:22 PM. Reason: add pix

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    Hi metalmagpie:
    I do pretty much what stephen thomas does with one small addition:
    I run a super narrow wheel like a 1/16" wide 46K and accept that I may have to dress it a lot.

    I find that a wide wheel once it wears to a taper shape, increases the friction on the workpiece so much it can rip it right out of the hold downs.
    A narrow wheel keeps that friction down no matter how badly the wheel is worn.

    Definitely use coolant as stephen thomas also recommends...coolness is your friend!
    On a last note; if your parts are big enough, a vacuum chuck is also a good way.

    Cheers

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

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    Double back tape is ok/good. Stephen's combs are good but rare to find and expensive.
    You don't say if they are 3/16 tall, x what length and width...?

    The go direction bump stop is best being almost as high and touching at the upper edge of the part, this helps the part from wanting to flip up. Just a stop is Ok for magnetic parts but not for non-mags. and bumped-in side block-ins (with not using tape the side block-ins may tend to lift the part off the chuck so there is another problem.

    long travel can be best grinding only in the grind direction(not the climb grinding direction), again to help a non-mag part from flipping up.

    Frequent dressing because brass loads a wheel.

    Grinding tape is very expensive if you can find it..I still have a roll down the basement (I think)
    carpet tape works fine/ok.

    Care to know where you will hit the part because a hard crash/hit may flip the part. I put a tab of marked masking tape on my down dial , dress off .001 or .002 , and know where I will hit the part.

    QT Stephen {Holding 4 parts at once is more than a little risky.]

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    I use black Loctite a lot to hold small parts for machining. I groove the gluing surface of the holder with a checkering file so the glue has somewhere to go, it really helps the parts sit flat, and also helps when degluing in acetone.

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    I was about to add some more after reading the first posts, but most everything I was thinking has already been said in the rest. Good job fellas. All I will add is that even if you use an adhesive or vacuum you should block the part. Every little bit helps and blocking is quick and easy. I wouldn't try grinding 4 at once without an adhesive, tape or vacuum. That's a recipe for likely disaster. Might even be so with the added help. All it takes is one accidental overheat...

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    Regarding tape, you can get transfer adhesive tape, which is just the adhesive layer, no substrate. I have 3M stuff with .001 and .002 thick adhesive, often used by guitar makers for pickguards

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    While I never ground brass, I did a fair amount of carbide on the SG. Two sided tape, and block it in. Note that the tape works better if you warm it up by a bit of dry grinding, then pour the coolant on. I had more trouble freeing the work from the tape than having it stick to begin with (thin section was easily broken).

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    QT machinistrt: [I had more trouble freeing the work from the tape than having it stick to begin with (thin section was easily broken).]

    Very important so worth saying twice.

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    Just blocking, one part at a time, no matter how big they are...it's just asking for disaster...

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    Brass can load up a wheel so make 5 parts, one for getting used to grinding brass.

    You can double back tape each to a flat parallel so a razor blade tapped under the tape can release, or leave a little overhang to one edge. The go-direction block in to bump just under your finish size touching the part near its top edge.. alcohol clean the tape residue between parts.

    + -.001 should be easy. + - .0005 and you might leave to the high side and finish .0005 by hand with abrasive paper.
    Brass gets hot quickly so a hand bottle coolant spray can be good.

    If you have a piece of scrap steel you might spotter the parts following after the first one.

    Yes, micrometer the tape and the parallel you use to know the finished size of that build up..

    *Likely this job is past done..if so let us know how it went.
    Buck

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    It's not hard to grind flat, but you can really mess it up during removal. I'm a big fan of this stuff- Home - Aquabond Technologies It's a hot-water-soluble thermal adhesive that people in the optics industry use. Get a puck or three of the stuff. I use the 55 for most things. I also have a small steel plate with adjustable sides I use. The sides can be raised just enough to block the part. That, plus adhesive does the trick. Then the small plate can be heated up to break the bond and release the part. Obviously you don't want to get the part hot during grinding, that's true of most adhesive methods!

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    dont forget shellac. i prepare a solution with solvent and brush on a thin coat. then i heat the part and carrier and glue it on. easy to remove.

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    Use the parallels. Clean everything spotless, clamp together and put beads of thick super glue on edges. Carefully avoid excess heat and then debond with superglue remover now available in most hardware stores.

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    Quote Originally Posted by dian View Post
    dont forget shellac. i prepare a solution with solvent and brush on a thin coat. then i heat the part and carrier and glue it on. easy to remove.
    Jeweler's dopping wax does the same thing. It's really stick shellac that can be melted on.

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    Quote Originally Posted by michiganbuck View Post
    Brass can load up a wheel so make 5 parts, one for getting used to grinding brass.

    You can double back tape each to a flat parallel so a razor blade tapped under the tape can release, or leave a little overhang to one edge. The go-direction block in to bump just under your finish size touching the part near its top edge.. alcohol clean the tape residue between parts.

    + -.001 should be easy. + - .0005 and you might leave to the high side and finish .0005 by hand with abrasive paper.
    Brass gets hot quickly so a hand bottle coolant spray can be good.

    If you have a piece of scrap steel you might spotter the parts following after the first one.

    Yes, micrometer the tape and the parallel you use to know the finished size of that build up..

    *Likely this job is past done..if so let us know how it went.
    Buck
    It went great. I didn't bother gluing them down, just blocked them in good. With the mag chuck on, I used a small stick of wood as a drift pin and tapped the blocks against my parts. Then I took super light cuts. The parts worked fine.

    metalmagpie

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    Quote Originally Posted by Scottl View Post
    Use the parallels. Clean everything spotless, clamp together and put beads of thick super glue on edges. Carefully avoid excess heat and then debond with superglue remover now available in most hardware stores.
    i have big problems with super glue. recently it doesn want to come of with solvents (acetone, mek etc.) any more, unless you soak the parts for hours. never saw a "remover" anywhere? what is it?

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    For some parts, a high top edge go-direction bump block-in and some grease or oil on the chuck can make enough surface tension to hold a part from lifting or chattering.
    I have done that and also have thinned Elmer's glue to go under a part..for one part I effectively used diary cream and that did an Ok job of holding.

    Just the high-edge block-in alone works.

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    Quote Originally Posted by dian View Post
    i have big problems with super glue. recently it doesn want to come of with solvents (acetone, mek etc.) any more, unless you soak the parts for hours. never saw a "remover" anywhere? what is it?
    I'm pretty sure nitromethane works as a super glue remover. Never tried it myself tho.


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