Magnetic chuck for holding brass sheet stock?

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SilverWorker

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I have some brass sheet stock (about .030 inch thick) that I'm cutting little parts (about 1/4 X 1/4 inch) out of, about a 100-200 pieces in one go using a cnc mill with a little 1mm endmill. I'm using double sided tape to hold the parts and trying to avoid having to leave tabs on them to hold them down as I really don't want to finish all those tabs off by hand. Problem is the sticky double sided tape tends to come loose, parts shift and get messed up.

I'm a neophyte to machining so I'm just scratching my head trying to figure a way to hold all these sheets and was reading about magnetic chucks- I know that it's not going to hold a sheet of brass down, but maybe can you put a magnetic top layer over the brass that can get machined through, that will provide enough force to hold those little parts down? Never having actually used or seen a magnetic chuck I don't know if its far off base. Wondering if there's something that would be easy to machine through, maybe sheet metal or that kind of plastic refrigerator magnet material. Don't have any idea of the holding force that could be generated, but guessing there's not too much force needed considering the size of the cut & endmill, and the fact that double sided carpet tape is almost doing the job...
 
The brass will stop the magnetic gauss from penetrating through it and magnetizing the steel for holding. Now it may not stop it totally but will reduce the gauss to a lot less holding power if any at all.
 
Try contact cementing the stock to a piece of cabinet grade plywood be sure to use a roller to get the brass sheet down tight & flat.
 
Why not use than cnc mill and and make a die to cut the pieces out?
Or have them laser cut. Seams like a lot of wasted time with a lil end mill and trying to hold the pieces down.
 
x2 for the laser cutting. I don't think milling is worth the frustration nor is the costr of a vacuum / magnetic chuck.
 
Thanks all, I'm going to try the contact cement as it's the cheapest and quickest alternative I've got available. I checked into a vacuum table with one company already but I was advised that the size of the pieces would greatly reduce the ability of the vacuum to hold them. Jamie, I would love to learn how to make a die to cut them out, can you point me to any resources that would help a beginner get started? I'll look into laser cutting services as well.
Thanks again!
 
Not to sure of your shape but you might try sandwiching them between alum sheet if your end mill is long and strong enough.
dickr
 
Been doing similar stuff for the last 14 yrs.
I use 3M 77 Spray glue to hold thin materials at .001" to .030" on a backer board of laminate. See here http://www.mscdirect.com/product/63408017 . This board is fairly flat and not affected by mineral spirits used in the removal of the glued up parts.

Running the spindle at 24K on the one machine with a 11 ipm feed and .020" 2 flute endmill. The other machine spins at 60K and 30 ipm with the same bit. The second higher spindle speed machine is much better and the tool life is twice the slower machine on average. Note the tooth load is only .00022"! Your spindle speed may not be this high but the small endmill and tooth load is the key for success for this type of operation.

The first three sides will cut just fine. It is the fourth side that you will run into trouble. At times the part will move at the last little bit to finish the cut and leave a tit/nub as the endmill plows through. In my experience a surface of .250" should not move if using a new sharp end mill.

Two ways to fix this.
1. Cut only 3 sides first on a matrix of parts and then using GOOD tape, tape down the parts. Be sure to use your fingernail to press the tape into full contact or use a rubber laminate roller. Better using the fingernail. Now using a NEW endmill just cut the fourth side. In my experience a surface of .250" should not move in this situation but it can and will happen. For example when cutting .030" thick .600" OD parts out of PT there is movement at the last of the cut. In this case I use high strenght Hot Glue and still tape for that last cut. If using Hot glue, temperature needs to be controlled. Use a cold air gun like this http://www.mscdirect.com/product/77314375?fromRR=Y but it is expensive! Yes I have one of these as well but rarely use it with my current method.

Option 2. If you cannot do #1, use a flat surface to place the finished part with the edge that needs to be touched up facing a 600 to 1200 grit sanding disk. A faceplate with a sheet of said paper works well for this. You do not need a lot of speed to remove that nub. I setup a spare chuck mounting plate and glued 600 grit paper on the outside edge and just placed a flat plate in the tool holder at the center point of the disk and ground off the offending nub. You can either use a holder or just your fingers in this case. Use a magnifier to locate properly your edge to keep things square etc.

I have tried flowing hot glue into the first set of cuts but found the tape method works the best due to being quick and easier to clean up in the end.

Pierre
 
Why not try a foot stomp shear cutter.?
snugrat :thinking:
 
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