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I make these. I use a shopbot desktop to machine the cutout in the puck. If you click this link you'll see how my current jig works (pictures and comments). I can machine 30 at a time and they definitely don't go anywhere. But loosening and tightening all those bolts hundreds of times a day gets pretty tedious.
Does anyone have any suggestions about how to hold these pucks down differently? Also, if anyone has general questions about my current process I'd be happy to answer them.
vacuum pods.
What are you making out of those hockey pucks?
I would say you're going too far in your holddown. It's been my experience that it seems like it takes more than it actually does to keep material from moving on the machine. All you need to do is keep it from STARTING to move. It doesn't have to handle more than that. If you're using a 1/4" bit, then the forces are fairly light and probably you could get away with 1/4 of the bolts or even less. If you're using 1/8" bits, the forces are even lighter. 1/2 bits can put out some force though. It also depends a lot on your feeds and speeds. But realistically, I think you've got way overkill on the hold down.
Another possibility would be to use an aluminum jig that's 10 times stiffer than the MDF you're using now and only have four bolts (at the corners). The bolts you're using appear to be way excessive. I would think that 1/4x20 bolts would be plenty strong enough.
Looking at picture #3 on your link (the top of the jig with the bolts in it)
I'd take all the bolts out. Then i'd make a aluminum angle frame that fit around the outside of the lid of the jig (see pic) that you just clamp down and it acts like cauls to hold down the perimeter and center of the jig.
You could even mount the center span to the underside of the frame and carve a dado in the center of the jig that the center span rides in below the surface to keep from having to raise the bit over it.
Have you tried it with just the middle row of bolts? I can't see in the pictures but do you have an non-slip material in the bottom of the puck holders?
I would run a few dual action air cylinders up through the table replacing the bolts with some ridged cross strips across the top.
Similar to what I did here holding down drawers for dovetailing.
The cylinder ends have pins that slide out when extended to remove the jig. I drilled holes in the ends and insert 1/4 steel rod
http://i.imgur.com/xfsUiJD.jpg
http://i.imgur.com/qA2u8lQ.jpg
I use shop-built cam clamps for discs. You could easily pocket out a Vee to cradle the pucks and then use PVC/Sintra or wood cams (just offset axle to make cam) and cinch the parts in that way. If you want to get fancy, add a pneumatic cyl to link all cams or just use a long wedge, like some of the sheet metal brakes for house flashing use.
I've cut well over 5,000 pucks using a jig like the pic shows. (2-min quick & dirty illustration...)
http://www.talkshopbot.com/forum/att...id=25304&stc=1
-B
I'd hinge the upper and lower plates and replace the nuts and bolts with tapered locating pin sets used in the moulding industry. You'd need to use your cnc to cut both sets of holes to ensure the very precise set to set alignment needed for them to mate up properly but that should save you a lot of time and keep it simple I think. Google images will show you quite a few variants.
PatSabre12,
Welcome to the forum. I'm a big fan of your openers and the Foundry. Last time I was there, around Christmas, I spotted your shopbot and thought it was a very cool way too machine your pucks. Seeing that they were shopbot made actually pushed me to buy a couple as gifts and one for myself, its my go to opener now.
As for your problem at hand, I think you could set up a vacuum fixture that would hold them without too much trouble. Since the pucks are very smooth and nonporous, a nonporous manifold and gaskets for each part should work very well. With no leaks in your system you could use a high vacuum gast pump or a Fein shopvac may work. The shop vacs dont create as strong of a vacuum but they are more forgiving of leaks.
I'd make a two layer vacuum jig with the bottom layer being the plenum and the top having pockets to receive the pucks. The jig would overhang the back of the machine and have a port for connecting a shop vacuum from the bottom.