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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.
I agree that there are too many bolts here... they have WAY more power than needed to hold those. I also like what some people have suggested- like Brady's suggestion for clamping them into a Vee. I like that one because it makes sure there are no protrusions into the "safe Z" volume. And what I think of when I look at this is: I would want a quantity that is a sufficient number so that you get a good long machining cycle out of your set up. And secondly, I like Brady's individual-puck hold downs, all-in-a-row idea because you can go in and set up for maybe two or three or four machining zones/areas. When the one area is done and the spindle moves to the next area, you can go in and remove and replace the parts that have already been machined with new stock. And when your machine gets to the end of all the zones or the cycle, you can have it programmed to automatically go back to the beginning and do the next sets(s). If someone is "tending" the machine, they can simply install and remove pucks in a succession without ever having the spindle turn off, go home and then have to turn on and go back to the first machining zone to begin all over again. Over thousands of parts- it will wind up being a significant time and wear and tear savings. Significant labor savings....
Don't get me wrong: I LIKE your set up. But you are using a lot of bolts, that are of a large size. And if you are going to be looking at making this process faster and more cost effective- I would be looking for ways to accomplish the task without having to un-bolt that many bolts, and then rebolt them. And make sure all the T-Nuts are still in place and make sure sawdust or rubber chips aren't keeping the assembly from going together properly, etc.... And make sure the MDF has not gotten soft from being pulled by all those bolts and then loosened, and tightened and loosened.... Brady's set up would save lots of time in the repetition of the processes required....
Best of Luck with it.
Monty Ma Gill
First off thank you to everyone who replied
@coryatjohn - I drop in a stainless steel plate and make the pucks into a bottle opener. I actually ended up adding a row of bolts on the outside edges because those pucks kept moving during cutting. It may be because I'm using a custom bit that starts at 1/2" and tapers down to 1/4" (that's how I get the taper).
@myxpykalin - Thanks for putting that drawing together. I think I might have to get rid of the MDF all together as it flexes quite a bit and if I hold down on the edges I'll end up with flex in the areas that aren't directly next to the aluminum. It might work if I use the aluminum angle with a few of the bolt holes I currently have in there.
@Brian - That's a pretty cool idea. I'd have to check to see if I could use that solution with the Desktop as I only have a bout 2-1/2" of play in the z direction. I can definitely see how that's super time saving on a larger machine.
@Brady - Another cool idea. I never though of using cams like that. And thanks for throwing the illustration together. I could see something like this working really well if I use some smaller cams, it would be awesome to throw all the pucks on, pull a few levers to actuate the cams in place then start machining. What were you cutting so many hockey pucks for?
@geometree - Stop by any time, I'd be happy to show you around. Do you have a recommendation on the size of vacuum pump I would need? Do you think something like this would work (the first pump listed)? I attached some pictures to this post. Would a vacuum jig like this work?
Attachment 25307Attachment 25308
The parts were wood discs that the customer sent in a box from time to time. Not hockey pucks.Quote:
Originally Posted by PatSabre12
Cams are super simple and work fantastically for this application.
You can use vacuum for this as well. A Gast or Welch pump is what I'd recommend, although a Harbor Freight one would work too. Gasketing is a must for these pumps. You *may* be able to sneak by with a Lighthouse vac et al or Fein Turbo III. You want 'open vacuum air' to touch the backside of the puck. No ultralight MDF bleeder board - or it won't work. See BradyVac II on SB main site.
-B
Did you take a look at the pictures in my most recent posts. I'm not sure if I posted them correctly. Here they are again. Do you think this type of vacuum setup would work, with the 'hollow' area underneath the pucks, is that what you mean by 'open vacuum air'?
Basically that's what I had in mind, but MDF wont work. You would need to use a material that is nonporous for your table (azek,corian,phenolic sheet,hdpe,possibly melamine?) and direct all of the vacuum to that area right under the puck, it needs to be absolutely air tight all around. With a high vacuum pump you could run a tube to each individual pocket. Here's a link with lots of good info on vacuum clamping. http://www.joewoodworker.com/veneeri...umclamping.htm
Ok, if I understand your post and the link you sent me I'll have to lay out a little network of piping underneath my jig. Something like this? Let me know if I'm on the right track thinking about this.
One thing I'm worried about is this is a lot more piping than what was shown on the Joe Woodworker site. Do you think I'd be able to make up for any losses by maybe having to vacuum inlets? One in each corner?