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Old 02-26-2019, 04:11 PM
SCHEPEBC SCHEPEBC is offline
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Default Dedicated vacuum fixtures

I have some parts that I am making dedicated vacuum fixture for (again). The first go around I made them from 1/2" HDPE with gasketing but used the table vacuum. It didn't work as well as planed and I now think I need to make a two piece version with veins and a vane pump that will pull it down more. I thought about using pvc foam because its light and cheap (don't have to worry about a lot of Z distortion if it moves because its all cut through) and gluing the top to the bottom. I also thought about making it out of plywood. The problem I have is these parts have 1.5" circles and there is 200 of them on a sheet. Right now i am tabbing them and it takes to long to cut out by hand. I tried to onion skin and it works but adds 20 mins to the program. I just got another order for a couple hundred more. This was actually the first part i ran on the router when I got it and I do them all the time. It is also a constant headache trying to make something work. I bought the gasket from All star and that doesn't see to be the issue, just the actual vacuum hold down. I have (2) black box hurricanes but i just don't think they pull enough inHg. Any ideas would be great.
Thanks!!
Brad
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Old 02-26-2019, 05:00 PM
rcrawford rcrawford is offline
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What if you used the fixture you already made with the vac table, and just left an onionskin on the parts. Then did one more pass at the end to remove the onionskin. If you start in the bottom left corner and cut towards the top right, and have each cut start and end in the top right of each piece, the piece you are cutting the onionskin through will be supported by the rest of the sheet right up until the last of it is cut, putting very little pressure on your vacuum hold down. I have used this method for cutting small objects without any vacuum at all, just a few Raptor nails around the periphery of the sheet.

A second method would be to use your table vacuum and a pressure foot.
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Old 02-26-2019, 05:20 PM
Jim Becker Jim Becker is offline
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The one fixture I've made so far I made from Corian solid surface and did a two-piece lamination to provide for the fixture surface and the internal pathways to support it. That also gave me the thickness I needed to attach the quick connect for my vacuum hose from the Gast pump I use.
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Old 02-26-2019, 08:25 PM
sylvan sylvan is offline
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Default Material

The best material I have found for vacuum fixtures is called "Paperstone". It is heavy, machines really well and does not warp, stays flat. Paperstone is primarilly used in high end kitchen countertop work. It is hard to find where I live but a good high end kitchen fabricator would probably have it (or the scraps I buy).
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Old 02-26-2019, 10:01 PM
rcrawford rcrawford is offline
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A lot of my vacuum fixtures are made of MDF with a good sealer applied (I sometimes paint on a layer of cheap PVA glue for the quickest seal). Cheap, stable, easy to cut. I keep a 3/8" NPT tap so I can drill a hole and tap it to screw in the hose bib for the vacuum. I can get 25"hg from those MDF fixtures with a piece of hardwood held in place, which is the max setting on my wet seal vac pump.
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Old 02-26-2019, 10:13 PM
The real JP The real JP is offline
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Is it something you could just laminate to a sheet of 1/4 mdf and cut all the way through your material and into the mdf a bit?
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Old 02-27-2019, 07:23 AM
TimPa TimPa is offline
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fwiw, you can tap off the vacuum supply line somewhere (drill, tap, hose bib, valve) to gain a dedicated vacuum port for fixtures, so you don't have to rely on spoil board vacuum.
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Old 02-27-2019, 08:43 AM
SCHEPEBC SCHEPEBC is offline
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Thanks guys for the replies. I never thought about the Corian idea as I have a customer who uses a lot of it so I will try to hit them up. The sheet i have a custom run on comes in at 55"x 109" so my only concern is the weight (could really use that overhead crane now). The problem with laminating the parts is I would have to pull the parts apart which would add some time and clean up to the parts. This customers quality department are sticklers on aesthetics so if there is particles still stuck to it that could be an issue.
I was thinking about trying the sealed MDF route but wasn't sure how well that would work with holding vacuum. I to plan on adding a small air compressor tank between the pump and the board so i can flip a lever and apply a bunch of initial vacuum to remove the air (I like your set up, TimPa, and may have to copy it haha) Since i am not worried about depth, that could be a good choice.
I set the machine back up yesterday afternoon and decided to switch it to a 3/16" DC bit and but one small tab on it. Not a fan but the program but it is 26 mins so it gives the operator something to do till the other machine shows up and he will have to run two. By the time the other machine shows up i want him to take a finish part off and install a sheet. I will order some 5x10's of MDF and try my hand at sealing them. Any suggestions on a sealer to use rcrawford besides the glue?
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Old 02-27-2019, 09:00 AM
Pscdouglas Pscdouglas is offline
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Quote:
Originally Posted by rcrawford View Post
...I can get 25"hg from those MDF fixtures...
Is this accurate? I thought that the maximum vacuum you could approach is ~15inHg because of atm pressure? If this is indeed what you are getting, then I'd like to hear more about your setup. Unless I am misunderstanding the theory here?
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Old 02-27-2019, 09:21 AM
guitarwes guitarwes is offline
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Quote:
Originally Posted by Pscdouglas View Post
Is this accurate? I thought that the maximum vacuum you could approach is ~15inHg because of atm pressure? If this is indeed what you are getting, then I'd like to hear more about your setup. Unless I am misunderstanding the theory here?
Maximum vac is 29" at sea level. Most Becker vane pumps pull close to 24-25".

Brad, are you buying a second machine? Seems like the trouble and expense to make a huge dedicated fixture to cut 200 of these periodically isn't the best way to go if you have a solution that already works and only adds 20-ish minutes to the cut path. That's just me thinking out loud. I may be missing something.

Kilz always works for me to seal MDF.

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