Wild idea for vacuum

My buddy (retired a/c ) says that the size of the pump only matters for speed, this little 3.5 cfm pump he gave me has been on jobs that took 24 hrs to pull a vacuum, but when it did, it was a vacuum, hence pulling a vacuum doesn;t take a monster pump, pulling a vacuum in seconds rather than minutes does take a larger pump. Of course no one wants to wait half an hour to suck the project piece down to the table. Think of calculating how many cubic feet of air could be held in the grooves and if the sealing is good than that should be how long it should take depending on the cfm of your pump. My hdpe test was almost instant. My pump is old and needs new seals but I donā€™t care right now (canā€™t afford repairing ) so I will just let it run and maintain the vacuum. The Joeā€™s wood working designs are great and when I can afford it I will make that one. But for now I will just use what I have . Your spiral groove only downside IMO is closing off the spiral outside a square work piece. But on doing that it should not require a large pump IMO. Hope this helps, Jude

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YES my thoughts exactly ā€œPlenumā€ is the key!
Please share your experiences

I test glues 2 pcs of hdpe together with contact cement the other day and checked it out today. The pcs are securely glued, would take lots of prying to separate them and would warp them like a potato chip. They canā€™t be slid apart but I donā€™t believe the contact cement can fully cure because it canā€™t get any air. It was just tacky when I put them together. I think contact cement would hold them together fine because they are absolutely sealed together like a vacuum seal, if I pry them hard air may get between them but why would I pry them apart? Iā€™m switching to pvc panels with plumbing glue, home depot 1/2" sheet 4ā€™ x 8ā€™ for 68$'s, lots cheaper than even hdpe cutting boards at sam cluub for 9$'s, pvc works out to 3 1/2 $'s for approx same size.

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Re HDPE, Iā€™m not sure, but it seems like some 8x8" HDPE pieces have curled a little sitting in my very hot garage (>100 degrees probably). Donā€™t know if thatā€™s even possible and I havenā€™t measured it, but does any know offhand if that would be a risk with using HDPE for a plenum?

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My hdpe waste board after I surfaced it once, like 0.1 mm off, warped like a potato chip from the heat just like in your garage. Someone mentioned that once you cut onto the surface of hdpe it has that tendency and I agree. I am switching to ovc board for that reason and itā€™s also cheaper than hdpe.

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Iā€™m interested in the pvc sheets, only seen boards about 5.5" wide so far in my area

Home depot has had it for a long time, I;d never seen it either but itā€™s in aisle 22 down here in bldg supplies, itā€™s for trim. I guess you have to look for it, I asked them and there it was. Maybe yourā€™s does also. It was on the bottom shelf maybe thatā€™s why I never saw it beforeā€¦

This?

You can check local availability online.


half the size but workable. I have the 4ā€™ x 8ā€™ panel here

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Unfortunately that is not available anywhere near me.

You can order it online and have it delivered to your local store for pickup. That option is available to me from the website.

A few minutes laterā€¦when I tried to get it shipped to the local store, thatā€™s not available. You canā€™t haz this, it says.

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If you canā€™t get it at your local HD, You can try to check with local plastic suppliers, it looks like PVC foam sheet, make sure to request closed cell foam.

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I havenā€™t had much success in my efforts to get a working vacuum table using a veneer press pump. It should work; I think my design scheme is fatally flawed due mostly to a health amount of ignorance. So Iā€™m going to try something entirely different. I was on veneersupplies.com and noticed that he sells some ball valves. http://www.veneersupplies.com/products/Mach-Ball-Valve-For-Vacuum-Clamping.html . So I ordered a bunch and some vacuum tape and Iā€™m going to have another go at it. Just the other day I started thinking about something like a ball valve that would activate only when something was pushed down to open it. So this right along the lines of my faulty thought process.

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My guess is that a veneer press pump just isnā€™t going to work. How quickly your vacuum removes air is just as important as the amount of vacuum pressure can it produce. There will almost always be a loss of vacuum pressure because it will draw air straight through the material youā€™re cutting as well as the vacuum board itself. You need a vacuum pump that can remove a lot of air quickly.

I remember being impressed at a CNC demonstration once. They were using an enclosed fan to produce vacuum. Much like the fans used in a dust collection system. The diameter of the fan was large, maybe 3 feet. The width of the fan blades was not that large, maybe 6 inches. But the fan was moving so much air they were not even using a gasket on the vacuum table. Nor were they plugging the vacuum holes on the table that the stock did not cover. They just dropped a pice of material down on the table and the vacuum held it in place.

So, remember itā€™s not just about how much pressure you have itā€™s also about the cfm ( cubic feet per minute). How fast can you create that pressure you need. Can your vacuum pump keep up with the amount of loss youā€™re going to encounter?

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BTW, try using something like this for the vacuum gasket.
https://www.zoro.com/e-james-rubber-cord-neoprene-14-in-dia-10-ft-csneo-14-10/i/G7603425/

On your vacuum table cut groves that are just a little under 1/4" in width and just a little over 1/8" in depth. Donā€™t stretch the cord when you place in into the groves on your vacuum table.

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Your vacuum pump has high vacuum and low volume as opposed to say a shopvac that had high volume but cannot attain a high vacuum. From what Iā€™ve read on vacuum tables, most people who what work holdings will rely on the latter so an MDF vacuum table should work with the proper high volume vacuum pump. Workholding vacuum tables donā€™t need anywhere need absolute vacuum to be effective. Of course the duty cycle for the pump is also important so a shopvac would probably not work when the system is used for hours on end but maybe a more robust dust collection system motor could be a solution.

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The problem I see is area. Holding force is pressure times area and a few 1/4ā€ holes is not much area.

edit: in fact, 20 would be required for just 1 square inch.

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