I’m messing around trying to figure out how to make a vacuum bag for veneering. The bag and fittings seems easy enough (there’s an old FWW article explaining how).
Haven’t had any luck finding a nearby source for a small vacuum pump, but read that it is possible to use a compressor to create vacuum.
So how?
Malcolm
New Zealand | New Thinking
0.06% of the world’s people are Kiwis
0.06% of the world’s people are Kiwis
Replies
Malcolm, If your compressor is not one of those little oiless versions, all you need to do is remove the intake filter and do the plumbing to get from 3/4" pipe thread or whatever to a hose-barb. Then open the tank so-as to not satisfy the pressure-switch. However, the first time around, I would recommend that you take the air-line between the pump and tank loose and place a cup with some tissue or something in it under the end, so you can tell if the oil is being drawn around the rings. It is best if your crank-case is sealed to prevent this from happening.
You can get vac-regulators fairly cheep now if you don't want your pump to run continuously. until recently they cost several hundred dollars but I think I have seen them en the range of $40 lately though. It is not so hard to just let the pump run though. If you are at sea-level, the best you can do is pull -15# which is about 1/10 of what it does on the positive side, and a lot of the heat from the pump is from compressing air with ambient heat into a smaller space so-that it becomes much hotter from the same amount of energy being compressed into a smaller space.
After it has been running for a while, I usually run my hands over the pump and motor to feel for heat.
If you T-off and put a vac-guage in the line. Just so you will know, you get 1 psi for each 2" of Hg. which doesn't sound like a lot, but if you draw say 28" of mercury, this would be -14 psi. and there are 144" per sq. ft. which comes to 2016 lbs per sq. ft. which is better than parking your car on top of your work even if your wife is in the car, and she is quite hefty.
There are lots of nifty bag and fitting sources around now, but you can use almost anything really. I have given demo's where I used laundry bags and carpet tape with a little rope caulk to seal where the hose goes into the bag.
I have also done parts that were too big to ever pick up, and ever hope to get into a bag, where the parts ended up on top of 1/2 of the bag, and the other half was taped on top, and with the help of friends we would bend this 2" thick 2' wide 22' long part around a form then draw a vacuum, After about 6 hours and 80,000 lbs of perfectly even pressure and we stripped away the bag, I ended up with something like this.
Just wanted to say, that is a truly wonderful stair case. I have done some hand rails but yours are superb
kiwimac ,
Not sure how much vacuum it takes but , there may be a few other more simple ways to produce vacuum with compressed air . You might try the auto parts store and look for an air nozzle with a vacuum hose coming out of the nozzle head . Also there is an adaptor that is used for evacuating or vacuuming the liquid out of tractor tires , we used to call it the reverse osmosis adaptor ?
good luck dusty
K',
http://www.joewoodworker.com gives complete instructions on how to build vacuum presses either pump style, or Venturi which works via a compressor. You can purchase all necessary parts and fittings right from the web site.
Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.
Dan, do you have and use one of thes systems. When I look at these contraptions, I foten think these are crazy enough to cause Rube Goldberg's eyes to spin in tight little circling spirals. I have never figured out how many CFM's it takes to keep a venturi system working efficiently, but I know that with an adaptor bushing and a hose barb, you will have exactly whatever efficientcy your pump can deliver for about $5. It is hard to get any simpler than that.Here is a site that I think has a lot of nifty stuff at prices that seem reasonable to me.
http://www.acp-composites.com/ACP-cat.htm
"Dan, do you have and use one of these systems. When I look at these contraptions"
The units that I use are vacuum pump style, not Venturi. I have a commercial vacuum pressing system, but I recently built a smaller set up that performs flawlessly. This is a photo of my shop built set up.
View ImageDan Kornfeld, Owner/President - Odyssey Wood Design, Inc.
Thanks Dan, I've emailed the guy at Joe Woodworker to ask how much of a complete system he can supply (freight costs to NZ are a problem). I think I'll stay away from a home-built compressor-based system. Looks like I'll have to track down a vacuum pump somewhere in NZ!
MalcolmNew Zealand | New Thinking0.06% of the world's people are Kiwis
Malcolm
I've been using a compressor off an old (Enzed built F&P) fridge to haul out the air on my bag press. It's so bloody simple it's almost embarassing & it cost me $25 (or 29.5 Kiwis) & an hour or so to make up a box & scrounge & hook up an old filter to stop crap going into the pump. It's just a matter of blocking all except 1 inlet & 1 outlet & connecting it up. It's been chugging along quite contentedly for about 4 years now. (What's the bet that it chuggs its last next Tuesday now I've said that:-) Only other piece of advice is that the refrig tech who sold it to me suggested I run it for about 10 minutes without a load after veneering.
A mate of mine frames pictures & uses a venturi gizmo off his compressor which we borrowed some time ago when I had a big veneer job to do. The nearly constant running of my compressor drove me up the wall & probably took 5 years off its life over a mornings worth of glue-ups. The fridge compressor is hard to hear in normal workshop conditions.
Don
Thanks
I'll talk to my local air and cool guys on Monday. If a fridge vacuum can work, I should be able to find one cheap enough!
MalcolmNew Zealand | New Thinking0.06% of the world's people are Kiwis
Malcolm, My first vacuum pump was the compressor from a very old walk-in cooler. I used it for about 15 years, and it still works.
I have a big gast brand rotary-vane that I can't stand to be in the shop with.The one that I am using now is another freebie from a commercial refrigerator, when they tore a store down around the corner, and is the best yet. It is so quiet, I hardly know it is running.I don't use the reservoir tank for vacuum bagging anymore. I don't think it really speeds anything up. Well, it may help get the bulk of air out of the bag initially, but as you are finishing off it will take longer to get there. However I guess if you are using a vacuum pressure switch, that would lengthen the duration between cycles.
Kiwimac,
I have attached a snapshot of a venturi vacuum system, operated off of a compressor, that the professor who taught bending & laminating used to provide suction to a vacuum bag press.
Unfortunately, I don't know what all of the gizmos are, or exactly how they work, but someone with more experience in these matters, like rootburl, charlie chan, or Richard Jones, will doubtless be able to look at the snapshot and tell you just how it works and what to buy.
I'm posting it because it looks relatively simple to build (I'd like to know more about it myself), and hope it can be of some use to you.
-Jazzdogg-
Whether you think you can, or you think you can't, you're right.
The venturi device shown is about $100 and is used by the surfboard industry. There are optional pressure controllers and mufflers to quell the hissing noise that add maybe another $80.00. All in all, a very good method if you have the compressor power for it. Aloha, Mike
Thanks, Mike.-Jazzdogg-
Whether you think you can, or you think you can't, you're right.
Kiwi,
You are'nt in the US, so I don't know how difficult it is on ebay. Look for a Gast diaphragm pump on ebay, you can pick them up for under $100 and they are quiet when running and have a running life of about 20,000 hours. After that a $35 kit and you are back in business. Because of this, you don't need tanks, or all the expensive add on stuff, just a bit of hose, a fitting or two and your platen. The pump runs continuously.
For vacuum bags, I use clothes storage bags from Wal-Mart at $9 a pop, they are vinyl, thick enough to use a number of times, they seal one end with a zip lock and they have a vacuum cleaner fitting, handy to suck out the initial air.
Hope this helps.
Edited 6/11/2005 12:10 pm ET by Jellyrug
Edited 6/11/2005 12:13 pm ET by Jellyrug
Why not just make a STRONG box.. Put your work in it.. Have a big bag to hold the air and blow it UP with the compressor..
I think I got my rubber bag Army surplus OR something like that...
Edited 6/11/2005 12:31 pm ET by Will George
From: Will George 12:31 pm
To: kiwimac unread
Why not just make a STRONG box.. Put your work in it.. Have a big bag to hold the air and blow it UP with the compressor..because sucking is better than blowing...... Remove the air from the bag and let atmosheric pressure do the work....its safer too. Aloha, Mike
Thanks for all the advice guys*.
I think I know where I'm heading.
Joewoodworker can sell me everything I need (except a compressor/pump, best bought locally).
But if I can find a used fridge pump and a cheap vinyly bag, I will start by putting together a 'quick and dirty' solution to see how well it works. My veneering needs are not of staircase scale (loved the photos!) and quick and dirty may be all I need.
Malcolm
* With the exception of Will's potential big bang solution. Cheez Will!
New Zealand | New Thinking0.06% of the world's people are Kiwis
Edited 6/11/2005 7:19 pm ET by kiwimac
Another source for diaphram vacuum/pressure pumps is used medical respiratory equipment. I bought a used, cased air-supply unit (to supply air to a mask) for $5.00 at a thrift store. Inside was a stainless steel body, teflon diaphram pump with a rated pressure of 30 psig. I measured 2 liters/minute delivery at zero psig ( upended soda bottle in a bucket of water method.) I have not used it for vacuum but it can be so used. The motor is something like 1/6 hp.
A bleed type regulator may be made by having a throttle valve between the pump and the vacuum bag, and a small bleed valve on a tee between the throttle valve and vacuum bag. This was an old chemistry lab technique to adjust vacuum for filtering volitile liquids.
HarryD
Malcolm
Clear vinyl (from a motor trimmer, used for the windows in convertable tops) makes a great bag. Just fold, then silicone two sides, leaving an openning at one end which can be sealed by wrapping around some 20-25mm PVC pipe & secure by attaching several spring clamps.
The ribbed mat can be got from a rubber store.
Don
I'm going pump-hunting on Monday!
Will update the story later in the week!
MalcolmNew Zealand | New Thinking0.06% of the world's people are Kiwis
I have not made one but I am told that the milking pump from a dairy farm is ideal. Hope this is helpful Peter
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