Vacuum veneering question

[William Batdorf]

Hello All,

I want to attempt vacuum veneering. I understand the process, but my question is regarding the vacuum pump. I frequently see commercial/laboratory grade vacuum pumps selling for reasonable prices at auction or on CL. One would think these types of commercial pumps would last several lifetimes for the average woodworker. What isn't clear to me is this...once my project is inside the veneering bag and sealed up, does the vacuum pump need to run continuously, or does it run intermittently? What turns it on and off, or is it up to me to keep an eye on the bag? Does a commercial vacuum pump possess (or lack) some important features of those pumps marketed primarily to woodworkers?

Your advice is appreciated.

[John K Jordan]

I use a vacuum pump for a lathe vacuum chuck. It needs to run continuously. Nearly any vacuum pump will work.

I haven't used vacuum for veneer or vacuum clamping yet but I have purchased everything to do it from Joe Woodworker.

From his web site and others I understand these: The pump need not run continuously unless you have a significant leak. The pump may need to come on occasionally if you have a very small leak. A vacuum switch can turn the pump on automatically as needed. It will run less often if you add a significantly sized vacuum reservoir to the pump. One problem with starting the pump on while already under vacuum is it may put excessive strain on the pump - this problem can be eliminated by adding a special valve which lets the pump start freely then switches to the vacuum load. You can build almost everything yourself, including the vacuum press itself.

Joe Woodworker provides free plans and sells everything you need at a reasonable price, including valves, switches, gauges, and pump. He as been gracious to answer all my questions on the phone as well.

https://www.joewoodworker.com/
The column on the left will link to pages of information. For some things you may have to hunt around a bit.

This is the starting page on building your own vacuum press/clamp system:
https://www.joewoodworker.com/veneering/welcome.htm
I bought everything needed for the Project:EVS Pump Press.
Look at the galleries at the bottom of the left column for pictures of presses others have built from Joe's plans.

I see he now offers a kit for an auto-cycling vacuum system, perfect for veneer work:
https://www.veneersupplies.com/categ...__Press__Kits/

There is also a gentleman selling pumps and parts to woodturners for a good price, lots of people have purchased these. https://www.frugalvacuumchuck.com/
A pump from him could be easily used with the vacuum system from Joe Woodworker.

There is also a venturi vacuum system that people use for vacuum chucking, pressing, and infusing to stabilize wood. This does not require a vacuum pump but runs off an air compressor.

JKJ

Hello All,

I want to attempt vacuum veneering. I understand the process, but my question is regarding the vacuum pump. I frequently see commercial/laboratory grade vacuum pumps selling for reasonable prices at auction or on CL. One would think these types of commercial pumps would last several lifetimes for the average woodworker. What isn't clear to me is this...once my project is inside the veneering bag and sealed up, does the vacuum pump need to run continuously, or does it run intermittently? What turns it on and off, or is it up to me to keep an eye on the bag? Does a commercial vacuum pump possess (or lack) some important features of those pumps marketed primarily to woodworkers?

Your advice is appreciated.

[Mike Henderson]

I've done a lot of vacuum veneering. I agree with John - go to Joe Woodworker's site and you'll find lots of information. I bought one of his rebuilt pumps some years ago and it's still going strong. He sells a kit that you can use to build your own vacuum pump system. I think it's easier and cheaper to buy the kit than trying to find all the pieces yourself.

The polyurethane bags will last longer than the vinyl bags but are a bit more expensive. When I started, I bought a 4 by 8 poly bag because I could put smaller things into that bag. But soon, I bought a smaller poly bag (2 by 4) and use it a lot more than the 4 by 8 bag.

And BTW, the bag size is the size of what you can put into the bag, not the outside dimensions.

Mike

[Steve Demuth]

If your bag and connections are good, there is no need for the pump to run continuously. The whole system, once drawn down will generally leak enough that over a period of minutes to hours the vacuum will have to be refreshed. So you need a vacuum switch to kick the pump back in when the vacuum becomes to weak.

Nearly anyone who has done this will tell you to get a Joe Woodworker kit to accomplish this. They are all right - that's the fastest, most effective, and probably least expensive way to get it right.

[John TenEyck]

I built my own vacuum bag and pump system around a commercial Gast pump. I use 20 mil vinyl for bags because it's cheap and easy to weld with PVC pipe cement. I'm still using the bag I first made almost 20 years ago, and I've used it a lot.

I've patched it maybe twice.

I think I spent about $50 for the vinyl at McMaster Carr. Now I buy vinyl from my local boat cover fabricator. . Twenty years ago there was no internet so I knew nothing about Joe Woodworker, so to cycle my pump I use an on/off switch that I had that can be programmed for how many minutes/seconds of run and idle time. Of course it's not as nice as the system the JW sells, but it doesn't need to be either. And you can run a pump continuously if it's rated for it. It wastes a little energy but it doesn't hurt anything and it allows you to build a system for not much more than the cost of a pump.

John

[jerry cousins]

there are both types - pumps that hit a high end - then stop - if the pressure goes down then it cycles back on. and there are continuous running pumps.
i have used a continuous running pump for many years - bought it from joe woodworker and believe it was rated for 40,000 hours - that's a lot of pressings.
jerry

[Bruce Wrenn]

Somebody explain to me why it's harder for a vacuum pump to start when it's already holding a vacuum. I read this often, but no one has explained why it's so, or is it?

[Mike Henderson]

Somebody explain to me why it's harder for a vacuum pump to start when it's already holding a vacuum. I read this often, but no one has explained why it's so, or is it?

It's pretty much the same as an air compressor. With an air compressor, if the pressure is in the piston, and the motor tries to start, it has to overcome the pressure at startup time. Compressors have valves that bleed the pressure off the pistons so the motor can get started.

With a vacuum pump, the same thing happens if the piston is under vacuum. The motor has to move the piston down while the piston has vacuum on it. That can be too much load for the starting torque of the motor. Same concept as an air compressor but it's vacuum instead of positive pressure.

Mike

[John TenEyck]

Somebody explain to me why it's harder for a vacuum pump to start when it's already holding a vacuum. I read this often, but no one has explained why it's so, or is it?

This problem is eliminated if you put a check valve between the pump and bag. You need to do that anyway if you use a simple on/off control system. Of course, if you run the pump continuously you don't need anything.


John

[Robert Cherry]

My pump is an old mass spec roughing pump. I ran it continuously for the first few projects, but because it is an oil bath pump is emits a plume of fine oil mist so the exhaust had to be piped outside. For my last project I built joe woodworkers setup around my existing pump and couldn’t be happier. Hardly any oil to contend with and I don’t have to listen to the pump run for hours on end.

702730D4-B8FB-481B-A842-46FB4290C84A.jpg

[Jamie Buxton]

I have a controller for the pump in my veneer press, but I don't use it any more. As my bags get older, they get schmutz -- sawdust, glue bits, etc -- on the sealing surfaces, and start leaking. This means the controller cycles the pump on and off more often. The start/stop is more annoying than just letting the pump run continuously. If I were ever to build myself a new rig, I'd dispense with the controller. Simple is good.

[Mike Henderson]

I have a controller for the pump in my veneer press, but I don't use it any more. As my bags get older, they get schmutz -- sawdust, glue bits, etc -- on the sealing surfaces, and start leaking. This means the controller cycles the pump on and off more often. The start/stop is more annoying than just letting the pump run continuously. If I were ever to build myself a new rig, I'd dispense with the controller. Simple is good.

My bags hold the vacuum for quite a long time and that's why I like the cycling pump. When the pump is running, it's loud.

I'd clean the sealing surfaces before I'd run my pump continuously.

Mike

[I use commercial bags and use a C-clamp for sealing them.]

[Joe Jensen]

I bought a used Gast pump from Surplus Center like 25 years ago, 3/4HP motor. When I bought it I took the model number to the local Gast distributor to get a check valve and filter. He looked it up and told me that it was built to run continuously for over 20 years in a computer system. Mine has graphite vanes. I paid like $80. I don't have a vacuum tank, I just turn it on and let it run until the glue sets. I have a gauge on it too. When bags are new it will hold a vacuum for hours with the pump off. My bags are now old and I have to keep it running. If you are at all handy I would buy a used Gast on ebay or from Surplus Center.

[Don Kondra]

I have my Gast pump set up with a manual system.

A water valve after the gauge

Evacuate the bag, shut the valve, shut off the pump.

While I'm working on the next laminate I watch the gauge, when it reaches 20" I turn on the pump, open the valve and run for 15 or 20 seconds.

Rinse and repeat...

Cheers, Don

[Bill Adamsen]

I too used the Joe Woodworker setup and found buying his "kit" a reasonable way to get all the right parts and instructions.
I used a wobble type vacuum pump (Thomas 2660) purchased on ebay and it works fine.
My experience with aliphatic glue is that it takes a long time to cure under vacuum, having the Mac valve (auto shutoff) is a nice feature.
I actually added a dpdt center off switch to allow either continuous or cycle (shown).