Cobbling Together a Vacuum Pump For Vacuum Bagging Veneering

[RoyG]

Greetings,

I'm not sure whether I've picked the right forum for this question ....... if you think there's a better forum for this post, please redirect me.

I've been doing some veneering using the Roarockit system that uses a hand pump to generate the vacuum. The system is OK, but it was designed for skateboard building, so the bags that the system uses are quite limited in size for doing furniture components. The hand pump is also slow to establish a vacuum, especially when using the bigger Roarockit bags. In general the Roarockit was a great way to get started in veneering, but I'm now looking to veneer larger pieces, and I'd like to be able to establish the vacuum a lot quicker than the hand pump is able to, and I'd like to hold the vacuum for much longer than the Roarockit system can.

I've looked at various web sites that talk about using various types of Vacuum Pumps to do vacuum bag veneering. I envisage that the Vacuum Pump might get used on only four or five projects per year, so I don't want to spend large bucket loads of money on a very occasional use tool.

A few web sites talk about using the Vacuum Pumps that Refrigeration Techs use to evacuate a refrigeration system when they are servicing it. The following link points to one possible unit on Ebay; http://www.ebay.com.au/itm/3CFM-2-St...item43d12ec2d1 At $145 plus freight, one of these pumps might be a suitable solution. This one is supposedly rated at 3 cubic feet per minute, so I don't know how long it would take to pull a decent vacuum on a big 1000 mm x 2000 mm vacuum bag. They have another rated at 5 CFM that is still under $200. Does anyone use one of these pumps (or similar)?

Other web sites discuss re-purposing an old Refrigerator, Freezer, or Air-conditioner motor/compressor sealed unit. One advantage of this approach is supposed to be that a re-purposed refigerator sealed unit will be much quieter. From a cost standpoint, this option looks attractive if I can get a hold of a working sealed unit out of a discarded fridge. However, I can't find any specs on the flow rate for a re-purposed refrigerator sealed unit. Would it pull a vacuum quickly or slowly, and will it pull sufficient vacuum ?

So, what sort of Vacuum Pumps are other people using to evacuate Vacuum Bags, or to drive Vacuum Clamps?

Regards,

Roy

[mark david]

Hi Roy, I am using something similar although don't know much about its specifications as the pump was given to me.
It is a small 110volt unit made by Gast in the U.S and quite compactmat around 220mm long and 120mm high.

I don't think cfm is terribly important, what is more important is what kind of vacuum it can pull.
As you are going to squeeze most of the air out of the bag before sealing in doesnt take long to acheive a good vacuum.

Professional vacuum veneering systems are very expensive and your choice is somewhat limited in Australia.

I am currently experimenting with West system epoxy and although expensive is excellent.
Pva works fine for smaller jobs.

[BobL]

I wouldn't worry too much about the low flow rates of small pumps.
The way to deal with this is to use something like a vacuum cleaner to get most of the air volume out and then use the small vacuum pump to get the rest out.

I was very lucky last year to pick up a 30+yr old Leybold Scientific 16A vacuum pump from a skip at work last year.
It sucks at 400LPM or 14 CFM and theoretically can reach a ridiculous 0.000058 psi (that's 29.9211" of Hg - a full vacuum is 29.9212" Hg)
This pump was used on an Electron microscope and so would have been well looked after and kept well service and clean.
When it was new this pump would have cost $3-4k - but it was incompatible with any of their new equipment and so it was thrown out.
There were 4 pumps in the skip and I scored two in working order and gave one to a friend.
While both pumps were in excellent condition they needed a service (i.e. replacement of a very special and expensive kind of vacuum oil ~ $100 for each pump) but I found the correct oil on ebay in the US. The oil cost $88 including shipping and there was enough to service both pumps another time.

[BobL]

. . . I don't think cfm is terribly important, what is more important is what kind of vacuum it can pull. . . . .

I'm far from experienced in this area but I would have thought it was more the other way around.

The pressure has to be applied reasonably quickly because if the glue even partially dries before the vacuum is reached then problems will arise.

As far as vacuum goes there's not much pressure difference between 27 - 28 - 29" of Hg
The difference between 27 and 29"of Hg translates to ~ 6% more pressure, is that really going to be significant?

Or are you perhaps referring to leaks?

[mark david]

Hi Bob, I am sure there are lots of vacuum pumps that can shift a lot of air but not acheive a very good vacuum, a vacuum cleaner would be a very good example of this.

As speed can be of the essence as you correctly point out.
What takes the time is accurately applying the glue to the correct correct thickness, too much is as bad as not enough.accurately taping the veneer to the ground, any significant overlap is crushed.
Placing the project in the bag, laying on the breather mesh, sealing the bag and then starting the pump.

These are all good reasons not to use pva on larger projects as you will quickly run,out of time.
This is why it is advisable to use something like West system epoxy as the thinner you spread it the slower it cures.The open time is significantly longer than pva.

Even my tiny pump acheives a full vacuum in less than a couple of minutes.

I'm far from experienced in this area but I would have thought it was more the other way around.

The pressure has to be applied reasonably quickly because if the glue even partially dries before the vacuum is reached then problems will arise.

As far as vacuum goes there's not much pressure difference between 27 - 28 - 29" of Hg
The difference between 27 and 29"of Hg translates to ~ 6% more pressure, is that really going to be significant?

Or are you perhaps referring to leaks?

[clear out]

I shared a workshop with some guys who vac bagged the 7m x 15m cabin roof of the Ena a 100 year old steam yacht.
They used an old 3 phase milking pump and west system.
They could leave it running all night if needed.
H.

[Cliff Rogers]

This subject has been covered several times before, use this search link & have a look a some of the other threads.
https://www.google.com/search?as_q=V...ts=&gws_rd=ssl