How to interpret vacuum pump specs /suitability for veneer ?

[oddsocks]

I need to do some veneering in the near future of large flat and uniformly curved (in one plane) boards.

I've been doing some research into the cost of bagpress ( £255) and airpress (£485) kits, plus looking on ebay and other sites (such as Cole-Parmer) for vacuum pumps. I'm confused as to what 'vacuum' is actually needed to be successful (seeing some threads have used clothes bags and vacuum cleaners) and how to compare the different ways of reporting a vacuum ("of Hg I understand, in that 30" = full vacuum)

Can anyone help....
some vacuum pumps specs from various sites earlier today
EDITED with info from responses elsewhere in this thread and from this link http://www.unitsconverter.net/

A - 25 micros - this is a very very light vacuum, also referred to as mtorr.
B - 3m3 per hour - the flow rate, higher numbers help bigger bags and shaped formers (get the vacuum in before the glue sets,
C - 23" Hg - 30" is a full vacuum. 23"= 11.3 PSI, 584000mtorr, 778mbar (I have seen motors that say 780mbar)
D - 10 psi - approx 20.3" Hg
E - 600 kg /m2

Anyone care to put this in order of highest vac to lowest and then identify what the threshold is for successful veneering??

Also many sites that sell new or used vacuum pumps imply they are for lab use - is this a relevant factor?

I have searched the forum for 'vacuum pump' and read most of the hits but not found the answer.

Thanks

Dave

EDITED again.... after the original title was answered the dialogue continued around the types of compressors, pumps etc and I managed to get a vacuum pump from freecycle

 

[CNC Paul]

Dave,

The only ones I know of that relates to vacuum are:

A. ?
B. Is the volume of air removed ... not a lot but OK for a bag press.
C. Is the max level of vacuum.
D. ?
E. Is the amount of pressure you will get.

They are all different types of measurement and cannot be put in the order of highest vac to lowest.

The max pressure you will get is about 12lb per square inch.... this is atmospheric pressure, remove all the air from the bag and atmospheric pressure will give you 1700lb per square foot.

It is better explained here. http://www.joewoodworker.com/

I bought a brand new Alcatel vacuum pump worth £2500 on ebay for £400.......Bargain......... You could use a compressor from a Fridge.

 

[custard]

Dave, I'm sure there are others on this forum better qualified than I to translate these technical specifications. What I can do however is comment based on practical experience of Airpress equipment and twenty odd years of venerring experience using many different techniques.

The first thing to realise is that obtaining the absolute best PVA glue bond requires truly astonishing clamping pressures. When you read the technical literature it's quickly apparent that, for practical cabinet making outside of industrial facilities, we're all dealing with "good enough" bonds rather than the theoretical optimum. If you produced a perfect vacuum in your vacuum bag (at sea level) you'd get about 15lbs per square inch pressure across the workpiece. As I said, this is only a small fraction of the pressures required for "perfect" bonding, none the less it's good enough and has the benefit of being uniform pressure right across the workpiece, something you'd find very difficult to achieve using clamps.

Now, the better the pump the closer you get to this 15lb figure. But let's keep this in context, 15lbs is itself far below the optimum, so if your pump only achieves 10lb or 12lb per square inch it's not the end of world. In fact before getting Airpress kit I cobbled together various vacuum presses that delivered perfectly acceptable results with bonds that have survived twenty years of service.

The second thing is that better or dedicated pumps have other benefits, like the ability to vacate very big bags quickly, or run multiple bags at the same time, or run continuously under industrial conditions. None of which may be appropriate to your needs.

Thirdly, there's more to successful vacuum pressing than the pump, and frankly I'd put the pump fairly low down my list of priorities. More significant in my experience is the quality and eveness of the glue spreading, the ease of getting the workpiece into the bag, how diligent you are about smoothing away any glue "puddles" as the vacuum is being pulled, how accurately you position the veneer on the substrate, and how effectively you keep it in position as the bag starts to "press" down on it. And this is all for flat work, for curved work the quality of the mould will generally have a far bigger impact on the finished job than the pump!

Personally I wouldn't sweat too much about pump specs, jump in on a small scale without spending too much and experiment. There's a learning curve like there is with virtually everything related to woodworking, but vacuum bag pressing is such a valuable tool in the veneering armoury that it's well worth perservering.

Good luck!

 

[Calpol]

D is surely the amount of pressure you'll get as well, just it's imperial. 10psi is about double 600kg/m2 I think...

Edit: Which might be worthless anyway after the previous post :lol:

 

[oddsocks]

Thanks Custard and Calpol. I have done a fair amount of veneering in the past using pearl glue and a veneer hammer on ash for wardrobe sides (I remember the joys of getting the bumps out of those!). I've also used the hotglue (useful and easy for small pieces) and spray contact (this worked well until the coffee table was put into the conservatory - I gave up trying to repair it ended up with a plain MDF top.

As you suggested, time to get bidding and get something cheap enough to experiment with.

 

[oddsocks]

i've just found this page that under the pressure section converts between the various units...

http://www.unitsconverter.net/

 

[CNC Paul]

Thanks Custard and Calpol. .

?

 

[oddsocks]

Thanks Custard and Calpol. .

?

for their earlier input ...not sure why i never summarised in quotes!

 

[oddsocks]

oops! sorry paul, not sure why I never saw your response earlier! just read it for the first time (i can only think the email alert took me straight to 'custards')

 

[oddsocks]

Dave,

.....It is better explained here. http://www.joewoodworker.com/

I bought a brand new Alcatel vacuum pump worth £2500 on ebay for £400.......Bargain......... You could use a compressor from a Fridge.

Thanks for the link Paul - I've just spent an hour browsing the various pages on his site.

Does anyone know if there is an equivalent supplier of Joes kits in UK? The cost of the V2 with 240v components and UK delivery is $232, so with import duty & fees it would work out at somewhere between £180 and £200.....so not much cheaper than the Bagpress electic system. I have seen links to the bagpress venturi design, but there is no supporting info and it appears to not be on their (temporary) website.

 

[neilyweely]

Oddsocks

I was lucky enough to get my hands on a Gebr Becker vac pump some time ago, and have been trying to get some info since from various sources. Becker UK have been useless so far.

Mine is capable of moving 40 m 3 an hour but is adjustable, so should be ok either way. The bags are available if you shop around, I found some on E-bay for about 50quid for a half decent one (I think).

I am not sure whether or not to go down this road myself or to sell the bloomin thing on and buy a, well a holiday in Bognor or something. I would love to use it, but am not so sure I would be any good at veneering anyway, so would be interested to see how you get on, and how you get set up.

so, best of luck.

Neil

 

[CNC Paul]

Dave,

I don't think Bagpress still do them, you can get them from RS Components, but there is a downside requiring you compressor to run all the time.

 

[crazylilting]

I don't know all the technical stuff on this but i do know that you can make a vacuum press out of a fridge motor. This is what i'll be doing when i get to a project that needs veneering.

I found this article on the subject.

http://users.telenet.be/Toothless/Toothless/pages/instructions/vacuum/vacuum.html

why waste hundreds of pounds on a ready made system?

 

[TheTiddles]

Vacuum pumps are something I know a bit about...

Whilst huge clamping pressures are nice, you really don't need them, a partial vacuum, when you multiply it out over a large area is a lot of load, plenty enough to ram a 0.6mm thick veneer into a substrate, even if it's all curled up to start with. There are a great deal of cheap vacuum pumps which will pull a 70% vacuum and run continuously for 1000hrs up to 100,000 hours without a problem. If I was in a commercial shop I would have kept the turbine compressor I sold recently, but as I don't I use a small diaphragm pump and a vacuum switch which turns it on and off as needed, plastic bags can be picked up all over the place for free and a bit of tape does the rest. Not everyone can get a hold of such simple pumps, others might have a few sat around in a drawer... :wink:

Aidan

 

[neilyweely]

Tiddles - PM sent.

Neil

 

[oddsocks]

I don't know all the technical stuff on this but i do know that you can make a vacuum press out of a fridge motor. This is what i'll be doing when i get to a project that needs veneering.
I found this article on the subject.

http://users.telenet.be/Toothless/Toothless/pages/instructions/vacuum/vacuum.html

why waste hundreds of pounds on a ready made system?

Thanks for the link - yet more information! I had seen the posts bout fridge compressors before but had the impression that the loss of oil was more significant than it appears to be (i.e it can be checked and topped up). I did ask at the local tip a year ago if I could have a motor and got a resounding no! If I opt for that route I will need to get yellow pages out and find a fridge repairer.

Thanks for all the other responses as well - Oh if i had a limitless budget

I have gone off of the venturi method as my sealey compressor is only a frame one (4l) with 5.2cfm so would be running too often and noisy.

 

[CNC Paul]

Dave,

Have a look on ebay http://cgi.ebay.co.uk/SAMSUNG-FRIDGE-CO ... 7C294%3A50

If it is too far ask the seller to put it in a box and use www.parcels2go.com , they collect and deliver.

 

[oddsocks]

Dave,

Have a look on ebay http://cgi.ebay.co.uk/SAMSUNG-FRIDGE-CO ... 7C294%3A50

If it is too far ask the seller to put it in a box and use www.parcels2go.com , they collect and deliver.

Thanks Paul - I created a search on ebay yesterday but for vacuum pump (with a fair few -words to remove the unwanted ones such as nipple and penis enlargers as well as aquatic pumps!) but didn't think to use 'compressor'. Last night I also posted a request on the local freecycle for a fridge motor (with the note not to offer complete fridges due to the gas needing to be removed).

I'll email that ebay seller now re parcels2go (a good service) and if I get no replies from freecycle I'll follow up that ebay link

 

[Imperial]

This has just appeared on the Rutlands website, and seems to be an easy and reasonably cheap way to get started! :wink:
http://www.rutlands.co.uk/cgi-bin/psProdDet.cgi/DK1135

 

[oddsocks]

This has just appeared on the Rutlands website, and seems to be an easy and reasonably cheap way to get started! :wink:
http://www.rutlands.co.uk/cgi-bin/psProdDet.cgi/DK1135

thanks - another one to add to the list of options. The pump looks a bit lightweight compared to some others (bagpress etc) but the price is better, expecially seeing as it comes with two bags which will need to be factored into any home build.

Time is on my side at the moment (as well as lack of funds) so i'll see if I can get a fridge compressor. Another factor is the size/floorspace of any homemade system - at least the professional ones are compact.