Vacuum bagging

[marcros]

I want to make some vacuum bags up. I have no idea what sizes I need, so was going to do a couple of semi disposable ones from http://www.ecfibreglasssupplies.co.uk/p ... -tube.aspx

what does the handling and safety statement mean?

How do I seal the ends?- something like http://www.ecfibreglasssupplies.co.uk/p ... -tape.aspx

or could i use 2 of the waste pipe idea, one on each end:

"To close the open end of the bag I made a closing system out of 2 pieces of waste pipe one 30mm one 40 mm 1.2m long. I cut approx 1/3 of the off the 40mm pipe all the way down its length. To seal the bag wrap the open end round the 30mm pipe once and then clip the open 40mm over the top of the 30mm pipe to make the seal"

from step-by-step-guide-to-building-your-own-vacuum-bag-press-sys-t59509.html

 

[PhillyDee]

Give them a call, they are a good bunch of lads and very helpful. Got some quite funny youtube videos on their channel somewhere. I might be biased since they are in the same industrial estate as me. . . .

 

[marcros]

i thought that they were Grimsby. I have heard good things- I will give them a shout to talk it through.

 

[tool-me-up]

you dont say what size of im unsure if these are any good or easier? they are probably cheaper elsewhere its just the first link i came to.
My local poundshop often has quite a few in ( smaller ones )
http://www.argos.co.uk/static/Produ...436447|rnd:21316805221609302120|dvc:c|adp:1o2

 

[marcros]

you dont say what size of im unsure if these are any good or easier? they are probably cheaper elsewhere its just the first link i came to.
My local poundshop often has quite a few in ( smaller ones )
http://www.argos.co.uk/static/Produ...436447|rnd:21316805221609302120|dvc:c|adp:1o2

that is never going to be sufficient pressure for veneering is it?

 

[tool-me-up]

Honestly I dont know, I know with a decent hoover you can get an incredible amount of clothes into one!

Find a cheaper one and try it out?

Just shove a plank of wood in and apply the vaccum and seal - check the next day to see if bag is still stuck down to plank or not.
If its still not wrapped round it dead tight then it has leaked or torn.

 

[nathandavies]

making a vacuum setup has been on my to-do list for ages. looking on e-bay there are several vacuum pumps on there, are there certain specifications that are needed? or would any of them do the job?

 

[marcros]

i found it a bit of a minefield, but found somebody that knew about them!

From what I have gathered and been told that, firstly you need to decide whether you want to do small items- box lids, or dining tables. Obviously you can do both with the larger setup, but the larger one would be more expensive.

I think that I read somewhere that you need a pump that does 2 something or others for a small bag, and 4 something or others to do a big setup, or 2 small bags. could be cubic feet per minute. if you want to do a larger bag with a small pump, squeeze as much air out as possible, and hook the vacuum cleaner up to get most of it. You need a pump that is rated to run continuously- a vacuum cleaner is not, and is sometimes suggested.

The one i got was a dry vacuum pump, if that helps the search. I don't think it is rocket science though, once you get the pump it looks easy enough to hook it up. I am at that stage now. Put a wanted ad in the for sale section maybe?

 

[tool-me-up]

CFM or cubic feet minute will only determine how fast the bag is emptied.
I am no expert on this and have never done it before but I know you dont measure a vacuum in cfm.
This is simply how many feet of air it will move in a minute ( much like the rating on a air compressor CFM and PSI - both useful but both very different)
The actual vacuum pressure which I assume is the most important for veneering will be measured in kPa (pascals ) mmHg ( mm of mercury - also torr ) or Bar.

You may have to convert from one unit to another to compare different units but ( personally) I would just go with the unit that provides the bigger vacuum as this will put more pressure on the pieces in the bag.

 

[tool-me-up]

I got my self wondering now I said that, so I've had a quick google.

This is the closest pump I could find to the one listed in your build thread
http://www.mastercooltools.com/vacuum-pump-90ltr-per-min-2-stage-110v-220v-mastercool-90063-2v-220
Its max vacuum is 15 Microns.
Convert 15 microns to mmHg and you get 0.001999835526316
Convert mmHg to kpa and you get 0.000266622808821
or in Bar 0.00000266622808821

Now I have seen a hoover with the following specs
60Ltr/sec airflow. 17 kPa suction power

which is 0.7 bar or
127.5104860597 mmHg or
127510.4860597 Microns!

So a Hoover would be thousands of time more powerful that that pump.
I must have something wrong but i cant figure what

 

[RogerS]

Don't forget that you will need to run your vacuum pump continuously probably.

This link shows how I went about making mine from various bits and pieces

http://thewoodhaven.co.uk/phpBB3/viewto ... ump#p26763

 

[Myfordman]

You have just got them the wrong way round.
The pump is thousands of times more powerful than the Hoover as proved by your calculations

 

[tool-me-up]

Don't forget that you will need to run your vacuum pump continuously probably.

This link shows how I went about making mine from various bits and pieces

http://thewoodhaven.co.uk/phpBB3/viewto ... ump#p26763

An air tight valve would mean you can turn it off - or it least im 99% sure it would.

Once max vacuum is achieved why make the pump run, isolate the bag with an inline tap, on even a one way check valve?
You can get check valves rated to ridiculous pressure for a couple of quid.
Surely if no air can flow back down the line because of valve or tap then the vacuum will remain - providing bag etc is air tight.

 

[tool-me-up]

You have just got them the wrong way round.
The pump is thousands of times more powerful than the Hoover as proved by your calculations

Is this with them being below atmospheirc pressure - so the lower below the more powerful the vacuum?

 

[Myfordman]

You have just got them the wrong way round.
The pump is thousands of times more powerful than the Hoover as proved by your calculations

Is this with them being below atmospheric pressure - so the lower below the more powerful the vacuum?

Of course! 1 bar is no vacuum at all.

0.1 bar will be fine, no need to go to the extremes of the refrigeration pump performance but the pump needs to be continuously rated so the Hoover type is no good at all on those grounds

 

[tool-me-up]

I thought 1 bar of vacuum would minus current pressure by 1 bar, so if current pressure was 2 bar with 1 bar vacuum pressure would drop to 1 bar.

Maybe im tired, yep that's it, ive been outside all day grinding rusty bolts out of a car chassis - that's my excuse and im sticking to it!

Learn something everyday!

 

[Myfordman]

Why would current pressure be 2bar???

Normal atmospheric pressure at sea level is nominally 1 bar +/- a gnats due to weather variations.

Taking the inside of the bag down to 0.1 bar, there will be 0.9 bar net pressure on the contents of the bag

More than enough for any gluing job

 

[tool-me-up]

Why would current pressure be 2bar???

That was just an example for easy math

 

[RogerS]

Don't forget that you will need to run your vacuum pump continuously probably.

This link shows how I went about making mine from various bits and pieces

http://thewoodhaven.co.uk/phpBB3/viewto ... ump#p26763

An air tight valve would mean you can turn it off - or it least im 99% sure it would.

Once max vacuum is achieved why make the pump run, isolate the bag with an inline tap, on even a one way check valve?
You can get check valves rated to ridiculous pressure for a couple of quid.
Surely if no air can flow back down the line because of valve or tap then the vacuum will remain - providing bag etc is air tight.

Fine. It's your call.

I base my information on personal experience.

 

[custard]

Hello Marcros. Like many woodworkers I use the AirPress vac system. It's pretty good and I wouldn't be without it, but vacuum veneering does have limitations and it may not be the best way to go.

Even when a vac set up is operating correctly it's only just giving enough pressure for an adequate glue bond, and there's not much margin for error so you need to put some thought into glue choice and glue spreading. Plus vac systems are better for some applications than others. If you were to vac bag a square board say 500mm x 500mm and then cut it into two you'd see the glue line was quite a bit thicker in the centre than at the edges, so vac bagging isn't the best approach for any piece that'll be subsequently sawn. And vac bagging wouldn't be my first choice for laminating a curved structural component, such as a seat rail on a chair. For that I'd prefer to invest the time in making a male and female former and cramp it all up. Or for a very long component I'd maybe just make a male former and cramp the laminates to that.

So depending on what you're making you might be better off with something other than a vac bag. For example even though I've got the Airpress if I'm making a typical veneered box component I'd more likely use a simple "book press" type arrangement that I got a local blacksmith to make up for me for about £20.