Vacuum Bagging

[MtnDon]

I am aware that bdosborn used vacuum bagging when assembling the inner skins of the walls on Boxcar. I was wondering if anyone else has done any vacuum bagging? And what sizes pieces were bagged, using what CFM pumps, glue types, etc. Thanks.

[KCStudly]

I sucked down the inner skins on both of my walls. Used a 16 gal wet/dry vac and bubble wrap as a breather felt medium.

Let's see where was that. Ah yes, starting on pg. 65 of my build I started experimenting and building my vacuum bagging set-up.

If I were to do it again I would have brought my shop vac over from the house, made another scoop (to prevent the bag from being sucked up against the vacuum nozzle) and run two vacuums. On such a large panel it was difficult to get it sealed up well (at least for me and the technique and materials that I was using), and I think the extra vacuum capacity would have given my the margin that I needed on the second wall.

It's glued down solid, for sure, but I think it would have been flatter and more secure around all of the edges if I had doubled up.

[MtnDon]

Cool idea on using the bubble wrap for a vacuum breather medium. Cheaper than the material sold by veneer suppliers too.

Thanks for pointing out the page number. I had not read that far along your topic. I have some 2 and 3 sq ft scraps of 1/4 and 1/8 plywoods laying about I plan on using for a test with a foam core.

[bdosborn]

Used a 16 gal wet/dry vac and bubble wrap as a breather felt medium.

I used cord. I looped the cord back and forth across the top skin, from the far end back into the vacuum hose. Seemed to work well enough. The hard part was getting the seams of the bag taped good enough for a deep vacuum. I ended up using a laminate roller to really stick the tape down.



Bruce's Vacuum Bag

Bruce

[pmowers]

I can't recall where I saw it, but one individual laid a sheet of heavy visqueen on his garage floor and duct-taped it down. A blanket was used on top of that followed by his laminates, another sheet of visqueen was duct-taped to the first sheet and vacuum applied using a valve cut off of a space bag and installed. A shop vac was used to pull the vacuum, and just left running for 24 hours.

If I can find the reference, I will definitely post it.

Pat

[angib]

A shop vac was used to pull the vacuum, and just left running for 24 hours.

I've seen that before and it's a big cost saving over a vacuum pump. But how many times can a shop vac be left running for 24 hours before it burns out the motor? They're not designed to draw no air and while a shop vac is cheaper than a vacuum pump, a new shop vac every two, five or ten pulls isn't that cheap.

[bdosborn]

A shop vac was used to pull the vacuum, and just left running for 24 hours.

I've seen that before and it's a big cost saving over a vacuum pump. But how many times can a shop vac be left running for 24 hours before it burns out the motor? They're not designed to draw no air and while a shop vac is cheaper than a vacuum pump, a new shop vac every two, five or ten pulls isn't that cheap.

That's what I thought too but that's not what happens. The shop vac motor is actually unloaded when the vacuum is highest, drawing less current than when it sucking a lot of air. Mine runs surprisingly cool and heat is not the issue I thought it would be. I have a purpose built vacuum pump and ditched it in favor of the shop vac, the shop vac worked much better. The higher volume of the shop vac compensated for all the little leaks in the taped seams better. I also used titebond II glue, which has a set time of 1/2 hour, so I only clamped mine for an hour or two.

Bruce

[KCStudly]

I also used titebond II glue, which has a set time of 1/2 hour, so I only clamped mine for an hour or two.

+1

45 min to an hour using TB2 and no signs of damage to the shop vac. For a hobbyist using it for a few jobs, I think it is the right choice.

[Martiangod]

Havn't done any vbaggin, but for smaller panels up to 60" x 80", would an air mattress work, would only have to seal up one sliced end, gorilla tape would work great, fittings for dumping air would make vacuum easy to hook up....Just a thought

[angib]

Boatbuilders using vacuum bags seal them with "vacuum bag tacky tape" - a strip of putty-like material with a tacky face. The putty part allows things like creases in the vacuum bag to be squished to make a seal. I see there is one American seller on eBay offering 25ft rolls for $7, so I would make a case for buying the proper stuff and saving yourself the hassle of trying to seal with non-ideal materials.

[bdosborn]

Here's builder capnTelescope using more pro like vacuum clamping materials. Pretty cool:





capnTelescope Vacuum Bag

Bruce

[tony.latham]

That SUCKS.





Okay.... I'm just jealous. And there I was last summer, "clamping" up my walls using buckets of water for weight with my vacuum pump parked below my wood lathe...
Sheeeeeesh.

Gotta boot-up and go shovel snow.

Tony

[eamarquardt]

A shop vac was used to pull the vacuum, and just left running for 24 hours.

I've seen that before and it's a big cost saving over a vacuum pump. But how many times can a shop vac be left running for 24 hours before it burns out the motor? They're not designed to draw no air and while a shop vac is cheaper than a vacuum pump, a new shop vac every two, five or ten pulls isn't that cheap.

That's what I thought too but that's not what happens. The shop vac motor is actually unloaded when the vacuum is highest, drawing less current than when it sucking a lot of air. Mine runs surprisingly cool and heat is not the issue I thought it would be. I have a purpose built vacuum pump and ditched it in favor of the shop vac, the shop vac worked much better. The higher volume of the shop vac compensated for all the little leaks in the taped seams better. I also used titebond II glue, which has a set time of 1/2 hour, so I only clamped mine for an hour or two.

Bruce

When the vacuum is "plugged up" the motor speeds up suggesting that it isn't under as much load and working as hard as when it's actually sucking. Also the motor cooling, by virtue of the design of the vacuum, is not cooled by the vacuum airflow but usually by a separate fan on the motor shaft which turns faster (and likely moves more cooling air) when the vacuum is unloaded.

My two scents.

Gus

[VijayGupta]

Titebond (Franklin International) makes a glue especially for this purpose.

http://www.titebond.com/product.aspx?id ... 94cc3ae102

If you have a compressor, you can also get a venturi that will draw the vacuum (sort of like running a refrigerator on a propane flame )

[bdosborn]

I don't think it would work with vacuum clamping:

Required pressure application
100-250 psi, depending on substrates

I think you can only get 14 psi with vacuum clamping.

Bruce