DIY Vacuum Bags - veneer press/bent laminate

[Dale Murray]

I've tried searching the forum for this information but as you can imagine, the words Vacuum & Bags comes up A LOT in regard to dust collection.

I am about to purchase a Vacuum press system from JoeWoodworker but would like to make my own bags.

It appears relatively straight forward but I've not seen a good example of it being done:
- materials
- adhesives
- valve placement
- etc

I am quite certain this is not terribly difficult but since I have never made one I could be totally wrong.

My project will involve bending several sheets of wood over a solid foam form.
The form will be similar to a parabolic arc 18" deep and 18" tall. The base of the form will be 16"x18"

I realize I will need to do some testing as this is my first experience with a vacuum press.

[Jim Becker]

I think you have to weigh the cost/benefit including your time relative to making your bags vs just buying them from Joe ready to go unless you feel your application is so unique that only a custom bag will work. I don't recall anyone posting about making their own bags in the past, but then again, I could very well have missed it or forgotten about it. I have bags from Joe and they are really nice quality.

[Kevin Jenness]

I think there is plenty of info on Joe's site as regards materials and adhesives. I wouldn't bother fabricating my own except for an odd size I could not buy but I guess you can save a few bucks that way. I would put the nipple near the opening end.

That is a deep form and will involve considerable deformation of the bag if included inside the bag during layup. A dry run is definitely indicated.

There is another technique that involves bagging the laminates outside the form, but it requires pulling the layup into shape by means other than vacuum and a breather fabric layer inside the bag.

The second video on this page is a good intro on basic vacuum bagging https://www.vacupress.com/videos/

[glenn bradley]

I agree that making your own bag would only make sense if you have a requirement that falls outside of commercially available bags. I make a lot of shop-made things but, there are some things that I just buy.

[John TenEyck]

I make my own bags out of 20 or 30 mil vinyl. Vinyl doesn't stretch as well as PU, but it's cheap and easy to glue with regular PVC pipe cement. I've made my own bag penetrations by gluing a small block of PVC inside the bag and then threading a hose nipple into it, through the bag. I've also used hose penetrations from Joe Woodworker, but never had confidence in them in terms of leakage. It only takes an hour or so to make a bag; no big deal. And I'm still using the first bag I made 20 years ago, after at least a hundred uses.

I've bent laminations similar to what you want to do. It works just fine as long as you tape the laminations together at their CL after applying glue, and holding them in place on the form as you pull the vacuum.

I read something here recently about Joe Woodworker's website no longer taking orders, so check before trying to place an order.

John

[Jamie Buxton]

I make my own bags. I can make a bag big enough to swallow a 4'x8' sheet for $30 in materials and twenty minutes of labor. Commercial bags cost way more than that.

I buy 20 mil sheet vinyl from a 54"-wide roll at my local plastics emporium. (Tap Plastics. Small chain in the SF area.) The vinyl is $4 per running yard or so. From the same source I buy glue that is intended for gluing sheet vinyl. It comes in a toothpaste tube, but is kinda runny. $4 or so. I buy 1/4" ID vinyl tubing from Home Depot. $10 for a 25 foot hank. 1/4" ID goes on the fitting on my vacuum pump. You might need something different.

Form the sheet vinyl into a bag with one open end. Around the other three sides you'll have some combination of folded edges and open edges that you will glue. The vinyl tube is going to run outside the bag, and inside the bag. I generally have it penetrate the bag at the end away from the mouth of the bag. The section inside reaches to the mouth of the bag or so. For the section inside, I make it a leaky tube by drilling holes in it. I use a 1/16" bit, and drill through the tube every 4" or so. This is not precision work.

Glue up the bag's seams. Form the sheet around the tube as it goes through the bag. The solvent in the cement makes the sheet more flexible, so it isn't difficult to achieve an air-tight joint. You may want to use cauls and a few clamps.

I use the bag by sliding the workpiece into the bag, and kinda looping the leaky tube along the edges of the workpiece. Again, this is not a precision operation. Those air molecules are teeny little things, and they'll make their way to the tube to get sucked out.

[Dale Murray]

I read something here recently about Joe Woodworker's website no longer taking orders, so check before trying to place an order.

John

Thanks for the info.

Joe's site was not taking orders temporarily.
I have been communicating with him this week and he is definitely taking orders again.

[Dale Murray]

I appreciate the comments on cost/benefit of making my own. I do see myself doing more vacuum press projects in the future but most of those would be MUCH smaller (small arched door panels, or veneering flat panels that are 18"x24"). Buying a bag large enough for this project knowing it is extremely unlikely I will ever do something this big again seems excessive.

Also, I just spent a load of money on a new piece of stereo equipment so I am a bit low on squandering cash.

[Dale Murray]

I suppose it is bad for to create three replies in succession but I'm doing it anyway.

It would appear I am over thinking the issues of making a bag. I thought that might be the case but until you do it you don't know.
Thanks for the information everyone.

[Don Kondra]

I also make my own bags, vinyl sheet and adhesive from upholstery outlet.

My caul is "scored" every four inches or so to aid in the removal of air. For a "valve" I drill a 1/4" hole into the edge of my platen and then up into an intersection of cuts. Insert 1/4" brass tube and attach hose. For gasket I use window caulking !



Cheers, Don

[Don Kondra]

For odd shapes, I just omit the platen...



Cheers, Don

[John TenEyck]

Here's a 20 mil vinyl bag I made just to do door stiles and arches. It's 10 ft long. Here is is gluing up a door jamb arch.




I put the penetration near the open end. Big mistake; I'll never do that again. If you look closely in this photo you will see a black mesh.



It's heavy duty plastic window screen. I used to use breather mesh from Joe W but it's too coarse and stiff for my liking. Then I saw this stuff at HD and it's perfect. You can buy it in several sizes, it's cheap, and you can cut it to whatever your needs are. If you make sure a piece always leads from your part to the bag penetration there will never be a problem with evacuating the bag. Using some sort of mesh eliminates the need for a scored platen, which simplifies use and storage.

For smaller arched parts I put everything inside the bag in the conventional manner.

John