Vacuum Press Construction and Use

[Jon McElwain]

Hello all. I just got some parts in the mail from Joe Woodworker to build a vacuum press. I will be using some 20 mil vinyl (I know, a little on the thin side) from the fabric store. I'll be using a Joe Woodworker valve stem, closure, and some HH-66 vinyl cement.

Before I start building this bag, I was hopping to get some tips about the bag construction. I have read the Joe Woodworker site, but I have a feeling that I could still use some more advice before starting.

My project is to vacuum press new veneer on a number of bent plywood seats. The existing top veneer is beginning to delaminate. I was able to scrape the old top lamination off the first batch of seats with relative ease. The remaining ply's are going to need some help as well - probably epoxy injection or something to stabilize the ply's. I am hoping that this experiment is successful, and that I do not end up having to go with all new plywood and bend new seats. I have about 100 to repair.

Any thoughts would be appreciated!

Edit: Also, I am using a Gast G588DX vacuum pump, 4.5 CFM, 1/4 hp.

[Peter Quinn]

I'm thinking Joe's tutorial is about as comprehensive as it gets, and the pictures are good too. There is a video on the wood whisperer site on bag construction where he attempts to make a bag only to discover it is a MAJOR PIA, and suggests perhaps using a pre made bag. I believe that was polyurethane which is apparently more difficult to weld than vinyl. For chair seats even a small poly bag would not be too expensive, though I suppose with a manifold splitter and shop made bags you could do multiples simultaneously which may be advantageous if making 100..

[Jon McElwain]

I had a feeling I would get that reaction to Joe's tutorial! You are correct, good tutorial and good photos. I have also seen the Wood Whisperer video - part of my hesitation is Marc's video!

Here are a couple of photos of the seats in question. They are bent plywood supported on a cast iron frame. The cast iron frames were left in place and the seats were brought to my shop.


Here is a photo of the top looking down on the seat after the top ply was removed and adhesive was sanded off.

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The photo below shows the profile of the seat. Pretty tight curve, thus the need for a vacuum press.

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[david brum]

Let us know how you do. I built one of Joe's vacuum press kits in September. Works great. I bought a complete bag from him (after watching the Wood Whisperer episode) but it would be nice to make up some smaller, cheaper bags for specific applications.

[Jon McElwain]

Will do. I am hoping to start gluing the bag up over the next couple of days

[HANK METZ]

I used fabric store vinyl cement too, along with cheap pvc pipe cement for a limited use bag, trouble is it won't die so I can build a "real" bag. You'll likely have to construct a support form for the lower portion of the seats to prevent distortion during pressing- this is assuming all you intend to repair is the seat top.

- Beachside Hank

[Matt Meiser]

I pretty much followed the Joe instructions on mine and a friend's. We laid a sheet of MDF on my workbench and drew some guide lines on the MDF instead of the material which seemed easier for making multiples, but probably not 1. We used fabric store material, the HH66 cement, and Joe Woodworker valves.

[Jeff Duncan]

Not too much to add except I think you'll be fine with the thin bag for what your doing. The main advantage for me with thicker bags is the resistance to ripping when you glue up panels with corners. For thin veneers on a rounded seat you should have no problem. You likely won't need all that much vacuum for your application either which is another factor for the thicker bags.

good luck,
JeffD

[Jon McElwain]

Not too much to add except I think you'll be fine with the thin bag for what your doing. The main advantage for me with thicker bags is the resistance to ripping when you glue up panels with corners. For thin veneers on a rounded seat you should have no problem. You likely won't need all that much vacuum for your application either which is another factor for the thicker bags.

good luck,
JeffD

Thanks Jeff! That makes me feel better about the bag. We bought some of the same vinyl, maybe a little thinner, that we used to put clear covers on some dinning room seats that had off white fabric a few years ago. Did the same thing with our breakfast table chairs. We've got three little girls and the fabric would not have lasted a week! Anyway, the vinyl has lasted remarkably well over the years. Hope the same will be true of this bag!

I anticipate some glue squeeze out on these projects as I'll need to get glue right to the edge of the veneer for a good bond. Any problems with glue getting on the inside of the bag? I assume it would simply peel off with little to no adhesion to the vinyl?

[david brum]

I anticipate some glue squeeze out on these projects as I'll need to get glue right to the edge of the veneer for a good bond. Any problems with glue getting on the inside of the bag? I assume it would simply peel off with little to no adhesion to the vinyl?

You're right, it comes right off. BTW, what kind of glue do you plan to use? I just finished a project and used Joe's waterbased veneer glue. It's very easy to work with and only required an hour in the vacuum bag.

[Jon McElwain]

BTW, what kind of glue do you plan to use?

I was planning to use tightbond original. I am hoping that the elastic nature of the glue will help it maintain the hold over the long term. Whatever they used originally on the seats has turned powdery and it is loosing its adhesion. I'll take any thoughts on it though.

[Jon McElwain]

I pretty much followed the Joe instructions on mine and a friend's. We laid a sheet of MDF on my workbench and drew some guide lines on the MDF instead of the material which seemed easier for making multiples, but probably not 1. We used fabric store material, the HH66 cement, and Joe Woodworker valves.

Matt, did you guys construct any sort of vacuum channels to make sure you have even suction over the entire work piece?

[Matt Meiser]

We just made the bags so far, or at least that's all I got done. I'd previously made, and then later sold, a different setup. For that, I used a melamine board and cut a grid of 1/8x1/8" grovves on both sides with holes at several intersections to distribute the vacuum. Then I made project-specific cauls with the top corners rounded to protect the bag. That was all for flat veneer work.

[HANK METZ]

Matt, did you guys construct any sort of vacuum channels to make sure you have even suction over the entire work piece?

Not Matt here, but I use onion or potato net bags placed under the suction nipple and it works just fine, good pulldown all over.

- Beachside Hank

[Jeff Duncan]

You should be careful when removing the parts from your bag. The glue squeeze out, (at least with yellow glue), will harden and can produce some razor sharp edges.

You can also buy netting to assist in removing the air. I use it on occasion, but to be honest with wood veneers I haven't found it to be an issue. Maybe on a bigger panel, but on the small parts your doing I don't think you'll have to worry about it.

good luck,
JeffD