Vacuum press for glue up?

[Christopher Clark]

Hi all,
I'm gluing up 4 piece locking miter legs. [Stickley quadrilinear]
Right now I'm using clamps. I don't have any experience with vacuum presses and I see they are used all the time for veneer and bent wood laminates.
Would this be a good application for a vacuum bag?
thx, Chris

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[Robert Engel]

I think the best application for a vacuum is large panels laminations, veneers, and bent laminations.

[Marty Schlosser]

I have a vacuum press, but feel it's not the optimal clamping system for this particular task.

I'd suggest you continue to use clamps, but add using cauls. Doing so would allow you to use far less clamps, and therefore save yourself a lot of time.

[David Pascoe]

No, for several reasons. You would need a custom made bag for that very long fabrication, and that would be quite expensive. Secondly, you can only get about 29 psi out of reasonably priced vacuum pumps. You'd need a very expensive pump to pull anything more. Look at the size clamps you are using !!! I'd bet well over 200 psi is being used. Thirdly and most importantly, you're gluing up 4-way miter and adjusting alignment with the clamps. With a vac. bag you get NO such control with vac. system. Bag pressure would collapse your glue-up

[Christopher Clark]

Thanks for the responses guys. I'll make some platens/cauls and that will reduce the clamps required.

[Steve Jenkins]

Whenever I glue up a miter like that I use clear packing tape. It will stretch to give good pressure and if the miters are accurate they will automatically square up.
As far as the Vacumn press the maximum pressure you can get regardless of pump is 14.7psi at sealevel. The 29 is inches of mercury.

[Brad Shipton]

I built clamp devices out of angle iron to glue up a bunch of lock miter box newels. That reduced the number of clamps to 8 per 60" box newel.

The vacuum press will not work very well in this case. To use it you would need to build some sort of device to apply equal side pressure as the vertical pressure is applied, and that would be challenging. Even then, I doubt you would be able to equalize the pressure on all four sides, and that could throw the boxes out of square.

[Steve Demuth]

Christopher,

I read all the earlier replies, and disagree with most of them. Quite a few are factually wrong.

Getting a bag that's a good fit could be expensive proposition, so that comment I agree with. Although, I have had very good success for some odd shaped glue ups using plain 8mil poly sheeting (I also use 2 gallon ziplock freezer bags for smallish jobs, and they work brilliantly). If I were doing those legs, I would consider just wrapping 3 layers around them in a continuous wrap, sealing the edges with teflon tape and giving it a go. I'm betting it would work just fine.

Beyond that, any good vacuum system will give you at least 10 psi, and 12 psi is quite attainable. 29, as suggested by one post is impossible - air pressure at sea level is less than 15psi. So, if your legs are 4" square and 50" long, you'll get 2000lbs (yes, 1 ton) clamping pressure evenly distributed on each of the four faces. If your joinery is any good, that'll be plenty. And despite what you read in another post, it will be on all four faces. Gas pressure is equal in all directions. Nor will it collapse your leg - these are after all lock meters, so you've got good alignment surfaces, and, again, the clamping pressure is equally distributed on the whole area of each joint.

[Wayne Lomman]

Steve Jenkins way is best if you like easy and simple. It works and costs almost nothing. The principle works in any situation like this no matter what size. If tape isn't doing it, use cheap ratchet straps. If you like engineering for the sake of it, do it one of the other ways. Cheers

[Christopher Clark]

Thanks again for all the responses. I ended up using a caul to make sure the thin edge was pressed. I put them on the 'show' edge. That's where I was most concerned. Locking miter joint like this one have a side that needs the clamp and the other side 'goes along for the ride'. I believe even pressure is more important than a lot of pressure. You're not trying to squeeze the glue out of the joint. Steve, I'll fool around with the vacuum option on some smaller pieces to see if it's doable. Vacuum bags are easy to make. I'm looking at canoe builder sites for inspiration. Here's the clamp up with hide glue.

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[Brad Shipton]

Found a picture of the jig I mentioned. I had almost 30 to make, so the time making a jig was worth it.

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[Christopher Clark]

Brad, that looks like a good option. Thx for the pic. Chris