Veneering Upgrades

[John TenEyck]

I use mostly shop sawn veneer for my work. Sometimes the veneer I make is not all exactly the same thickness. They may not be off by much, a few thousandths, but that's enough to give uneven contact between the veneer and substrate if it's on the bottom of the substrate, against the hard, lower caul. I had a couple of seams open up a year or so ago that I suspect was caused by that.

The solution is to put something compressible between the bottom caul and veneer assembly so that the pressure will be uniform regardless of any variations in thickness of the veneer. But you can't just use any old piece of rubber, etc. The material has to have the right compression characteristics to work with the approx. 14 psi of the vacuum. And the material should also be reusable, durable and, of course, not too expensive. After some looking, I found what looks to be a very good material at McMaster Carr. It's a 1/8" thick natural gum foam sheet (PN 860K41), in medium compression which has 25% compression at 13 psi. That means it will have about 1/32" "give" at full vacuum. It also has quick recovery after the pressure is relieved. It cost about $5/linear foot at 36" width.

Here's a picture of a piece that I cut to fit one of my lower cauls.

https://lh3.googleusercontent.com/-QnsI4gfYC-k/V1AspdBBMwI/AAAAAAAAfYI/9hujYuntN-QpkbUqWz5HKvD9QYSOkB_dACCo/s400/IMG_4609.JPG

I put a sheet of plastic over it to keep any glue squeeze out off of it.

https://lh3.googleusercontent.com/-FNP4kVbxjyQ/V1Asp_SLABI/AAAAAAAAfZA/O7e5VVrMWW854kBpmCwYKYLhQ_8Wkvy_gCCo/s400/IMG_4612.JPG

In the bag it looked like this. Yes, a home built bag. 20 mil vinyl glued with PVC pipe cement. An equally impressive end seal system. It's so simple it works.

https://lh3.googleusercontent.com/-RrbgSORBgOI/V1AsqX0TypI/AAAAAAAAfZA/wcBx7A6FR0c0hs1QcwEZV3BsZlm8YFpbACCo/s400/IMG_4613.JPG

https://lh3.googleusercontent.com/-32NFLq6x4UM/V1Asq4xvClI/AAAAAAAAfZA/BUkIG-m3plIKgp7JHYdsHIoYq4WizO_jACCo/s400/IMG_4615.JPG

Did you notice the heating blanket under the lower caul? I use Weldwood Plastic Resin Glue for veneering shop sawn veneer. It takes 13 hours to cure at 70F, but only 3-1/2 hours at 100F. If I put one electric blanket under the lower caul and another on top the temperature will get to a little over 100F in about 5 hours.

https://lh3.googleusercontent.com/-Nl3vwW_xAkc/V1AsrIxBPmI/AAAAAAAAfZA/J3LodlXHrhoGy_eFvkqCE5Ucf3sCg0rPwCCo/s400/IMG_4616.JPG

I leave it under vacuum for 5 or 6 hours to be assured I have given it enough time at temperature to cure, but now I can do two pressings a day instead of only one.

When I removed the pieces from press you could see where the plastic sheet had stretched as the piece was compressed into the rubber foam.

https://lh3.googleusercontent.com/-eNJdlLxqm70/V1Asr1UHVPI/AAAAAAAAfZA/cGTJaTVWDHIqOaReW-xixmdpNRPWJ0JlgCCo/s400/IMG_4618.JPG

The foam had completely recovered so it is reusable.

https://lh3.googleusercontent.com/-wzINtic0U_I/V1AssMD8WRI/AAAAAAAAfZA/agKvafcv3LMLDlENJnAu-pAL8YUZqGWvgCCo/s400/IMG_4619.JPG

Seems like a winner. If you use shop sawn veneer, or mixed commercial veneer that's not all the exact same thickness, you may want to consider using it, too.

John

[Stew Hagerty]

It's a 1/8" thick natural gum foam sheet (PN 860K41), in medium compression which has 25% compression at 13 psi. That means it will have about 1/32" "give" at full vacuum. It also has quick recovery after the pressure is relieved. It cost about $5/linear foot at 36" width.

Thanks for the tip. However, I went looking and the part number you gave was incorrect. Just a typo though... It's actually: 8601K41

[John TenEyck]

Oh, thanks for the correction Stew.

John

[David Zaret]

normal PVC cement works on vinyl sheeting? learn something new every day...

[Mike Henderson]

I've used heavy sail cloth and carpet padding (not at the same time) and both seemed to work pretty well. I'll look into your suggestion. Mostly I use commercial veneer so there's not a lot of difference in the thickness.

Also, I had a bag closure like yours one time, but I much prefer the C clamp style. It's fast and it's lightweight. But I think you can only use the C clamp style on commercial bags. If you fold the area around the bag when you glue it, that part of the bag is thicker and that prevents the C style clamp from working.

Mike

[Mel Fulks]

John ,just wondering if you put glue on both surfaces or just one? I dont use or own any vacumn bag equipment but have
had good luck with that glue mixed thin enough to immediately drip ,not stream, off stirring stick and applied to both surfaces. Was shown to me many years ago , works with little pressure.

[Gene Takae]

Thank you for the excellent tip and for sharing your veneering setup.

[Gary Muto]

Thanks for sharing. Time is money!!

[John Blazy]

That is really helpful to me too. I laminate glass and plastic composite panels for a living, and only lately have had to deal with uneven surfaces to the point that I was considering some kind of medium density foam that would be reusable. I have often used 1" blue styrofoam when doing uneven surface clamping for same effect, but Thanks a ton John for the McMaster source. I love that drool catalog.