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How long in vacuum bag

7/8/16       
John Bishop  Member

Website: selectwoodworking.net

I have some panels to lay up. We have a large vacuum bag set up and a bunch of different sized bags. I am in a spot where I need to layup multiple panels in the bag at the same time. I donít do this very often. How many panels do you guys put in a vacuum bag at the same time? The sub straight is 11/16 MDF, the face veneer is a recon 10mill with paper back. The bottom veneer will be Obeche used as a second for a balancing sheet. I use Tite bond cold press veneer glue and have had good luck with that glue.

Itís hot here in Cincinnati right now as well as very humid; I know all these variables affect my glue time in the bag. I was considering doing 3-5 at a time. Veneering the both top and bottoms on multiple sheets all at the same time if its possible. I will use top and bottom cauls which are typically ľ Masonite hardboard cut just slightly larger than the sheet. Which in this case will be typical full 4 x 8 panel.

I know we will have to wrestle them to get multiples into the bag, I am also concerned about the open time on the glue to be able to get all the sheets with top and bottom veneers into the vacuum bag and get it all aligned while staying in the recommended open working time of the Tite bond cold press glue.

Any advice would be greatly appreciated especially the recommended time in the bag.

Thanks a lot

DJB

7/11/16       #2: How long in vacuum bag ...
Charles Wright  Member

Website: http://www.northcreekwoodworks.com

We use a hot press for flat work, but we do dozens of curved panels per day in a vac. bag. We do 2-3 at a time and allow 1 hr after pressure is reached. We use a PVA. After they are removed you have to stack and weight them for at least 24 hrs until most if the moisture is released.

8/5/16       #3: How long in vacuum bag ...
Keith Newton

John, I use epoxy for most of my veneering, and especially when doing curved work, and needing plenty of open time. Epoxy doesn't contain any moisture and acts as a lubricant allowing the parts to slip while the bend is being made.
The Open time can be long by using slow cure, and keeping the temperature low while working.
Also mixing small batches that can be spread quickly so there is no heat buildup from the depth in the container.

I usually mix in 16oz solo cups, and pour it out ahead of the paint roller onto the substrate, rather than into a roller tray.

I always spread a little epoxy onto a scrap kept outside the bag to monitor when it is finished by touch. 6 hours is about normal. I live in my studio at the shop, so late night shut down is not an issue for me.

I buy the 1-1 ratio epoxy from https://www.fgci.com , which is much more reasonably priced than some, and higher viscosity to start with, but I still add some colloidal silica to thicken to about latex paint consistency.

Before going with epoxy, on some projects I was doing like what you described, I had buckling on the face and splitting on the outer due to too much friction from other glues. Epoxy is very slippery, and isn't affected by any slippage as long as it still has enough flexibility to do so.

I've done projects that took over an hour to get spread before starting the vacuum. But the sky is the limit if you are working in winter, you could take all day if the temperature is cool enough, then warm it up after everything is in the bag and under vacuum. Epoxy needs heat to kick.

https://www.fgci.com

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