Vacuum lamination: Form inside vs outside the bag

[Alan Kalker]

Getting a large form inside the bag can be clumsy and dowright difficult. I've recently seen an "outside technique" where the form is kept outside the bag. Obviously clamps would be involved. I'm wondering about others' experience using the outside technique, what the advantages and disadvantages are, when they would use it and any tips or tricks they can offer. Thanks

[Kevin Jenness]

I do it when the form is too big to get in the bag easily. I use a mesh (evacunet?) from vacuum pressing systems over the caul and laminates to evacuate the air evenly. A dry run is advisable. Clamping may be necessary, depends on the situation.

[Alan Kalker]

I do it when the form is too big to get in the bag easily.

I assume you apply the clamps after the vacuum has been applied or otherwise it would be difficult to evacuate the bag fully?

[Jamie Buxton]

I assume you apply the clamps after the vacuum has been applied or otherwise it would be difficult to evacuate the bag fully?

No. Think of it this way... The form establishes the curve. The clamps connect the laminates to the form in a few places. The vacuum bag ensures the laminates are close together while the glue cures.

There's no worry about evacuating the air from the bag. Air molecules are teeny tiny, and will move through small openings to get from areas of higher pressure to areas of lower pressure.

[Mike Henderson]

I haven't done that yet, mainly because I've been afraid of damage to the bag. What I've done instead of that is make a two part form and use clamps. Let me know how it goes for you. If you find it easy and safe, I'll try it.

Mike

[Kevin Jenness]

Any clamping is done to pull the laminates down onto the form prior to pulling the vacuum. If the form is gentle enough, hand pressure may be sufficient. The netting is to avoid air pockets that fail to bleed out, serves the same purpose as a grooved platen in normal use. Single form bending with vacuum is way less work than making mating forms in my experience.

[Larry Browning]

are there pictures or diagram drawings of this? Cause I'm not seeing it in my head from the descriptions given so far.

[Mike Henderson]

are there pictures or diagram drawings of this? Cause I'm not seeing it in my head from the descriptions given so far.

No pictures but let me try to explain how I understand it.

Suppose you were making a rocking chair rocker (or skids or whatever you want to call it). You might cut a board of proper thickness into 1/16" strips (maybe 1/8"). What you want to do is glue those strips back together, while at the same time bending them into the shape of a rocker. What I've done in the past is to put them on a form and with lots of clamps, clamp them to the form until the glue sets. When set, the glued up wood will hold it's shape (pretty much).

Another way to do this is to put the strips into a vacuum bag (with glue between the strips). Pump the air out of the bag so the bag is "clamping" the strips tightly together. Then, using maybe two clamps, bend the wood in the bag onto a form that is in the shape of the rocker.

This uses less clamps and gives a very even clamping pressure across the wood. If you have a "sleeve" bag (long and narrow) this should work even better.

I hope that's understandable. If others have a different view of what's meant by the OP, please post.

Mike

[Kevin Jenness]

That's basically it, but pulling the laminates down to the form has to happen prior to pulling vacuum. I think you can find some photos on the vacupress site.

[Larry Browning]

Man! was I way off! I was thinking he was somehow gluing veneer to a substrate using a vacuum pump with the pieces outside of the bag using clamps of some kind???? How was that gonna work????? I needed to see pictures!!!!!
I think I will just leave now