Posted by: @jamesbisset

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We’re trying to design assembly techniques that emulate methods Gibson pioneered in the 40s,

You can do a lot better than that!!

😉

Ref variable 11;
I’d be worried that the separate veneer leaves would firstly stick together as the pump is switched on, then relax (as you switched the pump off) and maybe separate a bit, then stick, then separate, then stick (etc).

You might end up with a bubbly surface, or one in which the veneers weren’t fully glued together, and would maybe separate / fail 8n future?

@jamesbisset 

Is it the speed with which the wood is being forced that causes the stress?

I really do think that you might be onto something there and worth a try.

Edit, I've just read TV's concerns.

Are you able to adjust the vacuum at all. I'm thinking increase the vacuum in steps building up slowly to full sook, rather than switching off and on.

@tv101

Posted by: @tv101

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I’d be worried that the separate veneer leaves would firstly stick together as the pump is switched on, then relax (as you switched the pump off)

I reckon the critical factor will be how airtight the bag is. If it doesn’t lose much air in 5 mins then (slowly increasing) pressure is maintained.

And the technique would only work if we used Darren’s recommended glue which takes 8 hours to bond.

That’s what the Bagpress needs - a volume knob!

Posted by: @robin

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Are you able to adjust the vacuum at all. I'm thinking increase the vacuum in steps building up slowly to full sook, rather than switching off and on.

Yup! A volume knob! I can’t resist it — is full sook 11?

@jamesbisset

Maybe you've just been unlucky with that veneer James. You'll probably be okay with the next one although given that you don't have unlimited wood it's always worrying to try the next one without trying to find a solution to the problem. 

Thanks. Enjoyed that wee Gibson video.

🎸🙂🎶🙏 

@jamesbisset 

ha ha I’ve been using car body filler for years to cover up my poor mold making, so does that mean I’m a professional 

I’m still accumulating little bits of advice from across the internet. Here’s one from Airpress:

“When a knife cut veneer (0.6mm) gets wet with glue - it expands. When it expands it buckles and wrinkles. Because of the flexible nature of the vinyl, if you press with the veneer against the inside of the vinyl bag, the atmospheric pressure outside the bag can actually make the wrinkles worse (rather like pinching the skin on the back of your hand).”

OFFS! Turns out there’s something called Veneer Softener!

Who knew!

Everybody but me, apparently.

I think you can get something called "veneer softener"?  Might help??

(I'd not heard of it either)

@jamesbisset 

I thought epoxy was developed for gluing wood veneer during WW2.

Before I continue with this enthralling build, I’ll just clarify that veneer softener is normally used to flatten veneer that is warping and curling. Once applied, the veneers are wrapped in paper towel or similar and then stacked between platens. A vacuum press applies pressure. After an hour or so, the wet paper is replaced with fresh dry paper and the process continues.

Do this three or four times.

While some folk may have used veneer softener on laminated guitar tops, it doesn’t look like this process lends itself to trying to glue the veneers at the same time.

And while we’re talking about glues, here’s some useful comparisons:

I decided to try and simplify things by bending and gluing the sides, which only require bending the lamination in one plane - not two.

We chose the side with the least curves too:

I had pre-assembled the veneers for both sides - this side had the slightly shorter set.

To prevent the veneers gluing to the former, Mark wrapped it in clingfilm. I spread the glue on the three thin (knife-cut) veneers, stacked them and then finally laid the face (sawn) veneer on top.

Mark helpfully pointed out that I’d glued up and stacked the veneers for the longer cutaway side.

Controlled panic.

Mark wrapped the cutaway former in clingfilm (very quickly) and then we started taping the lamination into place. There was no way the sawn veneer was going round that venetian cutaway.

I should have built a little shaped insert, shouldn’t I!

Instead I grabbed a nearby Pritt Stick and started pushing into the cutaway. Fingers would have broken the veneers, said Mark.

Mark started spraying water. The wood began to yield reluctantly. Mark rushed off and came back with a hot air gun. I tried to hold the Pritt stick and not get my fingers cooked. Slowly the veneers bent into shape. At some point Mark muttered something about fabric softener (?).

Then we wrapped it as tightly as possible in veneer tape and stuck it in the vacuum press.

For some reason, there are no photographs of this.

But the next morning:

Next day, the other side was a doddle by comparison.

Two surprises.

1. I just watched a 20min video on different types of glue
2. It was actually quite interesting and informative

Two questions.

1. Which glue did you use on the sides?  I'm guessing the Bagpress-recommended Resin glue of some kind?
2. How long did you leave it in the vacuum - a full overnight with the vacuum pressure maintained?

That's looking like progress Mr B.

🙂

@tv101 We used a two-pack urea resin. I doubt we’d have had time to correct my foolish error otherwise. And yes, left it overnight in the bag.

@tv101 

When I’ve glued veneer I dampen the non gluing side to even out the effect of moisture in the glue. Don’t know if this is usual or not but I always think out of the box.

@jamesbisset 

Ive been following your build with interest and trying to get my aging brain cells around the problem.

Once you have a concave mold made for the front and back would it be possible to make a convex one to fit inside using say plaster of Paris over cling film, body filler or even fibre glass sheets for more rigidity. This could be weighted inside the vacuum press to provide even clamping pressure all over. Veneer could fit inside both halves.

I’ve read that some antique instruments have been restored in this way using a steam press. Also wondered if you have tried using a heat blanket to dry shape the ribs before gluing. 

@rocknroller912 The adventure with the cutaway side suggests that the next stage in trying to force sawn veneer into a compound curve, without splitting along the grain, is gong to be using water in some way.

Using a second mould to trap the veneers before applying pressure is the technique used in the Making a Laminated Hollowbody book, using plaster of Paris. The author parks his pickup truck on it. 

But we don’t have any problem applying pressure. The vacuum press is amazing. It’s just persuading the wood to bend across and along the grain at the same time without splitting that’s the challenge.

I’m scraping out two new 12mm deep moulds right now. But this time I’m trying to imagine how the grain is going to respond to these bumps and dips. The horns and the waist are the obvious stress points.

Thinking out loud here: In 3D modelling, you usually build the shape and then wrap it in a texture - often a high res tiled photo of wood or bricks or whatever. You could probably use a 3D modelling app to ‘loft’ the guitar top, and then apply a striped material to the surface. The gaps between the stripes would be a simple indication of where the stress would lie.

But I’ve been down enough rabbit holes already...

*thinks some more* Maybe laying a tea-towel down on the mould might reveal something?

@jamesbisset 

I thought one of the comments was about wrinkling cased by the bag pressing, so I thought a solid outer mold would stop this.

I haven’t read any books on this it was just an idea I had. Hand held Steamer will soften veneer to press into shape. I’ve done that on some repair jobs going round edges.

@jamesbisset my dad had a 1965 es330, intersting stuff that