Filling it in is so much easier.
@tv101 But weirdly, much less forgiving.
If you cut out the various layers assuming that you’re going to be shaving them back, you cut them oversized. You can also cut them out quickly and roughly, because it all evens out in the planing and sanding.
If you cut the boards exactly right and then fill, your saw cuts will need to be much neater, unless of course you’ve got a CNC – ah...
Jack of all trades and master of my own destiny. It’s only a small destiny.
First hiccup.
It’s useful to think of a mould for a vacuum press more like a wrap, which is why my extensive copy routing for the sides fell at the last hurdle. Your lamination will wrap round everything, not just the bits you want it to.
So cutting side moulds based on half the body profile isn’t quite good enough.
Jack of all trades and master of my own destiny. It’s only a small destiny.
Your lamination will wrap roundeverything, not just the bits you want it to.
Looks like more learning curves.
First hiccup.
It’s useful to think of a mould for a vacuum press more like a wrap, which is why my extensive copy routing for the sides fell at the last hurdle. Your lamination will wrap round everything, not just the bits you want it to.
So cutting side moulds based on half the body profile isn’t quite good enough.
I'm going to make an admission here ... I'm watching this with great interest, not just because its Mr @jamesbisset, but also because I fancy having a go at something along these lines myself in the not too distant future.
A couple of years ago (when I first had this mad idea), I bought the Bagpress kit from Darren which has collected an impressive layer of dust over it in my workshop since then, and have some veneer pieces ready and waiting too.
I'd worked out each side would have to be slightly bigger than half the body and would then need splicing together. But I hadn't had the genius idea of using filler to smooth the carve, nor worked out how to solve the other minor hiccups that James will share with us shortly ...
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Moulds made. Veneers book-matched and joined. it’s time to get sooking no blawing.
But first, a test press.As I’ve only got enough veneer for the actual build, Mr Bailey volunteered a piece of book matched 1.5mm maple.
We put it in the press bag and watched the veneer form itself against the mould, and then heard a couple of quiet cracks.
What’s all that about no sound in a vacuum? In Ayr, everyone can hear you scream.
Jack of all trades and master of my own destiny. It’s only a small destiny.
We tried another piece of joined veneer, this time using the back mould. It happened again.
On the plus side, look how closely the veneer has followed the mould. Even the poorly finished ridge that I didn’t see on the lower bout is clearly exposed. But so are the cracks.
This picture also demonstrates the result of having concentric equidistant contours in your lofting layers. It’s basically a straight line down rather than an elegant concave curve.
Jack of all trades and master of my own destiny. It’s only a small destiny.
Both pressings were aborted. I now had two slightly bent veneers with cracks. To continue the testing, we took the two cracked veneers and put a leaf of cross-grain poplar in between. Then we glued them up and put the three ply lamination in the press.
The result is cool, and so close to the desired result, but we haven’t really learned anything from this test. Cracked veneers fit into the mould better than whole ones do - who knew!
So I went home and made a new, shallower back mould.
Jack of all trades and master of my own destiny. It’s only a small destiny.
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Hi James, Just wondering if it would be better not to tape the veneer to the mould and just allow it to slide into the hollow. 🤷🏻♂️
🎸🎶🙂🙏
🗝️ "Life's what you make it"🗝️
And so I returned with a new mould made with 6 layers of 2mm MDF rather than 5 layers of 3mm MDF - so approx 12mm deep rather than 15mm.
We were running out of fancy veneer we could risk on tests.
So this time we made 3 layers of 0.6mm veneer (the thin stuff you would normally build up behind the thicker face veneer).
- Trimmed the edges so there wasn’t a large area of flat in the corners which might resist the veneer pulling into the mould.
- Taped the lamination to the mould only at top and bottom centres.
- Wet the outer and inner face with a light spray.
- Added veneer tape across the width of the lamination to prevent splitting.
- And this time the lamination crumpled up like a hankie.
Jack of all trades and master of my own destiny. It’s only a small destiny.
- And this time the lamination crumpled up like a hankie.
You're certainly having challenges there. Do you think that wetting it is the problem there. I think I remember Darren using non water based glues, maybe for that reason.
Conclusion?
I can’t afford the time or the wood to do a full set of controlled experiments. There are too many variables:
- Mould depth
- The curve of the carve
- Thickness of veneers
- Number of layers
- Variety of glues
- Taped in position or free to flex
- Moisture content of veneers
- Dampen thicker veneers only?
- Full sheets or trimmed edge
So far, I found one YouTube channel which deals with the same issues.
https://www.youtube.com/@chriswalsh4027
He cuts a thin slot in from the edge (or sands open the join between leaves) which allows the facing veneer to close up instead of buckling. He intermittently releases the vacuum pressure to try and iron out ripples in the grain as they appear. Most significantly, he only does these things when using maple veneers.
So there’s another variable right there:
- What is the facing veneer made of?
So, while I let all these thoughts keep me awake at night, I’m taking a third pass at getting the moulds right, and then I’ll probably do it by the book. Y’know, that book.
Jack of all trades and master of my own destiny. It’s only a small destiny.
@robin I used Titebond for speed because we were only running tests, but I reckon the combination of Titebond AND spray AND thin (and a little warped) sacrificial veneers all contributed.
Jack of all trades and master of my own destiny. It’s only a small destiny.
Mr @darrenking is still here occasionally ...
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We’re trying to design assembly techniques that emulate methods Gibson pioneered in the 40s, but without building a factory full of heavy engineering.
Here’s the best tour video I’ve seen on the Memphis factory with full details on the veneers (rotary cut), the pressing (heated), the construction, the neck join of the ES series...
The Gibson press applies 860kg pressure at 120°C for around 1m 45s. Someone with more brain than me can work out how atmospheric pressure compares to an 860kg weight, but the Bagpress takes around 2 minutes to fully form a 3ply top. The only difference is that it’s not steaming the veneers.
But here’s a thing - I’ve spotted another variable:
- Time
It’s quite relentless the way the Bagpress grips the lamination and draws it down. What would happen if I switched on the pump and then switched it off after 30 secs, waited 5 mins and then switched it on for another 30 secs and off again, and etc.? Is it the speed with which the wood is being forced that causes the stress?
Jack of all trades and master of my own destiny. It’s only a small destiny.