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Discussion in 'Tele Home Depot' started by preeb, May 3, 2011.
A couple more make a quinte +1
Now to back track a bit.
Here is the making of the mold using plaster of paris.
I hope I am describing this coherently, I am a bit sleep deprived at the moment.
First I covered the cast with plastic tape. Next I mixed up some P of P and poured it into the holes. Vibrate the p of p into the negative space of the cast and ...
And after removing the cast, I am left with the positive mold. It is then ready to bolster or add to compensate for spring back.
There are always some areas to fix like this "worm trail" and of course the abrupt ridge needs to be filled and sanded smooth.
More refinement of the mold. In this case I am using automotive bondo. I also use some fiberglass mesh tape so I keep the "layers" and the exact thickness even. And after lots of sanding I am left with this ugly but rather smooth and effective positive.
Next I cover the master mold with tape (don't use masking tape like shown here, bad idea). And pour in plaster. In this case I used a product called Rock Hard Putty.
From this I got a negative of the master. And from this I made two working molds. I then refined the molds a little by filling in the imperfections and I have these molds to press plates.
Just for clarification, in the vacuum bag each of these will be used to press a plate. So the result will be one plate per mold. This is of course different than the mold that has a negative and positive.
A pressing issue
Now it is time to press the plate. The glue is mixed and the veneers are laid-up in their order. Then the two cross wise core sheets of maple get glue on both sides. The under side is placed down and the core sheets get laid on it and finally the show side.
Pressing the plates took a lot of R&D, trial and error and many many failed, wasted products. But for the ES product I had already done most of this work and these first plates turned out pretty good.
I have a method where I place the veneer inside of bleeder cloth and plastic sheet to keep the bag clean and to help evacuate the air.
Fantastic! Well researched and well made! Bravo!
One point about the Gibson current method of construction is to be aware of the difference between custom shop editions and standard production.
Also, with either vacuum pressing or heat pressing, I'm sure the plates acclimatize to the same moisture content, and since the inside remains unfinished, it probably continue changing.
I once measured the same Stradivari 'cello in England and in the USA and even on this 300 year old instrument the back was 3mm wider in damp old Blighty than in the USA and needed gluing up (not too strongly) because the joints had popped due to the change in humidity the wood had taken on.
It is well known that overheating wood weakens it and with the vacuum method, there is no chance of that.
More, showing the loading of the bag and massaging out the air pockets. When I said I don't use heat I meant "high heat" because I do use an electric blanket with a fiberglass insulation blanket that brings the bag up to 110 degrees F.
I usually leave the vacuum running overnight but 6 hours seems to be a minimum to set the glue.
Once cured, I take the mold out of the bag and flip it over and drill the registration holes through the plate for future jigs.
The pressed plate is ready now to be made into a top or back.
Ken, wow..... thanks for going to all the trouble of taking pics of the process, and explaining things. Makes me appreciate all your work even more than before. Definitely anxious to see Preeb build this.
Mike aka captainbraindamage
Fascinating stuff, guys. You two are birds of a feather when it comes to meticulous R&D.
Ken, are cellos & doublebasses made with laminates in a similar fashion? A violin or viola is one thing, but I imagine finding a single piece of good lumber big enough to carve plates so large is next to impossible.
Another thanks. I have a barely-healthy love for my Heritage 535. This is making me appreciate it even more - and appreciate the contribution that you guys are making to this great forum.
Could the springback be calculated, CAD'ed and a new mould carved by CNC?
Just curious, I like to see this done the traditional way.
Skip to 4:20
I was cringing watching the guy at the router table with the rabbeting bit.. I forgot to count his fingers...
That's where herringbone comes from. Mr. Herring in Kalamazoo got his fingers in there and they quite liked the pattern.
Maybe that's the station you get sent to if you annoy Henry?
Thanks. Do you make or repair violins? Or just measure them
I got some sleep now so I should be a little more dapper:
Once glued and cured the plates do behave like solid wood somewhat by expanding and contracting. But since the glue joints are very good it holds the expansion to a minimum. Plus once assembled, as you will soon see, the center block makes it into a solid body for about a third of the entire thing.
Violin family instruments , except flat back basses are designed to be able to expand across the grain. There is no cross grain gluing of braces or anything. Flat back bass backs encounter a tough life because there are cross braces that prevent the free expansion of the back when the humidity rises. This keeps luthiers in business for sure.
I have a dehumidifier in my shop to keep the veneer sheets all equal.