Michael Collins bends laminated sides

[ken cierp]

My point is that this process proposes that gravity pushing in from the left and/or right to get around the cutaway -- I still am not getting it, what compresses the laminations not to each other but to the vertical surfaces of the form? A full covering bag (which I've used) smashes everything downward pulling on all that is in the way of the bag. Not saying he does not do this -- but just trying to make sense of the procedure on a scientific level.

[Dave Bagwill]

I don't know what else to say - if they are clamped in place, and cure in place, they will hold their shape, right?

I've seen vids of folks not even using the bag, just bending and clamping lams over or into a mold and that worked fine as well. Lots more clamps in that case; in Michael's case the bag takes the place of all the extra clampage.

[John Link]

In his book and the video too Michael Collins shows an older method he used before acquiring the vacuum setup. Indeed it involved a rigid female form into which he laid the glued lams. Next he applied a flexible male portion that he then clamped every inch or so to hold the layers in place AND to apply proper pressure for the glue joints between the lams.

Ervin Somogyi uses a similar setup, except his flexible part is more elaborately constructed, his rigid side is configured as male, and he uses epoxy instead of urea formaldehyde glue. Somogyi uses only two plys and it looks like they are thick enough that he bends them on an iron in the ordinary fashion before laminating them.

The Collins vacuum setup Dave shows uses a male configured rigid form, just like Somogyi's. But the vacuum bag obviates the need for any additional pressure on the glue joints via Somogyi's elaborately hinged covering caul and multiple clamps. As long as the bag is held - somehow and any how - in the desired configuration until the glue has hardened, the final product should emerge configured as desired. As Dave and Michael say, the vacuum takes the place of all the extra clamps. My guess is it does a better job because the clamping pressure is more evenly spread.

I have a set of sides Michael laminated. When I compared their contour to that represented on his plans, it was clear there has been no spring back, including the Venetian cutaway side, which has a very sharp bend in it.

[ken cierp]

For me this one is "doing is believing" I have some vinyl here in the shop so I'll make a bag etc. --- the cutaway without a cauls seems impossible, I made forms for a couple of pro's and per spec's they had mating cauls to make sure the profile was tight --- I'll see. Dave have you ever used corrogated cardboard for the breather layer?

[Dave Bagwill]

Never used the cardboard, but it might work.
An experiment would be good. You might also want to contact Michael via email, he seems glad to answer questions.

info@collinsguitar.com

I'd be real interested in how he addresses your further concerns.

[ken cierp]

Just to be clear, my skepticism is only the result of the goofy stuff that runs through my brain – I am just thinking out loud here – I am sure what Dave and John posted is perfectly accurate and for sure I know Collins is a fine and respected craftsperson.

[John Link]

Ken,

I agree with your opinion of Michael Collins and can only add that he has made an invaluable contribution to our understanding of how the Maccaferri-Selmer type instrument was and can continue to be produced.

From my several views of the video, I feel confident that the breather layer is an important part of his approach. The bend on the gypsy cutaway is especially tight and looks like a real challenge.

I just got my venturi vacuum kit from Joe Woodworker, and am anxious to get it assembled. (Had a six day bout with A-fib that has put me behind.) The next parts I need to acquire are bags and breather layer. Anyone suggest better sources than Joe Woodworker?