vacuum clamping sides?

Maldoror

i'm building molds for my first guitar build...which is based on the charle plans.
i have a vacuum veneer press and i'm wondering how i should clamp the sides so that i can build the proper molds.

i guess my options are the traditional female mold with caul and clamps, a fox side bender set up, a long narrow vacuum bag clamped down onto a mold a la the Collins video, or a form that will go totally inside the bag.

should i use the collins method since i have the press...even though it can get annoying?
would a fox bender be useful for laminates?
any advise on the way to go?

Craig Bumgarner

I use a female mold, a matching semi-rigid cawl, clamps and an individual 20x20x100mm cawl for each clamp. These smaller cawls have a slight concave on the side that goes against the semi-rigid cawl which insure pressure full width with one clamp. This way I have clamps on one side only and the other side lays on the bench. The cut away area can get a little crowded so I have evolved a special clamp that takes the place of 8 for that, but regular clamps will do.

I've tried to think through other methods like vacuum clamping but can't as yet see how it would be any easier than the simple method above. Once the veneers are cut and glue applied it takes me ten minutes to clamp up.

(writing from iPhone, more details Monday if needed)

CB

Maldoror

do you have pictures posted anywhere? i'd like to hear more of or see the cutaway clamp.
i think i'll go ahead and get started with the female molds.
your guitars look great. thanks for the advice.

Craig Bumgarner

Here is a picture I took in August. It is not the greatest, but it shows the clamps and cawls. At the top, you can make out my cut away clamp.



My "cutaway" clamp only clamps the flat between the "horn" of the cutaway and recurve, and the flat up into the head block. The horn area curve and the recurve into the neck flat are clamped with fitted cawls w/ regular clamps top and bottom. Note in the picture above the cutaway end of hanging off the table, this is to allow for clamps on the underside in the cutaway area (only).

The cutaway clamp consists of a block of oak, about 60mm x 60mm x 200mm that fits on the back side of the mold. It has holes drilled through it that allow for bolts that run to cawls laminate side of the mold. I use T nuts in the cawls to avoid fumbling with nuts and washers. I've also cut a couple of flats on the back corner of the big inside block to allow for a couple of regular clamps to clamp the recurve area.

This clamp evolved over time and probably will continue to do so. I sure if you work one up it will have improvements over mine, but at the moment, I can set it up and apply pressure without too much angst in just a couple minutes. The laminates come out very tight and uniform. I'm getting enough pressure to squeeze glue all the way through the laminates.

Hope this helps,

CB

Maldoror

that helps a lot, thanks for that.
i was thinking of a larger fitted caul to cover the majority of the cutaway...but perhaps your design allows for more pressure in both directions.

where do you get your veneers? do you use the original 3ply .030 or 4 ply of the current standard?

Craig Bumgarner

Yeah, I worry about one big cawl for the cutaway area being able to apply pressure in both directions. I think it will work as long as you can clamp it in both directions but that is the problem, all those clamps get in the way of each other on the back side of the mold.

I get a lot of my veneers from Certainly Wood in Aurora, NY, near Buffalo. They have a large inventory and a good website with pictures of each batch. They have been very kind to me, working with me on widths and small orders. They accepted the return of the one order that did not suit without question. Very easy to work with, highly recommended. That said, I've been branching out recently, looking for the best exterior veneers I can find.

1/30" (.034") veneers are hard to come by these days. I have found some Makori that was 1/30" and three layers work well. Four layers of the modern 1/42" (.022") work well as long as you get the layers oriented right, otherwise you will have warping issues. The trick is to balance the grains so they react evenly to humidity and hydration from the glue. I have recently changed to epoxy for backs and sides to reduce (eliminate?) hydration from water based glue. Using modern 1/42" veneers gives you lots of options with the woods you choose, mahogany inside, poplar in the middle and fancy stuff on the outside. I initially worried about how thin the veneers, especially the outer layer are and that I would break through, but that has not been a problem. Careful work is helpful.

Maldoror

so i got a couple strips of 1/8" plywood with one veneer face shaved off. how do i get the tight corner bent?

Maldoror

for the caul i mean.
i've tried kerf reliefs with water and heat gun. can't seem to get it to bend without breaking the face veneer.

Craig Bumgarner

Humm....., it seems to me I made mine from a couple pieces of a "bendable plywood". One of the yacht carpenters in the shop where I work gave it to me. He called it Crazy Ply, but I can not find anything by that name. I found something similar by searching "bendable plywood".

It is a thin plywood with all the grain running in the same direction, allowing easy bending perpendicular to the grain line. Real easy, pretty wild stuff, defies logic. It bent easily to the mold and I laminated a couple pieces together on the mold. Even laid up, it is still fairly limber, but holds the shape sufficiently to make a fine cawl. In fact the flexibility is somewhat of an asset.

I'd consider just laying up 8 sheets of inexpensive veneer (poplar, mahogany) direct to the mold, without a big single cawl, just the little ones, lots of them. Be stingy with the glue or you'll have a puffy mess.

Another way would be to layup fiberglass, about 3/16" thick, that would make a nice one but the first two options are probably more reasonable.

Ken Bloom

I've have had great success heat bending 1/8" Baltic Birch plywood. I do it all the time when I make cases and you can do a pretty tight bend that way. I just do it the same way I bend a set of sides.

Maldoror

Craig Bumgarner wrote:

1/30" (.034") veneers are hard to come by these days. I have found some Makori that was 1/30" and three layers work well. Four layers of the modern 1/42" (.022") work well as long as you get the layers oriented right, otherwise you will have warping issues. The trick is to balance the grains so they react evenly to humidity and hydration from the glue. I have recently changed to epoxy for backs and sides to reduce (eliminate?) hydration from water based glue. Using modern 1/42" veneers gives you lots of options with the woods you choose, mahogany inside, poplar in the middle and fancy stuff on the outside. I initially worried about how thin the veneers, especially the outer layer are and that I would break through, but that has not been a problem. Careful work is helpful.

when you say "balance the grain" do you mean to keep the plies perpendicular, or to have consistent grain throughout, or something else? since you can't do horizontal on the outside ply, how do you arrange the 4 plies? 3 long layers and one horizontal? two layers of poplar in the middle? any recommendations for particular species and cuts of the substrate plies? just any straight grain mahogany and poplar?

also, finished up all the molds except for the multi-radiased dish. the plywood i was using was just really brittle...shaved a ply off a fresh board and it bent with ease. i'm following the Charle plans and the Collins method for the dish. my plans are to shape 1" or so cross-sections to the required radii for the soundboard and back to glue under a piece of hardboard. i think i remember reading something about the charle dimensions maybe not arched enough...or maybe it was the collins. any suggestions for the proper radius sizes to create the proper arch?