Laminating Cutaway Sides

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Dave M
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Laminating Cutaway Sides

Post by Dave M » Fri Feb 16, 2018 7:37 am

I am still struggling to bend my figured maple into the sort of sharp cutaway shape that Trevor uses. Having done the usual search of that sometimes useful store of knowledge I came across John Bogdanavich again. (I had forgotten that he uses three veneers) He is however using a pretty simple classical shape.

So is anyone using laminations for a sharp Venetian cutaway? And how do you do it? I can't see JSB's use of a caul and lots of clamps working round those tight curves...
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kiwigeo
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Re: Laminating Cutaway Sides

Post by kiwigeo » Fri Feb 16, 2018 11:44 am

Dave M wrote:
Fri Feb 16, 2018 7:37 am
I am still struggling to bend my figured maple into the sort of sharp cutaway shape that Trevor uses. Having done the usual search of that sometimes useful store of knowledge I came across John Bogdanavich again. (I had forgotten that he uses three veneers) He is however using a pretty simple classical shape.

So is anyone using laminations for a sharp Venetian cutaway? And how do you do it? I can't see JSB's use of a caul and lots of clamps working round those tight curves...
The sharp cutaway on Trevors OM is my arch nemesis. I went through 3 (solid) IRW sides before I got it right. I ended up modifying the plan slightly to make the radius of the horn a bit less tight..basically to match the radius of the big side of my bending iron (I bend my sides by hand). I also thinned the side in the region of the horn to as thin as I could go without causing "wrinkling" issues during bending. Once bent up I glued in a reinforcing layer of thin macro on the inside of the horn. Apart from that I just took my time with the bending.
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blackalex1952
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Re: Laminating Cutaway Sides

Post by blackalex1952 » Fri Feb 16, 2018 6:50 pm

There are a few ways to do this. I made my own heat bending iron using the sharp cutaway curve plus a little more of the classic Selmer Maccaferri guitar shape for one end and a lower radius curve at the other end. I used a 19mm thich piece of craftwood to make the original shape then screwed subsequent pieces one at a time on to this and used a pattern following bit to route the shape accurately until I hade a wooden version of what I wanted. Then I had it sand cast in Melbourne for $20 into an aluminium version. I drilled 10mm holes into the ends and used ceramic heating elements which I got from a Chinese ebay supplier with free postage and very low price. I also put a heat sensor drilled in to the aluminium as well. I installed these using some fire cement which I bought from a local slow combustion wood heating shop-the kind used for gluing in replacement door seals.
I got an ebay China pid controller as used for kilns and a solid state relay to switch the 240V high amperage and heat sync from Jaycar to make a control box. I mounted the bending iron on a block of wood using some electrical switchboard material, forget what it's called, that I got from a local sparkie, an offcut. This will do quite a sharp cutaway when the section where the cutaway bend is has been thinned appropriately. I soak solid sides in hot water, (have even boiled) and used hair conditioner as well. A steel strap helps along with a wet towel to maintain the steam. The temperature of the iron is critical to prevent the timber surface drying out as well. Try all of these tricks for difficult timbers and see what you think works.
For laminated sides I use the method outlined in this forum somewhere, I am away form home with poor internet at the moment so searching the forum is difficult. The method is also outlined in Michael Collins Selmer build videos. But basically it is using a vacuum bag, epoxy glue and a form onto which the bagged up sides are clamped until the glue hardens.
The disadvantages of this I have found are as follows. Epoxy glue is insidious stuff. Look at the OHand S section of this forum-one user posted his sudden onset allergy reactions to epoxy...scary.
Hide glue and titebond, any glue with water in it will not cure in a vacuum, although some report success with using paper as an absorbent material then removing from the bag when fairly dry the reclamping in the mold to air dry.
Vacuum bagging uses a electricity which is costly in Aus these days, and the vacuum has to be successfully maintained.
There is no way to see the laminations through the bagging material the release fabric and the bleeder fabric until the glue has set. I have had wrinkles, misalignment and other problems at times. With matched sides this can be a problem.
I am thinking along the lines of a more traditional hot hide glue method and getting some accurate male and female forms CNC'd or cast in aluminium and heating them first then applying the glue thereby keeping it hot until pressure is applied.
Another method for laminating is to use HHG or titebond in a form and using a piece of fire hose which is sealed at both ends with a tyre valve and inflating it to create pressure on to the laminations. I guess it could be done somehow with a boxed form and an inner tube. All you need is an air compressor and some ingenuity.
I'd keep persevering with your solid bending, You'll get it in the end! I think that thinning is the key, a bending strap and wet towel. Cheers .Ross
"Everything I say on the topic is based solely upon inexperience and assumption!"

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rocket
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Re: Laminating Cutaway Sides

Post by rocket » Fri Feb 16, 2018 10:14 pm

I use double sides on all my builds now and take them down to 1.5-1.75mm before laminating them, i bend them together and fit the outer to the mould and then laminate the inner to it while in the mould, had quite a bit of success this way.

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Allen
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Re: Laminating Cutaway Sides

Post by Allen » Sat Feb 17, 2018 6:45 am

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Dave M
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Re: Laminating Cutaway Sides

Post by Dave M » Sun Feb 18, 2018 5:06 am

Bender 3 small.jpg
Bender 2 small.jpg
Thanks for all the responses. Alex you certainly went for it!

As it happens I got nearly to success the next day. I am using this contraption: This is nothing new, I think Mike Doolin was one of the first to discus it.

As usual I changed several things:
Increased the tension by adding the third spring.
Took the temperature from 120 to 130 C though this just beginning to scorch the Maple so I'll have to pull it back a little.
I made a much closer shaped caul for the cutaway. You really need to allow for the width of the sandwich.



This was successful in that I got no breaking up of the Maple - I thin to 1.8 mm but it did not quite take the full sharp nose. I think I'll have to exaggerate the shape a little. It'll do for this build though.

Sorry the pics are all over the place but you should get the drift.
Attachments
Cutaway 1 small.jpg
Bender 1 small.jpg
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56nortondomy
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Re: Laminating Cutaway Sides

Post by 56nortondomy » Sun Feb 18, 2018 6:25 pm

1.8mm might still be a bit thick Dave, I thin to about 1.5 to 1.6mm for my cutaways and I soak for 30min in hot water with fabric softener.
Wayne

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