Guitar design and side bending irons...

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Brian Evans
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Location: Tatamagouche, Nova Scotia

Guitar design and side bending irons...

Post by Brian Evans »

So, thinking well ahead I designed my current build with sides that had a minimum radius bend of 1.5", the same as my side bending iron. Bending the sides went wonderfully, the .095" figured maple seemed to want to be a guitar... So, since every guitar I make I try something new I decided to make solid linings instead of kerfed, two layers of bent spanish cedar totalling 1/4", so each strip is around .120" thick. Hard to bend - yes. Take it slow and easy - yes. Got to the 1.5" radius inside bends and the ID of the bend is now less than the OD of my bending iron. Lesson of the day - you can get that last little bit of bend by heating the strip on the outside and coaxing it in to a smaller radius... Or you could make a new bending iron, I guess... :) Change the design - not an option, I am an "Artiste" Ha! 8-)

This is the shape, and it's the inside bends at the shoulders that are the challenge. The waist is the same radius, but it's an outside bend so the radius is a tiny bit larger instead of smaller.



Brian
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Bryan Bear
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Re: Guitar design and side bending irons...

Post by Bryan Bear »

You should be able to form the strips into a tighter radius than the bending iron without any trouble. while that section is still hot, bend it to the shape you want and let it cool and set in a tighter radius. With narrow strips of lining it is pretty easy to bend tighter in free space without getting it all wonky. If I may make a suggestion, I would use three thinner strips instead of 2 0.12" linings. Making a strip a third thinner will make it WAY easier to bend and less likely that irregularities in the bend of the linings reshape the sides during gluing instead of the lining conforming to the side.

I use three layers of linings roughly the same thickness of my sides (0.8 - 0.85ish inches). Gluing them up may take a bit longer with the extra step but it makes bending and fitting much less of a hassle.
PMoMC

Take care of your feet and your feet will take care of you.
Brian Evans
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Joined: Sat Aug 30, 2014 8:26 am
Location: Tatamagouche, Nova Scotia

Re: Guitar design and side bending irons...

Post by Brian Evans »

Good advice, Bryan, and I did go thinner on some of the tighter bends. For next time, three strips for sure. This time I ran out of raw material to rip down into strips. It's going well though, I just thought it was funny that I planned out the whole side thing, and totally forgot about bending the linings.

Brian
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Bryan Bear
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Re: Guitar design and side bending irons...

Post by Bryan Bear »

I forgot to add that if you absolutely can't get a tight enough bend at your thickness without breaking, you can glue in the broken pieces and cover the inside bend with another layer of much thinner material that will bend well. This will recover most of the stiffness lost from having the broken linings similar to revere kerfed linings. You won't have to worry much about having a thicker than usual lining width in the upper bout anyway. The only real problem is that you will be able to see it easily through the sound hole on the back but there are ways of cleaning that up too.

When I put my linings in I glue in side reinforcements the same thickness of my first layer of lining. Then I bend and fit my first layer between them. I cover the reinforcements with tape and glue in the second and third layers full length. The tape keeps the linings from being glued to the reinforcements. Once it is all dry, I pop them out so I can clean up the edge that will be visible inside the guitar, remove the tape and glue them in permanently. This makes it easy to have the reinforcements let into the linings and keeps things clean. This is a terrible picture but it should help show what I was trying to explain. I don't have a better pic handy right now; I cropped this from the background of a picture on my phone. . .
lining.jpg
PMoMC

Take care of your feet and your feet will take care of you.
Alan Carruth
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Re: Guitar design and side bending irons...

Post by Alan Carruth »

You can also make up a really simple form, and laminate liners on that from thin stock. I've used that trick on a few harp guitars, where I wanted the liners in the extension arm to take up most of the load, so that had to be pretty thick. Then your sides really have to be bent to the right shape!

For liners you make an outside form, with a curve that's the shape of the inside edge of the sides. I make mine out of MDF, about 2" wide all around. Line the form with a layer of packing tape to keep glue from sticking. I use a 'rubber rope', a long strip cut from a truck inner tube, to clamp things. You just spread the glue, and start at one end, wrapping the rubber strip around in a spiral that leaves a little bit of a gap for each winding, so that you can see what's going on. If you're making liners for a flat top with radiused plates, keep in mind that they will have to be made tall to you can trim them to match the side profile. You will NOT be able to bend then once the glue has set up, not even a little bit. I put the liner in place on the profiled sides in the outside mold before the blocks are in (so that you can get all the way to the ends) and mark off the trim line on the outer edge of the liner, Once that's pretty close, you can mark it to a uniform height, trim it of, and shape the cross section before gluing it in.
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