Frank's Solution for Bulging Sides Q.

[onewent]

I read years ago on Frank's .com site about the set up he uses to align bulging sides to a back or top.  So I made up a set of the aluminum 'side pushers', or whatever they're called, and have used the system with success, ..most of the time.  Once, though, trying to realign an old Stella side/back, I split the entire lower bout, so now I'm a bit skittish about applying too much force...and usually a lot of force is necessary.

A problem I can't sort out after years of using this is when one section gets aligned, the other end begins to bulge out, so I tighten that, and then the other end bulges again.  So I tighten and tighten, and sometimes just can't get the alignment for gluing. The bulge just moves up and down the open seam.

My question is, to Frank and others who use this system with success, when aligning a long section of lower bout as in the picture, is it best to start at the tight radius, glue that, then work to the wider radius?  Any other 'procedure' input for this task is appreciated.  

Has anyone made refinements to this system?

Thanks,

Tom

PS .. the sides are currently under a lot of pressure in this picture .. I'm entering the skittish zone..

[Roger Häggström]

I use the same method, the only difference is that I use wooden blocks and parts of cheap clamps and not machined aluminum.

Thing is, old wood bottoms shrinks across and sometimes a lot. There is no way to match the sides to a shrunken bottom perfectly unless you use force. With too much force the bottom will be in high tension when glued down and there will be cracks later on. For the best result the whole bottom should be loose to even out the shrinkage around the whole rim.

If the shrinkage is small, I match the bottom to the sides in the upper and lower part letting the sides bend inwards at the narrowest point in the middle. With every part of the bottom glued level, or just a little outside the sides, I level the bottom to the sides perfectly with a scraper, file and a sharp knife. After some staining of the fresh endwood, the result is that the sides is leaning inwards to the bottom a bit in the middle but not noticeably.

If the shrinkage is severe there has to be some added wood. Either in the middle seam or around the sides of the upper or lower part of the bottom. You can also add a binding around the whole bottom. With added wood, the bottom can be glued to the sides without using much force to match the bottom to the sides. The bottom will still have to be leveled to the sides and excess wood removed where the bottom is sticking out.

My preferred method is to rebrace the bottom and glue in a rosewood stick in the middle seam or adding a binding. Adding wood on the edge where it needs to be means that you have to match the color to the rest of the bottom and that's a hit or miss.

Other than that, the method is great. Having a jig like this makes the process both dependable and safe.

I also use adjustable dowels on the inside between the neck and bottom blocks and between the sides in the narrowest part when adjusting. The dowels can push the sides outwards. The dowel is in two parts, one has a glued threaded rod in one end and the other part a matching hole as deep as the protruding threaded rod in the other part. A nut is used for adjusting the length of the two dowels put together. Since they are in two parts they can be removed after gluing the bottom through the soundhole. One time I forgot that the top had f-holes, but I was lucky, the middle part of the f-hole was just wide enough for the dowels :-)

[Roger Häggström]

My jig in action. The bottom has a rosewood stick added in the middle. There is an added function with the clamp setup, it can be moved about 2 cm up or down or swung to the left and right.

[onewent]

Thanks for that very detailed reply, Roger, looks like a good system.  I'd thought about using a 'pusher' rod from end block to heel block to try to reshape the lower bouts .. I'll give that a try since I already have such a rod made.

I'm not sure what you mean by the 'rosewood stick' part.  Do you mean you split the back in half and add a thin strip of rw in the seam?  That gives you the lost wood to the back, due to shrinkage, I'd guess.  Can you clarify a bit?  thx..Tom 

[Roger Häggström]

You are correct about the "stick", I'm from Sweden and I think I used the wrong word! I usually glue a 2-4 mm wide (depending on the shrinkage) rosewood strip with hot hide glue in the middle between the two halves of the bottom to make the bottom wider. Then replace or reglue the old bottom bracing. You can always use the same wood as in the bottom for the strip and match the color of the bottom, but most of the time a dark rosewood middle strip will look nice enough - as it was meant to be there.

[Greg Mirken]

The only thing I can add is that you have to be patient. It took years for the sides to deform; they aren't going to comply with your demands in a hurry. My setup is just like yours.