side thickness sanding

[Happy Builder]

i am having some problem with highly figured woods at the waist bend using a fox bender - it cracks or splits where grain pattern changes

can i sand the whole piece at say 3mm and the waist part at 1.5 mm

which will gardually be incrementally sanded from 3 mm to 1.5 mm

will it have structural problem or any problem in the future

p.s. this is only for highly figured wood for normal straight grained wood there is no problem

 

[R.J. Fulton]

I use a similiar technique when bending sides for cutaway guitars. I start with the side at about 2.5mm overall, and then sand the cutaway area down to about 1.9 even with highly figured wood I've had no problems and I use a similiar side bending jig.
One thing that will make a difference is to start the bend by hand using a bending iron. You don't have to bend the side to perfect shape.You're just giving the wood the idea of what you're going to do to it to help coerce it's co-operation.
1.5mm seems a little thin to me to leave all by itself. If that's how thin it needs to be to get your bend then so be it. However I would add extra reinforcement side braces in that area or add a complete lamination of about .5mm to 1mm of a like wood that will match well on the inside.
Or just make completely laminated sides. Many top builders use that technique, and like the stiffness it provides for the top and back plates to work off of.
Hope this helps. Take care.
R.J.

[FRANK]

with the laminate sides the glue becomes a floating brace ?fyi anyway have had problems cracking figuer in the jig as you suggested and i have since turned down the heat a bit and given my self 5 minutes of heat to then complete the waist bend and about 2 minutes bending the upper and lower bouts so slowing down and heating slower has made the improvements for my self while bending sides.ps i bend at between .110and .095

[Rick Gentry]

I like the idea of laminated sides, and am considering them for my first acoustic build. I have laminated thinner stuff for curves in cabinets and it always works. Do you think a guy could actually use three or four thin thin layers?

[Happy Builder]

thank you very much
yes it helped a lot
i will give it a inner laminate of maple then sand it together
gr8 idea thanks

[FRANK]

i went to check my work and it was .110 about 2.5mm ?1.5 is very thin for my book

[Dave Yelverton]

Part of the problem could be the sides drying out too quickly- it's easily done. I use my side bender at a fairly high temperature and I found i needed to pre-bend the waist if there was any hint of figure or tricky grain. Now, I spray my sides and wrap in aluminium foil. The wood goes a lot more plastic although you might have to wait a little for the side to get up to temp.. The nice bit is it doesn't scorch; the downside is it takes longer for the wood to dry out, so now I leave the side in the bender for a while to cool, then take the foil off and give it a short burst of heat to dry it.
The bender is great for laminating (no heat). Bend the inner and outer ribs, slap on your epoxy, tape together for alignment and press between sheets of waxed paper. to protect your bender.

2mm should be the right thickness. At 1.5mm figured wood can start to go wavy; any thicker and it gets tricky to bend. I have gone up to 3.2 mm before I changed to laminating but it's a pain to bend!
Dave

[Happy Builder]

thank you very much
will stick to 2 mm
then will try

[FRANK]

2 OR 2.5 SEAMS FINE