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Tip: sides in molds before end block glue up
http://www.luthiersforum.com/forum/viewtopic.php?f=10122&t=19743		 Page 1 of 1
Author:  Michael Dale Payne [ Fri Nov 21, 2008 11:37 am ]
Post subject:  Tip: sides in molds before end block glue up
For new builders, be it kits or scratch builders:

Once you place your bent sides in position in your mold, glue up your end block immediately!!!!!! If you leave your sides in the mold unsupported, the spring tension of the bent sides will cause a crack to start at the ends just above the where the mold is not directly contact and supporting the side. This crack can and will rapidly follow the grain and split your side into. The sooner the end blocks are glued up to support the ends of the sides the better. However if for some reason you can not get to the end block glue up step immediately, then supporting the ends of the sides with a full side height vertical grain shim placed between the side and the mold will prevent the side’s spring tension from springing out and starting and running a crack along the grain where the side is not directly in contact with the mold. Now this cause the ends to the sides to slightly over flexed but this is not a problem in the long run. the shims are only temporary till you can glue up the end blocks.

There you go waddy ;)
Author:  WaddyThomson [ Fri Nov 21, 2008 11:55 am ]
Post subject:  Re: Tip: sides in molds before end block glue up
Thanks, Michael. It's a good tip. Hope it saves someone some grief.
Author:  Rod True [ Fri Nov 21, 2008 9:16 pm ]
Post subject:  Re: Tip: sides in molds before end block glue up
That is a good tip. I'll add to it that if your sides have a lot of spring back, that is also an issue. I know there are many guitars out there with lots of stress in the rims because they are forced into shape more than they should be.

So if you can, it's good to touch up your sides (even if you've purchased a kit with bent sides) to as close to your final shape as possible. This will help reduce the potential of side cracks before the head and tail block are glued on too. [:Y:]
Author:  Zach Ehley [ Tue Nov 25, 2008 7:00 pm ]
Post subject:  Re: Tip: sides in molds before end block glue up
That brings up an issue I have thought about. If you have spring back in your sides and you force then to shape, within reason not going down the road of cracking due to this, what affect does that have on tone? How long does that last? Will most woods relax to their forces shape after time? I'm sure it reduces, but will never be eliminated. I'd think it would increase the natural frequency of the box making it accentuate the high end.

Good tip. I do the same thing.
Author:  Rod True [ Fri Nov 28, 2008 4:56 pm ]
Post subject:  Re: Tip: sides in molds before end block glue up
Zach, that's a good question.

I think most builders see the sides as the rigid frame used to support the top and the back and I also think most think the sides attribute very very little to the overall tone/sound of the instrument. So, I don't think the stress' in the side from forcing it into shape (hopefully not to much out of shape) will effect the tone at all. Now it might increase potential for the side to crack if it gets 'bonked' at all, but that's just a guess.
Author:  Lillian F-W [ Fri Nov 28, 2008 5:01 pm ]
Post subject:  Re: Tip: sides in molds before end block glue up
My mold isn't full height. I was afraid of cracking a side when I put it in the mold, so I put a 3"x 5" piece of .007" shim stock between the side and the mold. My sides didn't have a lot of spring back, but I wasn't going to take a chance. It worked well, I used it when I was radiusing the tail and heel block as well. It supported the sides while I sanded the blocks to fit the sides.
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