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| Pre-heating to help bend top? http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10128&t=35040 |
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| Author: | cphanna [ Fri Jan 20, 2012 6:35 pm ] |
| Post subject: | Pre-heating to help bend top? |
Hi, my friends. I'm not talking about bending a side. I'm working with my second redwood top. The first one was brittle, but omigosh this one takes it to a whole new level. I'm working to a design that is very similar to my first mando. I will induce a 15' radius arch into the flat top with my bracing. I'm not worried about that. But, studying my plan, I realize I've got a vulnerable place where the top will glue down to the upper treble point. The sides were sanded with a radius dish, so the bend at this point is more or less diagonal to the grain lines, and the grain is very short on that point. Obviously, I don't want to crack my top there during glue up. I will thin the top a bit in this area prior to glue up, but my question is this: Can I ease the bend by pre-heating the point area of the top with a hair drier or light bulb before clamping it down? Take a look at the treble point on the outline plan, think about the grain orientation in that small area and you will see what I mean. Many thanks, Patrick |
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| Author: | WudWerkr [ Fri Jan 20, 2012 8:13 pm ] |
| Post subject: | Re: Pre-heating to help bend top? |
wow , yes i see what your saying and your concern . I "think" that will work however i am not sure . I would say experiment with a scrap before you try it on the top . I could easily see this going either way . |
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| Author: | Shaw [ Fri Feb 10, 2012 12:48 am ] |
| Post subject: | Re: Pre-heating to help bend top? |
Thats going to be a very fragile area in my opinion. Good chance part of the point will crack off at the grain line. I think maybe applying direct heat from say an bending iron or silicon heating pad to coerce the area into a slight bend...Mike |
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| Author: | cphanna [ Sat Feb 11, 2012 9:37 am ] |
| Post subject: | Re: Pre-heating to help bend top? |
Thanks, Mike and Wud. I've moved forward since starting this thread, including gently and gradually thinning that area of the top. The point is more flexible now. With the x-brace in, the top has taken its induced arch very nicely. I'll be letting the brace ends into the lining later today and then I'll have a better idea of how much farther I'll need to push the point down. With some luck, I'll glue the top on this weekend. Obviously, it's too late for the bending pipe, but I think I'm going to be okay. I'll do a dry run clamp down first. If a little triangle does crack off in the process, I'll plane down to a grain line (as if winging the top) and glue on a little replacement piece later. This is over the corner block, so it'll be secure once glued up. At this point, I'm actually more worried about trimming the overhang from this area. I will probably just patiently sand the overhang off in the point area. I do appreciate your responses. This redwood is pretty stuff, but omigosh it's tricky stuff to work. Patrick |
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| Author: | P Bill [ Sun Feb 12, 2012 3:23 pm ] |
| Post subject: | Re: Pre-heating to help bend top? |
It sounds like you have it sorted. How about some pix ? |
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| Author: | cphanna [ Sat Feb 18, 2012 6:44 pm ] |
| Post subject: | Re: Pre-heating to help bend top? |
One last update and then we can let this thread die a natural death. It turns out I was just in freak-out mode. I was worried that I had applied too much down-pressure on my sanding dish in this point area--and I had, but not by much. The biggest problem turned out to be keeping the top centered during the actual glue up, which I accomplished with two little registering pins. One is under the fingerboard ramp and one is under the tailpiece area. With everything dry-fitted and clamped, it was obvious that I had a gap of only about 1/32" to push down at the very tip of the point. I did the actual glue up this afternoon. Looks real good, but I'll have a fair amount of squeeze out to clean up. I'm counting that as a MUCH better problem than not enough squeeze out. The tip of the point rolled down and squeezed glue without any issues. I am a happy man. I'm toasting the glue up with a nice adult beverage at the moment. Later, I'm taking my loving wife out for a fabulous dinner (she'll be driving). I've been lazy about photographing this project, but will do better from here on. When I have enough together to make it worthwhile for everyone, I'll launch a new thread. Let's let this one die. My thanks to you guys for your suggestions and support. I really do appreciate the interaction and help I receive here. Patrick |
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