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| top of rim no longer flat after attaching back http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=23254 |
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| Author: | ayavner [ Thu Jul 30, 2009 1:36 pm ] |
| Post subject: | top of rim no longer flat after attaching back |
Hi all, Just want to see if I have a cause for worry, like most things I am sure it can be worked around. here's the background: My rims are complete, as well as the top and back plates. I decided to attach the back first, so I put the rims top-side down and checked the body length (good) and depth (good) and the blocks square (good). The back went on well, and the whole assembly really looks good, so I am happy with that. Here's the problem: Now with the back on, if I place it top down, the rims are no longer flat to my table but arched up length-wise such that I can rock it back and forth (neck to heel), and the ends are out of square. And, my question: When I go to set the top on, marking for braces etc, should I try to gently pull the blocks back to square? I am worried about the force required to do that, and subsequent stress on the assembly. It's not alot, maybe 1/4" - should I glue up as is and compensate later when fitting the neck? Or, if its as I fear, should I try to coax it back into the form so the rim lining will be square and flat to the tabletop? Or draw it together with clamps? Or?? Is all lost, or am I worrying too much? thanks in advance, adam |
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| Author: | Barry Daniels [ Thu Jul 30, 2009 1:38 pm ] |
| Post subject: | Re: top of rim no longer flat after attaching back |
I keep the rim in the form until the top and back are attached to prevent this. Put it back into the form and see if that straightens things out. |
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| Author: | ayavner [ Thu Jul 30, 2009 1:51 pm ] |
| Post subject: | Re: top of rim no longer flat after attaching back |
Barry Daniels wrote: I keep the rim in the form until the top and back are attached to prevent this. Put it back into the form and see if that straightens things out. yeah... guess I shoulda done that, just that I have a whole drawer full of spool clamps... well, you know....  I'll see if I can coax it back into the form, just don't want to hear that "ccc-rraaaaccckk" |
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| Author: | Kent Chasson [ Thu Jul 30, 2009 4:08 pm ] |
| Post subject: | Re: top of rim no longer flat after attaching back |
ayavner wrote: Now with the back on, if I place it top down, the rims are no longer flat to my table but arched up length-wise such that I can rock it back and forth (neck to heel), and the ends are out of square. adam That's to be expected if you take the rims out of the form. I'm assuming the rims are arched end to end in some way? If so, the back will want to flatten out and will pull the rims with it (until you glue the top on). It should go back into the form just fine. |
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| Author: | David Newton [ Thu Jul 30, 2009 4:13 pm ] |
| Post subject: | Re: top of rim no longer flat after attaching back |
Adam, I wouldn't worry too much about anything cracking, it's the sides that will be flexing back to their former shape. The sides and blocks do sorta need to be square to the top though, unless you are ok with something more free-form. Maybe you can pull the sides back in without putting them in your form, so you can use your spool clamps. This reminds me why I bought all the cam clamps. I drove right near your place on our last "hurrication" during Ike. Maybe one day we can meet. Who's the Roman? |
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| Author: | ayavner [ Thu Jul 30, 2009 4:46 pm ] |
| Post subject: | Re: top of rim no longer flat after attaching back |
Thanks guys, I feel a bit better. Yes, the top side is arched back to front. But that makes sense that the back as it tries to flatten would be pulling those out. David Newton wrote: Adam, I wouldn't worry too much about anything cracking, it's the sides that will be flexing back to their former shape. The sides and blocks do sorta need to be square to the top though, unless you are ok with something more free-form. Maybe you can pull the sides back in without putting them in your form, so you can use your spool clamps. This reminds me why I bought all the cam clamps. I drove right near your place on our last "hurrication" during Ike. Maybe one day we can meet. Who's the Roman? David, would be great to meet some time, talk some shop and maybe a little pickin' and grinnin'. The "Roman" is a certain centurion from Monty Python's Life of Brian, who's name I will leave you to look up on imdb.com (don't wanna be censored hehe) adam |
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| Author: | bluescreek [ Thu Jul 30, 2009 8:15 pm ] |
| Post subject: | Re: top of rim no longer flat after attaching back |
If you take it out of the mold , the sides will not be in proper position. Chances are your neck block is out also. That is the purpose for the mold. You can drill holes in the mold to let the spool clamps work but that is not a good idea, I will clamp my box using my dish. If you don't have a dish then you need to be careful that your clamping procedure won't distort the box. Building guitars looks hard , but it is harder than it looks |
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| Author: | ayavner [ Thu Jul 30, 2009 8:34 pm ] |
| Post subject: | Re: top of rim no longer flat after attaching back |
Thanks John... nothing good comes easy, right?  well i got it back into the mold with no drama, so think I will let it sit for a bit while I think this thru. Until I heard about dishes, I always read about it being done with spool clamps... might give those a pass next time. oh well, live and learn. Here's a pic, just for reference, back is on and if you blow up the picture you might be able to see just a hair of space under the neck block, and a tiny bit behind the waste. I think wtih the gentle push back into the mold, it should be back to flat, but I'll check it when i go out to the shop next. adam |
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