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| Oversizing backs tops and sides http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=53920 |
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| Author: | banjopicks [ Wed Feb 03, 2021 2:41 pm ] |
| Post subject: | Oversizing backs tops and sides |
Having completed the box on #1 thinking back. It seems like I left things oversize because that's what everyone else does, so it seems. I'm not sure any of this need to be oversized at all. So much material is removed for bindings that maybe it doesn't need to be that close to begin with. What could go wrong following the plan? |
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| Author: | Ken Nagy [ Wed Feb 03, 2021 3:42 pm ] |
| Post subject: | Re: Oversizing backs tops and sides |
banjopicks wrote: Having completed the box on #1 thinking back. It seems like I left things oversize because that's what everyone else does, so it seems. I'm not sure any of this need to be oversized at all. So much material is removed for bindings that maybe it doesn't need to be that close to begin with. What could go wrong following the plan? I've found that things can go wrong at any point. Maybe I'm just not that good? The overhangs on my violins are always all over the place. But Guarneri Del Gesu's were too, and he doesn't catch any flack. Then again he's been dead for over 200 years, and his stuff sounds great. The violin I'm varnishing now is not glued up yet. So we'll see how that works when I glue it up. I bend things by hand, and don't use a form, so If you use a bender, and glue the back or belly on when it is in a outside form, it might work. I know when I made my arch top I was glad for the lining because a couple spots the ribs were a little wider than the belly. I still had to put in some wood, because the edge on the back and belly has a wide inlay in mastic (I used zpoxy) that isn't that deep and it had to be sealed so the zpoxy didn't just leak out! But at least it didn't have to blend seamlessly. I read a good maker saying one time that making is all about how well you cover up mistakes. I cut my neck to the right length, and then when I set in in the block, I didn't have the belly on, so I thought it was almost 3 mm too long, because there was no overhang. I sawed it off, then glued it back on. Fixed. |
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| Author: | J De Rocher [ Wed Feb 03, 2021 3:58 pm ] |
| Post subject: | Re: Oversizing backs tops and sides |
How much oversize are you talking about? I typically leave the top and back 1/4" oversize all the way around. I did have one set of back plates that didn't quite reach full width of the lower bout, but the binding and purfling took care of it. |
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| Author: | meddlingfool [ Wed Feb 03, 2021 4:07 pm ] |
| Post subject: | Re: Oversizing backs tops and sides |
I go 3mm... |
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| Author: | James Orr [ Wed Feb 03, 2021 4:11 pm ] |
| Post subject: | Re: Oversizing backs tops and sides |
I went over initially because I doubted my ability to get a perfectly shaped rim. Now, 10–5 years into this pastime, a 1/16” of overhang is plenty. The more you have, the more difficult everything is to line up IMO, whether it comes to getting the top placement just right, or marking out the back brace locations on the rim, a little is plenty. Sent from my iPhone using Tapatalk |
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| Author: | surveyor [ Wed Feb 03, 2021 6:25 pm ] |
| Post subject: | Re: Oversizing backs tops and sides |
It's hard to stretch that top or bottom if you get too small. I use a flat washer with my pencil in it and draw a parallel around my template, seems to work for me. |
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| Author: | banjopicks [ Thu Feb 04, 2021 8:14 am ] |
| Post subject: | Re: Oversizing backs tops and sides |
If the body is in the mold when you attach a perfect to design top or back, I think the only possibility is the op or back may be large The side can't be any larger than the mold but certainly smaller. |
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| Author: | jfmckenna [ Thu Feb 04, 2021 9:14 am ] |
| Post subject: | Re: Oversizing backs tops and sides |
I go pretty close to the line for the back becasue I use stretched rubber to glue the back on and if it is over hanging it will crack. But for the top I leave plenty, maybe 1/2 inch or so then trim it off with a chisel and a flush cut bit. I build off the top so the top is on a workboard and the blocks and sides are glued to that. So I think it depends on your building technique. But cutting close to the line is one less step to have to do later anyway. Otherwise don't worry about it 
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| Author: | doncaparker [ Thu Feb 04, 2021 10:03 am ] |
| Post subject: | Re: Oversizing backs tops and sides |
I leave the top and back fairly oversized (1/4" to 1/2") while I am gluing and carving braces, but when I am ready to glue either of them to the sides, I trim back to whatever the NEW outline is, as defined by having the top/back in place, and tracing around afresh. Sometimes things shift a bit while the braces are being glued down. but when it comes time to glue plates to sides, I don't like having a lot of overhang; too much potential for something to push on the extra wood and cause a crack inside the outline. |
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| Author: | Dave m2 [ Thu Feb 04, 2021 12:38 pm ] |
| Post subject: | Re: Oversizing backs tops and sides |
I'm with Don, I trace the outline just before glue up (use a different coloured pencil) and trim to a few mm so not too much overhang. Dave |
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| Author: | Clay S. [ Thu Feb 04, 2021 2:21 pm ] |
| Post subject: | Re: Oversizing backs tops and sides |
I like to leave a little extra material in the waist area. It seems like that is where things can move a little bit. |
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| Author: | Alan Carruth [ Thu Feb 04, 2021 2:52 pm ] |
| Post subject: | Re: Oversizing backs tops and sides |
I work with the plates a little over size by 1/4" or so until I get the bracing on and the inlets cut. Then, with the braces to hold everything in place, and the rim in the outside mold, I flush trim the plates with a router. Then I go on to doing the Chladni tuning with the plates the right size, which avoids changes in the mode shapes or frequencies that can happen when you trim them. I take the rim out of the mold when I glue the plates on, starting with the back first. If there's any tendency for the rim to go out of shape you'll see it, since the back is the right shape, so you can push things around to correct it. In theory, if you get the top and back edges flush all the way around when you glue it up the rim is in exactly the same shape it was in the mold, with the sides parallel and no built-in twist. In practice this even actually works out pretty well. 
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| Author: | Bryan Bear [ Thu Feb 04, 2021 9:42 pm ] |
| Post subject: | Re: Oversizing backs tops and sides |
I always wondered why I see people cutting out the plates using the shape drawn on from the template. I use solid linings so my rims are pretty stiff. I use the actual rim to draw out my shapes on the plates. Sometimes I do this before I brace them and sometimes after. I would worry about shape variations if I cut to a template line. I use spool clamps so for my, process too much overhang can be a problem but too little, less so. I have used plates that were too narrow knowing the binding/purfling would take care of it. Lining it all up to the actual rim allows for that certainty. |
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| Author: | Alan Carruth [ Fri Feb 05, 2021 11:49 am ] |
| Post subject: | Re: Oversizing backs tops and sides |
So long as any under size is limited to the width of the binding and purfling it should not matter. I know at least one good maker who cuts his plates to exact size at the start, but he's a very careful guy. |
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