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 Post subject: Kerfing glue surface
PostPosted: Fri Jul 12, 2019 11:34 am 
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Koa
Koa

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I’m working on a short scale small instrument and somewhere along the line I messed up my rim radius. This resulted in reapplying the radius and consequently sanding down some of the kerfing. It is in a wedge so sanding cut down on the glue area. What surface area do I need to maintain past the binding channel to maintain a strong bond and ensure things don’t fly off?


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 Post subject: Re: Kerfing glue surface
PostPosted: Fri Jul 12, 2019 12:06 pm 
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Koa
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I'd say 1/8" lining surface would be fine. That plus the side thickness will give you around 0.200" total glue surface. Small instruments like ukuleles or violins get by with about 0.080" linings all the time.
Just be careful with your binding/purfling scheme. Your linings are shorter down the side....so don't to cut right through it when routing the binding channel.



These users thanked the author Quine for the post: SnowManSnow (Fri Jul 12, 2019 12:13 pm)
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 Post subject: Re: Kerfing glue surface
PostPosted: Fri Jul 12, 2019 12:48 pm 
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Mahogany
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On the guitar I'm building the ribs are about 1.5 mm and the linings maybe 2.5 mm. That's .16" or so. I'm not worried. But then again I don't ever worry about anything.

I'm thinking of using black dyed wood veneer I have sitting around for the binding. I'll have to do it with several strips going around, but it is only .02" thick. I can scribe the depth, and file it about .02 deep. Glue them on, and scrape the sides. It won't harm the strength at all. I had to glue a few thin pieces on three small areas of the belly yesterday. I just decided to use the thin veneer, and the belly was in almost to the linings in those spots. Easy to add wood now than to fill a thin spot later.

I don't do things normally either, at least not very often.


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 Post subject: Re: Kerfing glue surface
PostPosted: Fri Jul 12, 2019 1:39 pm 
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Brazilian Rosewood
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If you haven't closed the box you could redo those sections that have been sanded away. If the box is already closed and the plates are tight to the sides you could skip the binding and just smooth and finish the edges of the plates if it is a simpler instrument. The greatest risk is when you cut the binding rebate. Once the binding is installed most of the strength is regained if it is glued properly.



These users thanked the author Clay S. for the post: SnowManSnow (Fri Jul 12, 2019 1:43 pm)
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 Post subject: Re: Kerfing glue surface
PostPosted: Fri Jul 12, 2019 1:43 pm 
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Koa
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Clay S. wrote:
If you haven't closed the box you could redo those sections that have been sanded away. If the box is already closed and the plates are tight to the sides you could skip the binding and just smooth and finish the edges of the plates if it is a simpler instrument. The greatest risk is when you cut the binding rebate. Once the binding is installed most of the strength is regained if it is glued properly.

I think I’ll be ok as the binding won’t be anywhere close to the thickness of the available kerfing


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 Post subject: Re: Kerfing glue surface
PostPosted: Sat Jul 13, 2019 5:31 am 
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Brazilian Rosewood
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I can tell you that you need about 1/4 in glue surface for long time
you get below 3/16 it will fail.
it is easy to fix now

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These users thanked the author bluescreek for the post: James Orr (Sat Jul 13, 2019 11:21 pm)
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 Post subject: Re: Kerfing glue surface
PostPosted: Sat Jul 13, 2019 5:43 pm 
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Koa
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bluescreek wrote:
I can tell you that you need about 1/4 in glue surface for long time
you get below 3/16 it will fail.
it is easy to fix now

Are you saying 1/4 “ after the channel for the binding is cut???


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 Post subject: Re: Kerfing glue surface
PostPosted: Sat Jul 13, 2019 5:50 pm 
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Koa
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I’m going to rekerf the top. I’m not in a hurry and I need to get it right .
I’ll do a rekerf thread . Maybe it will help another noob one day


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 Post subject: Re: Kerfing glue surface
PostPosted: Sat Jul 13, 2019 6:58 pm 
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Brazilian Rosewood
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Location: Western VA, no not West VA
SnowManSnow wrote:
bluescreek wrote:
I can tell you that you need about 1/4 in glue surface for long time
you get below 3/16 it will fail.
it is easy to fix now

Are you saying 1/4 “ after the channel for the binding is cut???


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A lot of kerfed linings are 7/32 wide which is close enough 1/4in to start with. When you rout out for binding typically that's only about as thick as your sides maybe a hair bit bigger if you go with thin sides. In the end though you should have the full, or very close to it, width of the original kerfed lining. If you add purfling on top of that then you should not rout down to the lining but rather have a bit of top wood stair stepped in.


Last edited by jfmckenna on Sun Jul 14, 2019 7:35 am, edited 1 time in total.

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 Post subject: Re: Kerfing glue surface
PostPosted: Sat Jul 13, 2019 8:11 pm 
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Cocobolo
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I don't know whether this idea will help OP out , but.... I use a full-height laminate I get from LMI instead of purfling on the soundboard. Lots easier to cut one channel a bit deeper and install the 'purfling' layer first, and in a second step, install the binding proper. For me, it's easier.

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 Post subject: Re: Kerfing glue surface
PostPosted: Sun Jul 14, 2019 6:01 am 
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Brazilian Rosewood
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if you can end at 3/16 you should be fine if your under than you cutting it too close.

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John Hall
blues creek guitars
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You Don't know what you don't know until you know it


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 Post subject: Re: Kerfing glue surface
PostPosted: Sun Jul 14, 2019 10:07 pm 
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Koa
Koa

Joined: Fri Feb 24, 2017 8:43 am
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bluescreek wrote:
if you can end at 3/16 you should be fine if your under than you cutting it too close.

Top kerf is gone. I’d rather make sure it’s ok and sleep at night:)


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