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First acoustic build – fix gaps in kerfing?
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Author:  broken1812 [ Mon Dec 10, 2018 11:38 am ]
Post subject:  First acoustic build – fix gaps in kerfing?
I’m in the middle of building my first acoustic and I noticed my kerfing wasn’t glued completely flush on certain parts around the body (See image for example). It’s only on the thinner part of the kerfing, the top part where the back is glued to it was flush.

I plan on binding the guitar so I’m nervous about trimming away the wood there and not leaving much surface area for the back/kerfing to be glued to.
Can anyone recommend anything to fill that space? It’s only like that in a few spots.

I know this guitar isn’t going to be perfect; it’s only my first and this more of an educational process for me so I’d like to keep moving on rather than taking the back and kerfing off.

Thanks!

Image
Author:  Colin North [ Mon Dec 10, 2018 11:44 am ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
My first was the same in places due to rounding it when sanding the back of the linings, just stuffed some TB in the gaps, took binding Ok, still holding after 8/9 years under tension
Author:  J De Rocher [ Mon Dec 10, 2018 11:56 am ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
How thick are your sides? You could just rout the binding channel less deep so it doesn't go through the sides.
Author:  meddlingfool [ Mon Dec 10, 2018 12:21 pm ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
See how flexible it is. Sometimes you can reclamp and get them to go down. That's a very common place for that to happen, as well as in the waist on the back. The straight linings do not like the compound curves.

So I'd see how flexible it is and see if I could, glue it down as best as possible, and any gaps leftover, make a slurry of TB and wood dust and smush it in the gaps as best you can...
Author:  Alan Carruth [ Mon Dec 10, 2018 12:48 pm ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
As meddlingfool says, if you've profiled the sides to fit domed plates, the edges curve up and down. The tightest vertical curve is always just at, or a little above, the waist on the back due to the normally higher dome of the back and the taper in depth along the length of the box. The liner can't follow the curve and you end up with just the gap you've got. I always put my liners on in short sections to help avoid that problem. You may find that some sections will start out with the ends of the liner at the height of the edge, but the middle part sticking up a bit more. That's OK: the small variation in the liner height doesn't hurt anything. So long as the ends of the short sections are the same height it's not noticeable.

It can also happen that the moisture in the glue will cause this when the upper edge is very thin. The surface starts out flat across the height of the liner, but the moisture causes it to swell, and produces a convex surface. When the edges are feathered out too much they end up with gaps, and it's hard to get rid of those. That;s usually more of a problem when using separate glue blocks ('tentellones').
Author:  Woodie G [ Mon Dec 10, 2018 5:48 pm ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
Are you installing the linings with back in place? If so, and if the back is radiused, the point where the back and side joins will have an angle of greater than 90 degrees...if the lining is forced into making contact with the back, the upper edge (thin edge) will pull away from the side, creating the sort of gap pictured. This is addressed in the repair work we do by milling the requisite angle into the thick edge of the lining, creating a good fit.

For lining application in an external mold where both top and bottom edges can be accessed, standard kerfed lining can be installed in 3-4 pieces to better follow the curve of the lower bout...spring type clothes pins with an extra #64 rubber band for more tension and a bit of trimming on one of the tips keeps the thin edge of the lining in intimate contact with the side. There is no need to edge set the linings because keeping the web intact does almost nothing for side stiffness, so working smaller sections makes sense both from the fit perspective and - for hide glue users - easier installation.

All that aside, we find plenty of factory instruments with gaps in the lining, but still intact 10, 20, or even 50 years after they left the plant.
Author:  SnowManSnow [ Mon Dec 10, 2018 9:51 pm ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
Some of these guys have built hundreds of guitars and I’m on 10 so take this for what it’s worth.
I don’t think it will be an issue


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Author:  Goat Rock Ukulele [ Mon Dec 10, 2018 10:27 pm ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
Put some glue in there, sand up some sanding dust and scrape it in with the glue, then do better on the next one.
Author:  Terence Kennedy [ Tue Dec 11, 2018 9:42 am ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
Yep sanding dust and glue. It’ll be OK.

One thing I have been doing when gluing linings is to look with a mirror to be sure the edges are down in the difficult areas. If not you can readjust your clamping.
Author:  broken1812 [ Tue Dec 11, 2018 7:38 pm ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
Looks like I'll be filling with some dust and glue and moving on...thanks for all the feedback!
Author:  meddlingfool [ Wed Dec 12, 2018 3:12 pm ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
I’ll be adding linings in the next few days, I’ll try to remember to take some snaps showing how the linings do not follow the frame exactly, especially in that area...
Author:  meddlingfool [ Wed Jan 09, 2019 11:09 pm ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
What I do is get the lining flush beside the block (well, a hair proud so you bring the linings to the block and not visa versa), and flush at the waist, and let it ride in a straight line, allowing the linings to ride high to be trimmed later. Make sure your clamps are as close to the thin edge as they can be.

I will clamp from block to waist, sometimes with stronger clamps at waist if it’s being fussy, then from waist to tail. You can usually get the linings to follow the rims along that section fairly smoothly, depending on the type of linings...Image
Image
Imagea bit high is fine, trimmed rough with plane then the radius dish
Imagethat’ll do
Image

Hope that helps somewhat...



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Author:  meddlingfool [ Wed Jan 09, 2019 11:13 pm ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
How does 'the next few days' turn into three weeks so fast?
Author:  J De Rocher [ Thu Jan 10, 2019 1:10 am ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
meddlingfool wrote:
How does 'the next few days' turn into three weeks so fast?


You're traveling through another dimension, a dimension not only of sight and sound but of mind. A journey into a wondrous land whose boundaries are that of imagination. That's the signpost up ahead - your next stop, the Shop Zone.
Author:  Alan Carruth [ Thu Jan 10, 2019 1:44 pm ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
Back in the '80s many of us started using the 'Black Hole Filing System'. It's a microscopic singularity, and anything you toss in disappears from the known universe. Aside form making dust collection a snap (the radiation as stuff spirals down causes heating that produces the noise) it's really handy for things like bills and summonses. What we didn't realize at the time was that the enormous gravitational gradient at the event horizon causes a relativistic time dilation in the immediate vicinity. This lead to the phenomenon of 'luthier time'. You go into the shop in the morning and get a decent day's work in, but when you come out you find that's it's actually next week, and your customers are yelling about their repairs, or other things that you promised. Once you've got one of these there's no way to get rid of it: where do you dispose of a black hole? You sort of have to keep the thing in any event: it would simply be unethical to walk away from it, as the folks coming along behind might not realize the true nature of it, and misuse it. It gives 'Go away kid, you bother me' a sinister twist, to say the least.....
Author:  Bryan Bear [ Thu Jan 10, 2019 1:49 pm ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
Could you not offset a good deal of the time dilation with an appropriately sized and arranged array of buttered cats?
Author:  Colin North [ Thu Jan 10, 2019 3:10 pm ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
Bryan Bear wrote:
Could you not offset a good deal of the time dilation with an appropriately sized and arranged array of buttered cats?

laughing6-hehe [:Y:]
Author:  SteveSmith [ Thu Jan 10, 2019 9:26 pm ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
Careful, someone might get whapped.
Author:  Ruby50 [ Fri Jan 11, 2019 9:54 am ]
Post subject:  Re: First acoustic build – fix gaps in kerfing?
That explains a lot

Ed
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