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Kerfling Help


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hello all, i'm new to this forum and i recently bought a kit from stewmac, which seems from the few posts i've read that most of you wouldn't of gone this route. i wish i had signed up for this forum beforehand. the 000 kit comes with rosewood sides and back and a dove tail joint. i've started a bit of the kit so far but i had a few questions about the kerflings. the dvd instructor says to leave a 1/32" peaking from the top of the sides. now, the back face of the sides aren't completely straight but a bit bent being highest at the waist of the guitar. what's the best way to go around this bend while maintaining that 1/32" all around and not creating a slight lift on the other end of the kerfling? Does that make sense?

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He means kerfing, based on the context. Basically, I bend mine in the fox-style bender, and just don't worry too much about it poking up a little higher in one place, and a little lower in another. That's pretty much inevitable given the spherical geometry of guitar sides. I sand them down flush again with a radius dish once they're glued place.

Also, I can reccomend the OLF (luthiersforum.com) and MIMF (MIMF.com) if you're after acoustic guitar building tips, hints and discussions. We have some here, but the wealth of information is definitely elsehwere.

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He means kerfing, based on the context. Basically, I bend mine in the fox-style bender, and just don't worry too much about it poking up a little higher in one place, and a little lower in another. That's pretty much inevitable given the spherical geometry of guitar sides. I sand them down flush again with a radius dish once they're glued place.

Also, I can reccomend the OLF (luthiersforum.com) and MIMF (MIMF.com) if you're after acoustic guitar building tips, hints and discussions. We have some here, but the wealth of information is definitely elsehwere.

You need to get the top flat, and if its a flat top guitar, perfect flat. Use sandpaper 80 or 100, and a plane and a light and a mold fixture to hold it steady and sand it on a flat table top ala cumplianos method (for the back)-. How far off is it curved? The 2 sides should have been planed flat together (on the dvd), but depending on the mold you use, or how strait and 90 the sides were that could have messed you up. A kit is fine for your first guitar shaped object! :D Its just as much a pain to build from scratch or more. Just toss the plastic binding as he did !!

Oh, your talking about the back, are you using a radius dish? Do you have cumplianos book?

Edited by GoodWood
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Yep what Mattia said.

The sides are going to be at on a flat plane at the top of the rim. You will want to leave the kerfed Lining slightly proud of the top of the sides, because you will sand the radius into that surface to match the radius of the top. By leaving them slightly high you will not have to sand down the sides themselves much to get the radius. You will have to tweak the linings a bit as you glue them down for the back of the rim, but it is not that difficult. Remember you are going to sand the kerfed lining to match the radius, so it will be ok if they set a tiny bit higher initially(you will sand them right back were they are supposed to be). I am not familiar with the kit, but it sounds like they have been cut to match the appropriate radius, and the wedge for the back(neck side of the box being shallower than the tail area). I generally don't bend my kerfed linings in a bender(although it is just fine to do that), instead I will spritz a little water on them. This gives me enough flexability in conjuction with the kerfs to install them without breaking them.

P.S. If the sides are pre-shaped, don't screw around with sanding before you install the kerfed linings. I would imagine they have got the sides close to what they need to be, and you can make sure all is just as you need it when you sand the radius into the top and back of the rim.

Peace,Rich

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GoodWood: few 'flat top' guitars are perfectly flat. I build mine with a consistent dome (25') in the rim and the braces, many companies do the same, some flatten the upper bout and add a little drop-off (1/8" from waist the headblock), some glue domed tops to flat rims, some build true flat-tops (Kevin Ryan among them). Many, many ways to skin this particular cat, although getting neck geometry 'right' remains a challenge.

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thanx for all your replies. rich, thanx for expounding on mattia's original reply. my mistake, i meant kerfing, not kerfling. the guitar is a flat top and the top end of the sides is pretty much flat and gluing the kerfing to that was easy but the other end, the back end isn't quite flat and seems to peak higher than the neck or back ends. therefore, i was concerned that looking at a finished product down the sound hole, i would see that the kerfings near the waist wasn't completely flushed to the side walls because of the slight curvature of the back. i'm not sure if that makes more sense.

but from your responses, i'm reassured that although the kerfing doesn't rise above the sides at a consistent height, this doesn't become too much of a concern because i should still sand the kerfings to match the angle of the top and back. did i get that right?

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thanx for all your replies. rich, thanx for expounding on mattia's original reply. my mistake, i meant kerfing, not kerfling. the guitar is a flat top and the top end of the sides is pretty much flat and gluing the kerfing to that was easy but the other end, the back end isn't quite flat and seems to peak higher than the neck or back ends. therefore, i was concerned that looking at a finished product down the sound hole, i would see that the kerfings near the waist wasn't completely flushed to the side walls because of the slight curvature of the back. i'm not sure if that makes more sense.

but from your responses, i'm reassured that although the kerfing doesn't rise above the sides at a consistent height, this doesn't become too much of a concern because i should still sand the kerfings to match the angle of the top and back. did i get that right?

To be sure you are clear. You will have a radius or dome to the back, they are not flat. A common radius for a back is about a 15' radius. You also have a difference in the depth at the neck vs the end of the body. When you attach the kerfed linings you place them a little higher than the sides, because you will sand them to match the curvature or radius of the back. If you picture an arch or dome the final sanded kerfed lining will rise from the outside tward the center of the guitar. Because it rises you place the kerfing higher than the actual sides(which will be the lowest point). I hope that makes sense. It is very important that the radius of the back and radius you sand into the kerfed lining is the same(so you have a good glue joint and low stress transition).

As far as the top or soundboard. Most guitars are built with a radius built into the top. This is usually between 25'-32' radius depending(25' is very common). you can look at your top and back bracing and you will see they have most likely pre shaped this radius into the bracing stock. The term flat top is used to describe acoustics whether they have radiused back and top or not. Structurally there are advantages that adding the doming or radius add to the design. A truely flat top is much harder to brace and keep stable.

You are basically correct that a little difference in the kerfing height will make little difference, because it will be sanded to create the proper glueing surface. My point was mainly that the kerfed lining is somewhat flexable and you will not have a lot of trouble moving it a little as you are glueing to follow the shape of the sides. My advise to you is to simply do a dry fit with your clamps(no glue), and get a feel for how it will go when you are trying to get everything in place when you are actually dealing with glue drying. Another tip is to keep some rags handy to clean up excess glue that will be dripping. You will want to wipe it as best you can so the work will look clean when you are finished. It would be a pain in the butt to deal with if you let it dry.

Peace,Rich

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You need to make relief cuts in the kerfing with a knife (particularly on the back because of the taper) as necessary to allow the kerfing to lay down flat on the side while following the curve of the side. Otherwise, the kerfing will pull away from the side and leave a gap as you try to bend it in two directions at once. Once that is solidly installed, you can sand it to the correct radius so that the kerfing is even with the sides and has the correct radius.

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You need to make relief cuts in the kerfing with a knife (particularly on the back because of the taper) as necessary to allow the kerfing to lay down flat on the side while following the curve of the side. Otherwise, the kerfing will pull away from the side and leave a gap as you try to bend it in two directions at once. Once that is solidly installed, you can sand it to the correct radius so that the kerfing is even with the sides and has the correct radius.

Ryan, "Kerf" means relief cut. That is why they call it kerfed linings, as opposed to linings.

kerf (kûrf)

n.

1. A groove or notch made by a cutting tool, such as a saw or an ax.

2. The width of a groove made by a cutting tool.

But, yes you are spot on correct :D

Peace,Rich

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Just got my kerf cutter mostly done fryovani! Thanx for the link at OLF!!!! Do you actually use one of these? I thought you surrendered and went for the LMI premade, or something.

GW, I use my sliding compound miter(it locks, making it much the same as a radial arm). Many guys I know use the bandsaw(like the jig you are making), I cut the kerfs for several at at time, then slice them to size, route, and then finish with a couple passes through my sander.I bought eight pieces from Bob C. at RC Tonewoods when I didn't feel like making another big batch. I would recommend him he is a very nice fella and offeres well above typical quality.

Peace,Rich

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You need to make relief cuts in the kerfing with a knife (particularly on the back because of the taper) as necessary to allow the kerfing to lay down flat on the side while following the curve of the side. Otherwise, the kerfing will pull away from the side and leave a gap as you try to bend it in two directions at once. Once that is solidly installed, you can sand it to the correct radius so that the kerfing is even with the sides and has the correct radius.

Ryan, "Kerf" means relief cut. That is why they call it kerfed linings, as opposed to linings.

kerf (kûrf)

n.

1. A groove or notch made by a cutting tool, such as a saw or an ax.

2. The width of a groove made by a cutting tool.

But, yes you are spot on correct :D

Peace,Rich

Yes, I know that. My point is that a lot of the pre-kerf linings you buy are not kerfed enough to follow the contour of the back without making ADDITIONAL kerf cuts (or some alternative like perhaps the fox bender or water soaking that have been suggested -- I don't do it that way). The back curve actually is bending in two different directions at once, which is why the pre-kerfed lining doesn't always sit down well without some help. The point is just to make sure you maintain good contact with the sides.

At least if you want to avoid sanding off a lot of extra kerfing...

But I agree with all of the above ... whatever method works for you ... it's the result that matters.

:D

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Hmmmm, Im not sure, but it sounds like they might have put in the radius for the back, so this is a whole different animal. I dont know what your gonna do to get that into the back unless you brace it just right? There are a few people at OLF who have made these kits. That may be your best bet/

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