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Cutting brace half lap joints. How do you do it.
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=27768		 Page 1 of 1
Author:  Mike Mahar [ Thu Jun 10, 2010 9:34 am ]
Post subject:  Cutting brace half lap joints. How do you do it.
The bracing pattern that I use has lots of places where the braces pass over each other. The means that the braces have a lot of half lap joints. These joints are at weird angles too. I have tried multiple different methods to laying out the slots for these joints. None have been very satisfying.

I have tried drawing the bracing pattern on the soundboard and laying the braces on the pattern and marking the slot boundaries and then cutting the slot with a Zona saw. It doesn't seem to matter how careful I am, the fit of the brace is either too loose or too tight and the angle is almost always off by a little bit. At some point I have to decide whether to live with the flaws or make a new career out of cutting braces for this one instrument since cutting a new brace doesn't result in any improvement.

I know that some of you can cut these sort of things just by being careful. There must be others, however, that have to use some sort of jig or fixture to get this right. So, how do you all do this? I've looked through the archive, both here and mimf, and haven't even found the issue discussed. That means one of two things. Either the technique is so simple and obvious that every but me instinctively knew how to do it. Or, you're all much better than I am with saw and chisel than I am. (most likely).

I'm not a rank newbie. I've been building for years and I always thought that with time and practice I'd get better at this. But, alas, I have not.
Author:  David LaPlante [ Thu Jun 10, 2010 10:05 am ]
Post subject:  Re: Cutting brace half lap joints. How do you do it.
I use the slidng miter on my Proxon saw to set the angle for this type of cut. The depth of the cut is easy to set with the blade height adjustment.
The only tricky part is getting the correct width of cut but I usually just creep up on it with multiple passes whle I check for fit.
Author:  Tom West [ Thu Jun 10, 2010 10:22 am ]
Post subject:  Re: Cutting brace half lap joints. How do you do it.
Mike: Tried for years to do this with hand tools on X braces and was not satisfied with results. Converted over to the table saw and am very pleased with results. I make two scrape pieces the same size on width and height as braces. Set the depth of cut to 1/2 depth of scrap.Using miter gauge on saw to set the angle of the cut across the braces. Nibble the width of cut in the two scrapes at one time. Leave a few thousands of an inch narrow. Sand the sides so that they slide together with a push fit. Check angle on your plan and then adjust accordihgly and redo until the angle is correct. Then cut your braces.
Tom
Author:  Arnt Rian [ Thu Jun 10, 2010 11:14 am ]
Post subject:  Re: Cutting brace half lap joints. How do you do it.
I did it by hand for years, but I've started using the table saw too. Same results, only faster. Like David, I sneak up on a perfect fit...
Author:  Brock Poling [ Thu Jun 10, 2010 12:00 pm ]
Post subject:  Re: Cutting brace half lap joints. How do you do it.
I made a jig that cuts them with a router and a 1/4" bit. I leave them over sized (thickness) then thickness sand them until they are a squeaky tight fit. The really nice thing about it is the results are extremely repeatable from guitar to guitar and adding new models with new layouts is very simple.
Author:  SteveSmith [ Thu Jun 10, 2010 12:01 pm ]
Post subject:  Re: Cutting brace half lap joints. How do you do it.
I also use the table saw but I leave the depth and width a bit shy then cut to final width/depth with a very sharp chisel and knife.
Author:  Howard Klepper [ Thu Jun 10, 2010 1:03 pm ]
Post subject:  Re: Cutting brace half lap joints. How do you do it.
Bridge City makes a pricey but effective little device called a Kerfmaster. I got one for Christmas, and it has made this job go so much better and more repeatably, using the table saw and a good miter fence. If you are contemplating a lattice of half-laps (I am), I'd suggest looking at it. For just the one joint at the X 5-6 times a year, what Todd said.
Author:  Blanchard [ Thu Jun 10, 2010 2:18 pm ]
Post subject:  Re: Cutting brace half lap joints. How do you do it.
I use hand tools.
I rough the notch out with a small razor saw and then fine tune it with a bastard file.

The file makes it easy to sneak up on a good fit.

M
Author:  Mike Mahar [ Thu Jun 10, 2010 2:37 pm ]
Post subject:  Re: Cutting brace half lap joints. How do you do it.
Those of you who use a table saw. How do you deal with radius curve in the brace? Won't it rock on the saw table? At least one edge of the slot must be perpendicular to the tangent of the brace radius curve. If not, the mating brace won't ly flat on the soundboard. If you cut the slot before putting the radius in the brace, how do you keep the brace from flexing when you cut/sand/plane the radius? I use a jig that bends the brace to the proper radius and then trim on the table saw. That won't work if there is a notch in the brace.

Howard, The Kerfmaster looks like a pretty useful tool. How do you deal with the thickness of your blade kerf? Do you have different gauges for thin kerf blades?

I use a double X brace and an A brace to brace the upper bout. That makes for six half laps. The height and width of each of the notches is different for four of the cuts.

Todd, I envy you. If I could do that, I wouldn't have had to post the question.
Author:  Arnt Rian [ Thu Jun 10, 2010 3:21 pm ]
Post subject:  Re: Cutting brace half lap joints. How do you do it.
Mike Mahar wrote:
Those of you who use a table saw. How do you deal with radius curve in the brace? Won't it rock on the saw table? At least one edge of the slot must be perpendicular to the tangent of the brace radius curve. If not, the mating brace won't ly flat on the soundboard. If you cut the slot before putting the radius in the brace, how do you keep the brace from flexing when you cut/sand/plane the radius?

I cut the notches before the braces are radiused. Afterwards, I plane the radius on the braces on a shooting board (of sorts), where the brace is supported along one long edge while the other is being planed, so it won't flex at all.
Author:  Dan Roach [ Thu Jun 10, 2010 3:35 pm ]
Post subject:  Re: Cutting brace half lap joints. How do you do it.
Lance did a nice tutorial a while back on cutting lap joints using a router. You can find it at the following link. It works great [:Y:]

http://www.luthiersforum.com/forum/viewtopic.php?f=10117&t=15971
Author:  TonyKarol [ Thu Jun 10, 2010 3:35 pm ]
Post subject:  Re: Cutting brace half lap joints. How do you do it.
Table saw .. two diablo's, and spacers to get the correct notch width .. I pretty much get it right on with the Forrest stifferener, and 30 thou of shims as the dividers for the two blades .. Lee Valley for the dado shim set.
Author:  SteveSmith [ Thu Jun 10, 2010 5:25 pm ]
Post subject:  Re: Cutting brace half lap joints. How do you do it.
Arnt Rian wrote:
Mike Mahar wrote:
Those of you who use a table saw. How do you deal with radius curve in the brace? Won't it rock on the saw table? At least one edge of the slot must be perpendicular to the tangent of the brace radius curve. If not, the mating brace won't ly flat on the soundboard. If you cut the slot before putting the radius in the brace, how do you keep the brace from flexing when you cut/sand/plane the radius?

I cut the notches before the braces are radiused. Afterwards, I plane the radius on the braces on a shooting board (of sorts), where the brace is supported along one long edge while the other is being planed, so it won't flex at all.


I just tried this for the first time on my latest. Got a few bugs to work out but it works quite good.
Author:  Mike Mahar [ Fri Jun 11, 2010 8:40 am ]
Post subject:  Re: Cutting brace half lap joints. How do you do it.
Filippo Morelli wrote:
Mike,
Sounds like you have a high repeatability scenario (e.g. like a lattice). Can you be more specific on what you're trying to do? (maybe a photo) ... seems like everyone's answer is how they do it for their X brace. Sounds like maybe you have something different going on? Just curious ...

Filippo


Good idea Filippo. A picture is worth a thousand words. This pattern is based off of the pattern that Alan Carruth uses. The upper bout is A braced and the braces are inlet into the heel block. The double X passes through the X brace and becomes the finger brace. I count eight notches that have to be cut. Twelve if you count the mates. The A braces don't need notches.

Note that I have only just begun to shape these braces and I haven't put the caps on the X cross overs.
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