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- Bindings and Purflings
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Category Archives: Jigs
Got a little more work done on this step ladder I am making. It is progressing slowly as I haven’t had much time recently.
Yesterday, once I had set the level of the top step with the ladder in the open position I was able to drill my peg holes in the side of the step.
Once that was compete I inserted a mock-up peg in the holes allowing me to mark the bottom position of the peg. From that point I taped a piece of pencil onto the peg and made a mark for the correct arc.
Using a piece of 5mm ply inserted between the peg and outer leg to get that arc marked.
Here you can see the pencil mark clearly.
However I don’t need, and neither want a complete arc. Rather I want an arc just up until the arc reaches the apex. From the point the apex breaks and the arc moves inward I want a straight line so that the ladder closes on itself when the spread legs are pulled together. I will clean up this template a little more and then glue it to a piece of hardwood to make a perfect template from which I can route out the tracking on the legs of the ladder.
It has been a little too long since my last update. All sorts of things have been keeping me busy this past month as well as some holdups in the progress. But anyway I am still here and still going at it in my workshop.
So in the last post I made and bent the side bindings and the purflings.
In this post I will cut the dado around the back edge and attach the binding. For that I made an XYZ axis router trammel. This jig is otherwise known as the Fleischman/Stevens binding jig or a Universal Binding jig. It is practically foolproof for doing the binding cut on the back and top of the guitar body. The material I am using – curly maple – will match the end graft.
The Universal Binding jig. I am using a 12 inch lazy susan and 600mm drawer slides for the hardware. The rest is just nuts n bolts n plywood.
The back is not flat and I want the router to cut 90 degrees to the side. So I made a curved donut and glued it to the bottom of the router plate. This allows the router plate to ride the edge of the body all the way around. The router plate and donut I also made from 1/2″ poly sheet. The donut was turned on my lathe.
Here it is all together.
Here the body is clamped in place in the mold. Just one test cut to check the depth and I was ready to go.
The grain run-out is not consistent all the way around in regard to the direction of the router bit so a combination of climbing cuts and regular cuts is used with a final cut moving all around clockwise.
Once the cut is complete I size up the binding. The bindings are cut to size with a sharp chisel.
I used tape to hold everything together once the glue was applied. You can see the I am using purple masking tape. Purple masking tape sold here is the tape that has the least tack. When I do the spruce top a strong tacking tape will pull fibers away so I had to check around for a tape that would hold things together but not pull fibers away when I take it off.
A close up of the glued binding.
After a couple of hours I took the tape off, sharpened up a scraper and made the proud surface flush. The tape method worked well because there are no gaps all the way around.
Back view of the completed binding.
Side view of the completed binding.
I was a little worried cutting up the body with a router bit but the three axis router trammel made this step a simple, clean, no drama cut.
In the next step I will make and glue on the end graft. This is a tapered piece of quatersawn stock that seals up the tail end, where the bent sides come together.
For my end graft I am using some curly maple I have left laying around the shop from the Chef’s Prep Table I made last summer. This is where some luthiers get creative but this time I am doing a simple tapered end graft. I really like the tapered butt joint because it will be a perfect fit when it snugs up – no gaps.
My curly maple stock. For the taper I just eye the proportions. I think I had 35mm at the top and 12 at the bottom.
Put it in the vise and use a low angle to plane down to the line.
Ready to fit.
Marking the placement.
Start making a router jig.
The completed jig attached to the tail end of the body. Notice the napkin being used to protect the spruce top from the wood and clamping pressure. It worked great.
After a few test cuts on plywood I was able to set the correct depth. Here is a pic of the cut groove ready to accept the graft.
It fits perfect with almost no cleanup.
Glue it in place and clamp it with a caul.
A few hours later I took the clamps off and trimmed away the excess with a Japanese hand saw. Usually for this kind of flush cut trimming I lay a thin piece of protective stock and cut away carefully.
This turned out nicely. Once again I have confirmed best practice for so many things we do in woodworking are jigs and test cuts.
Before I can continue with the bracing on the top plate I need to make a jig so I can make another jig so I can glue up the bracing with a radius on the top plate.
I am not sure when this came into style but many acoustic flat-tops now have a radius on the top plate as well. Some say they sound better others say they are structurally stronger. The sound argument is likely one of preference. However the structural argument is likely to be factually correct. Case in point: I have an old flat-top that I always kept in tune. And quite recently while going over it I noticed the mid-section around the sound hole was dipping, while the lower bout below the bridge was arching. Closer examination showed the bridge to be at an exaggerated angle to the plane of the top. Obviously what was happening was the strings tension had pulled the bridge forward down, deforming the top. Over several years of string tension the X-bracing weakened. Probably the best fix is to remove the top and replace the X-bracing.
You can see the unnatural angle of the bridge even with the stings loose. It gets worse when it is tuned up.
At any rate with this flat-top guitar I have chosen to build it with an radius top.
Typically the most common radius is 25′ for the top and 15′ for the back. In order to put that radius in there we need to first calculate the arc of the bend we need. For that we solve for X using X=L²/2(R). Or you can use my nifty radius calculator I did in Excel today. Just choose the L and R value from the drop down list and it calculates X. All my values are in dreaded millimeters but I did a conversion table there for quick reference.
To make the radius jig I first glued up two 18mm mdf for extra thickness and added stiffness.
I then drill a 10mm hole in center and plug a dowel in it attached to my trammel.
The round, flat dish.
This is where that sound hole cutout comes in handy.
Support on the edges
Making my rails for the router carriage that will ride over top the round dish. My rails here are 790mm long. So I measure 790 and put a nail at each end point, mark center and using a piece of maple create an arc that is 17mm deep. pencil it in and then take it over to the band saw. Final sanding on the disc sander.
You can see my carriage sitting on the round board now. It already has 25′ radius rails on it and beside it are the newly made 15′ radius rails.
With my router in position I hold it down and rotate the round plate. Clamping the router is recommended. As the router slowly advances down the rails while I rotate, the radius arc is routed out.
Finally I scrape the dish smoothing out all the rough spots.
This dish is now ready to be used for putting a radius arc on the X-braces and gluing up the braces on the the top plate.