Sunday, January 3, 2016

Making a Ukulele mold

So, I built two tenor ukulele molds over the past few days, and they turned out great! Naturally, I didn't document a thing, so I documented my next build of two soprano ukulele molds. Again, naturally, since I was documenting my work, they didn't turn out as well, and I made some errors in my process.

So why post then? Well, there really isn't much information about how to make these things, other than "make a mold that matches the shape of the body you want to build". Thanks a lot for that terrific advice.

Thing is, I did make decent molds that are probably serviceable, but they have a couple of major flaws that ensure that they won't be useful for a very long time. I'll talk about it when it is time.

This is one of the tenor molds. The top and bottom have bolts that are tightened by wingnuts. These are made of three layers of 3/4" MDF from the hardware store. 

So, I had some more pieces that were 12" by 18", which I thought would make good soprano molds. I knew that there would need to only be two layers for these, since sopranos aren't as deep as tenors. 

I spent some time tracing my favorite uke body as a model for the mold. This was then sliced in half to make a template. 

I glued the paper to a piece of 1/4 plywood that would serve as a template. I then went to the band saw to cut away the body shape. 

Lots of relief cuts first, so that the blade doesn't get stuck. 

After being rough cut, I took the template to the spindle sander. 

Not bad! 

I then made a template for the other side. This may seem silly, but what it did was allow me to evaluate the template when I put the two pieces together. I found a major mistake in the bottom of the template, where the thing actually curved inwards, which wouldn't be noticeable until you put the two together. I refined this more on the spindle sander until I was happy. 

I countersunk three screws into the template and the first layer of MDF, 

Again off to the band saw. 

Making relief cuts. 

And cutting the bulk of the material out. 

I did not go all the way to the template. 

Now, using a template following router bit, I finished off the rest of the cut. I'm making two molds, by the way. 

Here is major boo boo number one. I really should have taken the time to align these. Instead, I ended up losing a fair amount of wood at the ends of the molds. Not good, these pieces were a tight fit as it was. 
This is the template following bit. The bearing is on the bottom, and will follow the template, cutting the MDF to match the pattern. I'm not sure why I didn't get a shot of the actual routing, other than the fact that I am using two hands and trying not to slice my fingers off. 

The screws left little dimples in the wood. This would be a problem for gluing. 

Release the chisel!

Nice slice, man. 
Plenty of glue, and spread it around. 

This part I did well. Here are the keys: 1) Make sure that you keep the piece in this orientation while it dries, so that the glue doesn't run up on the sides and mess up your attempts at routing the second piece of MDF. 2) let the front edges stick out a bit on your new piece, you can level them with the router bit when it is time. It is almost impossible to get it right otherwise, so don't bother. 

When it is dry, time for more relief cuts. 

Four pieces, ready to go. I put a bit with the bearing on top in the router table, and did the routing operation again. I then sliced off that extra protruding wood from the top and bottom of the template. 

This looks just lovely, but the top and bottom are too thin to allow drilling for a bolt. This is a problem. I chose to go with clasps instead. 

Predrill the holes, and treat with CA glue. 

Not good enough, but it will have to do. The MDF doesn't handle screws well, and the clasps were too wide for this to really work. It was a bummer of a way to end the project. These will work, but they might not be long-lasting. 

After the clasps are attached, I went to the spindle sander again to carefully refine the shape and remove the lumps around the sides. This also makes sure that the pieces truly meet well on the top and bottom. 

The finished molds. They look nice, but I really can't hope for them to last very long. 

The next step will be to finish the insides of the molds with polyurethane so that ukulele bodies don't stick inside. (I am really proud of the fact that I can type "polyurethane" without spelling mistakes. Twice.)

The good news is that I have templates ready to make more molds when and if I need to. This is important - these kinds of templates and tools need to be kept around for re-use. They don't take up much space, and should work the next time I need to do this. Hopefully I'll read this blog entry before going ahead.

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