This is part 11 of How to Make an Acoustic Guitar, and in this post I’ll cover head blocks and tail blocks, as well as tapering the sides in your mold. This will secure the sides, get them tapered down to be ready to be ready for installing kerfing. Enjoy.
Blocks and Tapering
In order to hold the sides together at the head and tail of the guitar, you need two pieces of wood that cover over the joints at each end. At the top of the guitar this is called the head block, and at the bottom it’s called the tail block.
The head block also provides a little bit of beef to mill into for a mortise and tenon, or a dovetail joint between the neck and the body. The tail black adds a little bit of weight to the bottom the guitar, and provide some meat to drill for the end pin.
The back plate of an acoustic guitar tapers from the bottom area up to the shoulders, making the thickness of the guitar smaller near the shoulders than the belly. This is a common feature, and it’s pretty easy to put on the guitar.
I’ll cover everything that I just mentioned, including lots of tips and tricks along the way, and you’ll see exactly how to put in the head black, tail black, and use a cool template/jig to create the back taper.
If you Missed Last Week, Check out How to Make an Acoustic Guitar – Part Nine
Cutting the Sides to Fit the Mold
At this point in the build, the sides are clamped into the outside mold and they are drying and cooling. This will set the bends in place, and greatly reduce the amount of spring back that the pieces will experience when you pull them out of mold.
The pieces of wood are also a little too long, so there’s overlap at the head and tail sections that needs to be trimmed down. This is a really easy process, and you can do the whole thing with the bandsaw or a handsaw.
Overlap the pieces, ensuring that they are flat against the sides of the mold, and flat against the surface that the mold is laying on. That will keep the boards nice and straight. Add some clamps for insurance, and you’re ready to start marking.
Using a square, marked straight line on one of the sides right where it meets the center line on the guitar mold. Do the same thing for both the head and tail area, and then pull that side from the mold and cut along the line.
This line is a 90 degree line that travels about 5 inches across the height of your sides, and you can easily mark this with a square.
Put that side back in the mold after you make the cuts, and then use that side as a guide to mark the other side. Remove the second side from the mold, and make your cuts like the first. Put both pieces back in, and see how well they fit.
You will more than likely have to do a tiny bit of sanding to adjust the fit, but a snug fit is exactly what you are looking for. It will help hold the pieces against the side of the mold really well, even in the absence of clamps.
Making the Head and Tail Blocks
Now it’s time to make your head and tail blocks. These only need to be a few inches wide, and the height of the blocks needs to be the same height as the final guitar will be with the taper or arch in place on the back plate.
The tail black is the easiest, and you can just cut it to be the same height as the sides at the bottom of the guitar. Especially if you are planning on leaving that at full height, then just make the black the same height and you’ll be fine.
If you are trimming down the tail area height, then make your block the final height, and glue it in place so that way it’s flush to the bottom of the mold, which would be the top plate of the guitar.
For your head block you need to do a little bit more work. Install your arching template, which I cover later, and cut the block so that we are perfectly fits the template. It’s kind of a pain in the butt to hand plane a tall block to remove a couple inches.
In contrast, it’s a lot easier just to do the cutting and shaping by hand before you actually glue the thing into your outside mold. Finish it first and get it prepared completely to match the taper, and then you can glue it in place.
Make a Template for the Taper
The taper on the back plate of your guitar is a predefined size and shape. You’ll either find this in your plans, or in your book, so take a look through that section before you make a template. Making your template is easy, and it will make the tapering process easy too.
Once you know your sizes, create a couple of tapered batons that can sit on top of your outside body molds, and skin them with a piece of MDF that’s really thin on the top. Cut a hole that matches the profile of the sides, and you have a template.
The next thing that you do is sink some inserts into your outside mold, and create some corresponding bold holes in the arching template for the top. Whenever you need to use the template, all you have to do is tighten a few bolts in place and you’re ready to go.
Plane or Chisel the Sides to Shape
From here, all you need to do is reduce the height of the sides to match the tapering jig and you’re all done.
Depending on which tool you’re more familiar with, you can choose between a chisel, or a hand plane to make this work.
Which ever one you are better with is the one I recommend, because it’s very thin wood, you don’t want to remove too much.
Typically going from high to low is the best practice, and take very thin passes with either edged tool. This will help avoid gouging out too much, or potentially taking a chunk or creating a crack that you can’t fix.
Get your sides down to final height, working one of them at a time.
In the end, you can use a sanding stick with light pressure to ensure that you are 100% even with the mold, and that there are no dips or valleys that you’ll need to address later.
Check Your Work Carefully
It’s important to really make sure that this joint is good when you’re done. Yes, you’re going to add kerfing later and increase the size of the gluing surfaces, but you still don’t want a poor looking joint.
If you have to, use the block sander a little bit more aggressively, even if it does wear off a tiny bit of your template. You’ll be able to use this several times, so even if you have to re-skin it one day, it’s not the end of the world.
Do what you have to to make sure that the taper is very even, and that it’s nice and straight. The amount of effort that you spend at this point will definitely return itself later on, it will be much easier to attach the back plate.
Coming Up Next Week
Coming up next week will take a look at kerfing. You can buy kerfing, or you can make kerfing, just depends on what you want to save. One of them will save you lot of time, and one of them will save you a lot of money.
The point of kerfing is to increase the surface area between the butt joint of the sides and the top and back plates. The top, sides and the back are all really thin pieces of wood, so there really isn’t a whole lot holding the guitar together without the kerfing in the joint.
Getting the kerfing in place is super easy, and it’s actually kind of fun to work with. If you’ve never worked with wood that is bendable before, you’re in for a real treat.
Next Post: How to Make an Acoustic Guitar Part Eleven
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