Here my highly trained shop assistants are demonstrating the proper technique for closing a box.
Actually closing the box refers to attaching the top and back to the guitar sides or rims.
However, using proper technique will ensure better results
and there is some prep work that must be done prior to closing the box.
The first thing that needs to be done is to radius the rims to the proper radius.
One of the most popular ways of doing this today is by using radius dishes.
This is also a very precise way of getting a perfect radius.
I start by using a block plane to make the sides flush with the heel block and end block.
Notice how I am planing downhill.
Planing the opposite direction can cause the sides to split, so be careful.
Once the sides are flush with the blocks I plane them so that they have a slight taper to them
like I show here.
Now I turn the side I am working on so that it is face down in the radius dish
and check the gap between the sides and the radius dish.
Everywhere the sides are touching the radius dish
needs to be removed so that the gaps go away.
I do this using a block plane until the gap is almost gone.
I also try and take the same number strokes on each side
so that the sides stay the same height.
I remove a little and then check the gap in the dish again.
Since I am constantly turning the guitar over to work,
it is very easy to get confused and put the same radius on both sides.
I suggest marking the top and back on the sides or on your form so this doesn’t happen.
Once I get close to removing all the gaps,
I sand the sides in the radius dish to get the perfect radius.
On this guitar I am using a 15 foot radius for the back and 30 foot radius for the top.
Rubbing chalk on the sides and blocks will let you know when you have achieved a complete radius.
Remember to repeat this step on the top and the back of the sides after the kerfing has been installed.
The next step is to notch the kerfing and sides where the back and top braces meet them.
It is important to do a good job here so that the joint is as tight as possible.
There is nothing worse than looking in the soundhole
and seeing sloppy workmanship where the braces meet the kerfing.
On a classical guitar the braces are usually inlet into the kerfing
and don’t go through the sides.
On steel string guitars the braces are tapered down to about 3/32nds or 2.5mm
on the ends and go all the way through the kerfing and the side to later be covered by the bindings.
This is the method I will show here.
Before I do let me show you a couple of tricks for tapering the edges of the braces to exactly 3/32nds or 2.5mm .
The first way is to take a couple scrap pieces from the back
and place them on either side of the brace to be tapered.
You can tape them in place if you like.
These back pieces should be almost the exact thickness of 3/32nds or 2.5mm .
Now use a sharp chisel to taper the edge of the brace.
Another way is to use a jig that I learned about from my good friend Kent Everett.
Basically you just glue the two pieces of scrap from the back that I mentioned earlier to a block of wood.
The two saw marks you see on the jig are about ¼ inch or around 6mm in from the edges of the block.
This distance is the thickness of the kerfing.
You can place the jig on the end of the brace as you are tapering it
and quickly see if it is the correct height.
Now I will show you how to notch the kerfing.
Start by placing the top or back on the rims in the correct position.
Make sure it is centered.
You can place weight on it or clamp it in place.
Next mark where the braces hit the edges.
You can do this from the inside of the guitar or from the outside.
If doing it from the outside, you can place tape on the wood to help you see your marks.
Use a straightedge to trace these lines on top of the kerfing at the correct angle.
Using a black marker to mark the area that will be removed
will keep you from notching the wrong piece of kerfing.
Believe me it happens.
Next I like to use a small saw to mark the right and left side of the area to be removed.
I am cutting just inside my lines so that my notch will be narrower than my actual brace.
It is easy to make it bigger but you can’t add material if you cut it too wide.
Also be careful to not cut deeper than what the bindings will cover later.
To remove the material I will be using a laminate trimmer with a carbide spiral bit.
You can set the correct depth by using a scrap piece of wood that is the correct thickness.
I want to cut a microskoshe shallower than the actual brace height.
Carefully hold the laminate trimmer with both hands on the base and remove the kerfing and side.
I start the cut in the middle and then approach each side until I hit my marks.
Once all the areas are notched place the top or back in exactly the same position as before
and if done properly the braces will not fit in the notched areas.
This is because we cut on the small side.
Now we need to do some hand work and I do this with a file.
Slowly and carefully widen each notched area until the each brace fits snuggly.
I then like to deepen each notch until I get a perfect fit.
This can sometimes be a frustrating process but go slowly and you will be rewarded for your efforts.
Be sure and check the fit on both the inside and outside of the box.
Now that I have the perfect fit I need to close the box.
Here are some ways of doing this.
One way, and a way that I do not recommend is to tape the top or back to the rims while the glue dries.
I just don’t think you can get enough pressure with the tape to guarantee a tight joint.
I would probably avoid this method and use one of the other ways I am about to show.
Another way to close the box is to use cam clamps.
If you have a bunch of them like I do here,
then why not use them to hold the back or top to the rims securely while the glue dries?
With access to this much pressure you can easily crack the top or back so use pressure sparingly.
Use only enough to hold the piece in place.
Yet another way is to use an inner tube.
I took an old Volkswagen innertube from Brazil and cut it into a long continuous strip about 2 inches wide.
These things are so rare these days I am sure they are on the CITES list of endangered species.
I use the innertube to rap the guitar and hold the top or back in place.
This method applies enough pressure to hold the piece in place while the glue dries.
I do suggest cutting the top or back almost flush with the sides before using this method.
If not the pressure from the stretched innertube could crack the edges of your high end Brazilian rosewood back.
Not that this has ever happened to me.
If you can’t find these endangered species innertubes you could also use rubber strips available from LMI.
My preferred method for closing the box is the Go Bar deck.
It is convenient and helps the entire process run smoothly.
It is always set up and ready to go and won’t hesitate when called upon to close the box.