Thursday, July 9, 2009

The End (Block)

You may remember that the braces for the back were radiused to a 15' radius and the top braces were radiused to 30'. Well, the sides now need to be radiused so that back and top will fit properly. To do so is simple: I just take the same radius dishes with 80 grit sandpaper and sand the sides while in the mold, first the back and then the top, until there are no gaps under the sides when they are on the dishes. It's not a lot of wood and 80 grit is pretty aggressive, so it doesn't take much time. Here's the back on the 15' radius dish:

I'm not quite done with radiusing, however, since the heel and neck blocks and kerfing will need to be radiused as well. I had to do the sides first, however, to get them down to their final dimensions. If I had waited until the kerfing was glued on and tried to do it all at once, it's possible that I would have sanded the kerfing so much that there would be a minimal gluing surface. This way I can glue the kerfing just proud of the surface and then radius it, leaving a good gluing surface.

Before gluing the kerfing I need to glue the end and heel blocks. This stabilizes the guitar shape in the mold. I have found that, unlike rosewood, the zebrawood likes to curl and twist a bit, and the heel and end blocks will bring the sides perpendicular to the top and back and keep them there.

Don't have a before picture to show you, but the end block starts as just a rectangular block of mahogany. I cut the width to 3" and the height so that it's just a shade over 4", which is the width of the sides at the butt end. The grain runs width-ways, parallel to the length of the sides, to give strenght in this direction.

Looking at an OM guitar straight-on at the top, you'll see that the bottom is not square but has a slight curve to it:
I have to match the curve on the end block so that it makes good contact throughout it's width with the sides. No gaps allowed! This is a critical joint, as it holds the sides together at the butt end and provides a good strong gluing surface for the top and back.

I bevel the inner surface to reduce weight. It may seem insignificant, but balance is an important part of a good-playing guitar. Plus it just looks better than a block of wood.

Here's the finished end block, held so you can see the bevel and the curve of the gluing surface:

After a dry run, I slather it up with glue:

And clamp that bad boy up, making sure the center line of the block is lined up with the center line at the butt end. I use a caul to protect the surface of the block:

You may wonder why I would bother with a caul, since once the back and top are glued on the end block will never be seen unless it's broken open, but that's the thing: maybe someday it will get broken or need repair, and someone will see it, and I want them to see that I took pride in my craftsmanship, not just in the parts everyone sees but also in the parts no one sees. So everything inside the box will get a good, thorough sanding.

Besides, I like Wayne Henderson's explanation for why he sands his end blocks: he says he wants all the notes to come out smooth and not get hung up on anything on their way out. Nice.

Once these two clamps are on tight I turn the mold sidewise and clamp it in my bench vise. This gives me access to the top and back ends of the block. Like I said, the zebrawood has a tendency to curl a bit, and where the sides extend beyond the mold they don't make good contact with the end block, so I use spring clamps to rectify this.

Here's the final mousetrap:

Seems that something as simple as making and gluing the end block shouldn't take much time, but all this took about 2 1/2 hours. Partly it's still my inexperience. I actually made two end blocks; the first one just didn't look good. If I hadn't had another end block I would have just fixed the first, but since I had another one I scrapped the first one, learned from it, and started over. The second one turned out nice, but the first one wasn't a complete waste; I used it as the gluing caul since it was the perfect size.

But inexperience aside, what seems simple and straightforward still takes time, and it's better to take the time because I'm more likely to avoid mistakes.

Now it's on to the heel block. This would normally just be a thicker version of the end block, but with the cutaway there's more carving to do.

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