A slight detour (happens all the time)

For a couple of years I’ve been fooling around trying to get a CNC machine happening so I can ‘rough in’ necks. This has become more pressing now because I’ve had some ideas lately about how to make the necks more playable by accounting for how the shape of the closed hand changes as you move up it towards the body of the guitar. As the forearm pivots the hand shape changes.  I think a correctly designed neck profile that accounts for this will both feel better and lead to less fatigue or injury.  To explore this I need to be able to prototype a number of neck profile shapes and try them out. It’s easier to change a CAD drawing and run it than to carve a whole new neck by hand every time; and once I have the shape perfected, I’d like to recreate it. Thus the need for CNC. I’ll still have to do a lot of hand work to make each neck but I’m OK with letting a machine get the wooden block 90% there.  But first I need a machine.

I tried building one from scratch out of plywood and angle iron a couple years ago. I could never get everything aligned properly so things would bind and break. So I bought a kit that is way to small to make a neck but will provide a springboard for getting the kind of machine I need, with modifications.

The first picture is of the base kit. The second is of the same machine but with a taller Z axis. I need a minimum of 6 inches of travel in the Z so the heel block can be roughed in.

This is going to take some time and thought. A lot of both. Plus a bunch of farting around.

 

 

Trimmed the top, then routed for the binding.

When the finished soundbox of the Boomer came out of clamps this morning, the tap tone was terrific. The sound is tight and big.

I routed off the lip left by the top, and then routed the top and bottom of the guitar with a special bit for binding. The only trick is to make sure you leave the depth set so the binding (oce glued) stands just proud of the surface of the top/bottom. Then it will sand flush. If the binding is lower than the top/bottom and you sand it flush you end up with endgrain showing and it looks like pre-boiled ass.

 

I used to use a weird contraption to hold the router perfectly perpendicular to the sides while routing, involving hinges and parallelograms and weird bearings. It was too much. I freehand it now. I find that a man, terrified of ruining several weeks of work and/or taking off a finger, can do as good a job holding a router true and steady as a more elaborate contraption. If I start binding curved tops I’ll need the contraption again, but with a flat top, it’s not needed.

I glued the binding on with about 100 pieces of blue tape and now I wait a day.

The top goes on.

I need more clamps. This is barely enough. It will do, but frankly I’d rather have clamping pressure along every single inch of the seam.

If anybody wants to know what I want for Father’s Day, or any gifting opportunity for that matter, it’s this: more bar clamps.

Top bracing… this will take a few days

I glued the maple bridge patch on here yesterday and now I’m starting the top bracing. I’m using Sitka Spruce, in an X configuration.

This picture is of the first spar of the X.  This involves a lot of careful whittling, lots of patience, taking only a little wood at a time so it hugs the contour of the top and the patch. Here’s the deal: I want this so well mated that only light finger pressure closes the gap between the 2 pieces of wood. If it closes but you’re using clamping pressure, that means there’s unresolved stress in the top. The glue will be fighting that, the wood will be fighting that, and it will affect how the top vibrates. When it’s ready to glue I do clamp strongly but that’s so I get a good bond. The glue won’t be holding the wood in a configuration it doesn’t want to be in. It will just be holding it together.

This is my constant goal with my soundboards: there should be as few stresses unrelated to actually vibrating with the string as possible. That way they vibrate most freely and project the most energy in the sound frequencies the string is producing. Or: such is my theory. With my theories and 5 bucks you can buy a cup of coffee.

In an earlier post I promised to show you how I support the braces. It’s simple: little posts, glued to the sides, which act like columns. Since their grain runs perpendicular to the grain of the side, they also act to prevent splitting.

 

Notice this brace: it’s Orange Osage. It has to take a lot of stress because the fingerboard will be laying on it, when the guitar is done, and the string tension will be trying to make the neck come up and make that fingerboard collapse the top. The Osage will prevent this.

Orange Osage is a weed tree; it’s hard to find big chunks. It is very hard, very strong, very bright sounding when tapped, very heavy and dense for its volume (so I only use it sparingly, in critical spots like this) , and naturally this color. Some people make tea from it, I believe, but I am not sure which part of the plant they make the tea from. It smells good. I’m the only one who uses it in guitars that  know of. I think some people use it to turn bowls.

A word about the woods I use: I don’t use toxic woods (except a little rosewood).  The wood I use frequently is a food tree– walnut, maple, cherry, osage… on the theory that, If I can eat it or something the tree produces, it’s probably OK to breathe a little of the dust.

 

Various and sundry odds-n-ends

I caught up the maple-bodied boomer while waiting for the fingerboards…

and today those came, so I am putting together a neck too.

The last thing today is making up a rosette, based on a new pattern I have been working with… using a laser engraver. Once it’s engraved I’ll cut it out.

This one turned out too small, so I re-scaled the image. I’ll try again tomorrow…

I think it will look nice when it’s done. I need the soundhole to be 4 inches for the boomer guitar to breathe properly. I’ll save this one for a smaller-bodied parlor guitar sometime.

Top and more bracing, also a little roadblock.

Light duty day. I sanded the top and cut it down on the bandsaw. Also added another brace to the inside of the guitar, after tap testing it and deciding where it would be best.

Discovered I’m out of fingerboards so there will be a pause in the action until they come. Can’t lay out where the bridge will go until I know where the saddle is going to be, and that’s driven by the fretboard.

 

Maybe I’ll work on the Maple Boomer this weekend and get it to this point. It’s always good to have more than one going so you can keep things rolling along if you hit a bump.

 

Gluing up the top, starting to brace the back.

I took the guitar body out of clamps and routed the back flush to the sides. It looks nice. It almost looks nice enough to skip a binding. I’ll have to think about that.

Next, I glued up the Sitka Spruce top the same way I glued the walnut back. This set has been sitting here seasoning for at least a year. It’s nice and dry.

Then, I ripped a plank of Sitka spruce down for bracing. I’ve had this chunk of Sitka laying around for about 2 years now, so it’s also perfectly seasoned.  I cut the first brace for the back, to go across the widest part of the guitar– where the back needs support. I don’t want it to be too bloopy when it’s vibrating; you get a better, more “useable” bass response, if you cut out the loewest frequencies with some judicious bracing. I do not chamfer it yet, nor do I cut grooves in the lining to accept it and secure it. That’s way more work than it’s worth, and if it’s not done perfectly, the result is a brace that comes loose and rattles around at some point. I secure braces differently than some people do; more on that later in a future digest entry.

I will be tap-testing the back and adding braces or chamfering wood away from braces until it sounds “right”.

It’s clamped with a block-n-clamp on each end and some weights in the middle. That brace is going on there strong.

Tomorrow, I’ll add more braces to the back and start messing with the top.

The back goes on.

I sanded the back after it came out of the clamps, laid the guitar body down on it, marked it with a No.2 Ticonderoga pencil (very important) and cut it out on the bandsaw. I sanded it with a drum sander.

 

I chamfered the edges of the tail block and head block with a sharp chisel and hand-sanded everything inside, just so it’s nice.

 

 

Then I glued it. If the surface is dead flat, it doesn’t take much clamping pressure to mate it up.

 

I laid this big heavy tabletop thing on it and micro-slid the sides on the back plate until it was exactly where I wanted it. then I added just enough clamping pressure to get consistent glue squeeze-out all around. It’s a good visual cue that clamping pressure is even. If there’s a lot more coming out in one spot and another spot is looking dry, it’s a sign of a problem. You need to pay attention to these things.  In this case the ribbon of glue was consistent all the way around and left me feeling good.

Sides nearly done; time to make the back

I pulled all the clamps off the sides today and started sanding them. I have about an hour more of working the surfaces that the back and top will attach to.

But it takes a day to glue the back up, and the same to make the top, plus time spent on making braces… so while I’m sanding the sides, its time to start gluing the back. Thing need to go down multiple tracks if you don’t want to spend a year doing this. I’m always waiting for something to dry/cure as it is.

First you mate the edges by running them through an edge planer. Fiddly work, that; multiple passes, taking only a little at a time. I stop and check after each pass. You hold the 2 halves together against a bright light and when simple hand pressure mates the halves well enough that you can’t see light, it’s ready to glue. If you can see light, it’s not good enough.

I lay the wood down on top of a bar or stick, so it’s in triangle configuration, and secure the sides; I apply glue to the seam; then I pull out the bar and push the wood down so it’s lying flat. It’s the simplest way to put clamping pressure all along the seam, evenly.  Wax paper underneath (and on top) if you ever want it to come free again!

 

Then I clamp a bar down across the top of the seam, so it can’t pop back up:

And I leave it alone for a day.

Walnut sides, Walnut back. It’s going to be a beautiful thing if I don’t screw it up.