Thursday, September 12, 2013

Perhaps I Need To Focus on One Thing

When I started off the the luthier idea, I sort of scurried off in all directions at once. I wanted to make guitars, but I don't know how to play a guitar. So how do I know if I've built a good one? So I bought a guitar, and started learning to play it. Which is nice, but it sort of detracts from my goal of building guitars.

I also started considering the problems of sound / resonation in a cigar box. I'm not starting off with tone wood, ideal shaping, bracing and tuning the way I would if I was building "real" guitars, but I'm trading that off for the ease and low cost of using a cigar box rather than building a guitar. But it means that I need to electrify them, or get by with very low sound levels. So now I need to make all sorts of decisions around pickups, electronics, etc.

And really, if I'm making electric cigar box guitars, I really need to make cigar box amps. So now I need to learn even more about electronic design, soldering, etc. And I don't even know how to read a schematic. Lovely. Time to start learning that.

Meanwhile, I've started setting up my shop, building prototypes, thinking about the jigs and tools I need to build to produce credible necks in the style of Les Paul and Stratocaster. Finding out that I don't know what I don't know, but making bits of progress along the way.

Oh, and if I'm going to build stuff I sort of need to have an inventory, which means I'm going to need to start sourcing all sorts of guitar parts, amp parts, woods, cigar boxes, etc. I don't need an actual inventory system at this point, but building one would be an interesting diversion from the rest of my concerns.

And finally, I'm going to need to find a way to sell stuff. I suppose I could start off with eBay or Etsy, since I don't think I'll ever have a storefront, but I probably need a more credible web presence than this blog. Fortunately, I write software for a living, so this part is something I can actually handle without additional training.

Time to go work on my guitar playing.

Monday, July 8, 2013

Guitar Fret Position Calculator

I've been using the googles a lot to get hints, tips and plans for my lutherie. One weak spot seems to be fret position calculators and/or templates. The few I found wanted to give me inches in a decimal representation, and that's not so useful unless I can find a ruler that will let me measure 1.3470 inches. I haven't found one yet. What I really need is a calculator with the ability to get inches as a fraction, or convert those inches to millimeters. So I wrote my own.

Calculating the positions of the frets was historically done with a technique called the rule of 18, whereby you successively divide the scale length minus the offset to the previous fret by 18. This could be done with a pencil and paper. Calculators and computers allow us to easily use a more accurate constant, and so the rule of 18 became the rule of 17.817.

Even with the more accurate constant of 17.817, there is a bit of cumulative error, as you add layers of approximation with each successive calculation. Calculators and computers to the rescue again, we can use a different calculation. The pitch of an ideal string goes up one octave if the length of the string is halved, and that midway point is coincidentally the position of the 12th fret. Thus, fret position offset will be a function of the twelfth root of two and the offset of any fret from the nut can therefore be calculated with the following formula:
    d = s – (s / (2 ^ (n / 12)))
That is the algorithm I use for my calculator. I convert to a fractional amount using a conventional formula with the default JavaScript rounding, and I convert to millimeters by multiplying the decimal inches by 25.4.

To use the calculator, enter the scale length you want in inches and hit the Calculate button. Typical scale length values are 24.75 for a Les Paul and 25.5 for a Stratocaster. You can adjust the precision, so that the fractional amounts are calculated as 16ths, 32nds, or 64ths. If your computer is slow give it a second, there is a lot of number crunching going on.

Calculate Fret Offsets from the Nut

Fret# Inches (Decimal) Inches (Fractional) Millimeters

Thursday, July 4, 2013

Getting Started: Table Saw Repair, Part II

I might as well admit it right now, when I got an old table saw for free, I didn't give any thought to maintenance. It worked, and worked better than the crappy circular saw I had at the time, so I figured that was a win. I wasn't until I started to consider my need to do more precise work than cutting 2x4's and trim molding for home remodels that I started to think about the idea that a table saw might need maintenance.

Getting a pulley reinstalled was just the first step. When I mentioned it to a friend at work, he got me pointed in the right direction for tuning up my saw. I started with a good cleanup. I hit the rusted cast iron top with 500 grit wet or dry sandpaper, then Bar Keeper's Friend and a green scratchpad, and finally Naval Jelly. The change was pretty impressive. It actually had a bit of luster. I gave the whole thing a shot of rust inhibitor.

Working my way down, I hit the undercarriage with a dry parts brush and a shop vac. After things looked respectable again, I gave it several liberal shots of dry spray lubricant.

Then I started truing things up. The throat plate (that red part that the blade sticks through) was visibly out of place due to decades of fine sawdust built up under it. I cleared out that mess an reset the adjustment screws. Next was the pulleys. I laid s straight edge across the face of the motor pulley and drive pulley, and immediately noticed that while they were more or less in the same plane, the motor pulley was at a cockeyed angle. Hmmm... this is not good. A bit of investigation revealed that the motor mount was bent.

Adjusting the motor mount consisted of clamping it down in the vise and whacking on it with a sledge hammer until it seemed straight-ish. I had to fine tune it a bit more by putting two washers under the the side of the motor mount nearest the pulleys, then measured and straightened and measured and straightened until everything lined up.

Finally, I tightened everything down and turned it on. The saw immediately seemed quieter. The rumble and vibration were largely gone. It looks like I might have a working table saw again!

Sunday, June 30, 2013

Getting Started: Table Saw Repair, Part I

First, I should probably explain the name "Ghetto Luthier." In the strictest terms, a luthier is a lute-maker, but the word has come to encompass the makers of all stringed instruments. I'm going to give it a shot. but I'm going to start by making Cigar Box Guitars, which are not the high-rent district of luthierville. Maybe some day, if the cigar box versions work out, I'll make a few "real" guitars. OK, on to the table saw.

About ten years ago or so, I got an ancient Craftsman table saw from one of my neighbors. His wife wanted it out of the garage, and free is a great price, so I snapped it up. It served me well until one fateful day about five years ago when the drive pulley fell off the saw shaft. This is an unusual situation, because normally you need a gear puller to remove it. Unfortunately, this one just fell off by itself.

Since this sort of thing 'never' happens, the shaft and pulley are nearly impossible to get to without completely dissembling the table saw. As a result I sort of ignored the problem for years by doing work with my other saws that would be better done on the table saw. But now I really need to get the table saw working again for my luthier work.

Step one: Find a Woodruff Key that fits. When the pulley fell off years ago, there was very small part that I never found, the woodruff key. It's a little bit of metal, half-moon shaped, about 1/8th of an inch thick and maybe 3/4 of an inch wide. The rounded part of this "key" locks into a rounded depression in the shaft and a notch in the pulley wheel slides over the straight side so that the three effectively become one. When the wheel took a dive, the key flew off into the sawdust somewhere in the garage and I never found it. First I checked for a replacement part Home Depot. They had no idea what I was talking about. So I checked at McLendon's Hardware. They had them, and knew right where they were, but the fit is very precise so it took me a couple of trips to the store to find exactly the right one.

Step two: Replace the Woodruff Key. This involved a lot of cursing. I eventually found that the best strategy was to gently flip the table saw upside-down so I had better (but not great) access. There is a small setscrew on the pulley to secure everything, but the shaft, the key and the pulley all "friction fit" together. After dropping and misaligning several times I finally got the key partially set in the shaft by compressing it into place with pliers, then finished by tapping it into place with a small ball-peen hammer.

Step three: Reset the pulley. This involved a only a bit of cursing. If the saw was fully disassembled I could just tap it into place with my hammer. No such luck here. Using a couple of scraps of plywood (I broke the first one by applying too much pressure) I finally coaxed the pulley into place on the shaft. Tightening the setscrew was child's play. I hooked up the v-belt that connected the motor pulley to the drive pulley for the saw blade and I was ready to rock.

I made about five cuts before I heard the annoying sound of a pulley falling off the saw, and the blade stopped turning. Arghhh! I walked around to the back of the saw, picked the pulley up off the floor and looked inside the saw. My newly-replaced pulley was still there, but this time the pulley on the motor shaft had fallen off. For whatever reason, the motor pulley has a straight spline rather than a woodruff key, or at least it used to. The spline flew off and now I can't find it. This is not starting auspiciously.