December 23, 2015

Metal Electric Ukulele

I like taking my gourd ukulele with me when I leave school for more than a week or so, but it's a little annoying to travel with, since it takes up pretty much an entire backpack and is somewhat fragile.  Inspired by Amy's lovely wooden travel ukulele and an awesome one-stringed electric instrument made out of a pipe made by Mike, I made this tiny electric travel ukulele.

The original intent was to basically make an aluimnum stick with four strings and a pickup on it, but after I machined a fretboard and it turned out really nicely, I figured out I should make the rest of the instrument nice while I was at it.

The entire project, from idea to finish, was completed between Thursday night and early Monday morning before I left back to Atlanta.  Some things could definitely be improved (the pickup and tuners, especially), but were done more simply for time.

I started out with this mystery strip of 1/8" x 1.75"  stainless steel found in the putz cruft closet.


I machined it to size on the MITERS Bridgeport, drilled and tapped six M4 holes in it, and fixtured it up in the newly-revived MITERS CNC mill (now running a modern computer with linux CNC, instead of the old DOS-on-a-Pentium-III system).

Squaring up the stock on the CNC mill

The fretboard was roughed out with a 7/32" endmill, and finished with a 1/8" ballnose.  Here's a crappy video of the roughing:


I have very little experience machining stainless, so I just copied some feeds and speeds off the internet.  Seems to have worked out well enough.  I used a brand new endmill for the roughing, and the surface finish turned out fantastic.  Thank you, internet.


Apparently this stock had a lot of stress pre-baked into it, so it warped like crazy when I unscrewed it from its fixturing.  Fortunately it will get pulled flat again by the neck of the instrument.


I laid out the fretboard and some big bar bar magnets for the pickup on a sheet of 3/8" aluminum plate, and started sketching out the rest of the instrument.  For compactness it's headless and has tuners built into the body instead.


Most people I know would have run to a waterjet cutter to cut out the profile, but I have a perhaps somewhat unjustified dislike of waterjets.  Instead, I roughed out the profile on a bandsaw and brought it to shape with some files.  Here's the rough profile after bandsawing:


After shaping the body with some coarse files, I milled the neck to size.  Now I had some nice parallel surfaces for referencing the rest of the machining operations.


Milling slots for the tuners to slide in:


Tuners made from bronze:


The bronze tuners slide in slots, and are each actuated by a screw with a thumbwheel.  I'd have loved to use a proper acme thread screw, but all I could find of appropriate size was a 10-24 threaded rod.

Drilling the holes for the screws to ride in required some interesting fixturing.  I only had an extra 1/2" of vertical space on the bridgeport, after recessing my part in one of the t-slots and putting the drill bit in a collet:


At times like this I wish MITERS had the space for a horizontal mill.  Would make drilling holes like this so much easier.




I CNC milled a bridge of similar style to the fretboard, but out of brass, and made knurled thumbwheels for the tuners:


Milled a cutout for the pickup:



I need to run wires through the body to the pickup, but didn't want to mill a channel in the back of the body.  Instead, I drilled a long hole through the body.  Again, the setup was too tall to use with a chuck, and the particular drill bit I needed didn't fit any collets.  I made a simple split bushing to fit the bit in a 1/2" collet.  These are super simple to make and really handy.  Put round stock in the lathe, turn off a tiny pass to get the OD concentric, center drill, and then drill through with the drill bit you want to hold.  Finally, just bandsaw a slot, and you have a collet to drill bit adapter.


Drilling all the way through to the pickup area:



Next step was finishing body - cleaning up the profile and rounding the edges.  I did the very rough work with a belt sander, and finished with files and sandpaper.

 My selection of files:


Most people seem to shy away from files, but I really love using them.  They can actually remove aluminum remarkably quickly, and you can basically sculpt the metal with files.  It's much more freeform than other machining, which is really refreshing.


And here's the body post filing and sanding:


And here it is assembled.  Yes, that's a carbon fiber pickup cover.  There were some sheets of if lying around, and I thought the contrast with all the shiny metal would be nice.  I don't have any good pictures of winding the pickup, but I just took a big neodymium bar magnet, glued plastic flanges on the front and back, stuck it to a piece steel of stock in the lathe, and put several thousand turns of 36 gauge magnet wire around it.


Side by side with the gourd ukulele:


Here's a pile of nicer pictures:








The only unfinished bit is the headphone jack for plugging it in.  When I get back to a machine shop I'll make a nice cover for it, but right now the jack is just heatshrinked and stuffed into its cavity in the body.

Perhaps a clip of it in-action will follow soon.  I don't have a proper guitar amplifier, so I've just been plugging it into whatever set of speakers is nearby.  A headphone amp for it would be nice, so I can play without bothering people.

5 comments:

  1. I would love one of these! Can you build me one? How much??

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    1. I put a lot of hours into this instrument, and chances are it would cost way more than you'd want to pay if I charge fairly to build another one. Feel free to get in touch over email (benkatz at mit dot edu) if you're seriously interested though.

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  2. Did you do anything to the frets after the cnc (leveling ect)? It looks really interesting

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    Replies
    1. I didn't adjust the frets, but I tweaked the height of the nut at the top later.

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