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AndyDove21

Guitar Chord Machine (Chordoma)

by AndyDove21 Apr 1, 2019
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Hello, I am a Chinese. I hope these pictures will be helpful to your design.

I will keep an eye on your design.

Oh that does look interesting. What chords does it play? What is it's name? There is a similar device here called ChordBuddy (you can see it on Ebay), but it only does four chords.

Hello, thank you for your reply. This thing is called "吉他神器" in China. It has a complete G-chord and C-chord. See the picture below.

Hi, thank you for the excellent design! I'm currently trying to replicate it, as I'm too lazy to learn the chords myself. However, the dimensions seem to be off... I printed out 4 of the normal hammers and they fit half the fretboard on my guitar. Are they designed in imperial? I'm kinda confused because the dimensions of your fretboard model match the dimensions of my physical fretboard.
Thanks!

Not sure what you mean. The units are mm because I'm a Brit (I could never get the hang of inches), but Sketchup would know that anyway from the file. If I were you I would just print the first two or three layers of the base, then lay that on your guitar and see if the three rectangular holes line up with the frets and the width of the fretboard. Everything else should fall into line with that. I am doing another version with a stiffer base plate, but it'll be a good few weeks until I'm ready to upload. It's summer up here in Michigan, so the basement workshop is being ignored for now.

Note this was sized for a Ruison TR-3 fretboard. I can't imagine guitar fretboards vary by that much, but I just wanted to let you know what the reference was.

Hmm. The hammers appear to be way smaller than those in your video. What thickness are they supposed to have? I measured 4 of them together for a thickness of 26.7ish mm. I'm hesitant to print more of them until I know they are supposed to be that small :D

According to cura, the hammers should be 7 mm thick, so the printed ones are probably close enough

EDIT: It does appear that my guitars fretboard is just a bit thicker. I printed some layers from the base and it didn't fit at all, see the second picture. Bummer! I might try scaling the width of the models though.

Interesting. How wide in the first fret on your guitar? I mean first fret, not the nut 'fret'. Mine is 44mm. The holes on my base range from 43 to 45mm. Each hammer is 4.67mm at the hammer, but they are slightly wider at the shoulder, like you say, about 7mm. With six strings, and each hammer about 7mm wide you can see that they would take up about 6x7=42mm, plus a little bit for clearance between each. Could be that you'll need to scale up for a larger guitar, but I wonder what that will do to the holes for the rods... Might make them a little loose, but hey, that's what epoxy is for :-)

Hi, I'm currently in the process of building this beast up. In the band anchor STL file, theres one tab that appears to be missing. Does that serve some purpose?

No, was just missing from my CAD as well. Hadn't noticed till you pointed it out. You could either put it back using Sketchup, or leave it off. Those little tabs that stick out are to make sure the elastic bands are dissuaded from coming off, but really they are unlikely to anyway.
Note though that only five hammers are in the middle. There were no chords using the bottom one so there's just a spacer there.

The first fret is about 53 mm wide. I'm now printing the base with only the part over the fretboard scaled up to about 129% (9/7).
Thats a 9 hour print, I hope it comes out nicely :D

Still think you should just print the first layer or two to check dimensions. If you scale up to make it wider then you'd also be lengthening it. If you scale one part then you have to consider the other parts as well. If it is longer then you might be miss-aligned on the frets.

This is an excellent idea. It does share its name with a type of spinal cancer though. So googling "Chordoma" to see if anything similar exists is a bit of a downer.

Yes, maybe I should have researched that a bit more before I gave it a name. I was just trying to make a play on the word Chord and liked the sound of the 'oma' at the end. Maybe Chordomer. C'est la vie.

This is... remarkable to say the least! Will be following future updates - I could see this getting very popular.

A thing of the week!

What does that mean?

It means we will be featuring it on our podcast; 3D Printing Today... threedprintingtoday.libsyn.com
Episode 285 which will release this Thursday.

Pity I didn't know or you could have had me say a few things about it for your podcast, or I could have told you about my motivation or the design considerations I struggled with. No worries, maybe next time ;-)

Took a little while but here is a video of Chordoma working: https://youtu.be/AU-Oaop_8AA Thanks to my son for video'ing it!

The thing I never really worked out a solution for, was a way of load balancing between the three strings that each chord has. If there was just two strings then I could have used a pulley on the key, with the chord wrapping around it so that pulling the axis of the pulley would allow the string pull force to balance. But you can only rotate a wheel in two directions - cw and acw - which is no good for three strings. Putting this design in the public domain in the hope that somebody somewhere can think of a solution for that. Share your ideas!!

Is your load balance problem related to the different gauge of each guitar string, a quality of the line / line friction you are using that is length/angle/routing dependent, or an issue with the resistance from those rubber bands you are using to create the off-string default hold, or a matter of the effective leverage at the mounting point of the string on the key mechanism? Just looking at your pics (I confess, I didn't look at your PDF), I think the first thing I'd try would be oiling up those steel bars with some sewing machine oil (and use something like teflon floss, not string). Setting aside the difference in gauge of the guitar strings for the moment, the only reason I can see for there to be variance in resistance is (1) variation in rubber bands and (2) delta friction based on routing angles.

If the problem is due to the guitar string gauges, then calibrate by using thinner rubber bands for the heavier gauge strings and thicker / more rubber bands on the wimpy nylon e, etc.

It's more like I need a whippletree on each line to ensure force is the same. I see what you mean about the strings of the guitar having different push forces, but I think that's a fairly small effect, though since the pressure is different for each string it should not be ignored. Friction is not a problem though - the cords I'm using are braided low stretch fishing line and they are only rubbing against the chrome poles, and do so very easily. I don't think that's a problem. Flexibility of the entire base might be more of an issue than friction, and I think the next version should be beefed up a bit, or made from something stiffer.

When is the next version coming out??

Funny you say that, I'm working on a new version which is stiffer. I think I'm going to bite the bullet an fix the machine to the neck in a more secure manner. It's a bit wobbly at the moment as there is precious little to grip onto round the back of the neck. The fact that it's not very stiff makes compressing the strings less than optimal.

Great idea, this looks very interesting - does it work on a normal 6-string guitar?
But it looks also a bit complex to build without an instruction. Please upload a video on Youtube.

There are instructions on a PDF in the download, otherwise, yes it would be hard to make. Still hard though... As you'll see from the video I was using this on a Ruison TR-3 Silent Guitar connected to a small amp. This is a slightly odd guitar in that there is no classic headstock, but fitting it to a normal classical guitar would just be a matter of changing the rear clips. If you got a cheap 'sacrificial' guitar then you could glue the clips to the back of the neck. I've not done that.

Wow. big respect. I'm looking for something like this. I have looked at your construction and have some ideas! A video would be very helpful here! please upload. Thanks.

Video freshly uploaded, I hope it's useful.

Looking to print this, as a start for a steampunked automatic banjo (trying to design my own strumming/picking device atm).Working video would be appreciated, to see what can be expected or maybe needs tweaking for my implementation..

heh, yes it's real. Just happen-chance that it is was uploaded April 1st. I'm away from home this week, off to a conference in Vegas (tough gig...) but I must put it back on the neck of my guitar and video it when I get back. But please take my word for it, it's an actual thing. Would have been a heck of an effort for an April 1st prank!

I wonder why it was uploaded on the 1st of April? Can we see a video of it being used on an actual guitar?......…..

I'd like to put this on a robot arm. I actually was working on my own design that works remarkably like this one.

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This is a really cool idea! If somebody wanted to build a guitar playing robot this would be a nice place to start!