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 ARCHIVED TOPIC: Guitar-Octave Mandolin

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Christoph Penny - Posted - 05/01/2019:  04:00:39

Hi everyone,

I hope you’re well, I’ve been watching on YouTube and also did a search and I was wondering if it really is an easy process to convert an acoustic guitar into an octave Mandolin, I know how to do it I was just wondering if it Really is that simple, would it work on an OM size or would I need a 3/4 size guitar to start with please?

MrMoe - Posted - 05/04/2019:  07:35:37

Hi there, I think a 3/4 guitar may be a better fit. Scale length and nut width will need to be considered. Sounds like a fun project. Good luck, Maurice

Christoph Penny - Posted - 05/04/2019:  08:51:56

Thanks for the help and I will gather the stuff for my project

Mandodennis - Posted - 05/04/2019:  17:58:25

I have converted a few guitars to either a mandocello or octave mandolin. It could be an easy process if you are somewhat crafty and have the tools. It kind of depends on the guitar you start with.

Standard guitars with a ~25 inch scale make a good mandocello.  Mandocellos are very expensive.  I started doing these to avoid the high price.  It works well enough for me.  My son and I converted a guitar for him too.  He played it for a couple of years and then he bought a Gold Tone mandocello.

You'll want a shorter scale for an octave mandolin, as has been said. I generally look for something with a scale length between 19 to 22.5 inches.  Commercial octave mandolins are not as expensive as mandocellos but they are not exactly readily available in many markets.   So a guitar conversion can be a way to add that voice to your playing until you find a ready made one.  

There are quite a few "mini" dreadnoughts and other "parlor" type guitars being made today that fit into that scale spec. If you can find a short scale tenor guitar that would be ideal - narrower neck.

There are a couple of strategies on how to do the conversion. The choices you make may depend on how much work you want to do, what tooling you have and how you want the finished product to look.

At the headstock you have two basic choices. 1) You can add an extra tuner to each side of the headstock above the existing pegs. This only works nicely for guitars with a longer headstock. They exist. So if you want to go this way shop wisely for the donor guitar. 2) You can plug the existing peg holes and drill fresh holes for a mandolin set. I do this myself. I fill the top two holes on each side and then measure for three new holes per side using the center of the lowest hole. Make a jig to facilitate drilling square to the head. I also cover the top and bottom of the head with veneer to cover the plugged holes. You could skip that if you want to do a prototype first on a cheaper guitar.

You can slot a new nut or base your new string spacing off of the slots in the existing nut. A new nut works best, IMO. If you start with a regular six string guitar the neck will be wide and you'll want to move the outside courses of strings in away from the edges of the fingerboard. So start with the inner two courses centered and spaced as you prefer, then locate the outer two courses based on them.   Some people shave the neck to make it narrower.  It's a nice touch, the finished guitar feels more like a mando, but not absolutely necessary.

The bridge also has a couple of options. How you proceed might be decided by the guitar you choose to start with and how the bridge on that guitar is shaped and installed. What I describe below assumes a regular "martin" style pin bridge. Many short scale guitars made in Asia have other bridge designs so just take that into consideration when you source the guitar.

Option 1 basically uses the existing bridge as it stands but installing a new saddle or re-slotting the existing one. You then run the strings up and over the saddle and down to a tailpiece. That could be a mando tailpiece or a re-drilled one if the guitar already had one. Mandolin tailpieces are inexpensive enough to go that route. This method works provided the guitar has a bridge that is a bit lower than the saddle height behind the saddle - so the strings clear it (or you can mill it down to get the clearance). You can fill the old bridge pin holes or not.

Option two is a bit more work. It requires you to add two or more new bridge pin holes in the existing bridge. That takes some care and a few special tools like bridge pin reamers and counter sink drill bit help. This will look a bit like a twelve string guitar bridge - but only eight strings. I also recommended that you add a bridge doctor inside the guitar to counteract additional string tension. I make my own. Or you can skip that if you want to see how it goes.

So that's how I see things. I used the quickest and dirtiest methods on the first guitar/mandos and then cleaned up my act on later conversions.

Have fun!

Edited by - Mandodennis on 05/04/2019 18:13:19

Mandodennis - Posted - 05/06/2019:  13:29:50

I just remembered that a lot of my son's instruments (and some of my own) appeared in supporting roles in a film he helped produce recently. And the first guitar that we converted to a mandocello ended up being used in several scenes in the movie. Here's a decent view of all but the tailpiece, We started with a brand new $100 guitar which we bought on sale for like $85. A few hours work and we had a mandocello. This one got the quick and dirty conversion - So the the plugged holes in the headstock are visible. It works pretty well though.


MrMoe - Posted - 05/11/2019:  06:18:10

It would be cool to see the film or a clip with the Mandocello : )

Mandodennis - Posted - 05/11/2019:  08:18:20

Yeah, it would be cool to see.   Even I have not seen the film - and I took part in a couple scenes, unless they ended up on the cutting room floor. laugh  I think the trailer/promo for the film might have a bit the scene the where photo above was taken.  But really it is more of a stage prop.

It took a long time for my son and his friend (the fellow in the photo wearing the red shirt facing away from the camera) to write the music and then the script and then go into filming and then sound track production and then editing, then color balancing, etc..  It's been in the works for a few years now.  Film being what it is, what we view on the screen and hear in the soundtrack are not always recordings of the same event. A lot of the music audio was recorded in the studio.  While the conversion mandocello is on the screen I do not know how much of it is heard on the final soundtrack.  As I said above, my son bought a Gold Tone mandocello along the way. I think that was in part about having the factory pickup to facilitate recording.  So this is what you are likely to hear in the soundtrack as evidenced by the photo below.  And yeah, the Gold Tone is being played acoustically into a mic for at least this bit of the soundtrack recording.  I think a lot more was done by him at his home studio using the pickup.

But that's not why I posted the pics.  I only showed the picture to illustrate what a quick and dirty guitar to mando conversion looks like.  The film just happened to get good shots of the instrument. Such a conversion is not particularly hard to do.  It Just takes the right donor guitar and some skill with tools.  The process is the same for a mandocello or an octave mandolin - just start with different donor instruments.

Edited by - Mandodennis on 05/11/2019 08:33:06

Christoph Penny - Posted - 05/11/2019:  12:48:27

Thanks for that everyone I will have a think

MrMoe - Posted - 06/07/2019:  15:49:04

I have had a think as well and suggest it may be best to find a trapeze bridge guitar and keep it that way for your conversion or vice-versa for a pin bridge...? We hope you post some pics when you get one done.

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