Yamaha JR1 to Octave Mandolin Conversion Questions

Hi all,

I've seen quite a few threads on octave mandolin conversions and I have a Yamaha JR1 (21.25" scale length) that I would like to try to convert to an OM. I haven't dealt in this realm of modifying instruments before and I have quite a few questions.

1. Do I absolutely need to narrow the neck? I don't have a problem playing a wider mandolin and this guitar isn't that wide anyways, but is thinning the neck for other reasons?

2. How about the nut/saddle? Should I just buy a blank nut and saddle and replace the existing ones and cut my own slots for the strings? Or is there some way to use the existing ones?

3. I've seen some ideas for putting 8 strings into the 6 holes on the bridge. Good idea or bad idea or what's the best way?

4. As far as parts I need to order, those would include new tuning machines, maybe a nut/saddle, strings, and a tailpiece. What else am I missing?


Just any tips for a first timer who has only really changed strings and that's about it would be greatly appreciated.

Thanks so much!

JD

1. You can try using the neck without narrowing it. It might suit you, it might not. You can always narrow it later if it is too cumbersome.

2. You will almost certainly have to replace the nut. Buy an extra blank in case you mess the first one up. You will probably have to shape and slot the nut yourself-- the chances of finding a prefabricated nut that will work are slim. It might be possible to reuse the saddle, but that is only a guess since I do not have the instrument in hand.

3. In item 4, you mention purchasing a tailpiece. If you are going to install a tailpiece, why do you need to use the holes in the bridge at all? If you do install a tailpiece, it might be necessary to reshape the back of the bridge to keep it from interfering with the strings between the tailpiece and the saddle. It could be done, though, and might be the best way to handle the conversion. Protect the top with thick cardboard if you do have to reshape the bridge.

If you are not going to use a tailpiece, you will have a rough time spacing your strings correctly across the bridge saddle using any combination of 6 holes. In that case, the easiest solution would be to plug the four holes in the center, drill 2 new ones, and string the instrument with 2 strings in each string hole. The holes would probably have to by enlarged somewhat to make that work.

4. Remember that you will have to install 8 strings on a peg head that was drilled for 6. You are going to have to find a way to make that work. At the minimum, you are going to have to drill holes to accommodate 2 more strings. If you are going to use a set of four-on-a plate mandolin tuners, it is likely that you will have to plug all the existing holes and redrill to accommodate the tuners that you buy. This will be difficult to do accurately with a hand drill. I would use a drill press for such a job. I would also use a reamer and tapered plugs for such a job.


You might find that a tenor guitar with a fairly wide neck might be a better conversion candidate than a 3/4 size 6 string. But it should be possible to convert the JR-1 also.

If you've never done this sort of work before and you're not at least an amateur carpenter or a mechanic, you might not get it right on your first try.

You might try browsing Frank Ford's frets.com website to get some ideas of what's involved with working on instruments.

I have done 5 guitar to OM conversion, one of them is Yamaha JR2. Here are my answers to your questions.

1. Do I absolutely need to narrow the neck? I don't have a problem playing a wider mandolin and this guitar isn't that wide anyways, but is thinning the neck for other reasons?
A: for first timer, you do not have to narrow the neck. I never did

2. How about the nut/saddle? Should I just buy a blank nut and saddle and replace the existing ones and cut my own slots for the strings? Or is there some way to use the existing ones?
A: Use blank nut and saddle and cut your own slots

3. I've seen some ideas for putting 8 strings into the 6 holes on the bridge. Good idea or bad idea or what's the best way?
A: 1/ plugging 6 holes and drill 8 holes is one way to go, very difficult to drill properly
2/ plugging 6 holes and use a tailpiece: VERY EASY TO DO

4. As far as parts I need to order, those would include new tuning machines, maybe a nut/saddle, strings, and a tailpiece. What else am I missing?
A: you need to order a set of OM string. DO NOT USE GUITAR strings. There are plenty on eBay, here is one
https://www.ebay.com/itm/DAddario-EJ...n+strings.TRS0

You know that you need to plug the 6 holes on the head stock and drill 8. Make sure the spacing match exactly with the mandolin tuning hardware you buy. This is very challenging unless you have a drill press. The holes have to be PERPENDICULAR to the head stock surface and line up perfectly with the tuning shaft. Otherwise you will have a hard time to turn the knobs !!!
Note that you also need to drill a bit larger on the surface to accommodate the bushings !!

For esthetic reason, you also want to glue a layer to head stock veneer to hide the plugged holes and make the headstock look nice. I tried sanding and re-finishing (even spraying paint) but the "plugging" is still visible.

Overall, the conversion is very interesting, not too difficult but quite challenging to get it right.

Another note: when drilling holes, make sure that you put a piece of wood UNDER the area you drill to prevent wood splitting.
I learned this after making mistake.

I just finished a Yamaha JR-1 Junior (21 1/4" scale) to an octave mandolin conversion and thought I would add it to this thread. $75, a few leftover mandolin parts, and a new set of strings turns a child's guitar into a good (pretty good) OM.
https://www.youtube.com/watch?v=GCuI_sulLN4

You do not "absolutely need to narrow the neck. I had a mandocello that had a neck that was too wide at the nut. I fabricated a new nut with conventional string spacing corresponding to the treble edge of the fretboard. This leaves extra space on the bass side of the fretboard which was not a hinderance in playing

This Stewmac drill jig is kind of pricey but will save you a lot of headaches. https://www.stewmac.com/luthier-tool...w-507410920383