putting 6string bass strings on a guitar for a D G C F A D tuning

In addition to having to perform a major filing operation on the nut (and possibly conducting surgery on the bridge) of your guitar to get the bass strings to sit, the substantial scale difference will result in the bass strings being very floppy indeed. You'd be way better off going up a few gauges in standard guitar string to get something playable that won't require radical mods to the guitar. They'll be way cheaper too.

 

Just get slightly heavier guage guitar strings. D really isn't that low. 48s or 52s are widely available.

 

If i’m understanding correctly, you’re just down tuning one full step (E to D etc.). If that’s the case, just use your favorite standard guitar strings, just maybe a slightly heavier gauge.

 

guitars are definitely an octave higher

 

i've been tuning to DGCFAD (D std) for like 30+ years with .009-.042's on 25.5 scale guitars, and .010-.046 on 24.75 scale guitars. No need for bass strings. If you have multiple guitars just mix up your string weights and scale lengths to have nearly the same tension on all of them.

 

You have to use very thick strings to get that an OCTAVE and a full step lower goal on a guitar with standard 25.5" scale length.

For comparison, on my 30" scale Ibanez SRC6 crossover bass guitar, a .095 string is only adequate low E since it still feels rather floppy compared to the same .095 string on 34" scale bass. Ibanez even put a .110 for low E on their AGB205A / AGBV205A 30.3" scale Artcore bass guitar.

But if you owned the SRC6, a Bass VI or any other crossover bass guitar alike, which is tuned E-A-D-G-B-E like guitar but an OCTAVE lower, you just might still have a usable bass guitar when you tuned it even lower a full step to D-G-C-F-A-D with certain string set like the one I'm currently using (La Bella flat .095-.026. Even thicker strings are still preferred for this kind of goal).

 

I used a Brice SS (30") 6 string bass for a while a couple of yrs ago tuned D std in guitar intervals like the OP desires. This was for a 'tiki-bar' trio of old guys, so the lowered tuning helped vocals.

I used the GHS short scale set that has a .107 E, and added a wound .030 and a plain .020 for 5th and 6 strings. It was hard to barre chord, but the occasional lead line on the upper strings sounded fine w some added overdrive.

I liked this approach better than the Bass VI approach, as this sounded like a real bass when played on the lower strings. I never bonded w the Bass VI...

I imagine the Ibanez crossover would do a good job, as well, since it's a 30" scale.