Hello, I wanted to build a fairly simple kinda “westernized” square Shamisen out of purpleheart, because its easily available at luthier shops where I live with a wenge or ebony fretboard with some guitar tuners, and because I come from a eletric guitar background I would like to install a Truss Rod on the neck for added stability and because Im paranoid about neck warp and such, so has anyone done this before and if so how was it?
Hey there, welcome.
Our grand poobah, @Kyle_Abbott recently finished a shamisen that includes a truss rod. I’m sure he can lend some input here.
However, I don’t think you need to worry too much about neck warping if you use traditional friction based pegs and a wood like purple heart. The tension just doesn’t get too high!
On some smaller shamisen analogues (specifically the shabo), which I have the most hands on experience with), I have noticed some curving on the neck at higher tunings - but the woods utilized in those aren’t always the strongest.
Cheers
Thanks for the tag, Mr. @Brown!
That’s awesome you’ll be making one out of Purpleheart, @Pinheiro!
As Christopher said, the string tension of the silk/nylon is quite low, so there’s not going to be the same issues of neck warping as guitars/mando/banjo/bass have.
While shamisen don’t traditionally use truss rods, I’ve put a non-adjustable truss rod in two of my shamisen (including my recent build - Overview of The Kokoa (10th Homemade Shamisen) - YouTube). Not for warping (because that hasn’t been an issue), but for increasing the sustain. Both shamisen with truss rods seem to have higher sustain than any other the others I made, so I think it makes a difference there.
Anywho, it’s not required but doesn’t hurt! 
Have fun!
Thanks for the input!
I will begin making it as soon as I finish another project of mine just so that I wont overload myself with multiple projects.