Sand the saddle?

I recently got a $40 soprano ukulele with terrible intonation. Each string is sharp by 20-30 cents. So I asked a guy at the music store how to fix it, and he told me to sand the saddle (it's plastic) slanting towards the top of the ukulele. Is there anything I need to know before I start randomly sanding it?

Thanks!

Gray, not clear on the direction you described, however, you can sand the saddle and change the length of the strings a little bit. If each string is sharp, sand a top edge so that the strings pass over the saddle at the back end of the saddle. That is, to the rear of the saddle and closer to the butt of the ukulele. Of course, the opposite is true for a flat string. Shorten the length by sanding an edge closer to the neck. If this does not fix the problem you will have to physically move the saddle back by getting an exacto knife and widen the back wall of saddle slot, clean out the slot to make everything true and square, including the bottom of the saddle slot. When you are happy with the intonation, you will then need to shim the front of the saddle slot to keep the saddle from tilting forward. Etc, etc....you get the idea. It's only $40... just think the process thru....e.lo....
PS a third solution would be to simply place a second saddle behind the current saddle. Use the current saddle to hold up the second saddle and cut the current saddle down a bit so the string will pass over it completely. Then sand the angle of the second saddle edge toward the neck to get the intonation correct...depending on how far off it is......

Intonation is tricky, if every string is equally sharp when fretted but the open strings are in tune, you could also work on the nut end. The basic test is to tune the strings 20-30 cents flat so all fretted notes are dead on. If this works, you can remove the nut, and sand the end of the fretboard (not the face!) and put the nut back effectively shortening distance between the "0" and first fret.

That's just one of many options, some of which are irreversible without some rather major effort, so my best advice would be to proceed with caution. Best case is you make a cheap uke playable. Worst case is you're only out $40.

E-Lo, I'm not sure what exactly you're trying to say...
Dave, how would I remove the nut and what would I use to glue it back?
Thanks guys!

gray, simply put. in your situation, you want to increase the distance (of the strings) between the nut and the saddle. The longer the distance, the flatter the intonation of that string becomes. To achieve this using only the saddle, you will have to sand the top of the saddle so that the string breaks over the saddle at a further distance from the nut than it is currently at right now...e.lo..