After having cut a few fingerboard blanks from a chunk of mesquite, I need to choose one and get it thicknessed and ready for use.
I picked the best one and flattened it, squared up one side and thicknessed in on the drum sander to about 0.15” which is slightly thicker than it probably should be, but wanted to ensure I could cut the fret slots adequately deep and in case I cut them too deep, I can always sand a little surface of but I can’t add any surface if I start too thin in the first place.
After getting the fingerboard ready, I need to cut the fret slots. This requires a pretty significant amount of precision, so the best method is to use some kind of miter box designed to do the job. You can buy special ones from the luthier supply houses but they are kind of expensive considering the amount of use mine would get, so I chose to make one. I am borrowing (stealing) this plan from Westfarthing Woodworks
Which looks simple and very accurate.
It requires a fingerboard blank with slots already cut so you can replicate the slots. So I’m planning to make a guitar blank and find the place on the guitar fingerboard that matches the fret spacing that the uke will use, then use that section of the guitar fingerboard to create the fret slots for the uke. Hope that makes sense.
Basically the uke frets are close together, much closer than guitar frets. But the upper registers of the guitar fingerboard have frets that are very closely spaced. My intent is to use the upper register fret spacing of a guitar fingerboard to make the uke fingerboard fret slots.
Here is the fingerboard ready for fret slot cutting:
Here’s the profile at 0.15” 
I cut the pieces of the miterbox. This is just some scrap I have. I flattened and put good, straight edges on it. Here it is ready for glue-up. I’ve brought this inside as it is a little chilly out and wanted to ensure the glue temp is a little warmer than the garage temp today. Plus granite countertops make a nice flat surface to ensure the parts are glued-up flat.
After gluing the sides to the base. I glued the top into place. The original design shows the grain running parallel to the saw kerf/guide. I started to do mine this way, but then decided that with changes in humidity, this would expand and contract making the kerf/guide wider or narrower. I need this to be constant and with minimal play. So I decided to rotate it and put this piece in with the grain running perpendicular to the kerf/guide. This will minimize the expansion/contraction of the kerf/guide and hopefully give me more consistent results. Here in Arizona this is typically not a huge deal as it is so dry. But we’ve had a lot of rain the last few weeks, so I started thinking, “This thing is going to shrink when it dries and the kerf is going to have too much play in it.” Hence the change to the design.
Here is the finished box. After putting it together and attempting to cut fret slots in a template, I found that I really needed to be able to see in there better. I should’ve used a smaller board for the top surface/guide but decided to just drill a peep hole instead which seems to work well enough.
Here it is with a fingerboard in place and a small backsaw to cut fret slots.
I attempted to cut some templates, but kept misaligning the cuts, and without being able to see, there’s no way to know if I’m missing the mark until I pull the template out and see that I’ve cut the slot a fraction of an inch off the line. Will keep at it. May modify this with some clear plastic for the top for complete visibility. Should’ve thought of that sooner.