Starting luthierie or the art of building- and repairing stringed instruments can be quite expensive. Fun thing is, you can make it as expensive as you like.
I just pillaged through all my stuff seeing if I could use some stuff laying around the house- and at the local stores which I could use as tools. Here’s a list of some stuff I came up with:
A digital caliper in both mm and inch is an indispensable tool for measuring thicknesses, widths and depths (use the back end for depths). Quite inexpensive and widely available in hardware- and DIY stores.
Anti slip mat
Found this stuff at my local household goods store. Very cheap, a roll of 2 / 3 meters long, about 50cms wide for under 2 euros. Comes in handy for scratch protection and useable when friction matters.
Use a school or mathematical ruler in plastic or metal: put it against various flat surfaces and check for light (this indicates a curve or concave in the straightedge); no light? Then you’re all set. You can even use a saw, rasp or Dremel tool to cut out the fret positions! I found out that “stamped” steel parts (especially used in door locks and door hinges) are quite straight! Use them as shorter straightedge or as a fret rocker.
A fret rocker is a straight piece of metal that covers 3 frets. Using it, you can pinpoint if frets are higher than neighboring frets, because then the fret rocker “ticks” back and forth over a high fret. Again, make sure that your piece of metal is dead straight by testing it on various flat surfaces. Due to the fact that fret spacings vary along the length of the neck, you can use several bits of metal to cover the fret spaces.
A cheap small laser pointer can serve as a straightedge in light. Shine across the tops of the frets on the fingerboard to easily tell whether the neck is straight; maybe build a jig around it.
I had some very coarse sandpaper I found out, the stuff you use to sand your woodwork around the house prior to painting. Checking the local DIY store, I found wet sandpaper with grits up to 1200. These come in very handy in repairs, fret work, removing burrs from screwheads and waterslide decals. Higher grits and textile- and or mylar backing papers are hard to come by in local stores but are supplied by specialty and automotive parts and paints supply stores or through auction sites.
Neck support block
Who needs those expensive neck rocker support blocks that cost tons of money; get a piece of scrap wood and make a neck support block. You don’t even need any neck shaped carvings in it, as long as you protect your woods and finishes with something soft (and grippy) like for instance that anti slip mat stuff I mentioned earlier.
Available in DIY and automotive parts stores. In mm or inches or sometimes both, quite inexpensive.
Hex- or Allen (Imbus) keys
Hex- or Allen keys (imbus) are widely available in DIY stores. However, they come in mm and inch sizes, also known as “metric” and “imperial”. This difference is very important and difficult to judge by eye. So it pays to own both; check out your local hardware or DIY stores or auction websites.
Specialized fret clippers can be quite expensive. You can also make your own; just buy a pair that looks almost flat and grind it flat using a sharpening station or abrasive stone. Make sure to pick one with longer handles, this comes in handy where the neck sits over the body of the instrument.