Making a radiused sanding block and a fret press caul

If there’s one thing I love almost as much as building guitars, it is making the templates, tools and jigs to make guitars. Today I set out to make myself a radiused sanding block and a fret press caul. Now I could go to any of the reputable luthier suppliers, such as Stew Mac, or LMI and buy these but, because I tend to build types of guitars that you can’t buy I decided that it would be worth the investment in time to work out how to make my own – for that time when I want to build something with a 17.25″ radius.

I had spent a few hours researching ideas for making a radiused sanding block. Most of them are router based, either routing the curve into a single piece of wood, or routing several slices which are then glued together. I tried a couple of these approaches with limited success (i.e. they were a complete disaster). I then hit on a solution I hadn’t seen anywhere else – to use my bandsaw. I clamped a piece of MDF to the bandsaw’s table. I drilled a 4mm hole 12″ from the blade. I then drilled a series of 4mm holes at 30mm intervals in a length of 75mm wide 18mm thick MDF. I popped the drill bit through the holes and hey presto it cuts a 12″ radius into the other end, step to the next hole and cut the next, and the next and the next. I put the first one to one side (more on this later) and glued the remaining eight slices together. Hey presto 12″ radius sanding block.

Last time I made a neck I tapped in the frets with a leather faced hammer and, whilst it worked, it left me with a big job of fret levelling. This time I’m going to have a go at using my drill press and a caul, to press the frets into place. Hopefully this way I can be much more consistent with the fit of each.

I took the first piece of radiused MDF and drilled a 22mm hole through the face, and an 8mm hole from the edge to meet the larger hole. This allowed me to fit a threaded rod and a couple of threaded plugs (both rescued from a long gone Ikea bed) onto it to create a post that can chuck into the drill press. Hey, once again, presto.

12 thoughts on “Making a radiused sanding block and a fret press caul

  1. Can you please explain this more. I am looking at your radius block method but it looks as if when you cut more off the wood piece, you are no longer 12 inches away as the board gets smaller and smaller. Please explain. Thank you very much for this helpful information.

    • It is an easy misunderstanding Nathan. The piece being cut has several holes drilled in it at approx 2″ intervals and they each pivot on the post that is always 12″ away from the blade, therefore the radius always remains the same.

  2. Thanks for the tutorial! I’ve seen the router trick, too, and just didn’t think I can make a solid enough jig for that. This method looks much more feasible for me. However, when you line up the pieces to glue them, how do you make sure each concave side is perfectly lined up so you have an even radius down the block? I can see mine getting wobbly and looking like a camshaft.

    • I found that, because the curved edge of each piece is exactly the same profile and width, they lined up perfectly. I glued them up against a straight edge to keep the pieces lined up and it worked fine. No camshaft!

  3. I tried to make the steadiest jig with my jigsaw that I could, and used a blade for curving. Despite my tries, it was not precise enough and the radii weren’t continuous or uniform enough. I have now borrowed a band saw, but my question is: Does it take a special size blade to exact a curved cut? How wide of a blade is too wide to cut a 12″ radius accurately?

    • I can imagine it would be tough with a jigsaw. The way the blade wanders slightly will always cause problems for this side of thing. I don’t think it particularly requires a special size of blade although I can imagine the wider ones may cause a problem. I made my block with a 1/2″ blade and it was fine.

  4. Hey everyone.
    The most efficient way to do the radius block is to buy 12″ fretboard from SM and sanded yours against it. 100% accurate and very cheap.

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  7. I’d switch to Maple, (at least) instead of using MDF for the fret pressing Caul.. I can just see all the “grooves” in the MDF already!

    • That is a good call, although if using a harder wood you may want to face it with a softer material like leather to minimise risk of damage to the frets. The MDF was perfect for a one off job and survived long enough to do all 22 (but only just).

      • Thanx for your response damacleod, Maple should, by itself, be fine, cause I’ve used the Stewnac Brass cauls for years now without fret ‘injury’, I’d just make sure of the grain direction when cutting the caul. Probably wouldn’t want a Vertical grain situation? BTW, speaking of the Stewmac cauls, years ago I bought their “JAWS” Hand Fret Press for around $170.00, (with an extra head, and extra cauls), and now see it’s up around $350.00!!! A lot of people are preachin’ that we should buy GOLD as an investnent security, I would suggest however, that purchasing Stewmac Tools would work out pretty good as well, Ha! Gb bg

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