Radius Sanding Blocks from Jig to Final

[eubie]

Making Things to Make Things to Make Things

One of the reasons I love woodworking is that it is simply what it is.  It’s me and the wood and nothing but a tool or two between us.  And that simple relationship gives rise to beauty and function with no pretension.  Well, most of the time anyway.  Sometimes it turns out that I’ve spent an entire day in the shop making something that I need in order to make something that I’ll use to make something, and that’s what today’s post is actually about.

Creative Problem Solving

The ultimate goal in this case is the Les Paul style electric guitar that Josh and I are building.  We want the traditional Les Paul 12" radius, but getting a radius on an eighteen(ish) inch by three(ish) inch board isn’t as easy as running it through a band saw.  There seem to be a few common approaches to making that radius (there are actually a million ways to skin this cat, these are the ones I see most often).

1. Hand planes.  If you are good, you can plane the radius into the board with a sharp hand plane.  Something along the lines of a Stanley #4 is a good choice.  This takes a good bit of skill though, and is easy to mess up – which is not what you want to do with a carefully selected, highly figured piece of wenge.
2. Router jig.  There are several approaches to jigs you can build for your router that will carve the radius directly into your board.  Many luthiers use this approach, and I may go there eventually, but these are often pretty involved builds, and the jig you end up with really only has one good use.  So sure, when I get to the point that I’m building a guitar each month or so, this is probably where I’ll end up, but for now I’m looking for a simpler solution that hopefully can address more than just this one need.
3. Radius sanding block.  Sanding blocks with one surface cut at the desired radius can be used to sand that radius into the fretboard.  If you have a block with a known and trusted radius, this is a very safe method of transferring that radius to your fretboard – it is unlikely that your sanding block will transfer a wrong radius, or will slip and gouge your board. Also, take the sandpaper off the block, and you’ve got a clamping caul with a matching radius.  Simple and versatile.  This is the direction I decided to go.

Buy or Build?

Radius sanding blocks are readily available from lots of vendors.  But I tend to be a never buy what you can build kind of guy, so before I started shopping, I started drawing up ideas.  Giving credit where it’s due, my initial ideas for the jigs came from a post by @hittitewarrior .  His jig is a pretty large contraption and that size seemed to introduce a little too much variance in his results, so I wanted to design something smaller and simpler.  I ended up with the following.

A simple tower on a flat base with a couple side-supports.

 

A small trim router attached to a board that hangs from the tower on a pivot point.

  

There is a pivot point in the tower, and a corresponding point in the board for each radius that I’m interested in.

    

As you can see in the pics above, I started with a metal pin in the pivot point, but I had a problem with the pivot board wanting to fall off the pin, so I had to switch that to a bolt.  This was much more effective in keeping the pivot board secured to the tower.

    

I used 1 x 3 poplar for my blocks.  These are just project boards from Home Depot so they are easy to source and very inexpensive.  If I wreck one for some reason or if I want more, it’s not that big a deal.  The block goes under the router (duh) with some shims to get it to the right height and to keep it centered as I run it through.  In this case, I attached two blocks with superglue/masking tape to get the right height.

I then ran the router horizontally across the block, cutting the radius into the surface (I did try running a block using vertical passes along the length of the board, but that gave me an inconsistent radius). After each pass, I advanced the block 1 or 2 mm, then made another pass.  I went halfway across the board, then turned the block around and did the other half from the other side.  This allowed me to keep my fingers out of the way, but also required that I had the block centered properly so the radius would line up when run from opposite sides.

    

After running through the jig the radius was good, but as you can see, not completely smooth.  I set the board so the shadows would accentuate the ridges – they are not actually quite as bad as they look in the photo.  Some sanding with a flexible sanding sponge took most of the waviness out of the block and left me with a perfectly good surface to attach sandpaper to.  After finishing the 12″ block, I made another with a 9.5″ radius (assuming a future Strat-style build).

  

Hard to Handle (so make a handle)

Since I used 1 x 3 stock for the sanding block, it is a little on the thin side when it comes to actually using the thing (i.e. holding and sanding block itself).  To rectify this, I made a simple handle from 3/4 plywood and attached it to the back of the block.  I chiseled out some recesses to create some extra support and glue surface, and clamped lightly while the glue dried.

     

  

After a couple coats of wipe-on, matte polyurethane to protect, and keep the wood from moving too much, these sanding blocks are ready for action.  They haven't seen any action because as of last night the ploy was still curing, but as soon as I can get some actual sanding done, I'll post a follow-up with some results.

  

This was a fun project with direct costs of about $5 for the wood, and whatever value you want to place on the shop scraps I used to make the jig.  I figure it saved me about $30 on two blocks, and now I have a jig I can use to make as many sanding blocks or clamping cauls I want in the future.  Let me know what you think or if you have any questions.

[ScottR]

Very nice tutorial Eubie. Thanks for sharing.

SR

[Prostheta]

Excellent work. I've seen a number of radius block jigs over the years, and this sort of design is one of the more successful types! There's a lot of convergent evolution in the basic design as you might expect, however these are very much fit for purpose. I might add that the wipe-on poly will be fantastic in the sole of these blocks, as it allows the use of double-sided tape or adhesive-backed sandpaper to be removed without leaving residue perma-stuck to raw wood. That happened to my original StewMac Maple blocks, which are now only ever used as clamping cauls and edge bevel file blocks....

[Prostheta]

Are those little trim routers cheap enough? Never seen them before, but they look like they'd serve as the basis for all sorts of low-duty binding, radiusing, slotting jigs, etc. If they're cheap enough, they could be considered by most for permanent fixture in those jigs....

[eubie]

7 hours ago, Prostheta said:

Are those little trim routers cheap enough? Never seen them before, but they look like they'd serve as the basis for all sorts of low-duty binding, radiusing, slotting jigs, etc. If they're cheap enough, they could be considered by most for permanent fixture in those jigs....

I got mine from Harbor Freight.  It's branded as a Drill Master and the regular price is $30, though with the ubiquitous 20% off coupon, it's $24. On Amazon, this exact same Drill Master trim router is listed by several sellers in the $45 - $60 range (not sure who is paying the Amazon premium?).

I know there are varying opinions about Harbor Freight, but this little trim router does exactly what I expect from it.  Light duty in tight spaces - easier to handle than the big router in a variety of ways.  And if I was doing a lot of radiusing like this, for $24 I would definitely consider mounting one up permanently.

[Prostheta]

I can tell you without even looking at it which corners they cut. The casing will flex, and the spindle bearing will move because of that. It means the spindle will have increased runout, and heat will make the casing flex even more. The laminates on the spindle won't be well-balanced either.

For what it's worth, it's perfect. I wouldn't use it as a router though! Great for jigs, and might even be a worthwhile basis for a pantograph like mine. Big Dremel, and just as crappy. For the price though....yeah....win win.

[eubie]

32 minutes ago, Prostheta said:

For what it's worth, it's perfect. I wouldn't use it as a router though! Great for jigs, and might even be a worthwhile basis for a pantograph like mine. Big Dremel, and just as crappy. For the price though....yeah....win win.

Agree! 

[bileshake]

Ok, just trial an error to setup the notch heights on the upright?

[eubie]

I clamped the pivot arm to the upright with the router mounted in it then measured from the tip of the bit up to my desired radius and marked it.  Did this for a variety of radii, then drilled through both the pivot arm and the upright so the holes would be aligned.  Initially I used a metal dowel through the holes, but the pivot arm tended to slip off, so I switched to a bolt to hold it together.

[Prostheta]

Jigs are almost as fun as making guitars. I swear.

[hittitewarrior]

I love this!  Glad you found some good solutions to some of the problems in the design I was working with.  I like the band clamps to hold the router in place, I think the way I mounted my router led to a decent amount of my troubles due to the extra joint in the base.  That, and (as you said), I fed it through lengthwise, which could have further confounded the issues.  I got a 12" radius out of it that looks ok after sanding.  My 10" one ended up being cut up for clamping cauls.  Gotta confess, I ended up buying an aluminum beam to meet my 10" needs... *hangs head*...  Anyways.

Great job and great write up!

[eubie]

20 hours ago, Prostheta said:

Jigs are almost as fun as making guitars. I swear.

So true!  Now, if I could get myself to stop tinkering with the fret slotting contraption I've been working on, I could get back to actually building my guitar.

[eubie]

10 hours ago, hittitewarrior said:

Great job and great write up!

Thanks!  And thanks for the inspiration.  

Just this weekend I actually used my 12" radius block to sand a radius onto the fretboard for the current build, and it worked great, so I'm happy with the result.

[Prostheta]

2 hours ago, eubie said:

So true!  Now, if I could get myself to stop tinkering with the fret slotting contraption I've been working on, I could get back to actually building my guitar.

 

Don't rush. The instruments will always be the better for using well-made jigs.