How to make long concave profiles with hand tools?

[CMax]

Hi all,

So I'm going to be building some guitars. In the past, I've bought and used pre-made radius sanding blocks, but I'd rather make them myself this time out (I've since sold all my guitar tools many years ago, hence I'm now starting from scratch).

For those not in the know, all they are is a length of wood, about 100mm wide and 150mm-1.5m long with a concave profile cut into it at a given radius (a half-pipe essentially), usually measured in inches (12-16 being common). These are used for sanding down flat, square fretboards to impose a radius across their width.

There are tons of tutorials on how to do this with a powered router, but I neither own nor want to own one and prefer to handle this by hand if possible. My first thought was to adapt an old Stanley no.4 with a heavily-cambered blade, not too dissimilar to a scrub. But this poses a width problem. I suppose it could be possible to do it in segments and glue them up, but I'm not sure how accurate that would be.

I thought of carving it in with a rasp. That would work for a short section, but I doubt I'd be able to do it accurately along longer lengths. Again, I suppose I could do multiple blocks and then glue them together, but it doesn't sound like an optimal method.

Am I missing a really obvious answer? Moulding planes, perhaps? Are there ones big enough for this kind of operation? My initial inquiries haven't found anything, or I'm not looking for the right thing. There's the issue that if I did find a moulding plane, I would need multiple to give me the different radii.

 

[Mike G]

Find yourself an old wooden plane with a curved cross-section. There's a knack to using them, but it is do-able, and it's the only way I can think of to achieve what you want to achieve. I start with making a series of grooves:





And follow that up with the coved moulding plane:

 

[AndyT]

Mike's exactly right. I'll add a few more thoughts. The plane he showed is simply called a "round". They were made in a range of sizes up to about 2" wide, marked with sort-of-standard numbers. Luckily for you, the bigger sizes are a bit easier to find, as they got used a bit less. Expect to pay somewhere between £5 and £20 for a single one from eBay or an old tool dealer.

Your idea of a flat soled plane with a deeply curved blade wouldn't work, you need the shaped sole to control the cut.

To finish off the profile you'll probably need to do some sanding. A good method is to wrap sandpaper round an offcut of plastic waste or down pipe. Alternatively you can plane a convex block with a flat plane.

And welcome to the forum!

 

[Doug]

Could you not just cut the waste pipe, down pipe or even soil pipe for a shallower curve down its length & stick some abrasive to the inside & you’ve got a radiused sanding block.
Just a matter of finding a bit of pipe the radius you want but there’s plenty of different sizes out there.

 

[Malc2098]

I think I might have a spare or two if you're stuck. I'll have to dig them out from the bottom of the bottom drawer to check on their radii.

 

[CMax]

Find yourself an old wooden plane with a curved cross-section. There's a knack to using them, but it is do-able, and it's the only way I can think of to achieve what you want to achieve. I start with making a series of grooves:

Thanks Mike, that looks to be just what I was after. Your photos explain it perfectly.

Could you not just cut the waste pipe, down pipe or even soil pipe for a shallower curve down its length & stick some abrasive to the inside & you’ve got a radiused sanding block.
Just a matter of finding a bit of pipe the radius you want but there’s plenty of different sizes out there.

That's certainly doable, though it gets tricker with the flatter radiuses. I'll likely give the wooden plane route a try but should I fail, this might be a decent option. Thanks for the suggestion.

I think I might have a spare or two if you're stuck. I'll have to dig them out from the bottom of the bottom drawer to check on their radii.

That's kind of you, Malc, thank you. I could just buy a set, but I'm mostly focussed on doing as much by hand if possible, mostly to learn and build the skill, but I appreciate the offer.

 

[Sheffield Tony]

This could be a rare contemporary use for an old pattern maker's plane ? If you're not familiar, a wooden bodied plane with a set of interchangeable bases and cutting irons to create a range of concave surfaces, usually larger radius than most "round" wooden planes.

I admit I bought a pattern maker's plane some time ago (I'm from a steelworking family, it must be in the blood !) and have yet to find a sensible use for it.

 

[CMax]

This could be a rare contemporary use for an old pattern maker's plane ? If you're not familiar, a wooden bodied plane with a set of interchangeable bases and cutting irons to create a range of concave surfaces, usually larger radius than most "round" wooden planes.

I admit I bought a pattern maker's plane some time ago (I'm from a steelworking family, it must be in the blood !) and have yet to find a sensible use for it.

Thanks for the suggestion. Having looked online for these, they do seem rather handy, if in short supply. I'll keep an eye out in case a decent set crops up. I wouldn't mind having a set in my collection.

 

[thetyreman]

you could do 98% of the fretboard radius with a hand plane, then finish it off with scrapers.