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best way to shape the fretboard's radius


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Hi everybody,

i'm building my second guitar but unlike the first construction, i want to make the neck.

After having studied the different steps of the neck's construction, I can not make a choice regarding the shaping of the fretboard's radius.

There is two way to process; the sanding block or the jig (with a router). Using the sanding block is the simplest process and I think the most used. But there is a small problem which I was even confronted with, it's the imprecision of the sanding blocks. I bought one and it was a little twisted in the length. This can create inaccuracies in the radius of the fretboard.

On the other hand, the second option requires the construction or purchase a jig, which is much more complex and expensive.

There is a third option, this is to make it's own sanding block but this require the construction of a jig too.

I would like to know if you can share your experiences with all of this. I feel like using aluminum sanding blocks is the best way, even though they are expensive.

thank you for your help!!

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There's more options than those two (three) although I guess they're the most common ones.

You can radius a fretboard with a hand plane. Or, should I rather say that it's a valid method if you're good with a hand plane. My skills aren't that good, neither are the planes at the public workshop. But it can be done and the result is both smooth and accurate. That's shown in early Crimson Guitars videos quite often.

Basically you could use a long sanding beam in a similar manner.

Also, if memory serves me right, I've seen a long sanding block equipped with plane type handles...

A big belt sander can be used to knock the bulk off. However it's also easy to round the edges too much...

At the workshop we are allowed to use the milled steel blocks of our Master. They were originally made for mass producing Flaxwood fretboards but the idea didn't work as such so now we clamp the blocks between the dogs of the bench and rub the necks/fretboards against them. A long aluminium block sounds like a good alternative to that plus it's lightweight enough to be used like a hand plane.

Last, wood can warp as you've seen with your sanding block. That said, aluminium blocks can also suffer from bumps and nicks, Even the milled steel blocks may deform when dropped on concrete. At that point they're defective and should either be fixed or discarded. If they're intact when you buy them you should get a replacement.

Good quality tools are worth their price in the long run. I'd vote for the aluminium block unless you know a machinist who can mill you a full length solid metal block with a radiused groove.

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3 hours ago, Bizman62 said:

There's more options than those two (three) although I guess they're the most common ones.

Given the tradeoff between experience, complexity and cost, a sanding block is still the best solution for radiusing the fretboard. Some of the options proposed require skills or tools that many beginners wouldn't have access to.

 

3 hours ago, Bizman62 said:

I'd vote for the aluminium block

Agreed. The longer ones can be pricey but they're worth it in the long run, particularly if you have intentions of building more than just a couple of instruments. Guitar and Woods have 450mm ones in a range of radii that are a good alternative to the extremely expensive (possibly overpriced?) 18" Stewmac ones. I can confirm from experience that both are good options. Failing that, there are Chinese knock-offs available on Aliexpress or Ebay that might be OK for even less money but quality may be questionable, and it would be a gamble as to whether you'd want to risk it.

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Have you considered making your own router jig? The bought ones are nice, but you can knock something up from plywood in a hour or so. This was made from plywood offcuts, and two steel shelf support. The curve was cut with a jig saw, and the curved edge treated with wax polish so that it runs freely. I keep thinking about making a more sophisticated jig, but this one works.

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I guess if you are planning on doing more than one in your lifetime... a jig is the way to go imo.  as demonstrated above it's not all that hard to do.  If I had to do it... I'd probably try to use a router and pivot point to make the arches so that they are smooth.  I've seen folks use pvc as the rails since it is slipery and won't hang up anywhere.  If you go google hunting for images of jigs... there are a lot of options out there.

sanding blocks: there is a lot of folks making these these days.  I had bought a couple back in the day and they were rock solid straight.  now-a-days there are even some folks making them out of plastic.  I think if you hunt around you can get something decent for cheap.  best of luck.

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this subject seems to be complicated. I find a post on this forum (subject When To Radius... in the forum inlay and finishing).

it appears that it's possible to use this kind of jig (with router) with inlay already installed on the fretboard but with "simple" and small shapes such as round. Everybody isn't agree when the inlays are big,  fine or have more complex shapes.

 

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27 minutes ago, Macarel31 said:

when the inlays are big,  fine or have more complex shapes.

That is because the inlay material can be much harder than wood which usually makes it more brittle. And it's thin, only about 1.5 mm or less. So if you have a large inlay that's 1.5 mm thick in the centre it may be only 0.5 mm at the edge after radiusing. Think about a 0.5 mm thin piece of porcelaine, it doesn't take much to break!

Same with complex shapes like vines. A thin and narrow piece can easily be torn off by the router bit.

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2 hours ago, Macarel31 said:

this subject seems to be complicated. I find a post on this forum (subject When To Radius... in the forum inlay and finishing).

it appears that it's possible to use this kind of jig (with router) with inlay already installed on the fretboard but with "simple" and small shapes such as round. Everybody isn't agree when the inlays are big,  fine or have more complex shapes.

The thread you refer to is asking a different question - "Should I inlay before applying the radius or after?" The mention of a router in that context is related to people asking how to use the router to cut the inlay pockets if the fretboard is already curved with a radius, rather than how to apply the radius in the first place. 

 

2 hours ago, Bizman62 said:

That is because the inlay material can be much harder than wood which usually makes it more brittle. And it's thin, only about 1.5 mm or less. So if you have a large inlay that's 1.5 mm thick in the centre it may be only 0.5 mm at the edge after radiusing. Think about a 0.5 mm thin piece of porcelaine, it doesn't take much to break!

Same with complex shapes like vines. A thin and narrow piece can easily be torn off by the router bit.

Yes - the router is not the way to remove excess material from brittle or very fine inlay material, and in that respect the router jig is most certainly not the best tool to add a radius to a fretboard if it has been inlaid first. Sanding is still the most appropriate method.

I'd still suggest that a quality sanding block/beam is your best course of action here. IME the router radius jig tends to be a one-trick pony (and even then, only if the fretboard timber lends itself well to being machined in such a fashion), and you'd have to weigh up if the complexity of it in comparison to a radius block is worth the trade off to you. Early on I built such a jig for radiusing fretboards. It worked OK for material like plain maple or rosewood, but for anything more unforgiving like figured wood, or extremely dense or 'chippy' material, it made a complete mess of things. The surface finish coming off the jig also tended to be fairly rough, so I'd have to use the sanding radius block to clean up all the router marks, which immediately negated the purpose of the jig in the first place.

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4 hours ago, curtisa said:

The thread you refer to is asking a different question - "Should I inlay before applying the radius or after?" The mention of a router in that context is related to people asking how to use the router to cut the inlay pockets if the fretboard is already curved with a radius, rather than how to apply the radius in the first place. 

 

Yes - the router is not the way to remove excess material from brittle or very fine inlay material, and in that respect the router jig is most certainly not the best tool to add a radius to a fretboard if it has been inlaid first. Sanding is still the most appropriate method.

I'd still suggest that a quality sanding block/beam is your best course of action here. IME the router radius jig tends to be a one-trick pony (and even then, only if the fretboard timber lends itself well to being machined in such a fashion), and you'd have to weigh up if the complexity of it in comparison to a radius block is worth the trade off to you. Early on I built such a jig for radiusing fretboards. It worked OK for material like plain maple or rosewood, but for anything more unforgiving like figured wood, or extremely dense or 'chippy' material, it made a complete mess of things. The surface finish coming off the jig also tended to be fairly rough, so I'd have to use the sanding radius block to clean up all the router marks, which immediately negated the purpose of the jig in the first place.

I think you are right.

The aim to use jig is to avoid sanding block. If after using the jig i must use anyway a sanding block at the right radius to level the inlays or to improve the surface's rugosity of the fretboard, it's not interesting. So I'm going on with the sanding blocks

In addition,  making a jig for making sanding blocs can be useful for all the reasons mentioned in the previous posts.

Thank you!!

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2 hours ago, Macarel31 said:

If after using the jig i must use anyway a sanding block at the right radius to level the inlays or to improve the surface's rugosity of the fretboard, it's not interesting.

That is very much so. You can't get a smooth surface with a router, no matter how fancy the jig is. WIth a sanding block you can go up the grits for a satin sheen, with a router you'd get something similar to 100 grit.

You can use a more aggressive tool like a belt sander to knock the corners off to speed up the sanding process, though. A facet or two will cut the actual sanding down to - dare I say an hour for the shape and another for polishing. Use a coarse paper (60 or 80) for the shaping and remember to brush or blow the dust off after every two strokes to prevent clogging.

kuva.png.782210af3e3b7d566f1fb99762c6fec1.png

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  • 2 months later...
On 4/19/2022 at 7:32 PM, Macarel31 said:

 

There is a third option, this is to make it's own sanding block but this require the construction of a jig too.

 

I made sanding blocks by cutting pieces of plywood and then glueing them together, works fine! It gives the opportunity to make the block as short or long as you like.

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On 4/26/2022 at 11:13 PM, Bizman62 said:

That is very much so. You can't get a smooth surface with a router, no matter how fancy the jig is. WIth a sanding block you can go up the grits for a satin sheen, with a router you'd get something similar to 100 grit.

You can use a more aggressive tool like a belt sander to knock the corners off to speed up the sanding process, though. A facet or two will cut the actual sanding down to - dare I say an hour for the shape and another for polishing. Use a coarse paper (60 or 80) for the shaping and remember to brush or blow the dust off after every two strokes to prevent clogging.

kuva.png.782210af3e3b7d566f1fb99762c6fec1.png

not sure I agree that you can't get a smooth surface w a router.  if your jig is smooth the surface is only going to have superficial tool marks that will easily be sanded away at 220 grit.  When I did the radius for my strats - by hand with a jig... the sanding prior to gluing on a top was absolutely minimal 5 mins max.  sure you are going to have to do some sanding either way... but the amount of sanding you'd do doing the radius-sanding-block vs the amount of FINISH sanding you'd do after a router/jig is night and day different amounts of work. 

i think above, you say after the belt sander you can do it in an hour... so figure 20 mins of belt sander + 1 hour of hand sanding... if you spent that 1 hour building a jig it's going to mean 10 mins of runtime and another 5 - 10 mins of finish sanding.

more importantly... a router/jig is going to be much more consistent and less prone to issues when leveling.  not saying it can't be done well... but even with guides at the side keeping your radius block flat... unless you use a 21" radius block... it would be very easy to get results that mean more sanding afterwards with a leveling bar to flatten things perfectly.  iow it's more idiot proof and I suppose that's why it resonates w me so well!

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37 minutes ago, mistermikev said:

not sure I agree that you can't get a smooth surface w a router.  if your jig is smooth the surface is only going to have superficial tool marks that will easily be sanded away at 220 grit.

Now that you said it... I must have been thinking about some awkward way of doing it! The end of the router indeed does make a smooth surface - there's usually no need to sand the cavities...

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2 hours ago, Bizman62 said:

Now that you said it... I must have been thinking about some awkward way of doing it! The end of the router indeed does make a smooth surface - there's usually no need to sand the cavities...

 Right on, I guess like anything else it all depends on how you do it . Now that I think about it when I was doing that with a jig I was using a bowl bit the whole time and that probably makes a big difference too not having sharp edges

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