I have a viola/cello-related problem that’s been bugging me for weeks. The fingerboard is a long slice out of a tall cone.

I cast it as accurately as I could. But it still has high points about 0.5 mm high along its length. I need to make it exactly straight along its length to an accuracy of 0.1 to 0.2 mm. But how?

I don’t have access to most power tools. I have an electric planer but how would that help?

One thought that occurs so me is to add more resin to the surface about 0.5 mm thick and then sand back using emery paper glued to a flat surface. But single sheets of emery paper aren’t big enough, A3 would only just be big enough. And I can’t think of any glue that gives a completely dead flat surface.

Even then, the polyester is so tough that sandpaper does nothing, and even files take ages to remove a tiny amount. Emery paper would take horribly many hours of sanding to take the surface down 0.5 mm.

But how else? Add more resin then wrap in a thin sheet of semi-rigid plastic to get the shape? But that’s expensive.

mollwollfumble said:

I have a viola/cello-related problem that’s been bugging me for weeks. The fingerboard is a long slice out of a tall cone.

I cast it as accurately as I could. But it still has high points about 0.5 mm high along its length. I need to make it exactly straight along its length to an accuracy of 0.1 to 0.2 mm. But how?

I don’t have access to most power tools. I have an electric planer but how would that help?

One thought that occurs so me is to add more resin to the surface about 0.5 mm thick and then sand back using emery paper glued to a flat surface. But single sheets of emery paper aren’t big enough, A3 would only just be big enough. And I can’t think of any glue that gives a completely dead flat surface.

Even then, the polyester is so tough that sandpaper does nothing, and even files take ages to remove a tiny amount. Emery paper would take horribly many hours of sanding to take the surface down 0.5 mm.

But how else? Add more resin then wrap in a thin sheet of semi-rigid plastic to get the shape? But that’s expensive.

Isn’t that a photo of a wooden one?

I don’t know what abrasives are recommended for the resin you’re using.

Seems much simpler to make one out of wood or buy a ready-made wooden one.

mollwollfumble said:

I have a viola/cello-related problem that’s been bugging me for weeks. The fingerboard is a long slice out of a tall cone.

I cast it as accurately as I could. But it still has high points about 0.5 mm high along its length. I need to make it exactly straight along its length to an accuracy of 0.1 to 0.2 mm. But how?

I don’t have access to most power tools. I have an electric planer but how would that help?

One thought that occurs so me is to add more resin to the surface about 0.5 mm thick and then sand back using emery paper glued to a flat surface. But single sheets of emery paper aren’t big enough, A3 would only just be big enough. And I can’t think of any glue that gives a completely dead flat surface.

Even then, the polyester is so tough that sandpaper does nothing, and even files take ages to remove a tiny amount. Emery paper would take horribly many hours of sanding to take the surface down 0.5 mm.

But how else? Add more resin then wrap in a thin sheet of semi-rigid plastic to get the shape? But that’s expensive.

might be worth buying the correct tools for the job

Bubblecar said:

I don’t know what abrasives are recommended for the resin you’re using.

Seems much simpler to make one out of wood or buy a ready-made wooden one.

I had planned to do that. Then realised that I had a weight problem. The wood would be so so heavy that it greatly changes the centre of gravity of the instrument.

Stumpy_seahorse said:

might be worth buying the correct tools for the job

Like a fingerboard shaper tool? Yes, they exist. But that only helps get the cross section correct, doesn’t help with high points along the length.

mollwollfumble said:

Stumpy_seahorse said:

might be worth buying the correct tools for the job

Like a fingerboard shaper tool? Yes, they exist. But that only helps get the cross section correct, doesn’t help with high points along the length.

I was thinking more a decent file, you’d get one at bunnings for less than $30

you can get rolls of emery. double sided tape to a flat piece of wood of desired length, i use about 300mm. prepping is always a task.

Stumpy_seahorse said:

mollwollfumble said:

Stumpy_seahorse said:

might be worth buying the correct tools for the job

Like a fingerboard shaper tool? Yes, they exist. But that only helps get the cross section correct, doesn’t help with high points along the length.

I was thinking more a decent file, you’d get one at bunnings for less than $30

That makes sense. Any recommendations for brand or fineness or, I don’t even know what to ask for? Bunnings files

mollwollfumble said:

Stumpy_seahorse said:

mollwollfumble said:

Like a fingerboard shaper tool? Yes, they exist. But that only helps get the cross section correct, doesn’t help with high points along the length.

I was thinking more a decent file, you’d get one at bunnings for less than $30

That makes sense. Any recommendations for brand or fineness or, I don’t even know what to ask for? Bunnings files

I just use a bastard cut half round file to shape stock steel and it does a good job.

you might want a second cut or finer to get a nicer finish on it, but any off the shelf brand should be ok

Bogsnorkler said:

you can get rolls of emery. double sided tape to a flat piece of wood of desired length, i use about 300mm. prepping is always a task.

This sort of double sided tape?
bear-48mm-x-4-5m-white-double-sided-tape

Rolls of emery? Bunnings doesn’t have anything it calls emery any more. They only seem to have Flexovit (which from what I’ve seen so far is pretty hopeless) or Diablo (which probably won’t lie flat). Which grit for fastest strongest cutting that won’t score the surface too much?

mollwollfumble said:

Bogsnorkler said:

you can get rolls of emery. double sided tape to a flat piece of wood of desired length, i use about 300mm. prepping is always a task.

This sort of double sided tape?
bear-48mm-x-4-5m-white-double-sided-tape

Rolls of emery? Bunnings doesn’t have anything it calls emery any more. They only seem to have Flexovit (which from what I’ve seen so far is pretty hopeless) or Diablo (which probably won’t lie flat). Which grit for fastest strongest cutting that won’t score the surface too much?

plastic rends to melt and clump.

mollwollfumble said:

Bogsnorkler said:

you can get rolls of emery. double sided tape to a flat piece of wood of desired length, i use about 300mm. prepping is always a task.

This sort of double sided tape?
bear-48mm-x-4-5m-white-double-sided-tape

Rolls of emery? Bunnings doesn’t have anything it calls emery any more. They only seem to have Flexovit (which from what I’ve seen so far is pretty hopeless) or Diablo (which probably won’t lie flat). Which grit for fastest strongest cutting that won’t score the surface too much?

buy a belt sander belt and cut to size. i have a thin 3M brand tape that i have had for years.

Stumpy_seahorse said:

mollwollfumble said:

Stumpy_seahorse said:

I was thinking more a decent file, you’d get one at bunnings for less than $30

That makes sense. Any recommendations for brand or fineness or, I don’t even know what to ask for? Bunnings files

I just use a bastard cut half round file to shape stock steel and it does a good job.

you might want a second cut or finer to get a nicer finish on it, but any off the shelf brand should be ok

> I just use a bastard cut half round file to shape stock steel and it does a good job.

I used one of those on the timber for my outdoor table. It was marvellous, a lifesaver. I could remove 5 mm thickness of timber with no problem at all. I haven’t been brave enough to use it on the fingerboard, but it might be just the ticket.

> plastic tends to melt and clump.

I managed to destroy a drill that way. Ah wait on, that was acrylic, I haven’t had that problem nearly as much with polyester.

I’ll continue with my negative parenting thanks. Stick to what I know.

Another approach would be to glue sandpaper to a piece of glass, which then sits on a bench face-up and the neck is rubbed against it.

Probably the flattest surface you’ll get without spending serious money.

Along the same lines, a cutting compound on a very flat surface (again, glass) which the neck is rubbed against would give a very fine surface.

Rule 303 said:

Along the same lines, a cutting compound on a very flat surface (again, glass) which the neck is rubbed against would give a very fine surface.

This is a good technique. I have used it on numerous motorcycle cylinder heads that were deliberately assembled without gaskets. I actually have a special piece of thick glass that was manufactured ultra-flat that I use for this purpose.

Thick glass is important. It bends less than thin glass.

Rule 303 said:

Along the same lines, a cutting compound on a very flat surface (again, glass) which the neck is rubbed against would give a very fine surface.

Any particular cutting compound capable of removing a 0.5 mm thick layer from a material much tougher than steel?

I have a piece of glass that will suit but don’t want it damaged, so … ?

mollwollfumble said:

Rule 303 said:

Along the same lines, a cutting compound on a very flat surface (again, glass) which the neck is rubbed against would give a very fine surface.

Any particular cutting compound capable of removing a 0.5 mm thick layer from a material much tougher than steel?

I have a piece of glass that will suit but don’t want it damaged, so … ?

It might be tougher than steel, but I doubt it’s harder. Plenty of lapidary compounds out there. Valve grinding paste. Even cut’n‘polish compound for cars would likely do the job. You want a layer removed? Better use coarse sand paper with (say) silicon carbide in it. I thought you just wanted asperities removed.

Don’t want your glass damaged? Buy another piece from a glazier. Or look where someone’s renovating, or demolishing an old house, or go to the tip shop.

use a carpenters plane?

“Ferrari’s Sebastian Vettel, who now trails Vettel by 17 points in the drivers’ standings, was only fourth after a change in strategy failed to pay off.”

Internally recursive reporting, I think.

Michael V said:

“Ferrari’s Sebastian Vettel, who now trails Vettel by 17 points in the drivers’ standings, was only fourth after a change in strategy failed to pay off.”

Internally recursive reporting, I think.

Maybe Fabian has taken up the sport

Michael V said:

“Ferrari’s Sebastian Vettel, who now trails Vettel by 17 points in the drivers’ standings, was only fourth after a change in strategy failed to pay off.”

Internally recursive reporting, I think.

Sorry.

Michael V said:

mollwollfumble said:

Rule 303 said:

Along the same lines, a cutting compound on a very flat surface (again, glass) which the neck is rubbed against would give a very fine surface.

Any particular cutting compound capable of removing a 0.5 mm thick layer from a material much tougher than steel?

I have a piece of glass that will suit but don’t want it damaged, so … ?

It might be tougher than steel, but I doubt it’s harder. Plenty of lapidary compounds out there. Valve grinding paste. Even cut’n‘polish compound for cars would likely do the job. You want a layer removed? Better use coarse sand paper with (say) silicon carbide in it. I thought you just wanted asperities removed.

Don’t want your glass damaged? Buy another piece from a glazier. Or look where someone’s renovating, or demolishing an old house, or go to the tip shop.

Thanks. Will try all four options you’ve suggested above:

1. Buy a new wood fingerboard and lighten it by filing pieces off to make it thinner.

2. Put a new 0.5 mm thick layer of resin on the home-made fingerboard and attack it with the flat side of a bastard file (try on a scrap piece first).

3. Flat piece of wood (or glass) with double sided tape and silicon carbide paper (if I can figure out which brand it is).

4. Buy glass cutting board from Target and get some polishing compound for final straightening.

mollwollfumble said:

Michael V said:

mollwollfumble said:

Any particular cutting compound capable of removing a 0.5 mm thick layer from a material much tougher than steel?

I have a piece of glass that will suit but don’t want it damaged, so … ?

It might be tougher than steel, but I doubt it’s harder. Plenty of lapidary compounds out there. Valve grinding paste. Even cut’n‘polish compound for cars would likely do the job. You want a layer removed? Better use coarse sand paper with (say) silicon carbide in it. I thought you just wanted asperities removed.

Don’t want your glass damaged? Buy another piece from a glazier. Or look where someone’s renovating, or demolishing an old house, or go to the tip shop.

Thanks. Will try all four options you’ve suggested above:

1. Buy a new wood fingerboard and lighten it by filing pieces off to make it thinner.

2. Put a new 0.5 mm thick layer of resin on the home-made fingerboard and attack it with the flat side of a bastard file (try on a scrap piece first).

3. Flat piece of wood (or glass) with double sided tape and silicon carbide paper (if I can figure out which brand it is).

4. Buy glass cutting board from Target and get some polishing compound for final straightening.

Glass cutting boards are thin, usually have legs, are bendable, and worse: often do not have flat surfaces – they are usually textured.

Go to a glazier. Or buy an old window for $5.

3M SandBlaster Pro

3M sandblaster ultra flexible sanding sheets feature an innovative film backing so you can fold, roll or shape into any form you need to get the job done. The tough backing resists puncture, tear and creases, helping the sheet keep its original shape. Use wet or dry. 220 grit.

Available in several Grits

This video may come in handy,
after all, a BUCKET is a sort of CONE …with a bottom. :-)

https://www.youtube.com/watch?v=GE7QA1chUzw

Ogmog said:

This video may come in handy,
after all, a BUCKET is a sort of CONE …with a bottom. :-)

https://www.youtube.com/watch?v=GE7QA1chUzw

The starting bit with the spokeshave is very similar to this “fingerboard tool”. I hadn’t realised that spokeshaves are still available.

Ogmog said:

3M SandBlaster Pro

3M sandblaster ultra flexible sanding sheets feature an innovative film backing so you can fold, roll or shape into any form you need to get the job done. The tough backing resists puncture, tear and creases, helping the sheet keep its original shape. Use wet or dry. 220 grit.

Available in several Grits

Oh wow, that’s two tools in one. The flex could help get the straight edge straight, because it could flex into a cone shape.

It’s merely another type of sandpaper

…sans the sand & the paper…

yes, it is thin & flexible enough to mold itself to just about anything you can wrap it around
AND lasts for a very very (very) long time since it can be WASHED and Dried repeatedly in order to dislodge any material that would normally load (cog) the grit

If you click the written link I left
you’ll find sponge blocks and whatall.

mollwollfumble said:

Ogmog said:

This video may come in handy,
after all, a BUCKET is a sort of CONE …with a bottom. :-)

https://www.youtube.com/watch?v=GE7QA1chUzw

The starting bit with the spokeshave is very similar to this “fingerboard tool”. I hadn’t realised that spokeshaves are still available.

Why wouldn’t they be available?

roughbarked said:

mollwollfumble said:

Ogmog said:

This video may come in handy,
after all, a BUCKET is a sort of CONE …with a bottom. :-)

https://www.youtube.com/watch?v=GE7QA1chUzw

The starting bit with the spokeshave is very similar to this “fingerboard tool”. I hadn’t realised that spokeshaves are still available.

Why wouldn’t they be available?

They are available, but they wouldn’t help with the straightness problem. I suspect that the flexible sandpaper wouldn’t either, there are too many ways for it to flex.

A very sharp drawknife of appropriate shape might work but you have to know how to use it and again, it’s really a woodworking tool.

Bubblecar said:

A very sharp drawknife of appropriate shape might work but you have to know how to use it and again, it’s really a woodworking tool.

Found a tool that is a combination of drawknife, spoke-shaver and rasp. It’s called a hacksaw. (To be specific a junior hacksaw). LOL. It does work, though.

Going back to first princples, the ideal shape for the edge of the cone is not straight.

There are two different approaches to determining ideal shape. One is to minimise the effort needed to do the fingering. That turns out to be an ellipse.

The other is to allow maximum string vibration without the string hitting the fingerboard. That turns out to be a logarithmic spiral.

The ellipse and the logarithmic spiral have similar shapes on this scale and both are concave upwards, not straight.

Next instrument perhaps.