How would you sharpen curved plane blades?

[Bumble]

I purchased two planes with curved blades a few months ago, one concave and one convex.

The only method that Japanese use that I could find with video searches is to copy the profile at the cutting angle and then carve the same shape on a whetstone. They do this across the length so one stone can do more than one blade. I did purchase a new stone for this purpose but wondered what other techniques there were.

How would you sharpen these blades?

 

[Orraloon]

Japanese plane blades in Japan then do it the way they do. Nearest to that round one I have is a stanley 40 scrub. I clamp it in the vise and touch it up holding the oil stone in my hands to raise a bur then rub the back flat on the stone. Being a scrub its not critical about keeping an exact profile on the blade but yours will have to match the profile of the plane sole. Extra care needed. The hollow I would use a slip stone. Fine sandpaper on a dowel could also get it done then the back flat on a stone.
Regards
John

 

[AJBaker]

For the convex one I just use a normal stone (I use diamond plates) and I lean the blade left and right as I sharpen. I try to get the whole bevel evenly. One challenge if it's an iron from a scrub plane, is that the middle of the bevel will be the only part that really needs sharpening, but you also need to remove material on the left and right to maintain the convex shape.

For the concave one, I use sandpaper around a dowel. They're a pain to sharpen, I try to use those planes as little as possible. If I can, I'll try to remove most of the material with a rebate plane first.

 

[Eshmiel]

3M "papers" are your friend here. They do them in rough as well as super-smooth grits. They're long lasting and effective. They can be stuck to wooden forms to make shaping-sharpening-stropping surfaces to match any shape. Workshop Heaven sell them in single sheets and collections but they're available all over the place.

https://workshopheaven.com/abrasives/3m-microfinishing-film/

Rather than shape a waterstone to those profiles (and how would you keep it at that profile, or dress it) you can make wooden forms with a groove and a hump having radii to match your blades. Do you know the radius of those blades?

There may also be ready-made wooden forms with suitable humps or grooves. For example:

https://www.cyclaireshop.co.uk/beavercraft-spoon-carving-knife-strop

 

[Jacob]

I purchased two planes with curved blades a few months ago, one concave and one convex.

View attachment 197886

The only method that Japanese use that I could find with video searches is to copy the profile at the cutting angle and then carve the same shape on a whetstone. They do this across the length so one stone can do more than one blade. I did purchase a new stone for this purpose but wondered what other techniques there were.

How would you sharpen these blades?

The convex edges are really easy to sharpen freehand. You simply scoop them along an oil stone, holding them at 30º to the surface, sideways (ish) say 45º across the stone, twisting as you go. A bit like scooping ice cream off the surface of a tub with a spoon, and about as difficult. Bring up a burr, turn face down and take it off.
I've been doing it for years with a scrub plane blade and it's about the easiest thing to sharpen.
The concave edges with a slipstone. Bigger radius better, but anything will do.

 

[Bumble]

Japanese plane blades in Japan then do it the way they do. Nearest to that round one I have is a stanley 40 scrub. I clamp it in the vise and touch it up holding the oil stone in my hands to raise a bur then rub the back flat on the stone. Being a scrub its not critical about keeping an exact profile on the blade but yours will have to match the profile of the plane sole. Extra care needed. The hollow I would use a slip stone. Fine sandpaper on a dowel could also get it done then the back flat on a stone.
Regards
John

Needing to keep the exact profile of the plane sole did not occur to me. I think this means I do have to carefully transfer the profile of both blades to a stone then. I need to go to the toy shop to buy some plasticine.

 

[Bumble]

3M "papers" are your friend here. They do them in rough as well as super-smooth grits. They're long lasting and effective. They can be stuck to wooden forms to make shaping-sharpening-stropping surfaces to match any shape. Workshop Heaven sell them in single sheets and collections but they're available all over the place.

https://workshopheaven.com/abrasives/3m-microfinishing-film/

Rather than shape a waterstone to those profiles (and how would you keep it at that profile, or dress it) you can make wooden forms with a groove and a hump having radii to match your blades. Do you know the radius of those blades?

There may also be ready-made wooden forms with suitable humps or grooves. For example:

https://www.cyclaireshop.co.uk/beavercraft-spoon-carving-knife-strop

This is interesting. Cutting the profile in to wood sounds easier and less expensive than carving a stone; I might attempt this method first.

 

[Bumble]

The convex edges are really easy to sharpen freehand. You simply scoop them along an oil stone, holding them at 30º to the surface, sideways (ish) say 45º across the stone, twisting as you go. A bit like scooping ice cream off the surface of a tub with a spoon, and about as difficult. Bring up a burr, turn face down and take it off.
I've been doing it for years with a scrub plane blade and it's about the easiest thing to sharpen.
The concave edges with a slipstone. Bigger radius better, but anything will do.

I will search for a slipstone. A quick look shows Japanese companies making them but only for export; those on sale have been reimported and are silly prices.

 

[AJBaker]

You can cut the profile into a piece of wood by planing it into a piece of scrap with the same plane. Then you can put stropping compound onto it to strop the edge.

 

[Derek Cohen (Perth Oz)]

I purchased two planes with curved blades a few months ago, one concave and one convex.

View attachment 197886

The only method that Japanese use that I could find with video searches is to copy the profile at the cutting angle and then carve the same shape on a whetstone. They do this across the length so one stone can do more than one blade. I did purchase a new stone for this purpose but wondered what other techniques there were.

How would you sharpen these blades?

First lap the backs of the blades. They are likely to be pitted, and you cannot get a sharp edge unless they are smooth, polished steel.

The convex blade (curves outward) is the easiest of all. You can either (a) hollow grind on a bench grinder, following the curve, and then freehand on stones. The hollow acts as a jig. Or (b) Lift the outside edge and create a secondary bevel on the stones, following the curve. Do this either freehand or a guide.

The concave blade (curves inward) would also benefit from being re-ground to ensure that the bevel extends to the back of the blade. Use a sanding wheel in a drill press (or a hand drill, but this is harder to hold steady) to grind the primary bevel. Either use a sanding wheel or sandpaper around a thick dowel to polish the edge. It is fine here to polish just the edge of the bevel and not the full bevel.

Regards from Perth

Derek

 

[Jacob]

Needing to keep the exact profile of the plane sole did not occur to me. I think this means I do have to carefully transfer the profile of both blades to a stone then.

No, assuming the plane has a matching sole you just need to sharpen it carefully and check it against the sole, and if necessary make slight adjustments if it's drifted out.

I need to go to the toy shop to buy some plasticine.

If you really want to!

 

[Jacob]

This is interesting. Cutting the profile in to wood sounds easier and less expensive than carving a stone; I might attempt this method first.

Easier not to do either and use a slipstone for the inner curve and a normal flat stone for the convex edge.

 

[Jacob]

I will search for a slipstone. A quick look shows Japanese companies making them but only for export; those on sale have been reimported and are silly prices.

No need to go Japanese they are readily available here. https://www.google.com/search?q=slipstone+norton+india&sca_esv=89dbe79c79dccf28&sxsrf=AHTn8zq-KU23j1FSR0ZnaBRjmYx3Dj9UVg:1739777913231&ei=eeeyZ7ziDbaBhbIP07OK2Q4&ved=0ahUKEwj8gobkmcqLAxW2QEEAHdOZIusQ4dUDCBA&uact=5&oq=slipstone+norton+india&gs_lp=Egxnd3Mtd2l6LXNlcnAiFnNsaXBzdG9uZSBub3J0b24gaW5kaWEyCBAAGAgYDRgeMggQABgIGA0YHjIIEAAYogQYiQUyCBAAGIAEGKIEMggQABiABBiiBEiLMFCABVjtInABeACQAQCYAXKgAd8IqgEEMTMuMbgBA8gBAPgBAZgCDqACrwjCAgoQABiwAxjWBBhHwgIFEAAYgATCAgQQABgewgIGEAAYBRgewgIGEAAYFhgewgILEAAYgAQYhgMYigXCAgUQABjvBcICBxAhGKABGAqYAwCIBgGQBgiSBwQxMi4yoAerRQ&sclient=gws-wiz-serp
PS Just noticed you are in Japan already @Bumble

 

[Jacob]

First lap the backs of the blades. They are likely to be pitted, and you cannot get a sharp edge unless they are smooth, polished steel.

The convex blade (curves outward) is the easiest of all. You can either (a) hollow grind on a bench grinder, following the curve, and then freehand on stones. The hollow acts as a jig. Or (b) Lift the outside edge and create a secondary bevel on the stones, following the curve. Do this either freehand or a guide.

The concave blade (curves inward) would also benefit from being re-ground to ensure that the bevel extends to the back of the blade. Use a sanding wheel in a drill press (or a hand drill, but this is harder to hold steady) to grind the primary bevel. Either use a sanding wheel or sandpaper around a thick dowel to polish the edge. It is fine here to polish just the edge of the bevel and not the full bevel.

Regards from Perth

Derek

I wouldn't go near a power grinding tool with such small blades. Biggest cause of problems for a novice. Instant overheating, rapid removal of too much material destroying the profile, etc etc.

 

[Derek Cohen (Perth Oz)]

I wouldn't go near a power grinding tool with such small blades. Biggest cause of problems for a novice. Instant overheating, rapid removal of too much material destroying the profile, etc etc.

Jacob, I have done many like these without an issue arising. How do you think that these blades were made originally?! Some poor sod sitting in front of a slowly turning sandstone wheel?

Regards from Perth

Derek

 

[Jacob]

Jacob, I have done many like these without an issue arising. How do you think that these blades were made originally?! Some poor sod sitting in front of a slowly turning sandstone wheel?

Regards from Perth

Derek

How they are made is one thing, how to keep them sharp is another!
Obviously a skilled craftsperson such as yourself can use a powered grinder successfully but we are looking at a beginner here.
I reckon overheating and over grinding are particular problems with grinders and novices.
But doing it freehand is a skill worth learning and much less error prone. Also the best way with small blades such as these.
New to sharpening and grindwheels tends to lead to second task being to remedy damage done with first attempts!
Bin there dunnit!

 

[Eshmiel]

How they are made is one thing, how to keep them sharp is another!
Obviously a skilled craftsperson such as yourself can use a powered grinder successfully but we are looking at a beginner here.
I reckon overheating and over grinding are particular problems with grinders and novices.
But doing it freehand is a skill worth learning and much less error prone. Also the best way with small blades such as these.
New to sharpening and grindwheels tends to lead to second task being to remedy damage done with first attempts!
Bin there dunnit!

Your answer begs the question: how does anyone progress from novice to experienced user of a power grinder - or anything else, including hand sharpening? I know only one surefire method .....

Still, given that these blades are one-offs for the OP, I tend to agree that going carefully would be best, which perhaps suggests that the quick actions of an unfamiliar power grinder might be best put off in the larnin' to some less critical blades. Hand shaping, sharpening and stropping are slow enough to make only small and easily corrected errors. Slow, yes.

Personally I'd use wooden formers to help shape the sharpening media (rough to honing grit will be required) as posted above. Doing curves on a flat surface is, when one is a novice, going to result in an uneven job, probably with them devil-facets and maybe also vari-curves!

Prep of front and back of the blades, as Derek suggested, is also needed. Perhaps a chemical dip to clean orf rust followed by a rub on various sandpapers stuck to float glass. Or a flat-plattern belt grinder..

Use of wooden formers to shape the sharpening media can still be hand-sharpening, tha knows. Mind, I suppose that worn cathedral step might have some suitable curves.

 

[okeydokey]

As a first step I would flatten the front, back and all edges to remove the rust and have something "nicer" to work with! Then freehand with a stone the convex shape, the concave go for broom handle sized dowel with grades of wet and dry (or 3m if its available in your location) glued on and you will work up a sharp edge (pushing away from the edge)
Would you upload some photos of the plane bodies please.

 

[Bumble]

No need to go Japanese they are readily available here. https://www.google.com/search?q=slipstone+norton+india&sca_esv=89dbe79c79dccf28&sxsrf=AHTn8zq-KU23j1FSR0ZnaBRjmYx3Dj9UVg:1739777913231&ei=eeeyZ7ziDbaBhbIP07OK2Q4&ved=0ahUKEwj8gobkmcqLAxW2QEEAHdOZIusQ4dUDCBA&uact=5&oq=slipstone+norton+india&gs_lp=Egxnd3Mtd2l6LXNlcnAiFnNsaXBzdG9uZSBub3J0b24gaW5kaWEyCBAAGAgYDRgeMggQABgIGA0YHjIIEAAYogQYiQUyCBAAGIAEGKIEMggQABiABBiiBEiLMFCABVjtInABeACQAQCYAXKgAd8IqgEEMTMuMbgBA8gBAPgBAZgCDqACrwjCAgoQABiwAxjWBBhHwgIFEAAYgATCAgQQABgewgIGEAAYBRgewgIGEAAYFhgewgILEAAYgAQYhgMYigXCAgUQABjvBcICBxAhGKABGAqYAwCIBgGQBgiSBwQxMi4yoAerRQ&sclient=gws-wiz-serp
PS Just noticed you are in Japan already @Bumble

I think the slipstones are just not used over here in Japan. The ones labelled *Japanese stone slipstones* sold in the US/UK are Japanese manufactured stones that are then cut to *slipstones* in the west. With the help of your link though, I have found an importer that sells the Norton India stone for a price similar to the resell price in the UK and have ordered one.

Thank you for the link!

 

[Bumble]

As a first step I would flatten the front, back and all edges to remove the rust and have something "nicer" to work with! Then freehand with a stone the convex shape, the concave go for broom handle sized dowel with grades of wet and dry (or 3m if its available in your location) glued on and you will work up a sharp edge (pushing away from the edge)
Would you upload some photos of the plane bodies please.

These are the blades in the planes

I think the convex one on the right is unused and probably from left over stock from a closed business. The original retail price sticker is still on it, showing a retail price of JPY 1480 (equiv GBP 8) and it has no hammer marks (blades on Japanese Kanna are removed by striking with a hammer). I purchased them for equiv GBP 1 each.