Japanese spear plane

[Pete Howlett]

I was watching an excellent video of a guitar-making company in Korea. They hand carved their neck heels using what looked like a Japanese spear plane. These are really hard to come by and cost a nose-bleeding fortune when they are available. I took a saber saw blade (what I make all my knives from) and profiled it. I now need to put a gentle curve into it. So this is a question for the metallurgists here. These saw blades are HSS. Do I need to anneal, normalize, harden and temper as if I was using high carbon steel, or does the HSS retain its hardness after being heated, formed, and then allowed to cool naturally?

 

[Timbuck]

I was watching an excellent video of a guitar-making company in Korea. They hand carved their neck heels using what looked like a Japanese spear plane. These are really hard to come by and cost a nose-bleeding fortune when they are available. I took a saber saw blade (what I make all my knives from) and profiled it. I now need to put a gentle curve into it. So this is a question for the metallurgists here. These saw blades are HSS. Do I need to anneal, normalize, harden and temper as if I was using high carbon steel, or does the HSS retain its hardness after being heated, formed, and then allowed to cool naturally?

I was watching an excellent video of a guitar-making company in Korea. They hand carved their neck heels using what looked like a Japanese spear plane. These are really hard to come by and cost a nose-bleeding fortune when they are available. I took a saber saw blade (what I make all my knives from) and profiled it. I now need to put a gentle curve into it. So this is a question for the metallurgists here. These saw blades are HSS. Do I need to anneal, normalize, harden and temper as if I was using high carbon steel, or does the HSS retain its hardness after being heated, formed, and then allowed to cool naturally?

It's not as straight forward with High Speed Steel ..see here https://www.vacfurnace.com/vacuum-furnace-faq/high-speed-steel-annealing-process/ best go for high carbon tool steel like here https://www.instructables.com/Make-a-Yari-Ganna-Japanese-Spear-Plane/

 

[Paul1973UK]

I've done a bit of back yard blacksmithing in the past, a cheap source of good steel for knives and the like are old vehicle coil springs or leaf springs, many auto repair garages will have a pile of them out back they send for recycling and will probably give you a few to try out, the centre shaft of a shock absorber is good steel too but be aware the outer tube can contain pressurised oil so be careful harvesting the main shaft.
They will need to be heat treated to harden and then anneal to reduce the brittleness and make it hard enough to keep a good edge. Ken's post has instructions that look about right to me for a good heat treat.
HSS will soften when grinding on it if you're not careful and it gets too hot (above 200c or straw colour), and need to be heat treated again for a good edge.

 

[BuzzBD]

A lifetime ago before I got into lutherie, I was a custom knife maker, so I always make my own blades for finger planes and carving tools. Mostly I use old SawzAll blades which are a medium carbon steel. While it is technically possible to shape a blade with out detempering the steel, it is very difficult to do so, so I always harden and temper them myself. After shaping the the blade, I harden it by quenching it in olive oil at the critical temperature. Here is the trick, the critical temperature is described as heating the steel until it is cherry red in color. The big problem with that is cherry red varies greatly with the ambient light in your shop. You do not want to heat the steel any hotter or longer than necessary. The secret is that steel loses its ability to attract a magnet at the critical temperature. So I use a small magnet to test the blade several times during heating it. As soon as the magnet doesn’t stick to the blade, I quench it. I then temper the blade in my oven for an hour at 400 degrees F.
Brad

 

[Timbuck]

I looked at some of these spear planes online and they reminded me of an engineers curved scraper that we used to use when I worked in the Tool room. .. .I spotted this one one on EBay for about £25
4E016360-D0D7-4DF7-9112-994FE372528A by Ken Timms,

 

[TheDudeAbides]

Is the video freely available on the internet? I'd yes could you share the link?

Just watched a few short videos on spear planes, and while they look like fun, I can't wrap my head around how these would be used on a neck/heel, and am very curious now.

 

[Timbuck]

Is the video freely available on the internet? I'd yes could you share the link?

Just watched a few short videos on spear planes, and while they look like fun, I can't wrap my head around how these would be used on a neck/heel, and am very curious now.

It's used like a spoon knife .. a regular carving tool.

 

[TheDudeAbides]

It's used like a spoon knife .. a regular carving tool.

That's why I'm confused. Half the videos show this with a long handle that's designed to be held with 2 hands:


but then there are some with a short knife handle, but the short handled ones just remind me of the sloyd knife I used to carve the heel on my current build with. Which is why I was curious about the video.

 

[Pete Howlett]

I looked at some of these spear planes online and they reminded me of an engineers curved scraper that we used to use when I worked in the Tool room. .. .I spotted this one one on EBay for about £25
4E016360-D0D7-4DF7-9112-994FE372528A by Ken Timms,

Brilliant idea Ken. I'd forgotten about these tools. You are a star - you always come up trumps (cards that is)

 

[kkimura]

I looked at some of these spear planes online and they reminded me of an engineers curved scraper that we used to use when I worked in the Tool room. .. .I spotted this one one on EBay for about £25
4E016360-D0D7-4DF7-9112-994FE372528A by Ken Timms,

We used to call them bearing scrapers.

 

[Pete Howlett]

One in the post. I hope the steel is nice and hard.

 

[Pete Howlett]

One in the post. I hope the steel is nice and hard.

UPDATE
I made one from a power hacksaw blade which works quite well; bought Moore and Wright bearing scraper which didn't work; started on a new design with the edge just on one side using a power hacksaw blade. I find this steel ideal for knives that don't need to be heat treated. If you have hot metal facilities then using Japanese, Damascus, and HSS specialist knife steels would be ideal. All I have is a grinder and Worksharp honing machine. Will take some pics for you and post them tomorrow. Thanks for the advice - some I took, some I logged. All good.