Question about a Stanley #40 blade

[Tynyyn]

A few months ago I picked up a very nice Stanley No. 40 Scrub plane.  A model that I've wanted for a few years.  I took it home and sharpened the blade and used it to scrub down some 5/4 red oak.  It worked exactly like I was expecting, yet one draw back.  The blade is straight, not curved.  Now I'm wondering what is the best/quickest/correct way to cut the curve into the blade? 

Anybody have suggestions?

[enjuneer]

A few months ago I picked up a very nice Stanley No. 40 Scrub plane.  A model that I've wanted for a few years.  I took it home and sharpened the blade and used it to scrub down some 5/4 red oak.  It worked exactly like I was expecting, yet one draw back.  The blade is straight, not curved.  Now I'm wondering what is the best/quickest/correct way to cut the curve into the blade? 

Anybody have suggestions?

I paint the end of the iron with machinist's fluid and mark out a suitable curve. I have a metal disk with a 6 inch radius that I use as a template to scribe a curve on the iron. Then the end of the iron is carefully roughed out on a bench grinder to cut the edge back to the markings. Go a little at a time so the steel does not overheat. If it cannot be held comfortably in your fingers, then it is too hot. I prefer to let it air cool, rather than dip it in water. The bevel is then roughed out on the grinder, again allowing lots of time for the iron to cool. Finally, I use a bench sander with a 120 grit belt to finish roughing out the bevel before using sandpaper on granite tiles to put the final edge on it. Start with 100 grit paper to quickly smooth out the bevel and then progress as far as desired.

[Admiral]

I paint the end of the iron with machinist's fluid and mark out a suitable curve. I have a metal disk with a 6 inch radius that I use as a template to scribe a curve on the iron. Then the end of the iron is carefully roughed out on a bench grinder to cut the edge back to the markings. Go a little at a time so the steel does not overheat. If it cannot be held comfortably in your fingers, then it is too hot. I prefer to let it air cool, rather than dip it in water. The bevel is then roughed out on the grinder, again allowing lots of time for the iron to cool. Finally, I use a bench sander with a 120 grit belt to finish roughing out the bevel before using sandpaper on granite tiles to put the final edge on it. Start with 100 grit paper to quickly smooth out the bevel and then progress as far as desired.

Agree with Bob on technique, but I’d be more aggressive on the radius, traditionally 3”, but if I reground an iron, I’d go 4”.

[enjuneer]

Agree with Bob on technique, but I’d be more aggressive on the radius, traditionally 3”, but if I reground an iron, I’d go 4”.

After reading your comment, I went to look at the template. It is a ring with a 6" outside diameter and a 3" hole. I had actually used the 3" hole to scribe the curve on the iron.

The iron is one that I made from 3/16" thick A2 steel and heat treated it myself. I was going to clean it up on a surface grinder, but it works fine as is. It is only a scrub plane, after all.

[Admiral]

After reading your comment, I went to look at the template. It is a ring with a 6" outside diameter and a 3" hole. I had actually used the 3" hole to scribe the curve on the iron.

Ah ha, ok gotcha.  Actually, it would be interesting to do a 6" radius, would slow you down some, but I don't have spare #40 irons laying around to try it out on!  

[JimReed@Tallahassee]

Ah ha, ok gotcha.  Actually, it would be interesting to do a 6" radius, would slow you down some, but I don't have spare #40 irons laying around to try it out on!  

I have #40 blades in abundance but I am not eager to try the 6" radius. When I scrub, I like to set the blade to cut a shaving about 1/2"  to 3/4" wide because that is my limit. Scrubbing is hard work for me and a larger radius means a wider shaving which means MORE effort. Of course, YMMV.

[JimReed@Tallahassee]

In this case, Bob's yer uncle. That is the way I would do it. Except I water quench.

[Phil S.]

You guys grind on the bevel to establish the camber?  Seems like I read somewhere the iron should meet the stone at 90° to grind the camber and then grind at your chosen angle to restore the bevel.  I think the idea is you're less likely to burn an edge removing a lot of iron at 90° than when grinding to a thin edge.

[enjuneer]

You guys grind on the bevel to establish the camber?  Seems like I read somewhere the iron should meet the stone at 90° to grind the camber and then grind at your chosen angle to restore the bevel.  I think the idea is you're less likely to burn an edge removing a lot of iron at 90° than when grinding to a thin edge.

My apologies if my description was not clear. Yes, I first grind at 90 degrees to the wheel to reestablish the curve, then tip the iron to grind the bevel. I go just far enough to remove most of the material while leaving a small flat area that is even all the way across the edge. I then refine the bevel and edge on a 120 grit sanding belt on a bench sander before doing the final honing on sandpaper glued to granite tiles.

[JimReed@Tallahassee]

You guys grind on the bevel to establish the camber?  Seems like I read somewhere the iron should meet the stone at 90° to grind the camber and then grind at your chosen angle to restore the bevel.  I think the idea is you're less likely to burn an edge removing a lot of iron at 90° than when grinding to a thin edge.

Yes, yes, and yes. I think it is a good practice to always grind at 90 degrees when working on the edge. Not only when putting on a profile but also when grinding out small nicks from the edge. 

When the steel touches the wheel, it absorbs heat from the friction and this heat can build up quickly. On thick areas of steel, the heat is absorbed and transferred but on thin edges the heat has nowhere to go and is concentrated. That heat builds up quickly and will ruin the temper of the fragile edge.

So the good money is on making the edge correct and then carefully reestablishing the bevel. Quick passes and frequent quenches is how I do it.