When to Replace Plane Iron

[Charles Travis]

Hey SMC Community,

In my last post, I spoke of the Millers Falls 14 I'm restoring. Well I'm starting to wrap up the process, and now I'm left to deal with the 60+ year old blade. It has a good amount of pitting on the back, mostly in the first 1/4 inch or so. I've been lapping it for day's hoping I could salvage it that way, but progress is minimal. My question is, how far down can you grind the blade? The pitting is, for the most part, localized to that first 1/4 inch so I'd like to just grind it away if possible.

I've been scouring the Internet for "When to Replace Plane Blade" but no results have come up. Thanks in advance.

Travis

[David Posey]

You should be able to grind it until you almost reach the hole. I think you're ok as long as you have about a quarter inch of blade left before the hole, unless MF blade assemblies are vastly different from what I remember. If you go this route don't try to grind with the bevel angle the whole way. Just grind it square and then put the bevel back on when you get the back to where you want it.

What medium have you been lapping it on? I would be inclined to try that part of the blade on the flat side of a grinder wheel, but I don't think I'd try that if all I had was a powered grinder. I'm sure there are reasons not to do this even on a hand grinder. The main one that comes to mind is that it heats the blade pretty quickly, but you can fix that with close attention and some water. If that weren't an option, I'd try a lower grit sandpaper.

[David Weaver]

They're not very thick to begin with, so if you can't grind it off in the length pretty easily, I'd just toss the blade aside and get another one of some shape or form rather than lapping it hard and having a very thin blade.

A decent option is as cheap as the $3 blade at home depot (buck bros brand), or as expensive as one of the finer replacement irons.

[Charles Travis]

I only have a few stones, nothing coarse enough to strip that kind of pitting away. I've been using 60 grit sandpaper on a slab of granite. Thanks for the info. I figured it would be okay to grind that much away, because mechanically, everything will still line up. I was more concerned about the integrity of the blade, and if I would lose any functionality from it.

Eventually, I'll be replacing it with a Hock/LN/Pinnacle (still undecided), but I like the idea of a complete restoration, so this will do for now. Thanks again.

[David Posey]

I had forgotten about that replacement iron David mentioned. That's certainly a viable option if grinding it back won't work. Just keep it cool if you do grind it.

[Jim Koepke]

Charles,

If you are using this for typical Jack plane work, a few pits might not matter.

Another way to look at a pitted iron edge is as a random toothing blade.

Buy the $3 blade for smooth work and use the pitted blade for rough work.

It is most annoying when there is just one or two pits on the edge of a blade and the surface is shiny except for a few ridges.

jtk

[Jessica Pierce-LaRose]

Nothing wrong with grinding away. I've done it before. I've actually seen planes with the iron ground down to the point that the slot was almost into the bevel, and they appeared that have been used that way. I don't know if I'd let things get that far, nor how far you can get away with before it's an issue, but if you've got most of the blade left, as others have said, I wouldn't worry about it.

When faced with a fair amount of lapping, I've used a technique mentioned in Garrett Hack's book with some success, and mentioned this before - I take a small grinding stone, the 2 or 3 inch type that mounts into a handheld drill or die grinder, and carefully grind a bit away in the center of the blade, staying away from the edges. This makes sort of a hollow grind - not as nice as what's on Japanese tools, but the same idea. Then when you return to lapping, you have less material to remove. I generally alternate between lapping and grinding, using the observations from one process to inform as to how to proceed with the other, so I don't go too far with the grinding.

It's a particularly helpful way to work when presented with a blade that has a bit of a belly, which can be hard to lap the back, and hard to get the cutting edge polished on the backside without a small back bevel which you may or may not want.

[Charles Travis]

Thanks for the additional tips. I just picked up one of the Buck Bros. blades at HD. Feels like a POS, but I'll fix up the old one and give this one a proper sharpening and see what feels best. I suppose it's good to try different quality products so I know exactly what I'm looking for in a nicer blade. And I'll be sure to post pics once the restoration is complete. Thanks again. This is definitely one of the friendliest forums I've been a part of.

[David Weaver]

You'll be surprised. the Buck iron you got isn't the hardest iron in the world, but it's hard enough and you'll be able to flatten the back easily and maintain the back by polishing off the wear. i have used one of mine quite a bit, it's not too bad. An absolute steal for $3, even if the bevel side doesn't look finish ground at all.

[george wilson]

As I've said many times here,the best plane irons I used were able to BARELY be filed a little,with a new,fine cut file. I haven't tried the Buck blades,but trust what David says about them.

[David Weaver]

It is like you describe, george. It's soft enough that it doesn't have problems with chipping, but if someone is honest with themselves about not needing a catalog spec contest hardness, it's plenty hard enough to use.

It might even be a better smoother iron for most folks because it's not so hard such that removing the wear on the flat back of the iron is difficult to do.

[Charles Travis]

Well I've started lapping the back of this new BB iron and, while I am making quick progress with it, there is a major cup form to it. I've been using 60 grit to try to cut down on the time, but it's taking some major effort to get it flat enough for
my comfort level. Nonetheless, I do agree that I may have underestimated the benefit of a blade like this. Without even having used it yet, I already feel better about not having to baby it so much. And I'm sure that will be multiplied many times over once I actually put it to use. I appreciate all of the input. Good to know there's a multitude of answers for all the questions I may have in the future available in a day's time. Thanks guys.

[Bernadette Semilla]

Another way to look at a pitted iron edge is as a random toothing blade.

Hah, I'll have to remember that one. :D

With a jack, I think it'll be worth it to keep the old blade, which doesn't have to be very pretty or precise for rough work. But then again, I am a miser.

[Jessica Pierce-LaRose]

Well I've started lapping the back of this new BB iron and, while I am making quick progress with it, there is a major cup form to it. I've been using 60 grit to try to cut down on the time, but it's taking some major effort to get it flat enough for
my comfort level. Nonetheless, I do agree that I may have underestimated the benefit of a blade like this. Without even having used it yet, I already feel better about not having to baby it so much. And I'm sure that will be multiplied many times over once I actually put it to use. I appreciate all of the input. Good to know there's a multitude of answers for all the questions I may have in the future available in a day's time. Thanks guys.

What sort of cup? If it's hollow in the back, you needn't worry too much as long as the cutting edge is honed across it's width - if nothing else, try David Charlesworths "ruler trick" to ensure you're honing the important part and cut down on lapping.

If it's bowed in the back (lapping just polishes the center) I'd try the grinding method I mentioned a few posts up - if not to make the lapping quicker, than because it will help be more accurate in your lapping - if the bow is enough on a narrower blade, the blade kind of rocks, and you end up with a surface polished but not flat.

[David Weaver]

If the blade is polished along the edge, don't grind the cup off of it. You'll appreciate it being there later, maybe. The two that I did were also cupped like that, just a thousandth or two. It's handy to have them made that way vs the other way around. If they do it on purpose, it's actually a nice feature.

[Jim Koepke]

Hah, I'll have to remember that one. :D

With a jack, I think it'll be worth it to keep the old blade, which doesn't have to be very pretty or precise for rough work. But then again, I am a miser.

I have also used an old blade that was short to make a marking knife.

http://www.sawmillcreek.org/showthread.php?85649-Home-Made-Marking-Knife

Here it is after a handle was attached:

235365

This image shows it with the bevel down. It actually works quite well.

jtk