Can a cast iron plane sole warp significantly?

[James Scheffler]

A friend of mine has what I believe is a type 8 No. 7 plane. He got it in untuned condition a year or so ago. He cleaned it up nicely and, if I recall correctly, didn't have to touch the sole except maybe to polish off some oxidized metal. After that, he checked the sole with a precision straight edge and feeler gauges, and found it was just a little concave, about 0.002" hollow in the middle. We both thought that was fine, so he used it like that up until recently and it worked ok.

Recently he checked the sole again with the same straight edge, and found that the sole is now dead flat from the toe to a point about 5" from the heel. From that point to the heel, it raises up about 0.005" (i.e. it transitions from flat to slightly convex).

I went through the obvious questions with him (I haven't seen the plane lately, so I'm just going by what he said):
- the frog was in the same position before and after.
- both measurements were taken with a blade in place, tensioned more or less the same, and retracted.
- there are no visible cracks anywhere or any other obvious damage.
- the plane has had what sounds like normal use. No knocks or drops. He has planed some oak and had the plane slam to a halt when it hit big knots (but that sort of use has never bothered any of my planes).
- I asked if he had dropped the straight edge at some point. He wasn't amused, but he said no. ;)

He is discouraged because he put a fair amount of work into this plane. We talked about whether it is worth trying to flatten the sole, but if it warped once, making it thinner might make it more likely to warp again.

So, is this normal? Is there anything else we should check? Will a 0.005" departure from flatness make a difference in a jointer? (My jointer is a Stanley transitional, which is easy to make dead flat, so I don't really have any experience in using an out-of-flat jointer).

Thanks,
Jim S.

[David Weaver]

It'll make no difference the way you've described it. If anything, you want a plane to be just a tiny bit proud heel and toe if you don't have perfect flatness as an option and you have a choice about which way you'll be out.

This is why doing a good job lapping is just as good for a skilled user as getting a plane ground - anyone who tells you otherwise doesn't actually use planes, or if they do, maybe they only imitate scenes from a few instructional videos planing a board after a machine has already made it flat.

As far as movement, I think unless a plane is dropped or something happens to it, most of the movement happened a long long time ago. I'm sure that some of the castings that weren't seasoned properly moved afterwards. I've had some that have not much wear on them, but have a bit of a twist in the sole (normal wear can create the same effect if the plane was used for edge jointing since most planes like that have the wear in a diagonal on the sole.

Anyway, he's ready to go, make sure everything is good and tight on the plane and the iron is sharp. Some paraffin will make life a bit nicer, too.

As an aside, I don't know if I've ever seen a woody jointer that flat (.005"), and plenty of work was done with those.

One last comment about why a high tail is better than a low tail - if you think about what a low tail does, if you're jointing a board, as the low tail starts to come in contact with the workpiece, it levers the iron up. If you back off the cut some to get rid of tearout, you can have the plane cutting until the tail comes onto the board and then doing the really annoying thing of stopping the cut a bit until you get onto a part of the board that is convex that you've matched to the sole of the plane.

[Roy Lindberry]

A friend of mine has what I believe is a type 8 No. 7 plane. He got it in untuned condition a year or so ago. He cleaned it up nicely and, if I recall correctly, didn't have to touch the sole except maybe to polish off some oxidized metal. After that, he checked the sole with a precision straight edge and feeler gauges, and found it was just a little concave, about 0.002" hollow in the middle. We both thought that was fine, so he used it like that up until recently and it worked ok.

Recently he checked the sole again with the same straight edge, and found that the sole is now dead flat from the toe to a point about 5" from the heel. From that point to the heel, it raises up about 0.005" (i.e. it transitions from flat to slightly convex).

I went through the obvious questions with him (I haven't seen the plane lately, so I'm just going by what he said):
- the frog was in the same position before and after.
- both measurements were taken with a blade in place, tensioned more or less the same, and retracted.
- there are no visible cracks anywhere or any other obvious damage.
- the plane has had what sounds like normal use. No knocks or drops. He has planed some oak and had the plane slam to a halt when it hit big knots (but that sort of use has never bothered any of my planes).
- I asked if he had dropped the straight edge at some point. He wasn't amused, but he said no. ;)

He is discouraged because he put a fair amount of work into this plane. We talked about whether it is worth trying to flatten the sole, but if it warped once, making it thinner might make it more likely to warp again.

So, is this normal? Is there anything else we should check? Will a 0.005" departure from flatness make a difference in a jointer? (My jointer is a Stanley transitional, which is easy to make dead flat, so I don't really have any experience in using an out-of-flat jointer).

Thanks,
Jim S.

If he tries to flatten it, that will be a lot of material to remove on a #7 resulting in a lot of time and work for probably minimal benefit. My experience (which is admittedly limited) is that perfect flatness is something that is often desired, seldom achieved, and generally unnecessary.

The real question is how does the plane work? If it is working ok, then I wouldn't bother. If it is not working well, then you really won't hurt it by making it thinner.

[Jonathan McCullough]

My understanding is that cast iron (and probably other metals) cools inconsistently, creating tension in whatever object you're casting. When you drill into or lap a plane body, you release some of that tension, so even as you get closer perfect flatness, you can get further away from it. The tension in a cast iron plane body can remain for decades. One of the ways to release the tension in a cast piece--from what I can gather and admittedly I'm not a cast-metal or machining or materials engineer--but one of the ways to release the the tension is to give it several heat treatments, sort of like tempering a tool steel, that raise the temperature uniformly throughout the piece and let the piece cool down slowly. Maybe if I invoke the Rob Lee genie by mentioning his name here, he could comment on the process but I think that Veritas planes are heat treated so that they don't have to be lapped for as long after machining. I remember reading an anecdote about how a machine shop first drilled then reamed to precise diameter a bunch of large cast engine cylinders. The tension they released by machining the castings slowly warped the cylinders so that they were ovoid shaped and unusable. Their solution was to drill the cylinder, wait two weeks for the casting to settle down, then ream it to specification.

If your friend is adventurous, he might heat up his plane in an oven and let it slowly cool several times--I don't know what the recommended temperatures are--then lap the sole, and find that a bit more stable. Other folks in the plane making business might say that's a headache you should pay them to do, especially on something as big as a No. 7. But think about the medium you're working with: wood. A bad hair day can cause it to swell enough to cause enough problems so that the difference between a .002 and .005 on your jointer sole is the least of your problems. I'll bet just bearing down on the plane with your body weight on a bench could warp it .003" at least. I just wouldn't worry about it.

[Rob Lee]

Hi -

Grey cast iron can continue to move decades after casting. True - most of the movement occurs early on, and castings were often left to "age" outside - the changes in temperatures remove some of the stresses. Castings can go though a stress-releiving heat treatment cycle as part of the production process.

Keep in mind that most antiques are going to be grey cast iron, and most higher end production is going to be ductile cast iron (invented/discovered in the 40's). These two types of cast iron behave quite diffreently. The basic difference between the two is the form of the graphite in the iron - for grey cast it's flake, and for ductile it's spherical (or nodular). Think of the flakes as fault lines or slip lines in the material - they enable movement. With ductile - the stresses can only release marginally - between nodes of graphite. Here's a useful analogy - think of a crack in a windshield.... if you score a circle around a small crack, it doesn't get larger.... if there are no limits to the travel - the crack can continue - or not. Sometimes being jarred will extend it, sometimes a change of temperature will extend it. Nodular (ductile) iron is the limited crack - grey iron is the unlimited crack.

(What follows is illustrative only....!) When casting iron - the molten metal hardens from the outside first, and the metal shrinks as it cools. As a solid shell forms, it will distort slightly as the core contracts. At a certain point though, the cooled shell is strong enough that additional cooling of the core cannot distort the shell - and the metal hardens with internal stresses - the metal is "like" a solid stretched rubber band - it's in tension. In some castings - you can actually have bubbles of vacuum formed in the material - porosity. In other castings, the shrinking core will cause sufaces to sink. So - you have this sort of eqilibrium where the outer part of the casting is resiting the stresses in the core. Now - a manufacturer takes that casting - and removes the sides and the bottom to establish the working surfaces of a plane. The stresses now begin to express themselves - and the casting moves. Any change in the exterior of the casting could conceivably cause additional movement.... which includes lapping, even decades after casting.

Ok - all of the above is a bit oversimplified - there's waay more to it than that - but in short, grey cast iron can continue to move - ductile iron stabilizes. Changing a surface can release stresses... stresses in ductile are limited, and stabilize quickly, stresses in grey cast iron don't.

Having said all that - I don't think that a .005" convexity at the heel of jointer is going to have much effect at all. If anything - the plane may act a bit "shorter" than it's intended length. I'd have to go back to some of the modelling work we did years ago, but I believe that the tail on a Stanley #7 is too long for the mouth position in the first place...

As long as it works well, the plane is good....

Cheers -

Rob

[Patrick Tipton]

I think Jonathan has it right. Wood moves alot more than .005 with normal seasonal weather changes. I would spend my energy learning how to sharpen well and not worry about the flatness of that plane sole. The plane is capable, even with the warped sole, of doing a better job than most of us have the skill to do.

Whenever I start thinking that I need a "new", "better" etc. tool because I am not getting great results, I try to send myself to the shop to practice and refine my skills. I was turning balusters yesterday with a particularly challenging piece of maple and could not get rid of a little chatter. I cursed the skew, then spent 5 minutes really sharpening it. Back at the lathe, the chatter disappeared on the first pass.

Regards, Patrick

[Jonathan McCullough]

Thank you for that informative explanation Rob. If that's only a superficial explanation of what's happening--and I'll take you at your word!--it's a good indication of how much thought and effort is actually going in to the planes made today.

[Johnny Kleso]

My opinion is you cant check a sole well with a straight edge and feeler..
You can hold it up to the light and check gap..
I think your friend may have been in error before or after checking..
Best way with straight edge is to hold both up to a light and check for a gap...

Checking one area is different than laying it on a inspection plate..

I would mark the bottom with a dry marker and with a very fine sandpaper give the plane a few rubs can check marks on bottom..

.003 out of flatteness is nothing for a plane IMHO We plane wood boards not rocket parts..


I dont think cast iron planes warp unless heated or sat on very much especially if its 100 years old :)

[James Scheffler]

As an aside, I don't know if I've ever seen a woody jointer that flat (.005"), and plenty of work was done with those.


David,

Thanks for all your comments. I think I can plane my jointer to within that tolerance (haven't tried to measure, so that's just based on using a straightedge and looking for light underneath). On the other hand, who knows if it stays that way for more than five minutes? So, as your comment implies, I probably have a ton of experience using a jointer that's at least 0.005" off. I've just never experimented to see if it matters. Sometimes I correct the sole before I do something critical with it, or if I haven't done it in a while. That may help, or it may just make me feel better. :)

Jim