Why do soles get cupped

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Forum topic by natenaaron posted 09-04-2013 02:46 PM 1474 views 0 times favorited 22 replies Add to Favorites Watch
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442 posts in 1819 days

09-04-2013 02:46 PM

I think that is the word for it. I am rehabbing a Bailey #5 and it has been a devil to flatten. How and why does this happen?

22 replies so far

View JayT's profile


5668 posts in 2233 days

#1 posted 09-04-2013 03:03 PM


Cast iron wears down with enough use. A well used plane, especially one that has been used for a lot of jointing, will nearly always have low spots in the center of the sole.

-- In matters of style, swim with the current; in matters of principle, stand like a rock. Thomas Jefferson

View CharlieM1958's profile


16274 posts in 4240 days

#2 posted 09-04-2013 03:43 PM

To amplify what Jay said, if you are frequently planing the edges of boards which are around 1” , and the sole of the plane is around 2”, it stands to reason that the center will get more wear from friction, thereby causing the cupping effect you’re talking about.

-- Charlie M. "Woodworking - patience = firewood"

View Loren's profile


10476 posts in 3669 days

#3 posted 09-04-2013 03:56 PM

If you are trying to flatten a plane with a lapping
plate or sandpaper it can be a lot of work. A more
efficient way to go about it is with machinests
blue dye and files or metal scrapers to get off
the high spots.

In any case, a lot of guys overdue it. I have not
flattened a plane sole in many years. Maybe I’m
just lucky with my collection of bench planes.

Your plane may be real messed up or at the problem
end of what came out of the foundry in terms
of usability. If it is such a dog (which I doubt)
maybe getting another old Bailey would be an

Precision matters to me in joinery planes and in
smooth planes mostly. I don’t expect it from
the Baily jack planes. Japanese planes aren’t
flat on the bottoms, but the skilled users can
joint edges with them and everything else a
plane has to do.

Knowing how “out of flat” your plane actually
is would help us in making recommendations with
how to proceed in getting in working well. If
you have an accurate straight edge and a set
of feeler gauges you can tell.

View Dallas's profile


3599 posts in 2509 days

#4 posted 09-04-2013 04:40 PM

A few years back I bought a spankin’ new
circa 1946 Millers-Falls smoothing plane at a yard sale. It was still in the original box and had never been opened.
Stupid me took the plane out and tossed the box as it was rotting and smelled bad.
The plane didn’t have a flat bottom, it was just like all of my other planes, a bit hollowed out in the middle.

I think this is the way they came. They were used by craftsmen for decades with no problem. I’ve always wondered why there was such a buzz about flattening the sole.
Since the outer edges are flat, as long as the blade is flat, the hollow won’t make any difference.

-- Improvise.... Adapt...... Overcome!

View natenaaron's profile


442 posts in 1819 days

#5 posted 09-04-2013 05:17 PM

Makes sense folks.

I wondered the same thing Dallas. But, since I have never restored a plane before, I figure I will do what the instructions say.

It is a lot of work lapping it but that is what a belt sander, and light tough and practice are for. Before people freak out I know what I am doing when it comes to getting metal pieces flat. I know when to stop and go back to the hand lapping.

View Woodknack's profile (online now)


11759 posts in 2402 days

#6 posted 09-04-2013 08:03 PM

This is why when someone starts a lapping discussion with… ‘you’ll only have to do this once.’ You should take what they say with a grain of salt.

-- Rick M,

View oldnovice's profile


6894 posts in 3389 days

#7 posted 09-04-2013 08:29 PM

Cast iron wears with use!

My 50+ year old Craftsman TS is proof as it has a. 003” front to rear cup. I believe that it was caused by the fact that 95% of the material cut was salvaged red oak. Red oak by itself is abrasive but this salvaged material was 100 years old and contained a lot of extra “grit” as much of it was base, stair steps, and flooring.

I didn’t notice the cup until I attached a Benchdog cast iron router table wing. At first I thought there was something wrong with the RT wing but further investigation proved it was the TS.

-- "I never met a board I didn't like!"

View unbob's profile


810 posts in 1925 days

#8 posted 09-05-2013 12:40 AM

All the Stanley bench planes I have “14 of them” tend to be convex instead of cupped.
The longer ones “no 8”can have a twist, with dips added also.
Lapping is a rather specialized process, not even close to sanding a planes sole with sandpaper glued to a flat surface.
Some of the planes I have were out .015” or more.
I have read that a planes sole does not need to be really flat. I found the flatter the better.
I hand scrape the soles flat, it takes considerable time.

View DKV's profile


3940 posts in 2526 days

#9 posted 09-05-2013 12:57 AM

Wow, doesn’t it take miles and miles of wood (circumference of the earth maybe) to wear a plane sole enough to even notice? Especially if you are among those that wax their soles. I’m far, far, far from an expert but common sense would seem to dictate it wouldn’t happen that way. If you do that much jointing you need to buy a machine. Help me understand…

-- This is a Troll Free zone.

View DKV's profile


3940 posts in 2526 days

#10 posted 09-05-2013 02:09 AM

Another wow moment. Did some research (should have done it prior to my other post) and learned a lot. Here it is.

-- This is a Troll Free zone.

View a1Jim's profile


117113 posts in 3599 days

#11 posted 09-05-2013 02:26 AM

Good info DKV
I was going to say the same thing as Dallas said.

-- wood crafting & woodworking classes

View unbob's profile


810 posts in 1925 days

#12 posted 09-05-2013 02:51 AM

I read Mr. Sellers blog there.
Perhaps the iron plane is an item best to get advice from a metal worker.
Really it is like this, there are people in the machinist trade that are so bad at it, they end up sanding metal parts in the machines, the internet is full of them. To get a surface flat sanding is not the answer.
Due to the shape of bench planes it is not possible to sand one as true as a LN plane new in the box.
Yet, it would be very hard to grind a #6 and larger flat in a precision surface grinder due to the thin cross sections, heat and induced stress. And odd shape of the top-fixturing into the machine, ect. I think it could be done with a really good fixture that would take considerable effort to make.
To get to the level of a new LN plane for flatness, hand scraping is the logical direction to go.
I have seen unused planes in the box, that are warped.

View mantwi's profile


312 posts in 1918 days

#13 posted 09-05-2013 03:23 AM

Thought I’d throw this bit of information into the mix. Wear takes place when an abrasive comes into contact with a surface softer than it is. Abrasion most frequently results from scratching a surface. As a general rule, a substance is only seriously scratched by a material that is harder than itself. Abrasives are rated by the MOH scale with a range from 1 to 10. For instance aluminum oxide is a 9 and silicon carbide is 9.2. The scale for rating other materials hardness is called the Brinnel Hardness Scale. On this scale softwoods are rated 1.6, hardwoods 2.6 to 7.0, mild steel is 120. stainless is 200 and gray cast iron is rated at 260 a whopping 200 times harder than anything but the hardest woods. Some woods like teak, ipe and ironwood have silica in them but what are the chances your plane has been used on these woods throughout it’s life? While hard use may cause some light surface scratching I seriously doubt wood will wear a groove in a cast iron plane sole. It’s like trying to rub a hole in a piece of glass with a feather. I believe that any cupping or twist is due to stresses created in the casting and cooling process that were not properly ground out at the factory. Cast iron will not twist, it will break by virtue of it’s composition. Most likely you are dealing with a problem that previous owners didn’t notice. They would simply look for that sweet spot where the tool performed best and take advantage of that. Paul Sellers is the man but I must respectfully disagree with the idea that any performance altering degree of deformation is caused by planing wood.

Read more: Abrasives – How do abrasives work? – Materials, Grinding, Hardness, and Material – JRank Articles

View DKV's profile


3940 posts in 2526 days

#14 posted 09-05-2013 03:28 AM

Since I have two posts taking both sides I may as well post a third. I am so confused. If you can’t believe Paul what is our world coming to? It is exactly like religion and science. Oh my!

-- This is a Troll Free zone.

View natenaaron's profile


442 posts in 1819 days

#15 posted 09-05-2013 03:41 AM

That paul sellers guy is pretty cool. Thanks for the link.

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