How Flat Do Soles Need To Be?

[Derek Arita]

In order for a plane to work properly, I'm wondering how flat the sole of my planes need to be? I suspect it has a lot to do with the size of the plane and it's purpose, but are there some generalities that I can apply, being a newbee and all? I have everything from a #1 smoothing plane, up to a #8.
I'm hoping this isn't one of those "can of worms" topics like I've experienced in the Power Tools forum concerning how flat a table saw table needs to be. Some say it needs to be dead flat corner to corner and others say they never concerned themselves with minute stuff like that, since wood moves.
Anyhow, looking for some guidance from those more experienced than I.

[Jim Koepke]

My rule of thumb is if the plane is working fine, then the sole is likely good enough.

What is working fine?

Being able to take an even full width shaving with a blade sharpened square. A cambered blade will cause the shaving to be thinner at the edges.

Being able to do consistent and predictable work with a tool is one mark of a proper tool.

Mostly for a smoother working properly means being able to take a very fine cut.

If Shavings Could Talk.jpg

These two planes work quite well at smoothing and are capable of taking shavings of less than 0.001" in pine with freshly sharpened blades.
BTW, pine is easy to get a thin shaving. Other woods are not so easy.

What are signs of not working well?

A block plane of mine seemed to always give up at the end of its work. Turns out the sole was concave from heel to toe. As my hand put less pressure on the plane at the end of a cut, the blade would disengage.

Another plane could be adjusted to cut at the edges of the blade while not cutting in the center. It was the victim of careless sole lapping.

In the long run, if the plane isn't having a problem, let it be.

If the plane does have a problem, let us discuss that before irreversible action is taken.

Now for two of my favorite graphics:

This is just my 2¢ Two Cents.jpg

and remember YMMV!!!.jpg

jtk

[Rick Whitehead]

I'll stick my neck out here and give you my answer.
It is true that as you observed,it IS a "can of worms" topic, with strongly held opinions on all sides.If you search, you'll find that this subject had been discussed at length on this and other forums.You can search and read these discussions until you've had enough.Then you can make up you own mind about the subject, and find support for almost any conclusion you might come to.
Hopefully, this discussion won't become one of many, on several forums, discussing this subject to death.
My advice is to sharpen and use the planes without worrying how "flat" the soles are. If you can use your planes to produce the finished surface you want, then in my opinion the plane doesn't need 'flattening".If you can't, then you can try to determine what is preventing that, and make the appropriate adjustments.
Rick W

[Kees Heiden]

There is a Britisch standard! Nowhere is the sole allowed to be more then 3 thou out of flat.

In practice this means:
- A jackplane, doesn't matter much.
- The most important parts are the toe, the area just in front of the mouth and the heel of the sole.
- A large concave area behind the mouth doesn't matter.
- Many planes have a convexity just behind the mouth, which is no good for a smoother or a jointer.
- If you wnat to use the mouth of the plane to control tearout (there are better methods) this 3 thou value is still way too much.
- You need a real straightedge or surface plate to measure.
- Listen to Jim Koepke and test the plane first, it might be fine allready.

[Tom McMahon]

If the sole of a plane needs to be perfectly flat then someone needs to tell the Japanese to quit scrapping hollows in the bottom of their planes.

[Paul Sidener]

I too would agree with Jim Koepke. I am a little surprised to hear you call yourself a newbie, and say you have a #1 through #8. You might be creating more confusion for yourself, working with eight planes. I started with three bench planes, a #4, #5, and a #7. The only one I had to flatten was the #4, a type 6 Bedrock. It still isn't perfect, it doesn't need to be for me. It does a fine job as it is now. If you feel the need to flatten one, do it with the iron in and retracted all the way in. It does make a difference. If you start with the three planes I mentioned. Learn to adjust them and use them. Then add the others one at a time, you will probably make it easier on yourself.

[Harold Burrell]

Wait...I'm sorry...but did I understand you correctly...

Did you say that YOU HAVE A #1???

Please tell me that it is something other than a vintage Stanley.