Fair Woodworking

January 29, 2014

Get the skinny on flat

EDITORS NOTE *** This post is experiencing 3rd party photo hosting “issues”, that will be addressed as time allows. ***

So what’s up with flat? Sure we know it’s important, but why? Many woodworkers demand that every tool they own be perfectly flat, because tools must be perfect if you want them to build perfect things. Often times the concept of flat takes on a mystical persona as the great savior to all your woodworking problems.

Often times flat does make things better, but to say flat = holy grail?


This last weekend, I had the chance to hang out with a friend in his shop. He is looking to get into the whole hand tool game, and he was looking for a little help coming up with a sharpening game plan. The part that seems to snag a lot of beginners is how to keep your stones flat, and really to that, how important is flat?

Well I think it is very important, but the reason is practical. Not mystical, and I decided to try out a simple little exercise to get my point across. It seemed to work, so now I’m going to try it on you poor suckers.

What I did was take a piece of paper from a small note pad, and ripped the top quarter off like this.

The rip makes a jagged line. It was easy to make that messy edge, but try to repeat it with any accuracy. I asked my friend, and to tell you the truth, he really stunk up the joint with this project… Just like I expected he would. But it wasn’t his fault. A random edge like that is near impossible to reproduce accurately. The only good example is the other piece of torn paper.

The edge of this paper was mind blowingly easy to make once, but is hopeless to reproduce. In woodworking, that won’t do.

A flat edge is so much better, if you know how to do it, and it really isn’t much of a trick.

I then took the larger of the two pieces of paper, folded it over, and pressed down a nice straight crease into it.

The paper now tears in a sweet straight line if you are careful.

And leaves you with a nice flat edge.

While the free thinkers may complain that I’m trying to squish their groove, It’s not just the anal people that can see that the straight tear is far superior. It doesn’t just match up with its mating piece, it also matches pretty well with other pieces.

Well, not every piece, but the factory edges would mate with them pretty well…

But what’s also really nice about flat.

If you flip one of the pieces over, it still mates beautifully. Not so with the loosy goosy tear on the top. If you notice, when you flip the top one, the inaccuracies compound.

In real life, this can be a real problem.

So you lap the blade of your new smoother with a slightly hollowed out stone. Let’s say it’s hollowed by 0.002 of an inch. No big deal, that it leaves the back of the blade with a 0.002″ hump in it. Then you tune up the chipbreaker, and go to flattening the edge, and it gets the same 0.002″ hump in the middle. When you put the two together, you end up with solid contact at the middle of the blade/chipbreaker point, but you will have a 0.004″ gap on either side.

When you go to take you sweet 0.001 inch transparent shavings, you end up stymied by all the shavings getting caught in the edges of the chip breaker.

Flat stones are important.

And that is why we all stopped setting the chipbreaker close to the cutting edge…

So ya, ok, stones need to be flat. What about the bottoms of planes?

I’m still chewing on that one.

Perhaps I’ll work up the nerve to tackle that one another day.


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