Technique: The cap iron effect

With this blog I want to explain what is the capiron effect or chipbreaker effect, what kind of surface finish you can get and how to set-up your plane properly.  It follow a previous blog about tear-out control.

Here is an exemple of "against the grain" planing and the kind of shavings you will get.



A lot has been discussed and written about this "effect" in the last few years.  It seems that, except for a few individuals, this technique had been lost.

There are a few writing, dating back to XVIII century, showing that they knew about it at the time.  Steve Voigt website discuss history for those interested.

What is that chipbreaker effect?
Most of our planes do have an iron and a chipbreaker.  When the chipbreaker (CB) is set very close to the edge, the shaving is pushed back (compressed) and the iron can cut it properly instead of lifting it out and possibly creating tear-outs.

This is not science.  The CB will have to be set differently depending on the type of wood or the shavings thickness.  It's more an art and it's not difficult to learn it.  When the CB is properly set the mouth opening is not important anymore.  In fact, if you want to use the chipbreaker effect, you should back your frog.

For this blog I will use an old Record no.5.  I could have used a Lie-Nielsen of a Woodriver but, using an old plane, should help convince you.

A few pictures.
Normal chipbreaker setting, cherry, 0.002" thick.

With chipbreaker effect (CBE), cherry, 0.002".


With CBE, cherry, 0.003"


With CBE, cherry, 0.004".


The next picture show the distance between the CB and the edge seen thru a magnifying glass.


It looks like this CB is properly set.  Let's try it with some tear-out prone yellow birch.
Let's begin with the result of a CB set far from the edge.





Tear-outs are all over the place.  Now let's go back to the Record no.5 with a properly set CB.  Five strokes will be required to remove all existing tear-outs.

Shavings first.


No more tear-outs.


With a microscope, let's see what was the real distance between the CB and the edge.  A calibration line 0.004".




This distance must be around 0.006" and, in this case, works perfectly.
Now, let's back the CB to around 0.01" and look at the shaving with the microscope.


Calibration line 0.016" because we don't want too much magnification while looking at a shaving.




You can see here that the shaving has been broken and is wavy.  This is exactly what you want to get.
As far as I know, the CB maximum distance from the edge is about 0.01".  Let's try at 0.012" and see.



The same piece of wood that was planed with the CB at 0.01" without any tear-out is now plane with the CB at 0.012" and lots of tear-outs can be seen.




Tear-outs are visible in the shavings as well.

There is absolutely no doubt that this technique works.  All you need is good eyes or a magnifying glass.  When your plane will be properly set you will find that it is more difficult to push.  It's normal and the additional force required is less than a bevel up plane set-up with a proper sharpening angle to avoid tear-outs.  This have been studied by Kees van der Heiden.

Normand