Abstract. Mechanics of chipbreakers and high cutting angles.

[Corneel]

Mechanics of chipbreakers and high cutting angles in woodworking planes.

Kees van der Heiden, The Netherlands, 2014.

Abstract.

When using handplanes, tearout is a typical problem. Two methods to prevent tearout are high cutting angles and chipbreakers set very close to the cutting edge. In previous work it was found that a cutting angle of 60° is equivalent to a chipbreaker setting of 0.1 mm behind the edge when the chipbreaker edge is beveled at 45°. Likewise an angle of 55° is equal to a 0.2 mm setting of the chipbreaker. To compare the two methods a planing machine is used with force transducers to measure the cutting force Fc and the force perpendicular to the wood surface, the normal force Fn. Fc proved to be 30% higher for the plane setups with a high cutting angle, compared to the equivalent chipbreaker settings. Fn is normally negative, pulling the edge into the wood in a standard 45° plane without the chipbreaker. When setting the chipbreaker close to the edge this negative force is slightly reduced, but in high angle planes this is reduced much more and tends towards 0 around a 60° cutting angle, under the circumstances of this experiment. A second experiment has been conducted to measure the forces after a planing distance of 100 meters. The rate of change of Fc is about equal for both methods. The rate of change of Fn is twice as fast for the high cutting angles. The conclusion is that the plane with a chipbreaker is technically more advanced then the plane with a high cutting angle. A hypothesis about how the two methods prevent tearout is proposed in this article too.

The complete article will be published on Steve Elliott's website http://planetuning.infillplane.com/, hopefully this weekend. As soon as I have a link I will post it here.

 

[swagman]

Nice work Corneel.

Stewie;

 

[jimi43]

Very good indeed...look forward to seeing the work on Steve's site...some great stuff there!

Jimi

 

[swagman]

Hi Corneel. The results from your report are rather useful. For example if I felt a need to change the bed angle of the next chamfer plane I would need to increase it to 55 to 60* rather than drop in down from 55 to 50*.

Very handy information.

Stewie;

 

[Trafalgar]

You can have it all with an ECE Primus smoother: high(er) cutting angle, adjustable mouth, and of course a chipbreaker.

With the ECE it is easy to experiment with mouth aperture since everything else (cap iron setting and cutter projection) can stay set while the mouth is adjusted.

With a close chipbreaker all the mouth needs to do is maintain the orientation of the chip as set by the breaker as the chip comes up through the mouth . This may not objectively be a 'very tight' mouth setting but it's tight in terms of what it needs to do to prevent tearout (and tight vis-a-vis the close breaker setting). Too close and the chip folds up and chokes the plane.

Most of this is largely moot with very fine cob-web like shavings in that they don't have the strength to tear the wood out in the front of the cutter, they can't act as a so-called "beam" (lacks beam strength). See Jeff Gorman who is absolutely right about this. The only time you'll get tear out with these types of shavings are when the surface has bumps in just the right places and the plane's sole dives into a valley and tears out a chunk (relatively speaking) as it comes up the other side - like a boat between waves. Sometimes you'll get tearout on one pass that's cleaned up by the next - the hump as been removed or at least mitigated enough that the plane can make a tearout free pass.

 

[Corneel]

Here is the link to the article. Steve did a great job. Many thanks also to Bill Tindall, the "professor" of the project and Wiley Horne for the support, critisism and feedback. Thanks also to the Popular Woodworking staff, because the revenue of the chipbreaker article in februari allowed me to invest some money into this project.

http://planetuning.infillplane.com/html/mechanics_of_chipbreakers.html

 

[J_SAMa]

I recently "discovered" that I could set the cap iron by placing the edge of the iron+cap iron assembly (screw still loose) on a piece of wood and pressing the iron into it, then tightening the screw. Extremely close and dead parallel every time.
I'm sure some old books described a similar method?

 

[Corneel]

Some other people have descibed that method too. I've never tried and am going to correct that omission asap. Seems simple and quite fool proof.

 

[swagman]

I recently "discovered" that I could set the cap iron by placing the edge of the iron+cap iron assembly (screw still loose) on a piece of wood and pressing the iron into it, then tightening the screw. Extremely close and dead parallel every time.
I'm sure some old books described a similar method?

That's a great idea. Nice one.

Stewie;

 

[J_SAMa]

Some other people have descibed that method too. I've never tried and am going to correct that omission asap. Seems simple and quite fool proof.

I should mention that it doesn't work too well if the iron has a significant camber (obviously), but then again smoothing planes shouldn't.
Sam

 

[Corneel]

Here is a quick video about Sam's method.

https://www.youtube.com/watch?v=oGhDV1jM0pU&feature=youtu.be

Works as advertised. 0.13 mm.

 

[jimi43]

Sometimes the most simple of solutions becomes the most obvious!

Nice one Sam!

Jim

p.s. that doesn't mean I am not fascinated by the mathematics involved though! :wink:

 

[GLFaria]

Corneel, Sam, thank you both for a most interesting thread, and for the opportunity to learn some more.

And, Corneel, thanks for the PDF - it's already in my files for reding more at leisure