Thread: Do chip breakers break chips?

The short answer is yes they do and they should be about 0.5-1mm back for fine planing, 2-3mm for rough work. The mouth opening also plays a role in limiting breakout. For an in-depth study of how they work see here: Chipbreaking

The other function they serve, especially in Stanley and Record style planes is to give support to the thin iron to help reduce chatter. The bevel up planes generally have thicker blades (Veritas blades are about 3-4x as thick as Stanley) and are less prone to chatter.

Not to mention they're part of the all-important Bailey depth adjustment mechanism....

My old wooden planes (smoothers and jointer, some jacks) have chip-breakers and very thick blades.

Hmmm.......

there are a lot of good threads you can search for ... try variations on 'bevel up vs bevel down" and 'tuning'. (i wish those threads were captured somehow for easy reference, as they cover it all quite well)
the first reply was on the money, particularly by starting out 'in short..'

I'll see if I can find those threads and link them in here.

Originally Posted by elanjacobs

The short answer is yes they do and they should be about 0.5-1mm back for fine planing, 2-3mm for rough work. The mouth opening also plays a role in limiting breakout. For an in-depth study of how they work see here: Chipbreaking

The other function they serve, especially in Stanley and Record style planes is to give support to the thin iron to help reduce chatter. The bevel up planes generally have thicker blades (Veritas blades are about 3-4x as thick as Stanley) and are less prone to chatter.

Elanjacobs, I have to take the opposite view, so my answer is "no it doesn't, for all practical purposes".

The article you linked to has some logical flaws, IMO - he uses the professor's findings where it suits his argument, and ignores them when it doesn't. The study findings are no doubt accurate enough, but they are for a very specific set of circumstances, and I would interpret tham as indicating there is no levering action from the cap iron in practical situations. On a regular Bailey plane, most folk would set the cap iron back a good deal more than 4 thousandths of an inch. A "fat 32nd" was what they used to say in old money, which is more like 30 thou.

If you set the iron too close to the cutting edge, you will run into several problems. The first is the accuracy of the edges - to set at 4 thou, you will need to do a LOT of work on the leading edge to make sure it is dead straight & mating along the entire back of the blade with a precision that would be very hard to achieve for most of us. I could not set any of my cap irons that close.

I contend that on most work-a-day planes, with the cap-iron at a typical set-back, it functions purely to pre-tension the thin blade & dampen chatter. As someone else pointed out long ago, the beam strength of a very fine shaving is insufficient to have any levering capacity, at the length it must travel before being deflected. This fits with the general observation that putting a thicker blade in an old plane makes an immediate noticeable improvement in performance.

Many years of using planes has convinced me that the surest way to prevent tear-out is to have very sharp cutters & take very fine shavings. A high cutting angle helps in many woods, and seems to make little difference in some. While you could eventually plane just about anything to a finished suraface, I take the view that it's better to strike a balance betwwen the various methods (planing, scraping & sanding) to reach the desired surface with the least effort!

Just to keep the discussion rolling......
Cheers,

Originally Posted by tonyw

I have been wondering about the purpose of back irons/chip breakers on Bailey pattern planes. In the past, I would adjust the chip breaker very close to the edge for fine planing but I am not sure it was useful. The usual BU planes without back irons seem to work as well. The width of the throat is possibly more important. Also the angle of attack of course.

Tony,
I've copied and added to a post I made a few years ago below.....

it might be informative to look at the thinking of the inventor Leonard Bailey, and the original patent of that particular part of his plane, and how it works in a Stanley / Bailey pattern plane...
IMPROVEMENT IN CARPENTERS PLANES - Google Patent Search
December 24, 1867.
It is used to stiffen the thin blades used in Stanley planes, and it must bear down at two places near the cutting edge of the blade when the leading edge of the lever cap is tightened down, about the center of the hump. Also it mustn't unduly interfere with the exit of the shavings.
This might help you understand what is important in the shape of the back iron (cap iron) and get the best out of your plane.
Interestingly he does not call it a chip breaker, a function attributed to it by others, for a reason I am still to fathom.

Regards,
Peter