Handplane Performance Tuning #3: Chip Breakers & Cap Irons

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Blog entry by OSU55 posted 01-21-2014 05:50 PM 18860 reads 5 times favorited 8 comments Add to Favorites Watch
« Part 2: Sole Flatness Part 3 of Handplane Performance Tuning series Part 4: Frog / Lever Cap »

Cap iron or chip breaker, blade or iron – Some folks write treatises about which term is “correct”. I use the one that comes to mind, they mean the same thing.

Chip Breaker Function

The chip breaker adds mass to the blade and adds stiffness to the blade, and with the lever cap pushing down, seats breaker & blade flat on the frog, creating more blade stiffness (cap iron). A very important, but lesser known, function of the chip breaker is to create a force down the wood fibers as they curl up from the cutting edge, down into the wood before the edge cuts it, reducing tear out. A steep bevel, 0.020”-0.030” tall, at an angle of 70°-80° to the blade, will achieve this. Typically chip breakers will have a bevel of 30°-45°, which does not turn the chip abruptly enough to create sufficient force down the fiber to prevent tear out. This doesn’t make a standard 45° bevel down plane equal to a high angle smoother, but it is a definite performance improvement. Always remember a sharp blade is the first step to reducing tear out.

Another method of tear out reduction is to put a relatively high angle bevel (10°-20°) for the blade back bevel (on top of the blade). This works very well, but I find it a real pain to create and maintain that type of back bevel due to the difficulty of honing off the wire edges.

The chip breaker needs to seat to the blade along a single line at the tip of the breaker to prevent chips from getting under the breaker. Also, the lever cap should contact the chip breaker across the entire width so that clamping force is equal. The chip breaker also “carries” the blade, allowing depth of cut adjustments.

Get The Most From The Chip Breaker

If you have not looked at the research done on cap irons by Kawai and Kato please do. Here is a link to their video (translated) , and a link to a good explanation with pictures and diagrams by David Weaver: I put a 70°-80° bevel on the front of the chip breaker. Aftermarket chip breakers can benefit from this as well as thinner factory Stanley or other brands.

I observed far more effect in tear out reduction from a steep chip breaker bevel than a tight plane mouth. In the video, notice Kawai and Kato did not have anything holding the wood fibers down ahead of the blade. Closing up the mouth just frustrated me with clogging. With a steep breaker bevel, the frog will have to be moved back to open up the mouth more than the standard “about chip thickness”. Something else to help clogging is to file an angle at the top front of the mouth – see Dwg 1 below. I use a small file from below, angled as far forward as possible without hitting the stiffening beam running across the plane body. I file down about 1/2 the casting thickness.

The chip breaker set distance from the blade edge is important. I set the chip breaker from ~0.005” to ~0.100”, depending on the cut depth and wood grain. For more of a jack plane cut, it’s far back. For very fine smoothing in tough grain, it is set as close as possible, 0.004-0.005”, and depth is 0.001” – tissue thin. Typically softwoods do not require as close of a setting as hardwoods. Because of the force generated by turning the chip so sharply, more force is required to push the plane. For very fine smoothing (0.001”) it’s not really noticeable, but once you get to 0.004”-0.005” thick shavings it is very noticeable.

Shavings generated with this set up vary depending on breaker set distance and depth of cut. They can be fairly straight, wavy or wrinkly, or accordion. Straight is best as long as it controls tear out. Keep moving the breaker closer to the edge to prevent tear out. The shavings will start to get wrinkly and wavy, and eventually take on an accordion look as the breaker is moved closer. The change in the chip is caused by the chip having to change direction more and more abruptly, increasing the force through the shaving. The accordion look is caused by total failure of the wood fibers. This is the same look shavings from my 63° high angle smoother have. Get a piece of wood with changing amounts grain angle and test different settings planing against the grain.

Dwg 1 below shows the various features discussed.
Dwg 1

. Illustration by Ellis Walentine
Below is a pic of the setup I use to create the high bevel on the chip breaker. Make sure front of the breaker above the new bevel is smooth and burr free. Some light sanding after creating the bevel can take care of issues.

The bottom surface of the breaker that contacts the blade needs to be flattened at an angle that will create line contact with the iron and prevent chips being driven under the breaker (“negative rake”). It only takes the slightest angle. Mine are about 5°. Remember that the breaker gets pushed down and flattened out on the blade, using up some of the angle. Here is a pic:

The bottom of the lever cap that contacts the chip breaker needs to be flat where the chip breaker contacts. The top of the chip breaker needs to be flat across its width where the lever cap contacts. A lot of the thin Stanley style chip breakers are not flat after stamping, and uneven pressure will be applied to the blade possibly allowing chips underneath even if the bottom of the chip breaker contacting the blade is flat. Also, poor mating of the lever cap to the CB can allow the blade to vibrate (light cuts). The surface does not have to be perfectly flat or smooth – a straight file and hand sanding works.

8 comments so far

View cabmaker's profile


1745 posts in 4269 days

#1 posted 01-21-2014 06:29 PM

You have a lot of information there my friend, but I can tell you we’re never a professional joiner !

Three things I have observed since I first discovered woodworking forums on line (about five years ago)
1) cap IIrons are routinely called chip breakers (what’s that about?)
2) grooves,gains and plows often referred to as dados , c’mon now
3) many actually call a cabinet component a gable,LOL

I think if your intention is to truly provide valuable information you may want to start with proper terminology
I see that as a little ironic, what with traveling that purist path using hand planes and all but not knowing the parts?!

enjoy Jb

View Texcaster's profile


1293 posts in 3134 days

#2 posted 01-21-2014 07:55 PM

Depends where you are from…end gables is end gables, internal gables is internal gables. Things are different other places. I have noticed everything seems to get called dado on this site.

-- Mama calls me Texcaster but my real name is Mr. Earl.

View OSU55's profile


3038 posts in 3449 days

#3 posted 01-27-2014 02:43 PM

Appears I’ve found two of the village idiots that exist in this community

View Bill Commerford's profile

Bill Commerford

37 posts in 2654 days

#4 posted 02-16-2016 05:01 PM

Nitpicking aside, I enjoyed your article. Thank you.

View OSU55's profile


3038 posts in 3449 days

#5 posted 02-17-2016 12:49 AM

If it’s something of substance I don’t mind at all – I’m always open to other thoughts & ideas.

View waho6o9's profile


9194 posts in 4037 days

#6 posted 02-16-2017 07:58 PM

Shavings were getting caught between the chip breaker and blade and I worked the chip breaker on the Atoma stone
and got it to work but then messed it up so I checked out OSU55s’ fine blog and fixed it. So….......

Thank you OSU55 .!!!

To get to the 5 degrees I used painters masking tape reassembled everything and now I’m making shavings instead of removing debris from the blade and chip breaker. 2 cool

View fivecodys's profile


1772 posts in 3096 days

#7 posted 06-28-2017 04:15 PM

I never would have thought of this on my own.
I’m getting ready to restore a couple of old Stanley Bailey No 5’s. This is great information to have.
Thank you very much!

-- A bad day woodworking is still better than a good day working.

View QuestionableAbility's profile


12 posts in 2615 days

#8 posted 03-08-2020 06:10 AM

Awesome video on the chipbreaker influence on a plane and preventing tearout.
This is the one mentioned in the writeup but with a current link.
Also, another web site with a lot of chipbreaker information is

-- If you think you can or can't you are probably right

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