Chipbreakers and Cap Irons. What do they do?

When we think about bench planes, the chipbreaker or cap iron is the same thing, just a different name. You can also add in double iron, back iron etc. The name doesn’t matter it’s an object! You say rabbet, I say rebate, who cares!

Do Cap Irons or Chipbreakers reduce vibration?

No, this was never the intention. When the cap iron was introduced,likely during some point in the 18th Century, planes had thick irons that were firmly locked in place with a wedge into the wooden body of a plane that needed no help with vibration. Planes continued to have thick irons with the addition of a cap iron until the Bailey pattern was adopted. Even though the cap iron has been part of plane design for around 250 years it’s still pretty new. After all, advanced woodworking has been around for thousands of years. Search for the Silchester plane for an example of a fourth century plane.

It has been said that the Bailey style planes do need the cap iron to stop vibration. There is no point arguing about this point, a demonstration is required. I cut the hump away from a surplus cap iron rendering it flat an with no ability to add tension. I still needed to keep the top part of the cap iron as the Bailey designed cap iron also locates with the Y lever for depth control. As you can see in the video, the plane functions perfectly well with no vibration issues.

Do Cap Irons or Chipbreakers actually “Break Chips”?

In a way the most recently adopted name of Chipbreaker is actually reasonably accurate. The cap iron greatly increases the working range of a plane, allowing you to work the full length of a board, even if the grain is against you. You see for the most part, using a plane is not what you see on YouTube or at a show. Planing the edge of short ends of easy working pine or a hardwood with compliant grain demonstrates nothing. It’s first day in school woodshop level. Real woodworking will often throw up issues and resorting to scrapers, high angle planes and a plethora of other methods that do resolve these issues we encounter is not always wise. That’s because a simple adjustment of the cap iron relegates those other methods in just about all cases.

It’s hard for me to describe exactly what happens in a phrase or a word. Perhaps I could say that the cap iron stops the grain levering? Well I tried, let me break it down for you like this, try it for yourself too.

Pick up a smoothing plane and set the cap iron back from the edge 1 to 1.5mm and plane some wood. You’ll find the shaving curls into cylinders. Halve the distance visually (measuring this process is pointless, it’s a skill and a feel you develop) and plane some wood. You’ll feel more resistance and the shaving should no longer be curling, it should be straight(ish). You’ve now got a pretty safe plane to use. If you hit a bit of nasty grain you won’t tear it to shreds. If you now move the cap iron closer again you’ll need to lighten the cut and you’ll feel even more resistance. This can be useful for really nasty bits of wood. If you have it too close the shavings will turn into accordions!

All of this does take some practice but it’s not difficult to master. The hardest part for you is developing the feel for where the cap iron is. For those who prefer to avoid the nuances this process won’t be for you. Grab a sander. And don’t obsess, the cap iron is adjustable for a reason. You don’t want to fight with more resistance than you need, after all, it’s a craft and skill for you to master. Here’s a video I knocked up to show you how it all works

But what about the sole of the plane? Surely a very tight mouth helps?

It’s on the pile of things that can work. However it’s not very practical. The mouth of a plane, even on metal planes wears very quickly in terms of preventing torn grain. So much so that the mouth needs to be so tight, the sole of the plane needs to be in near perfect condition and the cut so very light. This means constant faffing about and slow progress. It’s also true to say that the cap iron ended the single iron bench plane. Period. Single iron planes were often described as roughing tools once the cap iron came into being. Imagine the extra cost of making a pre Bailey cap iron. It’s a work of art and not cheap. If it didn’t do it’s job improving the versatility and working range of a plane it would of been thrown by the wayside. Working people would never of paid for something that made a tool worse.

But my life coach says different!

It’s harsh to say but many Guru’s vehemently deny that it works and it’s a position I can understand. If you are arrogant and verbose enough to of thought something was one way and espoused it to legions, you’re then unlikely to climb down and say you’ve learned something new. All I can encourage you to be is open minded, give something a try. The experimentation should take not much more than an hour. If you can’t get it, buy your scraper planes, scrapers, high angle frogs and sanders. You’re work wont suffer. But if you want to try a skill that practical people mastered you’ll enjoy using a hand plane all the more.