Button Your Lip: The No. 5 Way to Reduce Tear-out

I have held (and used) three of Karl Holtey’s revolutionary No. 98 planes. The first thing you notice about these tools is that they are flawless in their fit and finish. Holtey lavishes attention on his planes like Gollum on the Precious. Every surface, inside and out, is flawless.

Once you take that in, the next thing you notice is the non-adjustable mouth aperture of the tool. It is, by most tool snob standards, big enough to drive a scrub plane shaving through. What gives?

To find out, I sharpened up two planes: My trusty Lie-Nielsen No. 4 with a 50° frog and a mouth aperture between .002” and .0025” wide. Then I sharpened up the Holtey so its angle of attack was also 50°. Then I took a board of nasty, surly, almost-as-mean-as-coconut Jatoba and planed it with both tools. Then I turned the board around and planed it against the grain with both tools.

I know this board, and it’s about as bad a board as I ever want to work. Most standard-pitch planes tear it out. But both the Holtey and the Lie-Nielsen cleaned it up with no problems – both with the grain and against the grain.

This little experiment calls into question the plane snob’s obsession with tiny mouth apertures. (By the way, I’m the chapter president of the local plane snob club.) After planing that Jatoba, I had to ask myself: Do you need a fine mouth for high-tolerance work?

I think the answer is: It depends. I think tightening up the mouth aperture of your plane is just one of the weapons you have in your battle against tear-out. But I don’t think it’s the doomsday weapon.

The long-held theory about the plane’s mouth is that a small aperture is preferred because it will press down the grain of the wood as the cutter slices it. If the mouth is tight, then the cutter will be unable to get under the grain and lever it up ahead of your cut, tearing out the grain. This sounds reasonable, but there’s more to it.

The sometimes-forgotten problem with a fine aperture is that it makes your tool much more likely to clog, especially if you have the chipbreaker set closely (I’ll be writing about the chipbreaker in the coming weeks.) So a tight mouth is usually a time-consuming set-up, unless you have a smoothing plane dedicated to fine cuts only.

I start closing up the mouth of a tool only when my other efforts fail: I’ve sharpened the iron, I’ve set it to take a fine cut, and I’m using the tool that has a high (62°) angle of attack. If all those efforts fail, then I’ll weigh my choices: tighten up the mouth and face some clogging issues, or get the card scraper or sandpaper and call it a day.

Now, lucky for me, I’ve been at this a while and so I have a few smoothing planes in my toolbox at work, some that belong to be and some that are on loan. So I can set them up with different mouth apertures and pitches. Here, in brief, are the tools I’ll juggle during a project.

For easy-to-work woods that aren’t giving me trouble, I use my Wayne Anderson miter plane with a .019” mouth and a 55° angle of attack, or I’ll use my Lie-Nielsen No. 4-1/2 with a 50° frog and a .009” mouth. Both of these tools will easily pass a thick shaving, which gets the work done. And their relatively high angle of attack tames little patches of reverse grain.

When things get nasty, I have two planes set up for dealing with tear-out. My Lie-Nielsen No. 4 in bronze with a 50° frog and a .002”+ mouth. This tool can take only the finest of shavings. Anything else clogs it up right quick. The other tool is the Veritas Bevel-up Smooth Plane. This tool is sharpened with a 62° angle of attack, and the mouth is variable – it opens and shuts with great ease. If neither of these tools can do the job, then it’s time for the scraper.

So how do you measure a mouth aperture? First adjust the tool so it’s taking a shaving you would expect from that tool. Then set the tool on its sidewall and get some feeler gauges. Probe between the mouth and the cutter – you shouldn’t have to probe far before you are stopped by the chipbreaker. Start with a small size of feeler gauge and work your way up. When you encounter a size that won’t fit through the space between the cutter and the mouth, you can stop. Your mouth size is just a bit less than the size you couldn’t fit up the throat.

You don’t have to have four smoothing planes to do good work. Heck, you can have just one, as long as you are resigned to fiddling with its settings in the middle of a project. Or you can have one smoothing plane and one scraper. Or one random-orbit sander and a nasty cough. Your choice.

— Christopher Schwarz