How wide is too wide when it comes to mouths on wooden planes? When looking out for a used one this could be one of your key areas of concern, but that worry might only be justified towards the finer end of the spectrum, and even then it’s a quick and easy fix.
A cap iron can control your tear out regardless of mouth width, as we covered in our videos here, but a huge gapping mouth on a smoothing plane is still not ideal.
A wide mouth on a single iron smoother would prevent the tool working for it’s intended purpose, whilst at the opposite end it’s going to be essential on a scrub plane or very coarse jack, to allow the thick shavings to escape freely.
But what do you do with something in the middle; a long plane which you want to take a medium cut, such as a jointer?
Should you patch up a wide mouth or leave it be?
This is a question we were asked by Ian on Helen’s post on the wooden jointer plane, and I’d thought I’d cover a few thoughts.
Ian’s jointer has a fat 3/16″ of space in front of the cutting edge – should the mouth be closed up? Well that is bloody wide.
If it was my tool though I’d do the minimum essential work to put it to use and get to know it first. The wide mouth is unlikely to be the culprit for a poorly working jointer, my priority would be to straighten the sole and ensure that the iron is sitting flat and registered well to the bed. Hollow spots on the bed won’t matter but any high spots that cause the iron to rock will cause the plane to do stunts, particularly when put under load in hardwoods. You also need a well fitted wedge.
A tight mouth isn’t always essential to the work of a jointer plane, particularly if you have a cap iron, so if you’re happy with your results you could leave it be.
But fixing it isn’t a big job either, and if you don’t want to worry about faffing with your cap iron, or you’d like to take some pride in the tool, then it’s not time wasted to fix it. Once you have a jointer that you know and trust, you’ll find yourself using it a lot more than you might expect, they really are lovely tools, particularly the heavy ones.
My preferred approach for closing up a mouth would be the infill in to the sole as shown in the photo, rather than packing between the bed and iron. This jointer was altered long before I got my hands on it and has been given a very nice tight mouth, too tight for coarse work.
The row of mouth openings in the photo below show what I get by with, with a handful of current users.
Left to right: Dog of a Jack plane (this hand plane’s extremely worn but is still my favourite for rough hogging), Double iron Jointer, Double iron Smoother, Single iron Smoother (notice how tight the mouth is in front of the iron).