How I make small mitre planes, part 13: Tuning

For the plane to work properly, the leading edge of the blade must be held firmly against the bed and the mouth open just enough to take a shaving the thickness you want (I like the mouth to be between 0.005″ and 0.010″).


  • The blade needs to be pretty square, there not a whole lotta room for lateral adjustment. I don’t like camber, personal preference.
  • If the blade looks square but doesn’t fit right (can’t get the lateral adjustment  right,  one edge cuts deeper or can’t get centered in shell), something is outta wack: the sides of the blade are not parallel (common with cut down blades), the mouth isn’t square, the sides of plane are not square, the kickers aren’t symmetrical (my fav) or the blade doesn’t seat on the bed (nasty).
  • I use a bevel angle between 25º and 30º. If there is pitting on the back, I just use a tiny back bevel (I strop to create one).

Caution: if using old cut down bench plane irons, be aware that the manufacturing quality can be truly variable. Take, for example, the iron I used for this series: I just could not get it right in the plane, no matter what I tried. Finally, I mic’d it and it tapers like a roller coaster, with a peak under the bridge. While the peaks and valleys were within two thou (ie not really noticeable without measuring), the cutting edge just would not sit flat on the bed. This made the mouth look skewed, the bed warped, and more. Even though the wedge fit the bridge well, it was pressing on that peak and the cutting edge could float, which made it almost impossible to adjust. Flattening it (PSA sandpaper + stone) fixed the problem [somewhat] even though the iron still tapers front to back (by almost five thou). As long as the taper is consistent, it can be worked with.

A further issue with this blade is it isn’t flat across the face. The wedge, no matter how tight it is, is going have trouble pressing that corner against the bed. But a lever works wonders. Notice the tiny bright line at the cutting edge, that is the back bevel to get rid of the pits without removing a bunch of the blade.

Make sure the bed hasn’t warped or have bumps on it. Check with a piece of flat flat [ground] stock (such as a vise parallel) and a feeler gauge (fed in from the mouth) or lightly run a file over it to check for high spots.
The photo shows checking the fit of the blade to the bed and while it isn’t ideal, it is good enough. When one corner of the blade back isn’t coplanar (see the photo just above), you either live with good enough (see the lead photo) or grind the blade back to the flat part.


  • It is critical that the front of the wedge get tight before rear or the business edge of the blade can rise off the bed. Your thinnest feeler gauge won’t fit under the front of the bridge, maybe a little at the rear.
  • The wedge jams the blade flat onto bed, even if blade has twist or lengthwise bow. If the back is cupped (ie bowed across the width), you’ll need to flatten the back, the top can remain non-flat. It really important that the cutting edge be flat or can be pressed flat against the bed, otherwise you’ll probably open the mouth too far.
  • A feeler gauge (I use 0.0015″) must not fit between the bed and blade (insert from front) or the plane will chatter and/or you won’t be able to adjust for a thin shaving. If the blade prevents getting this right, a lever cap works wonders.
  • Use sandpaper on flat surface to tune the wedge.
  • It should only take hand pressure or a light tap to lock the wedge.

Open the mouth as a last resort, after you have tuned everything else twice. It is probably already open enough, I like a mouth opening between 0.005″ and 0.010″, as measured with a feeler gauge along the bevel. Note that this number changes depending how far the blade extends (ie the deeper the cut, the tighter the mouth, opposite of what you want).
I can’t emphasize this enough: The blade, as it emerges, must lie flat on bed.
If you are convinced the mouth needs to be a bit more open (ie shavings won’t fit through, it is under a couple of thou), draw file it.
Be careful, center will want to bow as you file. Check often, using a square (from both sides in case the sides aren’t parallel). Hold the plane up to the light and gauge the line (using the square as a reference), it really needs to be sub thou straight, which is easy to judge with light.

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One Response to How I make small mitre planes, part 13: Tuning

  1. Pingback: How I make small mitre planes, part 12: Wood | ZK Project Notebook

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