This step is optional if a wedge works for you. However, I plan to use levers in all future planes, the functionality and ease of use is just so much better than a plain wedge. Adding a lever to the wedge accomplishes the following:
- Mitigates the problems caused by blades that aren’t flat, eg twisted or humped. The thin bench plane blades I’m using are pretty flexible so a lever can press them flat against the bed.
- Eliminates the need for hammer, the plane is adjustable by hand.
- You can fine tune the depth of cut with the screw
- See this post for more whys.
You could just use a threaded insert and turn the wedge into a lever, it seems to work. I dislike that just because I don’t like it (or at least can not articulate why). One worry is, over time, the wedge will dent and not work so well. What and how:
- The screw is 1/4″ x 20 tpi (NC). I make these but anything will work. I use a coarse thread because it works fine. Also, a course thread won’t tighten as much as a fine one, this, combined with the small cap, helps to prevent over tightening (an eighth of a turn is around the max). To much pressure and the innards will bend and wood will dent.
- Screw length is long enough that you can grasp the cap but short enough that it doesn’t dig into your palm in use (which is a surprisingly long distance). The minimum length is determined by the wedge height.
- Locating: You can build the wedge first or the lever first. Or even in conjunction. I like the screw to poke up just behind the end of the wedge ramp (¼”, at the end of the cove) and the pivot located under the bridge.
- The lever hammer should press on the blade about 1/8″ above the bevel. This is close to the business end but a bit back from the thin part of the ramp. It would be bad if tightening the lever caused the sole to bulge.
- The leverage ratio is somewhere around 1.5 (see photo: 1.6 (top) and 1.3 (bottom)). I prefer the < 1.5 ratio (bottom).
- I welded some 1/8″ steel into a tee and welded that to some 3/8″ threaded rod (you could use a nut) and machined it to a height of 1/4″.
- The screw side is tapered on top to give the lever more clearance (total taper is on the shy side of 1/16″).
- The toe side has an arc on the bottom just behind the hammer (I want only the hammer to touch the blade).
- The screw hole in the wood needs to be elongated towards the toe for clearance when tightening.
- I cut the mortise with an 1/8″ end mill and drilled with forstner bits (1/4″ on top and 3/8″ on bottom). When drilling, you will get blow out so drill a 1/16″ pilot and drill from both sides or cut the wedge cove and trough after drilling. Use small gouges to fit the lever to the mortise.
- The pivot is 3/32” steel welding rod.
- Drill the wedge for the pivot, then install the lever and mark (use a punch or just touch it with the drill). It would seem like a better idea to drill both holes at the same time but the flash really does a good job of locking the lever in the wedge.
- The wedge should NOT move when tightening the screw. If it does, the mortise is not deep enough (and the lever is topping out), the screw has threaded itself into the wedge or you need a bit more taper on the lever.