A couple of weeks ago, I did a free seminar on sharpening and tuning up hand planes at the Chestnut Creek School of the Arts. Two of the questions that the attendees had pertained to making adjustments to the plane that I had not thought to include in the presentation. The first was how tight to make the lever cap screw. The second was how to adjust the position of the frog without a lot of trial and error. I’m going to talk about the lever cap setup today. I’ll discuss positioning of the frog in a future post.
The lever cap’s job is to hold the iron and chipbreaker securely to the frog, and put pressure close to the cutting edge where it is most critical. In order to apply pressure at the cutting edge, the screw that passes through the center of the lever cap creates a pivot point so that when the lever cap’s lever is locked down, it raises the rear of the lever cap, and therefore presses down at the front of the lever cap. When the lever cap is properly set, the blade should not move rearward or laterally during normal planing, but should be able to be adjusted for depth of cut or lateral position without having to loosen the lever cap.
My method for adjusting the tightness of the lever cap is pretty simple and reliable. I first remove the lever cap and loosen the screw so that things are too loose. Then, with the iron and chipbreaker installed but retracted, I place the lever cap into the plane but leave the lever in the open position. I use a screwdriver to tighten the lever cap screw until it just barely makes contact with the lever cap. Do not snug the screw at all. If you’ve tightened the screw correctly, it should barely be in contact with the top of the lever cap, but you should still be able to remove the lever cap without any resistance. If there is any friction between the lever cap and screw when you try to remove the lever cap, then the screw is too tight. Back it off until the lever cap is easily removed and reinstalled but the screw still makes contact with the top of the lever cap.
With the lever cap under proper tension, you should now be able to adjust the iron’s depth of cut and lateral position, and once adjusted, the plane should hold that setting. If your lever cap has a keyhole shaped hole for the screw, you might notice a small gap at the top that opens up when you lower the lever. This happens because the lever cap slides slightly rearward when being locked down. Don’t worry if this happens, it’s normal, and with the tension properly adjusted, it won’t move in use. If you’re lever cap has a kidney shaped hole, you won’t have this happen.
If you want to see an example of this adjustment being made, here’s a video I did on the same subject back in 2009.