No. 40B Butt Mortise Plane Lie-Nielsen Toolworks

No. 40B Butt Mortise Plane



No. 40B Butt Mortise Plane

Our Butt Mortise Plane will help you cut neat, precise mortises for hinges, lock fronts, and strike plates in a fraction of the time it takes to set up an electric router and template.

Based on an original 1948 design by W. A. Dohmeyer, this tool does a job no other plane can do. The elongated slot in front of the blade provides a clear view of the work. It is easy to use to make precise mortises with sharply square corners to an accurate, uniform depth. Useful for mortising dutchmen to repair flaws in jambs, furniture, and doors.

  • 9-5/8" long x 1-1/2" wide.
  • Blade is .875" wide by .115" thick, A2 Tool Steel.
  • Iron body, 1.70 lbs.

View our YouTube video"Butt Mortise Plane: Set Up and Use" here:

Click here to download a PDF copy of the instructions for this tool.

Butt Mortise Plane

This tool is easy to use and will make precise mortises with sharply square corners to an accurate, uniform depth. This plane is also useful for installation of hardware, such as hinges, lockfronts and strike plates, as well as mortising dutchmen to repair flaws in jambs, furniture and doors. This tool does a job no other plane can do.

A Scrub Blade is also available for rapid planing when large amounts of stock need to be removed, such as backplaning trim to fit an uneven wall surface.


The blade comes ready to use, but honing a secondary bevel of 5° or 10° will increase performance, help achieve a razor edge quickly, and improve edge life in hardwoods. You can find sharpening instructions in a printable PDF format here:
Sharpening Instructions PDF

For more information on advanced sharpening we recommend David Charlesworth’s video Plane Sharpening, available in both DVD and streaming formats.

Mortising a Door Jamb:

1. With your utility knife or a butt gauge, outline the hinge leaf to the approximate depth of the mortise. Take your time here, as this is the only part of your work that shows in the end.

2. Now you’re ready to set the blade of your Butt Mortise Plane, using the leaf of your hinge. We recommend that, on your first several mortises, that you not set the plane to the full depth. Start with a healthy cut, though — at least half the depth of the finished mortise.

3. The final step is to plane out the area to be mortised. Start on the outside or open edge. Work the length of the hinge in both directions and with overlapping cuts until you have a perfectly square and smooth mortise.


The body is cast from Ductile Iron, a virtually unbreakable alloy. The castings are fully stress-relieved, a process that removes inherent stresses and ensures that the tool will remain flat and true. The cap is Manganese Bronze. Other parts are Brass, Steel and Cherry.

The blade is A2 Tool Steel hardened to Rockwell 60-62, cryogenically treated and double tempered. Our heat treating technique ensures that the blade will take and hold a very fine edge for a long time. After heat treating, the blade is fully surface ground on the top, back, and cutting edge, giving a smooth, flat surface that will take a mirror finish very quickly.


Depending on how much use your tool gets, an occasional light sanding with 320 grit or finer wet/dry paper on a flat surface will keep the sole in as-new condition. Blades and tools with Iron bodies should be kept lightly oiled or waxed to prevent rust. We recommend Jojoba Oil, a plant based oil product that is non-toxic, odor-free and easy to use. Also, in our shop, we use a fine abrasive handblock to remove any light surface oxide from tool bodies and blades. Jojoba Oil and abrasive handblocks are available from us.

Find everything you need for tool care.


Materials and workmanship are guaranteed for the life of your tool. Call for repairs or replacement parts. We are available for advice if you ever have a problem using your tool.

Proposition 65 Notice:

Bronze and brass alloys contain lead, a chemical known to the State of California to cause cancer and birth defects, or other reproductive harm. Wash hands after handling.