Build - Thumb Plane Honing Guide

Thumb Plane Honing Guide

[March 2015]

This honing guide was made specifically for the thumb plane described elsewhere in this website at this location. The picture above shows the honing guide with the blade in place for honing. In practice the honing guide is quite workable, but it does have some limitations:

• As it is made for a specific blade, it is not generally usable for honing other types of blades.
• Due to the small size, it is a bit tricky to lock the blade in place.
• It does not clamp as much of the blade as I would have liked (but it does work).

On the other hand, it does the job and is a good addition to the thumb plane. Also, the guide enable the back if the blade to be honed without removing the blade, which simplifies the honing process.

Overview

The honing guide is made from a piece of aluminum, milled to shape, and fitted with a brass axle with nylon wheels. A socket head screw is used to compress the "jaws" of the guide to clamp the blade in place.

Two views of the completed aluminum body are shown below.

Plans

Plans for the honing guide are included with the plans for the accompanying thumb plane, and may be found here:

https://sites.google.com/site/lagadoacademy/machining---lathes-mills-etc/build---thumb-plane

Making the Body

To start a rough blank was sawed out a block of aluminum (in this case a 1.2" thick piece from my scrap pile). The two sides which are at a 90° angle are milled first. The block is positioned in the mill vise (shown below) using a parallel to align the flat horizontally, then milled flat. The milled side is then used a reference with an angle plate to rotate the piece 90° and then mill the second side flat.

Next the sides of the workpiece are milled flat, first with an endmill, and finishing with a fly cutter. To position the piece in the vise, and angle plate is used against one of the previously milled sides, and the "flatness" is verified with a dial indicator. The opposite side is milled similarly, and at the same time the piece is milled to final thickness.

With the two sides milled flat, the long side ("hypotenuse") of the right angle can be milled. I did this my first laying out the cut using the shape cut out of the plans ("stencil") to position the line, and then scribed it on the workpiece; the scribed line was aligned with a parallel (not shown), and the piece was milled down to the scribed line.

The round end of the piece was also marked out with the "stencil" and a series of straight milling cuts were made to approximate the final shape. The final round shape was completed by filing and using abrasive cloth. The completed basic shape is shown in the third photo below, along with the paper "stencil" (in the background - the blue color is from the layout dye used).

Following this step, the hole for the axle is drilled and reamed (not shown).

Washers

The washers are made from teflon rod. The rod is turned to the finish diameter, drilled for the axle center hole, and then parted off.

Axle

The axle is made from a length of brass rod, of the same nominal diameter as the axle hole. It is only necessary to use abrasive cloth to remove small amount of materiel to achieve a smooth fit. The wheels, washers, and body are "stacked" and measured to get the required axle length, and one wheel is pressed on for a test fit. The second wheel is left off pending further milling operations.

Completing the Body

Next, a groove is milled for the blade - the groove is just barely wide enough for the blade to fit. The groove is also shallow enough to allow the back of the blade to protrude, so that the hoing guide can be used to grip the blade when honing the back. After that a deep central groove is milled.

Next, the holes for the clamping screw are drilled, the "top" hole is drilled for a clearance fit, the "bottom" hole is drilled for threading (I had to use a "long reach" tap which I had previously made for another project by grinding down the shaft of an ordinary tap). After tapping, a shallow counterbore is milled in the "top" hole to fit a small stainless steel washer.

The final step is to reposition the piece and mill "side lobes" into the body; the purpose of this is to reduce the effective width of the body wall to enable them to flex when the clamping screw is tightened, and thus to grip the blade.

The two photos below show the completed body with the clamping screw in place, but without the wheels.

Finished Honing Guide

The picture below shows the completed honing guide with the blade in place. I used the guide to re-hone a blade which had been previously honed by hand, and got a straighter and sharper finish, with less effort than before.