Threading and Trimming a Bike Fork - 1941 Schwinn Henderson New World

Cutting Threads on a New World Steerer Tube

 

Late in 2024, I bought a 1941 Schwinn Henderson New World bicycle project from a bike shop in Pennsylvania. This bike was relatively complete, but the fork had been swapped for a later, post-war fork that was spray painted black. Given how unusual the "Henderson" New World variant is, I thought it would be nice to have a correct fork for this bike. 

 

1941 Schwinn Henderson New World with Incorrect Fork

The correct fork is the Schwinn-made "D" profile fork. This fork has tapered arms with a "D" shaped cross-section. This style of fork would be correct for a tourist New World from 1941 and earlier. I located a fork from a donor frame. The fork was in good shape, but the steerer tube was too long and not threaded low enough to fit this men's 21-inch frame.

The fork material is a pretty basic, soft steel. The steerer can be threaded and trimmed to a size that will fit the fork.

The first step is to have the correct tool for the job. I'm using the Hozan #426 die and handle. The correct size is 1-inch diameter by 24 threads per inch.  The die has an adjuster screw that helps set the correct depth of cut. The screw is adjust until the die fits snugly around the existing threads, but does not substantially cut those threads much deeper. The goal is to match the threads as closely as possible.

The die is mounted into the handle and is threaded onto the existing threads, turning clockwise until it reaches the end of the threads. 

 Oil is liberally applied to the cutter. Cuts are made by turning the die 1/8 or 1/4 of a turn (depending on how much resistance you meet) and then backing off (counter-clockwise) the die. You'll feel and perhaps hear the die cutting and then releasing the broken metal chips. You need to back off the die after each incremental cut in order to free the metal chips from your cutting.

The die is frequently brushed clean with an old tooth brush and re-oiled. Work slowly and carefully.

 

Notice the Oily Chips - Cut and Back Off. Also Notice Black Line.

 Every so often, the die is removed and the fork test fitted in the frame until I get the threads in the correct location all the headset parts to grab. Once that is done, the die and threads are cleaned with an old toothbrush.

Cut Threads, Down to the Mark After Test Fitting.

 

Now that the threads are cut, the fork needs to be trimmed. Again, the fork is tested fitted to the frame and I mount the headset parts. And measure the excess. In this case, I need to account for the threaded top cup (the knurled, round piece), the lock ring (the thin ring with the tooth on it), and the lock nut (the six-sided large nut on the very top). I compare what I need in terms of length to what I have. Measure twice, cut once. [In some cases, you will need to use a rectangular small file to extend the groove that the lock nut's tooth sits in. Do that before measuring if you have to do so.]

After I'm a sure of my measurement, I thread the fork into a cutting jig and cut it off with a hacksaw. 

An Old School Tube Cutter with Internal Threads 

 

After cutting, I clean all metal dust and chips from the fork and the steerer tube. I then take a Dremel tool with a fine emery drum and gently remove the cutting burr from the inside of the steerer tube. 

Once that is done, everything is test fitted again. Sometimes I don't cut enough off the first time and I need to make a second cut. If that is the case, the cutting and cleaning steps outlined above are repeated. It's better to have to make two cuts than to cut too much off...

Everything is then cleaned, greased, and assembled.

When I'm done, I have a handsome and correct fork for this New World frame, ready for polish and matching touch-up paint.