3" Burrell Traction Engine build.

Screw Cutting The Square Thread-Brake rod (Part 2). Hello again, this time I intend tackling the screw cutting problem, head on. Previously I eluded to the thought of cutting an acme thread but through some useful feedback, I've learnt that a square thread is, as the name suggests (square) and not acme form. The 2nd thing I have found out is my previous thinking of a pitch 0.108" is also incorrect. 1. Why the first lathe change gear setup didn’t work I selected from the longitudinal feed section of the chart instead of the threading (metric pitch) section. These feed settings are designed for fine carriage movement per spindle revolution , not for synchronizing the carriage with the spindle to cut a thread. So the gear train I spent hours installing: 24T stud 72–18T compound 80T 60T screw was creating a very small feed ratio , which explains why: ten turns of the chuck certainly wasn’t giving 1" of carriage movement That’s expected — feed rates are ...

  Screw cutting Acme Thread - Brake rod (Part 1). Welcome to this month’s traction engine build update. With the weather not helping motivation, I decided to tackle some straightforward lathe work — the brake rod. The drawing specifies a 3/8" × 10 TPI left-hand square thread. While anticlockwise operation to apply the brake would justify a left-hand thread (as seen on some full-size engines such as those by Aveling & Porter and Burrell ), cutting an internal LH square thread at this size would be challenging. A right-hand thread will be perfectly adequate for the model. My plan is to screw cut a trial thread in silver steel, mill flutes to create a tap, harden it, and use it to thread the bronze nut. I’ll then cut the matching screw so both parts mesh correctly. Since the nut is bronze, machining should be manageable. Although the Boxford metric lathe is the easiest machine to set up for screw cutting, producing true 10 TPI would require imperial conversion gearing. Instea...