Rear Wheel Tread Pair

My first go at machining a rear wheel tread pair for my miniature traction engine was not that successful. That meant I needed another go.

The rear wheel tread pair are handed and the tread grooves are 4mm wide and machined at 7 degrees with a depth of 0.75mm, 35 grooves in total.

The rear wheel rim blanks take a lot of machining and took me around 3 hours each to machine on the Warco WM240B lathe.

The treads are then machined on the milling machine with an index plate on the rotary table.

wrong angle on treads

My first pair of machined rear wheel rims. As you can see, I got the angle on the second wheel wrong. The problem is the angle of the treads are handed and this means moving the rotary table to the opposite angle.

In the process I checked the angle of the rotary table against the milling table using a simple metal protractor and ruler. The trouble is the ruler flexes.

Hence one of the above treads was at 7 degrees and the other was at 8.5 degrees. This small difference in angle was very visible in the final pair.

a pair of rear wheel treads

So, I had to machine another rim from a solid mild steel round blank.

One the blank was machined I carefully marked the 7 degree angle onto the surface of the rim and then with a centre point in the spindle of the milling machine I aligned rim carefully on the table.

The result is a pair of rear wheel rims.

I need to now carefully index and drill the rims to take the rivets for the wheel spokes.

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