Eccentrics & Bearings

Using the 1875 drawing (at right) as a guide, I prepared my own 1:8 scale drawing of the eccentrics & straps.


I have made the eccentrics from bronze. Here you can see how I sawed off the next-to-last eccentric out of a longer bar already turned to dimension, long enough for all the eccentrics. I removed the bar from the vise after each cut, and trued up the face again. This meant I always had one perfectly true face when continuing machining.

The straps will be cast, and I'm working on the pattern, which I make of plywood.

I made the axle boxes into "bearing blocks" of solid brass, modifying the original design to suit the needle bearings. The nylon washers function both as dust guard and axial bearings.

Here I'm boring the hole for the needle bearing that will go inside the block. Note the spacer at the arrow - it's a piece of 4 mm acrylic that I put behind the block so as not to risk running the tool into the chuck. I've found acrylic (Perspex) ideal for this, since it is very flat and true, and it's easy to see when I've cut far enough - I get acrylic shavings instead of brass chips...

Photo note: It's interesting to see the behaviour of the chips: The electronic flash (1/15.000 of a second) has frozen the chips in the air, but the worklight and the longer exposure time of the camera has resulted in weak ghost images of the flying chips...

Here's the main driving axle with its eccentrics and bearings. The suspension will be a combination of axle box springs and "cosmetic" equalizing flat springs (the latter were used on the prototype). The final adjustment won't be made until I have all the valve gear finished, and that will not be some time soon...

...but here you can see how I've already got the axle bearing blocks tentatively attached to the frame. I have obtained needle bearings for the journals, not exactly prototype (and not exactly cheap!), but this will reduce friction substantially. The bearings have an inner sleeve (see the two in front, where the sleeves are removed), so I won't have to case-harden the axles. And, they will be totally hidden within the bearing brasses, so no-one (except you who read this) will know I've cheated...



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