A journal following the history, design, construction and operation of Bernard Kempinski's O Scale model railroad depicting the U. S. Military Railroad (USMRR) Aquia-Falmouth line in 1863, and other model railroad projects.
©Bernard Kempinski All text and images, except as noted, on this blog are copyrighted by the author and may not be used without permission.

October 22, 2020

Rolling Chassis

Close-up of the sub-chassis
 I decided that I needed to rework the sub-chassis as I was getting some binding. I believe it was because the hornblock bushings were not parallel. To solve this I made a new jig with some scrap MDF that held the axles parallel, while I re-soldered the hornblock bushings to the sub-chassis beams.  The result gave smoother operation.

Next I started on the main side frames. I built these from 0.09 inch square brass tube.  Again, I made a jig to help hold the small brass pieces while I soldered them.  The frame dimensions are not too critical as long as they allow the sub-chassis to rotate about the pivot axle. With the jig they came out pretty close to identical, or at least close enough.

Jig to keep axles parallel
To make the top beam I soldered two brass tubes together. Then I measured where the bends should be. Using my mototool with a cut-off disk I cut small slots on the beams on the acute angle side of  the bends. When I bent the beams I bent both of  them, thus both were identical. I  unsoldered the beams and put one in the jig. I soldered the additional members one-by-one, cutting and fitting as I went.  I used my disk sander to square up the ends and my mototool and files to make the mitered joints.
Frame jig showing top beam with bend.

With both frame sides built, I cut two brass 0.5 by 0.8 by 1/32 inch  plates and two 0.09 by 0.09 by 0.8 inch square tubes to act as transverse members. Again, I soldered them together and used my disk sander to square the ends and make them all the same length.  The photo below shows the completed sub-chassis and the main frame.

I have to figure out a way to cover the gaps at the bottom of the hornblocks. I'll probably add small keeper plates that will be soldered on or maybe screwed in if I decide they need to be removable. I don't think they do, so solder may be OK. 

The sub-chassis installed in the main frame. 

Next I fitted the gear box and motor to the front axle. This took a little bit of fiddling to make it work.

Motor and gear box on the front axle. 

Here is a short video showing the chassis rolling on Potomac Creek  bridge. The results have been encouraging so far.

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