With the wheels all painted it was now time to machine the wheels. There are several methods involving various jigs. These are described in the various Model Engineering books. I decided to start with the bogie wheels as their casting was quite simple and fairly easy to reproduce in solid steel if I cocked up. I've modified my method with the main driving and coupled wheels so would recommend looking at that.
I'm gripping the casting in the 3-jaw chuck here to and using the DTI to make sure the back of the wheel is fairly perpendicular to the lathe axis. This is pretty tricky as the part being gripped is tapered slightly due to the cast method.
Taking the first cut accross the back of the wheel. Note the use of newspaper to keep the dirty iron filings off the lathe bed.
Second operation was to skim the flange. Ignore the hole. I only drilled this on the first wheel subsequent wheels were difficult to true up in the chuck.
This was repeated for all four wheels. The two operations meant the wheels would sit securely in the 3-jaw for the hole boring operations. I started with a slocomb centre drill then a drill that was about 30 thou under size. And then bored the hole so it would be perfectly central. Most of these operations were done at 290RPM.
When the hole was about 6thou under size I engaged back gear to drop the speed to 40RPM and reamed the hole to final size.
This was repeated for all four wheels. The next step was to make a mandrel. I tried a between centres setup to see how that would work.
The wheels had their treads cut to size and the front face of the flange roughed out.
Now that the tread and inner flange are concentric with the hole. Wheel can be gripped by the tread accurately.
The backs of the wheels were turned to the finished width.
The Profile of the back matches the front so the start and finish cut was read from one wheel.
Each wheel was profiled.
Finished backs with fronts still to do.
I wasn't happy with the amount of flex in the between centres mandrel - I had actually managed to bend it whilst removing a wheel. First thought was a stub mandrel in a Myford patent collet.
This didn't work very well, too much leverage from the wheel meant the mandrel turned inthe collet. Next attempt was with a stub mandrel held in the four jaw to get it perfectly concentric with the lathe axis. I initially held it in the drill chuck to get it nearly centred.
The mandrel was then dialled in.
The Flange inner edge was machined parallel to the rear (not with 20 degree angle)
The flange was rounded off with a file being very careful.
Each wheel in turn was mounted in the three jaw to finish machine the front to size.
Then the wheel bosses were turned.
Here's the result, after turning.
The 45 degree chamfer was put on using a 4mm parting tool swung to the required angle. Half nuts are engaged and the cut is applied via the lead screw hand wheel. A technique I picked up from DAG Brown of SMEE during his turning demo at the Myford open day.
The finish wasn't great (insert was worn) I have some Cast Iron finishing inserts so will try them on the driving/coupled wheels. Here I'm using a Champagne cork as a sanding block. I started with 60 and finsihed with 240 grit.
I thought I had finished at this point but I am missing the distinctive square bottomed groove which marks where the tyre and wheel centre meet
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