Modelling the Kerr-Stuart Brazil Class 0-4-2ST locomotive in 16mm scale. - Keith Bucklitch
Wheels, Axles and Cranks.
It is quite common that your chuck is slightly out of true. Therefore to ensure the wheels are concentric, make a wheel turning mandrel to fit in the chuck as follows. Firstly, cut a 30 mm length of 6.5 (1/4") mild (or silver) steel rod. Thread one end 1/4" by 40 tpi for 10 mm. Place on one side. Take a piece of mild steel bar, around 30 mm diameter and 20 mm long. (These dimensions are not critical.) Mount this in the chuck, face the end, centre drill and drill 7/32" and tap 1/4" by 40 tpi. (If you wish, mark the mandrel alongside No 1 Jaw of the chuck for future use, although you may find it is not accurate on a second use. However, retain the bar as you can easily make a new mandrel for another set of wheels.) Hold the piece of 6.5 mm rod in the tailstock chuck and screw it into the piece of bar as tightly as possible. Loosen from the tailstock. Face the end of the rod then carefully turn down until one of the wheel
blanks will just slide along the rod without any slackness. From this point on ALL the wheel turning must be done without disturbing the mandrel. Thread the end of the rod 4 BA leaving approximately 6 mm plain to mount the wheels. Place a wheel blank on the mandrel and tighten a lock washer and 4 BA nut to hold the wheel firmly.
Using a freshly sharpened tool, turn the wheel blank to 43 mm diameter. Note the setting on the cross slide. Remove the blank, and repeat with all the other wheels. Now turn the tread of the wheel to 40.5 mm diameter for a length of 5 mm. Remove the wheel and repeat for all of them. Now, after re-sharpening the tool, turn the wheel to 40 mm diameter. Note the cross-slide setting. Remove the wheel and do the same for each one in turn TO THE SAME SETTING. You can leave the treads parallel if you wish or turn a 2 degree taper on them by now setting the cross-slide over to the desired angle and working from the flange root, carefully turn the taper. Again repeat for each wheel. . Using a file, break the edge where the face meets the tread, to leave a slight bevel. Also, using the file, shape a slight angle on the flange, and round off the edge. You should now have a set of wheels that are all the same diameter.
To turn the recess in the wheel face, use a round nose tool with sufficient overhang or a boring tool. Treat each wheel in turn noting the cross-slide setting for the first one and working to the same measurements. You have now finished with the mandrel for this set of wheels. Remove it from the chuck. You may use it again with a fresh stub axle for the pony wheels.
Take a wheel, mount it in the chuck gripped by the tread, with the flange pressed hard against the jaws. Face off the back of the wheel until the flange is 1.5 mm thick. Note the setting on the top slide. I usually lock the saddle traverse and use the top slide to ensure that all the wheels finish to the same flange thickness. Before removing the wheel from the chuck, use a file to create a slight bevel at the flange. As before repeat with each wheel in turn.
I usually secure my wheels to the axles with 8 BA grub screws. A 1.8 mm hole is drilled through the wheel boss into the axle hole and tapped 8 BA. If I am certain that I will not want to move the wheels at some later date, I also drill a 1 mm hole and secure a pin through the wheel and axle with Loctite. Alternatively, drill two 8 BA holes and use two grub screws for each wheel. This model is capable of changing gauge, and therefore you may not wish to secure the wheels on the axles permanently. However, as the frame axle bushes are removable it is possible to remove the complete wheelset and replace with a different gauge.
If you have any questions, or comments or find any errors in these notes please contact me by email. Email Keith Bucklitch.
Copyright © 1998, Keith Bucklitch
Last Edited - October 1998