Making Driving and Coupled Wheels for "Spencer" a Hunslet 4-6-0 Narrow Gauge engine in 3.5" Gauge

Driving and Coupled Wheels

After my experience with the Bogie Wheels I modified the machining sequence I use. Here is the list of operations for each wheel. Note you will probably need to modify these depending on how much machining tolerance is built into your castings, with mine most of the excess could be taken from the rear of the casting. I had to create a machining jig (or dummy faceplate) to mount the wheels on and grind an accurate round nose tool. As you can see after 180 different machining steps I'm pleased with the results

Machining Sequence

1. Chuck with front facing outwards in 4 jaw chuck by flanges, turn treads pararllel and 1/16" over size. Make sure flange sits flush to back of each jaw.

2. Mount in 3 jaw chuck by the turned treads with back facing outwards. True up flange and face back so that wheel width is 25thou oversize.

3. Drill / Bore / Ream central hole (see seperate amchining sequence below)

4. Mount wheel on jig held in 4 jaw. Turn front face of tyre to size.

5. Turn flange to size.

6. Turn Tread to maximum size and parallel.

7. The flange is cut to size with the top slide set over by 20 degrees using round nose tool. Flange is 51 thou thick at narrowest point.

8. The tread is coned with the top slide set to 2 degrees again using the round nose tool blending into flange root.

9. The outer corner of the tread is chamfered at 45 degree using a 4mm parting tool. fed in to 1/32"

10. Mount wheel in 3 jaw chuck front facing outwards gripping flange. Face front face of balance weight / hub to size.

11. Mount wheel on jig with rear facing outwards. Cut recess on back face to match spokes on front.

12. Round off flange with a file. Being very careful.

13. Chamfer / counter sink axle hole slightly to cope with axle shoulder root being slighly rounded.

14. Turn wheel round on jig and cut slot that defines tire. Use parting blade to get square sided slot.

The above sequence is the way I did it. Step 14. is at the end as it took me quite a bit of research to find what was correct and looked right for the model. Getting all the axle holes accurately bored (step 3.) took quite a bit of effort and heres the sequence I used to get an accurate 5/16" hole.

Drilling/Boring Sequence

1. Deeply Centre Drill wheel with 1/4" Slocombe drill.

2. Drill through with L letter drill (0.2900")

3. Bore until M letter drill fits easily (0.2950").

4. Bore until 19/64" drill fits easily (0.2969").

5. Bore until N letter drill fits easily (0.3020").

6. Bore until chamfered part of reamer wil enter hole

7. Ream to 5/16" in back gear @ 130 RPM (0.3125")

Basically I use various drills as plug gauges so I can monitor the boring operations accurately. Heres some pictures showing the setups. Once step 3 is out of the way I perform each operation on all the wheels before moving to the next operation. This speeds things up, but its a lot of work however you slice it!