JimG
Western Thunderer
With all the work proceeding on the base for the garden layout, I thought it best to start thinking about a locomotive to run on it. the choice was a MacIntosh Class 782 tank - the Caledonian workhorse 0-6-0 tank as shown here in LMS days
https://en.wikipedia.org/wiki/Caledonian_Railway_782_Class#/media/File:Balornock_(St_Rollox)_Locomotive_Depot_CR_McIntosh_geograph-2823562-by-Ben-Brooksbank.jpg
Some may recognise it as the prototype for the Wills 4mm whitemetal kit of many years ago.
As is my habit, I never start a locomotive until I've got the wheels in hand - a habit with modellers in S scale. The 782 tank needs 4' 6" drivers and I could find no suitable 1:32 scale ones ready made, so it was back to wheel making on the mill. The first thing was to purchase a sheet or 1/4" clock brass from Ian Cobb - I use clock brass because it is flat and is of CZ120 brass which machines very well.
The first job was to machine the basic front profile of the wheel. The brass plate was screwed to a sheet of MDF which was in turn bolted to the mill table and the profile milled with a 5mm cutter to get rid of a lot of brass quite quickly. The Caledonian had quite deep bosses on its inside cylinder locomotives - hence the depth of the boss.
The next job was to cut the basic spoke shapes, drill an undersize axle hole, and drill a pilot for the crankpin.
The next process was to finish the shape of the boss and machine the front profile of the spokes. This was done with a 4mm diameter ball-nose mill, and the first c**k up happened - as can be seen by the half round groove through the boss. I worked out the reason fairly quickly. I had hand written the CNC program for the ball nose milling for S scale wheels and the last operation on my CNC program is to raise the tool to safe height and reset to (0,0). I had changed the values throughout the program for the 1:32 scale wheels but had forgotten to change the rise to safe height. It was still set to 5mm for S wheels and the 1:32 wheels are 6.35mm high, so a nice furrow of 1.35mm was ploughed across the boss when the tool was en route to (0,0). The joys of CNC.
The first question was what to do. I could just scrap the wheel as it stood and start again. But the brass sheet had been purchased of a size to do ten driving wheel centres and four bogie wheels (there's a Class 104 0-4-4T in mind after the 0-6-0T) and this would torpedo that idea. So I opted to try a repair.
I first cut across the area of the groove to remove the problem.
...then soldered a piece of brass of just more than the required thickness in the machined area. I managed to do the soldering with my 100 watt Weller - I wasn't too happy at the thought of using a small torch for the job with the MDF base under the brass.
Next I machined the brass to shape - oversize to allow for the shaping with the ball nose cutter.
Then I milled the brass to get it level with the existing surface of the boss
...then finished off with the ball nose cutter, and the top of the spokes are further machined with a smaller diameter mill to get the proper shape.
The repair is pretty well invisible and the only noticeable area is the joint area in the axle hole. I attempted to re-bore the hole but the cutter picked up the edges of the existing bore. However the hole diameter is 6mm at the moment and it will be opened out to 6.35mm for the 1/4" axle, so that might minimise the problem, or I will have to use some filler if the problem still shows. The bosses will be painted, so there would be no obvious problem using a small amount of filler. However, it's the first time I have tried doing a repair using CNC and was quite pleased at the end result.
I then started off on the next wheel and that is now finished. It takes about three hours to do all the machining and I'm now working on one or two things to speed the process up a bit.
Once all six wheels are cut, they will be released from the plate - each one is held in place by four 0.2mm tabs after machining. After that, the final shaping of the spokes will be carried out by hand with scrapers and needle files.
By the way, the bit of Plastikard held upright by the toolmaker's clamp to the right of the spindle is a quick and dirty chip fence to keep the chips out of the rest of the workshop. CZ120 brass machines beautifully, but the chips go everywhere.
Jim.
https://en.wikipedia.org/wiki/Caledonian_Railway_782_Class#/media/File:Balornock_(St_Rollox)_Locomotive_Depot_CR_McIntosh_geograph-2823562-by-Ben-Brooksbank.jpg
Some may recognise it as the prototype for the Wills 4mm whitemetal kit of many years ago.
As is my habit, I never start a locomotive until I've got the wheels in hand - a habit with modellers in S scale. The 782 tank needs 4' 6" drivers and I could find no suitable 1:32 scale ones ready made, so it was back to wheel making on the mill. The first thing was to purchase a sheet or 1/4" clock brass from Ian Cobb - I use clock brass because it is flat and is of CZ120 brass which machines very well.
The first job was to machine the basic front profile of the wheel. The brass plate was screwed to a sheet of MDF which was in turn bolted to the mill table and the profile milled with a 5mm cutter to get rid of a lot of brass quite quickly. The Caledonian had quite deep bosses on its inside cylinder locomotives - hence the depth of the boss.
The next job was to cut the basic spoke shapes, drill an undersize axle hole, and drill a pilot for the crankpin.
The next process was to finish the shape of the boss and machine the front profile of the spokes. This was done with a 4mm diameter ball-nose mill, and the first c**k up happened - as can be seen by the half round groove through the boss. I worked out the reason fairly quickly. I had hand written the CNC program for the ball nose milling for S scale wheels and the last operation on my CNC program is to raise the tool to safe height and reset to (0,0). I had changed the values throughout the program for the 1:32 scale wheels but had forgotten to change the rise to safe height. It was still set to 5mm for S wheels and the 1:32 wheels are 6.35mm high, so a nice furrow of 1.35mm was ploughed across the boss when the tool was en route to (0,0). The joys of CNC.
The first question was what to do. I could just scrap the wheel as it stood and start again. But the brass sheet had been purchased of a size to do ten driving wheel centres and four bogie wheels (there's a Class 104 0-4-4T in mind after the 0-6-0T) and this would torpedo that idea. So I opted to try a repair.
I first cut across the area of the groove to remove the problem.
...then soldered a piece of brass of just more than the required thickness in the machined area. I managed to do the soldering with my 100 watt Weller - I wasn't too happy at the thought of using a small torch for the job with the MDF base under the brass.
Next I machined the brass to shape - oversize to allow for the shaping with the ball nose cutter.
Then I milled the brass to get it level with the existing surface of the boss
...then finished off with the ball nose cutter, and the top of the spokes are further machined with a smaller diameter mill to get the proper shape.
The repair is pretty well invisible and the only noticeable area is the joint area in the axle hole. I attempted to re-bore the hole but the cutter picked up the edges of the existing bore. However the hole diameter is 6mm at the moment and it will be opened out to 6.35mm for the 1/4" axle, so that might minimise the problem, or I will have to use some filler if the problem still shows. The bosses will be painted, so there would be no obvious problem using a small amount of filler. However, it's the first time I have tried doing a repair using CNC and was quite pleased at the end result.
I then started off on the next wheel and that is now finished. It takes about three hours to do all the machining and I'm now working on one or two things to speed the process up a bit.
Once all six wheels are cut, they will be released from the plate - each one is held in place by four 0.2mm tabs after machining. After that, the final shaping of the spokes will be carried out by hand with scrapers and needle files.
By the way, the bit of Plastikard held upright by the toolmaker's clamp to the right of the spindle is a quick and dirty chip fence to keep the chips out of the rest of the workshop. CZ120 brass machines beautifully, but the chips go everywhere.
Jim.