The Drivers

Making the main drivers with CNC

I studied long and hard how I was going to make the main drivers for the A3 loco. This seems to be a major concern with all A3 (and many other designs). The usual method is to make or purchase cast iron casting and machine to finish. That was my initial plan.

However, I have a great interest in CNC machining and the drivers seemed like a most natural application to that process. When I first started this construction. I had already built a low cost CNC machine and was having a good time doing light duty projects. I wanted to be able to do more so I moved to the TAIG micro-mill and have been improving its CNC capabilities ever since. In this series you will see some changes to the CNC mill due to this experience.

What you will see here is my experimentation in developing drivers for use with the A3 and actually any other design of my liking. In fact if enough other folks are interested in a machined rather than cast wheel, I will look into what a production run should cost. The wheels I have done so far does not justify the total CNC machine development and experimentation cost I have incurred. That was not the reason to spend so much time and effort on these wheels. The wheels are just an excellent target product for the CNC learning process. That learning benefits the A3 project.

I assume many readers have been following my loco wheel project over in the TEDEX forum in the CNC section. I intend to find many more real applications for the CNC process and the tiny Taig mill. It is a capable machine.


I decided my first attempts should be machined in wax. This is great stuff in which to develop a product. Here it is easily cut into a one inch thick disk using a band saw.	I do not recommend using something so simple as you see here for holding metal. It was adequate for the wax but I did not feel real secure. The CNC is programmed to start from the top dead center of the disk.

The mill is running in this shot but the fast lens stopped the action. A little compressed air would be nice to clear the chips. No cooling or lubrication is needed when milling wax. Also the program is run at a high rate of speed.	This is the wheel at the end of the run. All measurements can be checked for accuracy. Mistakes can be melted down, recast and used again. Note the clean swarf in the background.

This is a wax wheel after it has gone through the lathe work. The blue object on the bench just under the finished wheel is a mill machined wheel before it is cut off the wheel blank.	This is a 3.5 inch 1 inch thick 303 stainless disk I am preparing for the CNC milling process. The disk has been sawed on both flat surfaces so these surfaces must be faced trued flat and parallel to each other. The perimeter is not important.

This is after several light facing passes. You can see that some of the saw marks can still be seen. All I want to do is clean up this face. When clean, reverse the disc and face the rear side. The faces will be true to each other because the 3 jaw has been check as true to the Y axis.	This is the new and improved fixture for holding the wheel disks. This is much better and professional than what I used for the wax models. Again the CNC start point is the center of the disk. The facing I did on the lathe created a very easily to see center point on the blank.

Here the 1/8 hp motor is in use cutting the first stainless steel wheel. It is enough power but I did notice the motor load up and slow down on the plunging cuts. More power would be nice.	I used a hand powered spray bottle for misting the work in progress, sort of between a mist and a mini flood. This is way too much work in my book. It did do the job. I also broke many 1/8" mills from using and experimenting with feeds and speeds. I discovered I was going much too slow.

The first side of this disk I broke all my mill bits before I could finish. So then I stopped and ordered more mill bits. I flipped the first disk over and had enough material thickness to make a complete second run at making the wheel. I band sawed the two wheels apart.	Here is the good 2nd wheel and the incomplete first attempt (at the top), next to the wax master. Here the second SS wheel has been finished on the lathe. I have not done tread or flange work on any of the wheels as that requires mounting on a mandrel and run all at one time without removing the mandrel from the lathe... That will be done later.

This shows the 1/16" recess in the rear side of the driver wheels. These blanks when held by their tread in the 3 jaw are running very true. It is nice to see how accurate the CNC program runs and the proof is in the quality of this output.	This is the Taig mill with the new 1/4 TEFC motor and the air mister installed. What a pleasure this is to run long programs like the loco wheel. This photo was taken after I cleaned up the mess shown below. Note the level in the mister reservoir. The amount missing is what it took to run the entire wheel sequence.

Here you can see the air line connected. This is at the end of the Cast Iron A3 wheel CNC run. The rag on the right keeps swarf and moisture off the the X-axis motor and coupling.	Some folks think I don't mess up my machines. Yes, I do and the carbon in Cast Iron does a particularly good job of making a mess. The CI and the SS are both running easily at 20 ipm feed rate.

Here is the set-up I use for slicing a 1" disk. That saw is well suited for making a close to dimension cut. Now I know why they put square sides on vices.	Here you can see I am actually cutting dead on the bottom of the milled spoke pockets. This leaves little clean up needed on the lathe.

I have to show this (almost) same picture on every project. Yes, I do get my lathe dirty. That Cast Iron is again wonderful stuff (NOT!) And yes, I cleaned it all up immediately following this shot. Ha!	Here are three wheels. The one on the left is made from gray class 40 Cast Iron. It is beautiful. The middle wheel is 303 stainless steel. A little brighter and also very good looking. I have one more to run in 12L14 leaded steel. Then I will decide what material to use to make my final set.

I have decided to make my A3 drivers from 303 stainless. I CNCed 5 wheels from three blanks. Then turned them on the lathe much like the tender wheels. Here is the mandrel I made so I could turn the driver's tread and face the counterweight line true. The thread is 3/8 x 24.	This is the final cut on the lathe where I am cutting the groove to highlight the counter weight. I have already cut the 3 degree tread taper and the 10 degree bevel on each side of the flange. The flange cutting is the most difficult part of the setup. After doing the eight tender wheels I have the knack.

Here is what the driver looks like when mounted on the lathe. You can see there is plenty of room on my Lathemaster 8 x14. That is a different mess than the picture above. Ha!	Here are five of the wheels. The usual scale human hand is provided again for reference. The driver on the bottom right has already had its spokes dressed out. The gold looking driver is due to the incandescent shop lighting.

This is how two wheels are cut from one blank. The gap you see around the flanges is the 10 degree back taper on each flange. There is also a 10 degree taper on the inside of the flange.	There is a lot of swarf removed when when I cut away everything that doesn't look like an A3 driver wheel. The blank is about 1.250 inches thick before truing.

I am detailing the spokes with the Dremel Tool. Some hand filing is required too. It takes awhile so I protect my hearing with the ear muffs. The ol' eyes need a boost too.	This is my collection of 303 stainless steel A3 drivers. I will detail the one at the left front and then select the four best for the project. All the others are done!

The Drivers

Making the main drivers with CNC

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