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Last weekend, I made a cheap little device that worked well, so I thought I'd share the idea on the 2-rail forum. I'm sure someone has already done this, but I haven't read about it before.

I needed to spread some 2-rail wheel sets, because the flanges were catching on switch points and guardrails (too narrow according to the NMRA gauge). Four of the wheel sets were in some unpowered, painted diesel units, and I did not want to bother with removing the microscopic screws that secure the journal retaining plates on their beautiful OCS F-unit trucks from P&D. Therefore, I wanted a way of spreading the wheels on their axles without having to remove the axles from the trucks.

At ACE hardware I bought a small compression "union" designed for joining two sections of 3/8" copper tubing, then removed the ferrules and threaded caps at each end and cut a slot along the full length of the main body of the union wide enough to clear the diameter of the axle, all the way through to its hollow center.  Next, I cut a similar slot through one of the threaded caps and replaced it on the union. With the slots lined up, the union and cap can be dropped over the axle. With only one of the compression caps in place, the overall length of the device is short enough to fit over the axle, between the wheels. Twisting the cap a little will allow the device to "capture" the axle.

Using two small wrenches, the union and the cap can be turned in opposite directions, causing them to spread apart and push the wheels into gauge. Even though it wasn't strictly necessary, I also added a washer with a slot cut into it so that it could also be slipped over the axle. I did this to maximize the number of threads engaged between the union and the cap. The 3/8" compression union is made of pretty heavy brass, so even with slots cut through it and through the end cap, there was no distortion and no slipping of the threads.

I was able to re-gauge all the narrow wheels on my A-B-B-A F-unit set in just a few minutes. Fortunately, all the wheels on the powered axles were OK, because this device clearly won't work on an a geared axle.


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Here are some photos to show the spreader. I apologize in advance for their poor quality (taken outdoors with a flip phone), but I think they show the basic idea.

I cut the slots using a fiber-reinforced abrasive disc in a high-speed rotary tool.

I added the spacer (washer) because the device was too long to fit between the wheels with both end caps in place, but was a little short with only one (i.e. only a few threads engaged between cap and body of the union).

With slots on cap and union aligned, device can be slipped over the axle.

Hope this helps.

UnionSlotsWasherDevice on axleWrenches


Images (5)
  • Union
  • Slots
  • Washer
  • Device on axle
  • Wrenches

I cut the slots with an thin fiber-reinforced abrasive cutting disc chucked in a rotary tool (like a Dremel, but mine is from Black & Decker).  I removed the end caps and ferrules, put the body of the union in a vise using the flats on the hexagonal central part to clamp it tight, then made two parallel cuts along its full length all the way through. Same procedure with the end cap. Finally, I dressed both parts with a file to clean up the sharp edges. The union cost about $3.50 at my local ACE. 

I use Athearn trucks on all my freight cars (except cabooses), so it's easy to pop out a wheel set that needs to be replaced or adjusted. But the spreader could be used to adjust a wheel set in a brass passenger or freight truck without having to disassemble the truck in order to remove the axle. 


I have had a jar of Brass Unions sitting on the workshop shelf for 20 years from my Automotive days and never gave them a second look until I read your article!

Thank you for providing a simple solution to what you would normally do... "put them in a vice and a tap with a soft hammer"  your idea is much better and more professional. Roo.

I only needed to move the wheels apart by 10 or 15 thousandths of an inch in order to fit the NMRA gauge, which wasn't enough to adversely affect centering on the axle. I guess I would say that this thing works well for fine adjustments, but it might not be as useful if the wheels are extremely out of gauge. In my case, some wheel flanges were picking the switch points and pinching at the frog -- but it did not require a large adjustment to correct the problem.

Also ... these particular wheel sets have a Delrin insulating bushing on only one of the wheels. The other wheel is a press fit on the axle without a bushing. I think probably the wheel with the plastic bushing will move on the axle before the other one does, so when the gauge is correct the wheels will again be centered. That's just a guess ... I haven't experimented with it.

Don't want to start into a great discussion on measuring wheel sets as this thread is about a great idea that works for Smithy and myself because I am going to make one as well might use the mill and mill a slot. Anyhow I have also found when measuring "Back to Back" on modern wheel sets it's very little you need to move the wheels like Smithy said, if it was anymore than a few thou there would be something wrong with the wheel sets or they are 50 years old then you would put them in the cabinet as collectors items and go modern. (opinion!) Roo.

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