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Kadee 830 / 930 Rotary Coupler Conversion
If Kadee won’t make them, then do it yourself!
By: Keith Stratton

 This installment is the fifth in a series of ‘How To’ articles dealing with Kadee 830 or 930 straight shank couplers.  To find out why I decided to go with body mounted Kadee couplers in the first place you can read my first article, which appeared in Issue #130 (November – December 2012).
Do you remember the first time you saw a rotary dumper in action?  Whether it was in person or on YouTube I’ll bet you were absolutely amazed.  I felt like Will Smith in Independence Day when he first piloted the alien spacecraft and shouted, “I have got to get me one of these!”
This naturally got me thinking about the couplers themselves and wondering not only how they work, but also how a rotary coupler could be replicated in G scale.  I poked around some websites, hoping to see exactly what the prototypical rotary coupler looks like but was unsuccessful (a ten year old could probably find it in 5 minutes…) so I had to rely on my knack for figuring things out.
At first I was trying to determine how to rotate the complete draft gear box and then further work out how to mount it.  Given the amount of Kadee 830/930 installations I’ve done over the years I didn’t think this would be a successful approach.
Then, as I was sitting at my workbench studying the coupler inside the draft gear box it came to me – why not simply modify the coupler itself and leave the draft gear box alone!  This would solve the mounting issue and now I could concentrate on modifying the coupler.

Picture 1

Picture 2

Pictures 01 and 02 are taken of the very first coupler I modified, just before the HAGG meeting at Charlie Caggiano’s on June 9, 2013.  I was able to finish the conversion, mount the coupler and took the hopper to the meeting to show fellow members what it looked like.  It wasn’t until I returned home later in the day that I was able to test run it on my layout.  It worked great at the front of a long consist (25 cars or so) and had no problem pushing the consist in reverse.

Picture 3

Picture 4

 Otto ‘I need articles’ Halek didn’t take long to ask when I would have something prepared for the newsletter, so now you are reading the fruits of that request.  The tools needed are very basic for this conversion as shown in Picture 03.  What is needed is a flat screwdriver, an Atlas super saw or equivalent, a #43 and #51 drill (and pin vise depending on your drill press chuck), a 2-56 NC tap and tap holder, a 2-56 NC x ¾” long cap head screw (I have a bin full of the ones Kadee used to supply with their 830 and 930 couplers), a draft gear box and two couplers (you will need two couplers in order to make one rotary version).  Not shown are a ruler, scribe, vice and miniature drill press.
So, let’s get down to the task at hand!  Basically, we are going to cut the coupler shank in half, but at different places on each coupler, hence the need for two.  In Picture 04 you can see where I have marked in red where the coupler is to be cut in half.  This cut needs to be just beyond the draft gear box end when the coupler is fully retracted into the draft gear box.  The coupler end that is cut off can be discarded, as the shank will be too short on this end.

Picture 5

Picture 6

 Now for the other coupler:  We need sufficient shank length to drill and tap a hole into it.  You will see in Picture #05 where I have marked in yellow the line where the cut will be made.  In this example I have left ¼” of the shank on the coupler end, but in future installs I might reduce this to 3/16”.  I have yet to do pull tests to the point of failure to see what this setup will take (my next fun project) but so far they seem to be fairly robust.  This is important to me as I like to pull long consists so the couplers need to be able to ‘pull their weight’.
In Picture #06 you can see what I’m up to.  The cut off pieces are at the top and bottom of the picture; whereas, the two pieces in the middle are the ones that will comprise the rotary coupler.  I have placed the 2-56 screw on the draft box mounting end of the coupler so you can see how it will work.  In Picture #07 I have marked the center of the end of the shank prior to drilling.  Use an awl or scribe to make a center ‘pop’ for the drill.  It is very important that this hole is drilled exactly in the center of the shank end.  Place this end in a drill press vice and drill a clearance hole with a #43 drill through the entire length of the shank, as shown in Picture #08.  Install the screw into the hole from the inside of the mounting loop at the end of the shank, so that the threaded end protrudes as in Picture #09.

Picture 7

Picture 8

Picture 9

Picture 10

 Now we will need to mark and drill the shank of the coupler half.  To do this we will drill a pilot hole for the tap with a #51 drill, and then tap the hole with a 2-56 NC tap, as shown in Picture #10.  Next, screw the two halves together as shown in Picture 11.  You might need to shorten the screw slightly if it bottoms out before the two shanks come together, but only cut off as much as is needed as we need as much thread engaged as possible.  Screw the two halves together so that the shank faces are just shy of touching.
Picture #12 shows the modified coupler mounted in the running position in the draft gear case, and you will notice the mating area of the two shank halves is just beyond the end of the draft gear box.  Pictures #13, 14 and 15 show the coupler rotated through 180 degrees; however, the coupler can freely rotate through 360 degrees.

Picture 11

Picture 12

Picture 13

Picture 14

I have shown pictures of both couplers that I have converted as of this writing in Picture #16.  The hopper car on the left was my first conversion and the coupler protrudes out a bit farther than I like.  The hopper car on the left is my second conversion and the coupler is about 1/16” shorter on the shank and looks much more prototypical.

Picture 15

Picture 16