Large Scale Central

Narrow draft gear box for tighter curves

Modeling Technical Modeling
#1

I have been putting Kadee 906 body-mount couplers on my rolling stock, and like how they work. The slack action is more realistic, and looks great. However, my basement layout required some curves that are a little tighter than I’d hoped.

The point of contact between the wheel flange and the gear box is the sleeve on the size that accommodates the mounting screw. Looking at the 906 (which is comprised of a 900 coupler in a 910 gear box), I realized that there is a lot of wasted space inside in that area.

The opening for the coupler is also much wider that needed, considering that the wheels will hit the gear box long before the coupler hits the side of the pocket. After some trial and error, I came up with the following design.

The lid (upper part when mounted) connects to the box with a screw through the center. This screw doesn’t need to continue into the deck of the car. In the rendering, 3 mm of shim is integrated to mount to Aristo rolling stock. The shim has holes in the normal positions, but the screw head is high enough that the wheel flange won’t contact it.

The pocket opening is 2 mm narrower than the 910 box, but the coupler still never reaches the side under normal circumstances.

Here is a comparison of the 910 and my gear box.

And the coupler installed.

And finally, on a box car. Again, that center screw is short, and doesn’t penetrate the car. The back screw goes through all of the pieces into the car.

#2

I like that. I bet it would work with Accucraft couplers too. I’d like to try a pair- are you going to put the file up on Shapeways or make them available direct from you?

#3

Here are the files. <- that’s a link!

#4

A very cool Idea! Well done!

#5

Do you have a pic of the wheels fully cocked against the draft box ?

#6

Here are a couple of shots showing the clearance. The first one is from directly over the relevant wheel, and you can see the overlap with the screw head.

#7

This is a very interesting design. I’ve always used the Kaydee draft gear with the lid on the bottom. It appears you have flipped that around incorporating the shim thickness and two of the mounting screws into the lid attaching that to the car as a mount then attaching the modified box underneath.

Thanks for the link.

#8

Jon: How do you use the lid on the bottom when the recess for the limiting tab on the coupler is on the box itself?

#9

Eric,

You have done an excellent job on the coupler box. It looks like the box lid also includes the amount needed to space the coupler at the correct height to the railhead, so that issue is taken care of, too, along with the use of Kadee trucks.

As to the standard Kadee box, notching and tapering its sides does help for wheel flange clearance for operation on tighter curves - example box below done when I chose to lower an Express box car during the process of mounting Kadee couplers.

Modified Kadee 906/830 Coupler Box

Eric, Thank you for sharing your excellent work.

Much appreciated,
-Ted

#10

Eric Reuter said:

Jon: How do you use the lid on the bottom when the recess for the limiting tab on the coupler is on the box itself?

Well, for one I confused the #830 type box you are working on with the smaller #831 type box. I actually use both together (and modified) to mount and Accucraft coupler to Bachmann Fn3 cars. My completed mod looks like this…

And when I go back an look, I do in fact mount the larger 830 with the lid up. The smaller 831 is used with the lid down (831 was installed incorrectly in the above photo). This is what they look like on a car…

#11

I take the coupler and spring out and make the cut-outs with a drum sander on a dremel. Been doing that since 1990.

clean up the burrs with a small file and reinsert the coupler and spring.

Takes 1 minute.

#12

Eric, thanks for posting the STL files!

#13

My pleasure. I modified them slightly to add a little clearance where are the parts overlap. I have not updated the Files yet, so you may want to wait before printing them.

#14

Files updated https://www.thingiverse.com/thing:2780691

Note that this includes an equivalent of 3 mm of shim, which is appropriate for Aristo box cars, etc. May need to extrude the bottom one way or the other for other rolling stock.