Re: [SergentEng] Re: New HO narrow coupler box now available

Dale Buxton

People, people, people,

I am struggling to figure out why it is so paramount to have a special self-centering coupler box for the Sergent RNB87K Sharon coupler. Am I missing something here?

As already discussed, the preferred method of coupling Sergent and prototype couplers is to open both opposing cars coupler knuckles and bringing the couplers together. This method gives the couplers their maximum gathering range for a mate-up.

Virtually all of the HOn3 plastic, rolling equipment, kits and RTR on the market today have a clone of the Kadee 714 coupler box molded into the body of the cars. This coupler box can be QUITE EASILY modified to accept the Sergent RNB87K with a centering spring as per the Smoky Mountain design. Just a few bits of plastic are needed to keep the spring in place.

This modification is far easier and less catastrophic than removing the entire 714 clone coupler box from the car and then installing a new one!

One other point that needs to be mentioned here: The Accumate Coupler box was completely unacceptable for use on HOn3 equipment. Period! The boxes width was so wide the HOn3 wheel sets inner wheel rims, riding under the box would hang up on the sides of the box on any track radius under 22 inches. I know this because I tested this extensively!

The bottom of a Kadee 714 coupler box is just a tiny bit wider then the Sergent RNB87K's pivot area of the draft gear shank. Plus, this part of the coupler box has the pivot pin molded on it. Coupler box/truck pivot problem with Sergent couplers solved.

You can also avoid the whole coupler box dilemma altogether in one of two ways. The pivot opening on the RNB86K coupler is roughly 3/32's in diameter. So, you can clip the Kadee 714 pivot pin with some of the boxes floor off of the Kadee coupler box and use this to mount the coupler with a screw. Or, you can make your own pivot pin with a short length of 3/32 brass tube and washer with a screw through them to affix the coupler to the car.

Either way, these options are far easier than hacking the molded coupler boxes off of the car and replacing them with a new one.

On scratch built HOn3 cars, If you widen the inner width of the draft gear area, the Sergent RNB87K's can be mounted between the center sills with one of the above two methods. Again, you could make up a centering spring arrangement here as per the Smoky Mountain design if you so desire.

Dale Buxton 

On Saturday, January 13, 2018, 2:40:19 PM MST, Mike Conder vulturenest1@... [SergentEng] wrote:


I totally agree, need a similar product for the Sharons.  The new pocket is great for the larger couplers, just need one for us narrow gaugers and ToC modelers.

Mike Conder

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