Kadee  #1 vs. G  Gauge couplers in Datum Precision Metal & 3-D Printed Plastic Coupler Boxes


Kadee #1 vs. G Gauge couplers in Datum Precision Metal & 3-D Printed Plastic Coupler Boxes

Ted Doskaris
January 12, 2013
Rev GE-A, Initial Release

October 29, 2016
Rev GE-A1, Fixed broken link

February 17, 2020
Rev GE-B, Added more info about Kadee #1 scale couplers; Added coupler fitment info in 3-D printed "CamPac" plastic boxes; Added Contents table; Fixed broken links


History & Applications
Kadees & Datum Precision Metal Coupler Box
Coupler Comparison Detail
Kadee 1907/907 Mounted on GP40
Couplers Mismatch
Kadees & 3-D Printed Plastic Coupler Box
Kadee Coupler Height Gauge vs. Prototype
Thoughts & Comments



The "#1 Scale" centerset coupler from the Kadee 1907 kit is evaluated for installation in both Datum Precision Metal Coupler Box and 3-D printed plastic "CamPac BoxTM". Various couplers are included in the illustrations that follow.

Though the coupler from the Kadee 1907 kit is the primary focus of this topic, consideration is, also, given to the Kadee 1917 kit's "#1 Scale" centerset coupler that has an extremely short shank.



History & Applications 

Custom coupler boxes (CNC machined from aluminum) were designed by me (Ted Doskaris) in concert with Datum Precision Company located in Grass Valley, CA. The boxes were initially made exclusively for me for my own use, but as the benefits of the boxes became known other folks sought to acquire them, too.  Limited quantities of these metal boxes are available, and they can be obtained by contacting Colin Camarillo via his website.

The boxes are meant to accept Kadee centerset "G" type couplers, plastic lids, and springs from Kadee kits such as the Kadee 789 and Kadee 907 "New Generation" assemblies, evolutionary differences of which are illustrated below.

The initial intended use was for the Aristo-Craft GP40 and SD45 diesel locos - but from the onset the boxes were, also, configured for potential applications on others.

Accordingly, applications have been expanded and include the following locos:

Aristo-Craft applications listed do NOT require cutting of the loco (except RS-3 notching pilot).

GP40, SD45, Dash-9, RS-3, E8 /E9, RDC

Articles / vignettes about the coupler boxes and their applications are available.

For Aristo applications, see article title below. (A very large file - may take notable time to load)

"Custom Made Coupler Boxes & Kadee Centerset Couplers for Selected Aristo-Craft Locos"

USA Trains applications do require cutting of the loco (notching pilot) and include:
GP38, SD40-2

For the USAT GP38 application, see article title below.

"USA Trains GP 38 - Kadee Centerset Coupler Install, Abandoning Traction Tires & Various Mod's"

The USA Trains GP38 and SD40-2 (along with other loco & car) coupler boxes are also available in 3-D printed plastic "CamPac BoxesTM ". These boxes are designed by me (Ted Doskaris) in concert with Colin Camarillo who has the 3-D printer and software expertise to implement them. In addition to the boxes, mounting pedestals and plugs to cover the large pilot openings typical of USA Trains locos are also included. An example GP38 is subsequently described in section, Kadees & 3-D Printed Plastic Coupler Box.

The 3-D printed boxes are obtainable by contacting Colin Camarillo via his website.


Kadees & Datum Precision Metal Coupler Box

I obtained a Kadee 1907 "#1" scale coupler assembly, compared it with the Kadee 907 "G" type, and installed it into a Datum Precision metal coupler box. I then mounted it on the Aristo-Craft GP40 (in place of the coupler from the Kadee 907). The Aristo-Craft GP40 with Datum Precision coupler box is used in examples described here for 1/29 scale environment.

The Kadee 1907 assembly has identical plastic box, lid and springs when compared to the Kadee 907, and the coupler itself fits and operates perfectly in the Datum Precision box; however, there is more to consider than just this!


Coupler Comparison Detail

Compared to the coupler from the 907, it can be seen, as shown below, that the coupler from the 1907 does not appear to be truly center set as it has a notable downward offset!

The Kadee description for the 907 & 1907 includes the statement ".... #1907 #1-Scale Centerset Couplers & #911 Gearboxes"

However, compare the Kadee 1907 with a Kadee 1917 - shown below.

Unlike the Kadee 1907, the Kadee 1917 (above) coupler appears to look like it is truly centerset! "#1917 #1-Scale Centerset Short Shank Couplers & Extra Short Gearboxes"

It's intended that the Datum Precision coupler box is to accept a Kadee centerset coupler (e.g. having no up or down offset - coupler from the Kadee 789 or 907 kits) for mounting on the Aristo-Craft GP40 and other applications.

The following pictures provide information for helping understand the significance with respect coupler height to rail head distance and the impact of coupler offset.
In this regard, drawings of a prototype loco and of the Kadee coupler height gauge are included:

These pictures and the ones to following show an Aristo GP40 with couplers from the Kadee 907s as well as the smaller 1907s for comparison sake.


Kadee 1907/907 Mounted on GP40

The picture below is an overall view of the UP GP40 having the #1 scale coupler from the Kadee 1907 in the Datum Precision box mounted on the front of the loco.

A close up of the pilot is shown below.

The picture below shows how the loco's installed #1 Scale coupler aligns with a Kadee 980 gauge having the noticeably larger "G" scale coupler type. (I did not obtain the "1929 Type E Coupler Height Gauge" meant to be used for the smaller 1/32 scale Kadee coupler.)


Couplers Mismatch

At first hand, one would expect when using the 1907 coupler on a 1/29 scale loco (or rolling stock) that the center line of this smaller #1 gauge coupler should still align with the center line of the larger 907 coupler of the Kadee 880 and 980 gauges. However, when the coupler from the1907 kit is mounted in the GP40, it is too low compared to the 907!

The loco (when it had the 907 mounted in the same location) and car both had been setup and verified for coupler alignment with the Kadee 980 gauge at the time couplers were installed. Shown below are pictures showing the loco with coupler from the 1907 and a tank car with the 907 coupler assembly. Thus, as expected, the horizontal centers of the couplers do not match just as they don't with the gauge.

Above is the loco equipped with the coupler from the 1907 kit coupled with 907 of tank car.

Below is the loco originally equipped with the coupler from the 907 coupled with the 907 of the same tank car.  The centers of these couplers line up.

With the loco equipped with the coupler from the 1907 having the mismatched centers, I found that they still function over the Kadee track magnet for uncoupling - though not always consistently.



Kadees & 3-D Printed Plastic Coupler Box

Couplers from the Kadee 907 and 1907 will be exemplified using a USA Trains GP38 equipped with the CamPac BoxTM.
When using the 1907, the shank hole needs to be enlarged to fit over the pivot post on the box.

Note: It's preferable the shank hole be enlarged closer to the higher 0.215 inch diameter.

Illustrated below is a side by side comparison of the GP38 fitted with couplers from Kadee kits 907 and 1907.

Note: Adapting the 1/29 scale loco to 1/32 scale rolling stock with the coupler from the 1907 kit is subsequently described in section,Thoughts & Comments.



Kadee Coupler Height Gauge vs. Prototype Railroad Coupler to Railhead Height

The Federal Railroad Administration (FRA), Department of transportation (DOT) is codified by the Code of the Federal Register, CFR 49. It includes section 232.2 having information about coupler height.

CFR 49 section 232.2, includes the following stated requirements (expressed in terms of a drawbar) for prototype 1/1 railroad freight car coupler heights, including standard-gauge railroads in the United States that "... shall be 34 1/2 inches, and the minimum height of drawbars for freight cars on such standard-gauge railroads ... shall be 31 1/2 inches".

The Kadee 880 coupler height gauge is the predecessor to the newer Kadee 980 gauge with the newer gauge having the "new generation coupler". The specifications for both gauges are intended to be the same. For more info on the gauge, see "Kadee 880 Coupler Height Gauge Measurements Vignette"

In that vignette an example Kadee 880 gauge coupler height measured 1.115 inches from the rail head surface (or 32.33 inches if scaled up to prototype 1/1) - thus, the Kadee gauge is within the prototype allowance with respect to CFR 49, section 232.2 - it being somewhat below the center of the CFR range of 33 inches.


Thoughts & Comments

Studying the pictures comparing the two coupler types, it appears the #1 gauge coupler from the 1907 kit is offset downward somewhere near a 1/16 inch (0.063 inch) with respect to the "G" coupler from the 907 kit. Thus, scaling up for 1/29, that would be (29 x 0.063) = 1.83 inch. Thus, with the Kadee gauge at a measured 32.3 inch less the downward offset of the # 1 coupler of 1.83 inch (32.3 - 1.83) = 30.5 inch (up from the rail head when scaled.) Therefore, it would appear to be out of spec. by 1 inch too low (31.5 inch minimum) as defined by CFR 49. It's reasonable to assume Kadee's initial intended application for the Kadee 1907 was predicated on 1/32 scale rolling stock, whereby, the coupler height to rail head distance would be smaller (lower to the rail head) compared to 1/29 scale rolling stock. In this regard, evidence is illustrated below that shows how the coupler form the Kadee 1907 kit will align with the Kadee #1 scale 1929 gauge.

Similarly, illustrated below is how the older design coupler form the Kadee 1835 kit will align with the Kadee #1 scale 829 gauge.

If using the Kadee #1 coupler from the 1907 kit on 1/29 scale products, it's prototypically logical to use a coupler height to rail head distance for 1/29 scale so that the horizontal centerline of the coupler aligns with the center line of coupler of the Kadee 980 / 880 gauge.

Therefore, if it is desired to use the #1 gauge coupler from the Kadee 1907 in the Datum Precision metal coupler box mounted on the GP40 (being 1/29 scale), one would have to correct for the mismatch. The same would be true for other 1/29 scale applications. Alternatively, the coupler from the Kadee 1917 kit that appears to be a true centerset coupler may possibly be used; however, this coupler has a very short shank with small hole.

That said, consideration must be given for the shorter shank of the #1 Gauge 1917 couplers with the expectation of limited operation for only the widest of curves when the loco is equipped with them being coupled to another loco or train (closer coupled proximity).

An overhead view of the nose of the loco (below) shows the projection of the coupler used from the 1907 kit.

As to mounting the #1 Gauge coupler from the 1907 kit on the GP40, it seems possible that some shortening of the loco's post and the pilot lip that protrudes could be trimmed off to obtain the proper coupler to rail head height. Since my original intent for designing the Datum Precision coupler box employing true Kadee centerset couplers was to avoid doing any cutting on the GP40, this would seem counterproductive.

Alternatively, I suppose a slice of about 1/16 inch off the upper portion of the shank of the #1 coupler from the 1907 kit could be done, then use a spacer washer on the Datum Precision box pivot so when the coupler is installed, it would raise it up, but this would notably weaken the coupler's shank and may introduce some vertical wobble.


- Ted

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