Coupler height

[ConducTTor]

Don't know if it matters but when I designed the 4 cars and U Boat, I used GC's coupler height as reference.

[CSD]

^^^ That's what we're doing for the SW too.

[Rob M]

Excellent idea! This is a bottom from a GC "Fowler outside braced wood boxcar kit". Lines up perfect with the GC trucks.



And, measuring the height gauge shows it is correct. Not sure where my math went wrong in the first post. So, never mind

[Richard-B]

I'm a little confused about proper coupler height and how much tolerance is acceptable. (snip) The NMRA standards say it should be .281” to the center of the knuckle. Elmer’s coupler height gauge puts it at .2685”

Here is a dimension page I made-up for the MT couplers... from the artwork on the Micro-Trains site.

IMHO 0.281 is the key number.

MT dimensions for TT

[Rob M]

[quote="Richard-B]
IMHO 0.281 is the key number.
[/quote]

Yep, that seems to be the way to go.

Now the question is, with which trucks? Or, what should the offset be from the bolster height to the coupler pad height? Looks like the Gold Coast box car has about .01"

[railtwister]

I believe in the other scales at least, the NMRA lists the bolster height dimension for truck (probably referencing the bolster height off of the rail-head. If NMRA lists a similar number for TT scale, it would be interesting to see which trucks (if any) match up, HP, Kemtron, GC, Tillig, etc.

Bill in FL

[railtwister]

Okay, I found it at NMRA.org. The page showing RP's for trucks is:<http://nmra.org/standards/sandrp/rp-23.html> .
The NMRA lists truck bolster height as an RP (Recommended Practice), rather than a Standard, and the dimension they show for TT scale, either freight or passenger equipment is 15/64" (or .234375" by my calculation). To my mind, this is an important dimension that should be maintained if at all possible in order to allow use of any trucks under any given car. It also is dependent on wheel diameter, and will have a critical effect on coupler height, so that needs to be considered as well.

Bill in FL

[Rob M]

Checked and they show it as 15/64" (.234) Below is what I measured.

Gold Coast, .224 (-.010)
HP, .310 (+.076)
Shapeways, .242 (+.008)

[ConducTTor]

I was the closest? Cool! I'll have to shave those 2mm off and be spot on.

As for wheel diameter dependence, that's tricky. Well, not tricky but there will have to be multiple sets of each truck depending on the various diameter wheels that can be used with it.

So speaking of diameter - Rob, what diameter wheels did you use for your measurements?

[Rob M]

The HP had regular HP wheels, the other two were measured with GC 33" wheels.

The HP's need 2mm take off. Yours only needs about 1/10 of a mm taken off.