Coupler heights

[6axlepwr]

I have been working on some things here and have noticed something that never really came to mind before.

I do not  know the prototype height off the rail head that the centerline of the coupler is supposed to be at. So I was wondering, is N-Scale there or is it some arbitrary height that was picked at an early stage and that is where it is?

Reason I ask is because I am working on an Atlas C630 and comparing the pilot to a prototype photo, the coupler centerline is higher on the pilot plate than the prototype. The prototype has the centerline of the coupler well down below the top edge of the bottom bolt plate or foot board plate. I was trying to build a proper coupler pocket for the model, and then noticed where the couple rlift bar was and wher the top of the coupler pocket falls on the model. Unless I lower the coupler about 0.030" or so, there is no way to build a proper coupler pocket.

[6axlepwr]

OK, I found this information. I'll have to go check the MT gauge and see where it is.

"Problems in maintaining the required coupler heights have persisted over the years for the railroad industry for both new and existing railway cars. Measured from the top of the rail to the center of the face of the coupler knuckle, the AmericanAssociation of Railroads (AAR) requires a minimum of 321/2 inches and a maximum of 341/2 inches for empty cars and a minimum of 311/2 inches and a maximum of 331/2 inches for loaded cars. Various approaches have been taken in attempts to comply withthese standards, among these being the use of a shim secured over the coupler carrier wear plate. The coupler knuckle or face is therefore elevated a distance equal to approximately three times the thickness of the shim because of the length of thecoupler draft bar. However, these coupler carrier shims are required by the AAR to be of a minimum 1/4 inch thickness because of the wear to which they are subjected upon cross shifting movement of the coupler draft bar. A 3/4 inch vertically upwardadjustment is therefore the minimum made possible with the use of such shims."

So if te measurment falls within 0.203" to 0.216", then I figure it is good.

I measured my MY gauge. It is right at 0.225". The MT instructions state that the centerline should be 0.216" off the rail head. Which falls within prototype height. My gauge measures 0.225" off the rail head, but that could be due to teh casting as well. So it must be the Atlas pilot is just off a bit to not allow a scale coupler pocket to be fitted. HMMM, just an observation. Not complaining about anything.

[Sokramiketes]

Wait, you're saying that the MTL height gauge doesn't match their published dimensions?

[GaryHinshaw]

Yep. The published standard (in the MTL literature) is .216", and I measure something like .230" +/- .005" on my gauge.  I find the couplers on MT truck-mounts to be closer to .216" , so I've set aside a single MT truck to use as my standard height gauge.

[bbussey]

I don't use the gauge.  I go by .216" + ½ thickness of the coupler box to get where it should be mounted underneath the floor.  For offset couplers, I would subtract .038".

Actually, I measure in millimeters because it is more precise, and I use the #1015 box as the housing.  Coupler head is 5.5mm over the rail top, and the top of the #1015 coupler box is 7mm for the standard shank and 5.6mm for the offset shank.

[bbussey]

... I measured my MY gauge. It is right at 0.225". The MT instructions state that the centerline should be 0.216" off the rail head. Which falls within prototype height. My gauge measures 0.225" off the rail head, but that could be due to teh casting as well. So it must be the Atlas pilot is just off a bit to not allow a scale coupler pocket to be fitted. HMMM, just an observation. Not complaining about anything.

There should be enough room in the Atlas pilot to slide in an MTL #1015 spacer, which should drop the coupler head down to .216".  The MTL spacers also will work with the Atlas #23015 coupler boxes if you're still using Accu-Mates.

[nkalanaga]

Trivia:  The 34.5 inch height is the average of 33 and 36 inches, which are (were?) the primary wheel sizes in North America.  The Colorado narrow gauge lines usually used 26 inch wheels, and their standard coupler centerline was 26 inches. 

Question:  Is there a reason for the coupler centerline being at the top of the wheel?

[robert3985]

Actually, I measure in millimeters because it is more precise, and I use the #1015 box as the housing.  Coupler head is 5.5mm over the rail top, and the top of the #1015 coupler box is 7mm for the standard shank and 5.6mm for the offset shank.

Just curious.  Why is measuring in millimeters more precise than measuring in mils?

[6axlepwr]

There should be enough room in the Atlas pilot to slide in an MTL #1015 spacer, which should drop the coupler head down to .216".  The MTL spacers also will work with the Atlas #23015 coupler boxes if you're still using Accu-Mates.

This is where I find the problem to be with Atlas. Coupler pockets. The Atlas coupler is an offset shank coupler. Not as offset as the Kato coupler, but offset. At least the one they use on the C628/630. When I put an MT 1015 box into the pilot, the coupler center line is 0.020" lower than where it should be. Putting a spacer in there will only lower it more. In order to get the MT coupler centered at the correct height is to have a 0.010" lid on it. Tried it and it does not work well, The lid has no support and collapses. I cannot get anything but an Atlas coupler in an Atlas box in there. I had the same issue wit the GP38. I put in a 1015 and the coupler is 0.020" lower than where is should be.

[bbussey]

Just curious.  Why is measuring in millimeters more precise than measuring in mils?

Because millimeters is a smaller unit of measure than inches, and metric is easier to work with than imperial. 

[bbussey]

This is where I find the problem to be with Atlas. Coupler pockets. The Atlas coupler is an offset shank coupler. Not as offset as the Kato coupler, but offset. At least the one they use on the C628/630. When I put an MT 1015 box into the pilot, the coupler center line is 0.020" lower than where it should be. Putting a spacer in there will only lower it more. In order to get the MT coupler centered at the correct height is to have a 0.010" lid on it. Tried it and it does not work well, The lid has no support and collapses. I cannot get anything but an Atlas coupler in an Atlas box in there. I had the same issue wit the GP38. I put in a 1015 and the coupler is 0.020" lower than where is should be.

Use the offset #2001/2004 coupler in the #1015 box.  Sounds as if that is the issue.

[6axlepwr]

Use the offset #2001/2004 coupler in the #1015 box.  Sounds as if that is the issue.

If it was only that easy. Wish I could explain more about it. Offsets will not work in my application.

Tonight my task is to make myself a new coupler height gauge. More like a go/nogo gauge. For now on I will work off a 0.216" off the rail height.

I do not use mm because I cannot visualize it. I have been working in inches for so long that I can visualize 0.001" and by looking at something, i can very closely estimate the measurement in inches. For instance with the coupler heights. When I lined the locomotive up with the gauge, I could easily tell off the top of my head it was off by 0.020". After measuring it, I was correct. I would be all bamboozled if I had to think in mm.

[bbussey]

I guess I'm confused then.  If you inserted #2004 couplers in a #1015 box and used the #1015 shim on the Alco, wouldn't that get the coupler centerline to where you want it?

I work smaller than those numbers and work digitally for the most part, and I deal with European and Asian contractors, so I prefer to work in mm.  As an example:  it's much easier to work with etched metal thicknesses as being .30, .20 and .05 mm instead of .012, .008 and .002 inches respectively, especially when dealing with the half-etches. 

Metric is so much easier than Imperial.  It boggles my mind as to why the United States will not convert.  Even the Brits have switched, and they invented Imperial.

[Sokramiketes]

I guess I'm confused then.  If you inserted #2004 couplers in a #1015 box and used the #1015 shim on the Alco, wouldn't that get the coupler centerline to where you want it?

A #2004 coupler is never the answer for a prototype modeler.  The head is even worse than a standard MTL coupler. 

[6axlepwr]

I guess I'm confused then.  If you inserted #2004 couplers in a #1015 box and used the #1015 shim on the Alco, wouldn't that get the coupler center line to where you want it?

I guess that is where I am going wrong. I do not have any #2004 couplers to work with. Only the #1015. Regardless though, that is not the real issue. The issue is with how the defacto standard is these ridiculous bulky coupler boxes on locomotives. Absolutely no need for them. Over the weekend I redesigned them and redesigned them to be manufacturable. I would be more than happy to show them how to do a pilot plate if they would ask. But I know that will never happen. Insert Fringe manufacturing  .

I work smaller than those numbers and work digitally for the most part, and I deal with European and Asian contractors, so I prefer to work in mm.  As an example:  it's much easier to work with etched metal thicknesses as being .30, .20 and .05 mm instead of .012, .008 and .002 inches respectively, especially when dealing with the half-etches. 

I am just to old to change at this right now. To much I would have to rethink. nuts and bolts are fine. Deal with that all the time now, but standard measuring. I just cannot wrap my brain around it and be productive.