NOTE: Page is presented partially complete to permit use of finished data and methods. Updates will follow as car classes are developed. There should be enough projected work to keep anyone interested quite busy.
The predominant freight car practices throughout this era seemed to evolve during the latter 1890's, concurrent with the development of all steel cars. They were solidified with the 1910 Safety Standards.
Knuckle couplers and striker plate castings, mounted on end sills, are the norm. The striker serves as a stop for the raised horn, on the rear of coupler head castings, to limit the common 3" travel during pushing. Strikers are usually less than 4 1/2" and some are recessed into end sills. Earlier knuckles had an 8 3/8" pulling face to horn (PF-H) dimension, which gives an 11 3/8" pulling face to striker distance (PF-ST). No present operating coupler in HO or smaller can meet this requirement. Around 1910 the standard Pf-H became 12" with a PF-ST 15" or ST-ST of 30". Again no full size, operating coupler in HO meets the requirement exactly. Only Accumate Proto Pro can fit with only minimal alterations to cast on draft draft gear
TACKLING THE PROBLEMS
To determine correct spacing, some research through prototype data will be required. Most car diagrams were designed to provide car inspectors with needed data, including inside length, length over strikers and coupled length. Not usually included is the length over corners or even corner posts. Erection drawings may or may not include this datum, but it can be calculated easily.
Floor height may require adjustment before determining pad requirements. MEASURING ROLLING STOCK HEIGHTS can be tricky, but some aids are easily made.
Note: Since it is assumed that knuckle couplers will be used, pulling length will referred to as length over pulling faces (LPF). For all cases, a reference point (REF) must be established as the optimum for judging spacing. This may be the end sill or end corner dependent on type of car or height.
The important reference to mounting center distance (REF-MC) is found by subtracting the prototype pulling face to reference (PF-REF) from PF-MC (model coupler):
REF-MC = PF-MC - PF-REF
Since the Accumate Proto Pro is the best fitting full size coupler, it will be used as an example. The reference to mounting center (REF-MC), where the screw hole will be located, must be determined. If the striking plate will be used as reference (REF), its position should be verified and modified, if necessary.
From MEASURING COUPLERS, the Accumate Proto PF-MC = .350:
REF-MC = .350" - PF-REF (prototype)
Since most 20th century freight cars use an ST-ST = 30", for a PF-ES = 15" or .172". Thus for striker reference:
REF-MC = .350 - .172 = .178".
Normally the provided box can be inserted into most cast-on boxes by simply removing the center post. If the box is too long, it may be trimmed as per instructions. Having a mounting height of 27/64", in most cases the center height will be close to correct; but shimming or milling may be required.
Since the box front edge is the lip to MC of .152" + lip to front edge of .016" = .168". This will recess the edge .010" or .871" behind the cast-on edge. To slide box back the required amount, the lip must be removed and possibly the box may require shortening.
The horn top is slightly above the box top and in the full swing positions, the horn to edge clearance is about .006". The cast-on box or striker edge must be beveled slightly to clear safely.
Placing the box edge flush with the cast-on striker edge would yield a spacing of about 16.74", which might be acceptable , except to the purist. In many older wood and metal kits (Varney, Athearn, Ulrich), mounting will require major surgery.
FLAT CARS
Regardless of type, these cars are almost always judged at floor level. Prototype spacing is set, at the strikers, where striker to striker (ST-ST) is 30" or pulling face to striker distance (PF-ST) is 15", with very few exceptions. On models the distance should be judged at the more obvious, endsill corners. Striking plates generally extended 4 1/2" from the endsills. This places the pulling face to endsill distance (PF-ES) at 19 1/2".
Only the Accumate Proto will fit without butchering the striker plates. See ATEARN 50' FLAT CAR EVALUATION
A late vintage cushioned car, the PRR F-48, had an ST-ST of 32" or PF-ST of 16", while the ST-ES was 24". This yields a PF-ES = 40 " or ES-ES separation = 80".
In some long load cases, several cars are coupled together with pivoting supports on end cars and may be treated as a set. Correct spacing, between cars, greatly enhances appearance. Since uncoupling would be rare, scale dummy couplers, with very little slack, could be used.
TANK CARS
Since development of these cars originated from vats and tanks mounted on flat cars, the same basic philosophy seems to have been applied to most earlier cars below nominal 12 k gallons. Often the same frame was used for different capacities with only a tank diameter or length change. One GATX 8 K gallon car had a striker to tank head distance of 22 1/4", with no PF-ST data. ST-ST seems to vary from 28 3/8" to 30 1/2" for PF-ST variations of 14 3/16 to 15 1/4". Again horns must be recessed, if strikers are used for reference.
On many cars, the underframe consisted of just a centersill with body bolsters over the trucks. Braces extended laterally to support running boards. A pair at the ends could cause problems in modifying draft gear boxes, since they are often attached to them by a structural member running beneath the box. In some cases they may require trimming and re-attaching later for support.
Similar to the MDC "oldtime" tank, a UTLX 6K gallon car had a length over tank ends (LOT) = 26', length over strikers (LOS) = 27' 2" and LPF = 28' 11 3/4". The 8 3/8" PF-H couplers were used with a 2 1/2" clearance.
The striker to tank end would be (LOS - LOT) / 2 = 7"
ST-ST = LPF - LOS = 21 3/4 and PF-ST = 10 7/8" = .125"
This would necessitate recessing the horn 2 1/8" = .024" with Accumate Proto or 1 5/8" = .019 with the Kadee 711, requiring surgery. Additionally the 711 would require milling for pad height. This car might fit better with the 19th century group.
Another 10 k gallon using a Bettendorf frame with braced wooden tank end blocks had an LOS = 38' 4" and LOT = 34' 8" for a striker to tank end = 22"
A later 38 k tank had an ST to tank head distance of 13 1/2" and PF-ST of 18 1/4" for an ST-ST of 36 1/2". It would appear that the length over strikers, of 77' 2", required a greater ST-ST. The Intermountain might also be acceptable.
From data found, it seems that no standards were established for these dimensions, possibly since most cars are privately owned or leased.
GONDOLE
Most older gons had varying length, extended end sills which place end corners 10 or more inches from strikers. The most obvious point for separation judgement is at the endsills. ST-ES varied as do most models, some excessively. It may be necessary to modify striker castings to achieve a believable appearance.
The PRR G-25 (USRA) had an ST-ST =30" or PF-ST of 15" and 4 1/2" strikers for PF-ES = 19 1/2" or 39" ES-ES. The ES-EC = 6" for an ST-EC = 25 1/2" or EC-EC of 51".
With the included, Bachmann EZ couplers, the Walthers model has a pulling face to endsill reference = .307" = 26.74" for 53.48" spacing or 9.6" too wide. The pulling face to end corners = .388" = 33.8" for a toy-like separation of 67.6" or 16.6 too wide. The striker to end sill reference is .042" = 3.659". If the endsill is used for reference, the space remaining for the knuckle would be .1816" = 15.819". It is apparent that only Accumate Proto will fit. See WALTHERS USRA GONDOLA EVALUATION
Since many later gons had higher walls and shorter sills, they can be handled much the same as other high side cars, where the end corner to end corner distance (EC-EC) is usually the most obvious judging point. It may be necessary to modify castings to achieve a believable appearance.
With fixed end types, the EC-EC is usually easier to determine. There are some cases where B (brake) end sills extend farther than A end, requiring separate derivation for each.
Drop end versions present problems in determining length over corner structures. In some cases, they are flush with end sill or extend slightly beyond. Determining inside length, doors are usually recessed, exposing part of end sill. Striking plates usually project past corners.
Once again unwarranted work and compromises are forced upon the caring modeller.
HOPPERS
Due to wide variation, hoppers present diversified challenges. Some have wide end sills , while others have almost none. Still others have wide separations between end plates and corner posts. Since no coupler has the correct 12" PF-H dimension, decisions must be made in determining the points for distance reference that effect their appearance the most. Often it is difficult to derive the length over end corners (LEC). In older open box types, the angle corner posts were outside, but some had sheets on the outside. Since end plates were commonly 3/16", the corner would be equal to the inside length (IL) + 3/8" with external sheets.
Since corner angles commonly had 3/8" webs, on outside braced corners, length over end corners (LEC) would be IL + 3/8" + 3/4" or IL + 1 1/8". Bulb angles and wall thicknesses on models are usually over scale, so their IL should not be used as reference.
On a PRR H-31, subtracting LEC from length over striker (LOS) yields 13 7/8" for ST-EC = 6 15/16", very close to the common 7". The ST-ST is 30". The EC-EC = 43 7/8", very close to that of house cars. Tolerances could be the same 44" to 45".
Older cars might vary, like the PRR GLa with a EC-EC = 50 7/8" separation, or PF-EC of 25 7/16". Endsills extend 10 7/16" or 10.4375" beyond the end corner posts, but the end member appears to be a channel with the striking plate casting recessed flush with edge. This leaves the usual PF-ST of 15" and ST-ST of 30".
Measuring on track with Kadee short couplers installed, Bowser's GLa yielded approximately: EC-EC = 58" and ST-ST = 38" It is evident that short couplers can not meet the tolerances, without relocating stud and recessing horn. This would create a very unsightly appearance and require a butcher job.
Endsills extend .118" = 10.28" for about 5/32" less than the prototype. Subtracting this from the PF-EC of 25.4375 gives an available PF-ST of 15.158" = .174 hin and 30.315" ST-ST, if the corner posts are used as the reference. Subtracting the minimum horn to plate clearance of about 2.25" leaves a usable PF-H of 12.90". From coupler measurements, it seems that only Accumate Proto, with shortened box, can be mounted without excessive recessing of horn inside the cast-on box, behind the striking plate edge, to provide clearance. The front edges of the box will require relief to clear horn throughout swing, . If you plan to run a long string of these cars, this is a lot of uncalled for work.
In many cases, the striking plate castings are mounted on the end sill face, which adds about 1 1/2" to 2 1/4" to the extension. There are also some cases where B end sills extend farther than A end, requiring separate derivation for each.
Some covered hoppers can be treated the same as open types, but there are many types with over 3' between the end plates and corner posts. Too often drawings reveal no clue to the actual distance. Probably the best solution is to use PROPORTIONAL DIVIDERS. or establishing the ratio between a finely divided scale and the drawing, and measuring distance.
Another method uses a fine, flexible, metric scale to establish a ratio. Using a known dimensioned length, converted to decimal inches or feet, divide the measured length in millimeters into it for a stored ratio. Multiply any measurements taken in millimeters by the ratio.
Since it is the most critical for sake of appearance, the problem is: How to determine the distance from the end corner to the pulling face (PF-EC) on the cars in question.
On most steel cars, the sheathing plates are outside the corner posts, so the corner is measured from the end sheets which are used as spacing and mounting center reference (REF). For single sheathed cars with outside corner posts, these will be used. Most drawings state inside length (IL), but not length over end corners (LEC), which must be found by deriving end wall thickness. This is usually the sum of liner, angle web and end sheet thicknesses.
The PRR XL, with knuckle couplers, had 36' IL, LPF of 40' 11" and length over strikers (LST) of 38' 6".
ST-ST = LPF - LST = 29" and PF-ST = 14 1/2"".
Sheathing was 7/8" and corner post was 5" for a double sheathed, thickness of 6 3/4" .
Adding two thicknesses at 13 1/2" to IL gives 37' 1 1/2 length over corners (LEC). Subtracting this from LES gives 16 1/2" or end sill was 8 1/4".
EC-EC = LPF - LEC = 45 1/2"
A 40' 0 3/4 IL car, with knuckle couplers, had an LPF of 44' 2 3/4" and LES of 41' 11 1/4".
Subtracting IL from LPF = 50"
Subtracting LES from LPF = 27 1/2" for PF-ES of 13 3/4""
A typical 50' 6" inside length box car (IL) = 50' 8 1/4" over the end sheets (LEC), 51' 10 1/8" over strikers (LOS) and 54' 4 1/8" coupled, pulling face to pulling face, length (CL).
Here LEC is given and
Wall thickness = (LEC - IL) / 2 = 6 15/16"
The difference between CL and LEC is the end sheet to end sheet (EC-EC) distance for two coupled cars.
EC-EC = IL - LEC = 3' 7 7/8" or 43 7/8" = .504" HO inches (hin).
Unless you have calibrated eyeballs, 44" is close enough, so PF-EC is half this for 22". or .252 hin.
Striker to end sheet (ST-EC) is
ST-EC = (LOS - EC-EC) / 2 = 7".
The striker to striker distance (ST-ST) and pulling face to striker distance (PF-ST) are:
ST-ST = CL - LOS = 30" for PF-ST = ST-ST / 2 = 15".
Subtracting the pulling face to horn distance (PF-H) of 12" leaves 3" horn to striker clearance. The 30" striker to striker distance (ST-ST) is consistent with others and should be used with flat, tank and other low side cars with extended end sills, where distances are judged at floor level. Until someone offers a coupler head with a PF-H of 12", undesirable compromises are necessary, where possible.
Since the Athearn 40' box car is probably the most common car in HO and it yields about 45" EC-EC with Kadee 5's, this might be used as a maximum tolerance. Plus it would avoid a lot of work. The minimum might be set at about 44" since closer distances may interfere with operation and be more noticeable. Mixtures of cars would fall between the extremes. For prototype coupling see: ATEARN 40' HOUSE CAR EVALUATION
The Athearn 40' house car boxes have about .045 height, requiring no shim with most couplers. However very often the weight sheet is slightly curved, enough to bend the floor and underframe causing coupler box tilt. Eyeballing along one edge, the sheet can be straightened with finger pressure.
Another very common group of cars, the Athearn standard 50' box cars and reefers, measure at about 56" EC-EC. Resembling cushioned cars, the draft gear housing extends to place pulling faces 6" too far from the end sheets. Several optional remedies are available. As shown in ATEARN 50' HOUSE CAR EVALUATION choice will depend on tools and ability.
A fairly common practice , on older coupler boxes with square posts, was to remove the post. A Kadee 5 box lid was trimmed to fit, slid in and screwed in place. In this case and many others, the box rear must be milled back to allow room. The front edge must be cut back to clear horn. Since the box center mounting hole is .090" and the nominal OD of #2 screws is about .083", the .007" clearance will permit about .61 hin adjustment. Using a #1 screw with .070" OD gives .020 clearance for 1.74 hin. A washer may be added under smaller heads for more security.
Locating the mounting hole requires a little thought and observation. If the pulling face to mounting center (PF-MC), for the chosen coupler, has been found, and the prototype pulling face to reference point, end corner, (PF-REF) is known; the reference to mounting center (REF-MC) is
REF-MC = PF-MC - PF-REF. Locating REF position at the car centerline requires judgement and sharp vision in most cases. While the end sheet's bottom edge may be visible along portions, it is not usually available near the centerline. A narrow straight edge may be used to mark a reference point at the line for measuring. Similar methods may be used in other cases . Unfortunately in some cases, previous mounting screw holes interfere with new desired locations, requiring a different shank length or plugging hole.
In some cases, short shanks may reduce EC-EC, about 5.5", to acceptable values, without relocating mounting center. To use these in cast-on boxes, the upper edge of box may be beveled with a file to clear knuckle horn. The amount is usually in the order of .030" and does not detract from appearance, if done carefully. In most cases the cover plate must be trimmed to clear.
In some other cases, the best solution might be to use Accumate Proto as described above .
This represents a cumbersome amount of unnecessary work, due to lack of compatibility standards in both coupler and draft gear design.
PASSENGER CARS
About 1890 open platforms started to disappear , being replaced by fully enclosed cars. Vestibules and diaphragms filled gaps between them to protect passengers from exposure. Many open platform cars were converted to include these features. As a holdover from open platform cars, usually heavy weight cars were measured and classified by the length between the body corner posts. Vestibules were considered extensions. Other terminology was also carried over. Thus the corner posts are at the inside edge of vestibule doors. A PRR P-70 coach is 70' 5 3/4" over corner posts and 80' 3 3/4" over strikers, buffers or diaphragms. These terms seem to be used interchangeably .
The most obvious separation points are the corner ends or platform corner posts, which may be difficult to dimension. End configurations varied, dependent on car type and era, adding to the difficulties.
HEAVY WEIGHT
Vestibule ends often differed greatly from those without them, even on the same car. "Platform" end sills usually angled outward from corner to extended door jambs. On vestibuled cars, end sheets usually paralleled them, while on those without, they were often perpendicular to sides. As anti-telescoping devices, a pair of I beams usually flanked the door area. Some "strikers" were actually sprung buffers flush with diaphragm plates. Other drawings show both strikers and horns on draw bars, inside draft gear, usually with pivoting heads. Length over buffers is sometimes noted as uncoupled, but more often omitted. It would appear the pulling face is at least 1 1/2" behind the buffer. All this adds to the difficulty in determining dimensions.
Since the corner posts are at the corner ends, head or blunt end cars are probably the best place to start and gain a feel for the more difficult vestibuled cars.
A fairly common PRR B-60 baggage car had a 60' 3" IL and was 60' 9 3/4" over the end posts. The length over buffers was 64' 3 3/4". This indicates an EC-EC of 42" or BU-EC of 21".
While a later PRR B-60B had a 60' 3" IL and was 60' 1 7/8" over the end posts. The length over buffers was 63' 7 1/4". This indicates an EC-EC of 41 38" or BU-EC of 20 11/16". See BETHLEHEM CAR WORKS PRR B-60B for an evaluation of model couplers and diaphragms.
An M-70a RPO had a length over buffers of 74' 9 3/4" and 71' 4 3/8" over end posts for EC=EC of 41 3/8" and BU-EC of 20 11/16".
These appear to be uncoupled with buffers and diaphragms extended.
Most vestibuled car plans present only buffer to door edge distances. Pullman listed outside corner to door edge as 4" and a buffer to end post (BU-EC) of 21". The PRR P-70 lists "striker" to door edge as 23 1/4" for a computed 19 3/4" BU-EC. These are probably uncoupled lengths.
A C & O car shows a 79' 4 1/4" length over buffers coupled and a buffer to door edge of 18 7/8" for BU-EC 14 7/8", assuming a 4" corner to door edge. This would indicate that PF-EC was also 14 7/8" and EC_EC was a very close 29 3/4".
Determining the gap left for diaphragms between car body ends at door jamb is also difficult. With no allusion to coupling condition, Only one reference was found in The Car Builders Dictionary (1906) as 8 3/4" or .100" in HO. The C & O floor plan verifies this closely. This value would represent a compressed or coupled distance.
LIGHT WEIGHT
In the 1930's streamlined lightweight equipment was introduced on premium trains with changes in construction, classification and measurement philosophies. Classes were based on nominal length over buffers. Most vestibuled cars had them at one end only At the blind end, BU-EC was reported as 15" for an EC-EC of 30", with no reference to coupling conditions. End sheets were flat and apparently diaphragms extended the full 15". Square corners simplify measurements.
From the above data, it might be concluded that the general practice for coupled heavy weights was a BU-EC of about 15". Thus
both types may be treated essentially the same. The prototype often mixed them, including coaches and especially head end cars and diners.
It appears that this spacing might not be achievable with longer cars except on very large radii, therefore compromises would be indicated. Even nominal overall length, 70' cars like Athearn, Roundhouse Harrimans and Bethlehem Car Works Reading/CNJ coaches might present difficulties. Pushing could create major problems, resulting from tight clearances and excessive slack in all present couplers. More research is needed and will be done when time permits. However for better appearance, consistency would be required at any practical spacing established.
TENTATIVE SOLUTIONS
A recent article suggests using an L jig placed over car end, to locate the mounting center. A cursory check revealed greatly varying distances from end sill to the corners (ES-EC. An ECW heavy weight PRR P-70 coach gave .050" = 4.36", while a Rivarossi LW with cast-on diaphragms gave .132" = 11.5". Using the ends as reference produces a difference of 7.14" at the corners or 14.28 times the tolerance of .5" discussed under freight cars.
The suggested Kadee #5 coupler and box has a pulling face to mounting center of .4775". Setting the P-70 at the recommended HW = 3/8" distance yields a pulling face to end corner reference of .152" = 13.24" or 26.48" spacing., which is 3.52" closer than the prototype. The Rivarossi LW gives .238" = 20.73" or 5.73 wider. Setting the Rivarossi LW to the recommended 5/16" yields .3005 = 26.2 for 52.4 spacing or 32.4" wider. The difference in spacing between pairs of each type would be a ridiculous value of about 25.92". Worse yet, these cars were frequently run in blocks in the same train. Here the wrong reference was used and again, one size does not fit all.
Due to the proximity of corners, the spacing may be more noticeable and the tolerance might even be reduced to improve appearance. Each make and model car must be considered separately.
If, more correctly, the corners (EC) were used as reference, all passenger cars, using the same coupler and box, would use the same EC-MC. On curves, the only different problems, that might occur near corners, could be caused by projections extending past corners, such as end sills. At the door jambs cast-on diaphragms or buffers might interfere.
Note: Adjust brightness and contrast for optimum viewing.
RIVAROSSI LIGHTWEIGHT ON 36" RADIUS, PULLING.
Prototype separation .
In pulling position, the clearance for EC-EC = .1722 = 15". But note: The cast-on buffer extends .136" = 11.8" and yields a -.016" for endsill overlap. The narrower cast-on diaphragms would clear by .002". In the pushing position, things would be worse. The only way to add diaphragms would be to remove the cast-on ones back to the end sheets as shown in RIVAROSSI (AHM) LIGHTWEIGHT EVALUATION
Assuming the worst mechanical condition, where the optimum close coupling PF-EC can be attained, little head clearance problem should be encountered. From coupler head measurements, it is obvious that all present couplers will have part of the head under the end sill and all, but Accumate Proto, will extend past the corner post line. On almost all cars, heads were below buffers, floor plates and end sills. While on many models, extra clearance is provided for Talgo type coupler mounts. Any surgery required would be hidden by diaphragm extensions, in most cases. The major problems would be establishing EC-MC and padding coupler height.
NOTE: Floor height is too frequently incorrect and should be corrected beforehand. This is a standard, set to match elevated station platforms. Although roof heights are more noticeable, they did vary, particularly between heavy and lightweight equipment. Many models of the same car vary in floor to roof top distances, requiring a compromise. Bottom step heights are too frequently wrong. Some are well above Knee level.
Other than too sharp radii, the two major obstacles to achieving close coupling are establishing end post to mounting center and fitting diaphragms.
DIAPHRAGMS
As probably the greatest instigators of problems with passenger car, close coupling; diaphragms require special attention both in solid, cast-on or added flexible types. Solid types may be beveled back from center line to edges and still yield the filled-in appearance at a distance. But there will always be a varying clearance gap.
The best solution would be lightly sprung, flexible add-ons. Over the years, many attempts were made, but most fell by the wayside in a short time. Those that performed well were not very prototypical. Consistent with the wide coupled spacing of the day and with an excellent idea, back in the 50's, MHP offered neoprene bellows with metal end plates having tabs to preserve lateral alignment. Excessive spring required heavy weighting to avoid derailments. Coupling and uncoupling were often foiled by car movement. Removing folds helped , but did not eliminate problems.
The perennial Walthers paper version lasted through the years, in spite of its shortcomings, among which was durability in humid places. The compressed length is .060" and the end plate is .65" wide, which permits a fit in tight spacing. As provided, bellows spring can interfere with coupling and derail light cars. Some modelers reduce the force by pressing the bellows together on a hard surface. This may reduce the travel and produce visible gaps on the outside of sharper curves. A lively plastic rubber material would be better. Probably the largest drawback is the exorbitant price for two pieces of folded paper and vinyl stampings. Surely the design costs have been returned, a great many times over.
Lacking any semblance of bellows folds, American Limited Models offers the most ingenious design to date. Concealed plastic spring rods are cemented in place to provide very light pressure, which permits plate tilting in any direction. No provision for lateral alignment is made. The Heavyweight version yields .138" = 12" compressed and about .223 =19.5 free for .085 = 7.4 travel. Using the BCW B-60 above with its 9 1/2" end to corner post distance and a PF-EC of 15", the space left for a diaphragm would be 5 1/2". It is obvious, the compressed Heavyweight diaphragm value of 12" would not fit. By recessing to end plate, an additional .091" = 7.93" could be gained for a total of 13,43". This version would fit at the expense of losing the two end beams.
Unfortunately offered versions are designed for application to specific groups of cars with bad, wide spacing and end detail measurements. Limited tests revealed no problems, when mounted on recommended cars with as delivered spacing. Listing the dimensions would help in selection.
Full width diaphragms, with various foam type fills, have been offered; but none was successful.
In conclusion, it might not be possible to attain the 15" PF-EC or 30" EC-EC with radii used. In most cases coupler mounting should present little problem. Adding good working diaphragms will probably require end detail modifications. As a compromise, a more practical minimal separation value might be suggested. However for optimum appearance and operation, end corners should be used as reference and all cars should have consistent spacing.
ACHIEVING OPTIMUM CLOSE COUPLING WITH DIAPHRAGMS
Probably the best way to determine the closest coupling attainable is to thoroughly examine a car with a difficult mounting problem. Others can then be handled with relative ease. Since Bachmann's Spectrum cars have draftgear boxes linked to trucks internally, they can not be relocated. BACHMANN PASSENGER CARS EVALUATION contains a very thorough discussion of potential couplers, diaphragms mounting and optimum spacing compromise, with drawings.
Once a usable standard is set, other cars can be handled with it to maintain constant separation.
More specific examples will be presented in EXAMPLES, when developed.
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