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Design of Tomix and Kato N-Gauge Sectional Track Systemsby R. D. Kerr |
Did you ever wonder why a model railway straight track piece is the length that it is, or why a curved track piece has the radius that is has? Or why some sectional track systems seem to have better layout design capabilities than others? This page presents the Tomix N-gauge Fine Track system in the context of basic sectional track system design considerations, with a direct comparison to N-gauge Kato Unitrack, which is actively exported and internationally better known. It will explain why the variously sized pieces are offered and how they are designed to meet particular needs. Tomix is the model railway product line of Tomy of Japan. Over the years, Tomix has produced a sectional N-gauge track system with brown roadbed, then with gray roadbed, and finally the improved "Fine Track" variety with gray roadbed and snap-together roadbed joiners. The tables below do not include "accessory" track pieces like power feeders, bridges, end bumpers, rerailers, pier sets and so on. They include just those track pieces that essentially determine the overall layout designs possible, and that determine the capabilities of the entire track system. Tomix actually produces two related and compatible track systems: its basic railway system and the more recently introduced Mini Rail system, which offers tight-radius curves and points/turnouts. Both will be presented here. I will use the metric system dimensions used by the designers themselves, since I find them the easiest to use. For those people used to the "English system" of measuring distance and who do not yet have a sense of metric size, remember that 280mm equals about 11 inches, 140mm is about 5.5 inches, and 37mm is about 1.5 inches. (Note that 1.5 inches is also the standard track spacing for N-Trak modules.) I also use the term N-gauge rather then N-scale, because while the gauge is always 9mm, the scale distance represented depends on whether one uses the 1:160 scale for "N" common in the U.S. and continental Europe, the 1:150 scale generally used for "N" in Japan, or the 1:148 version of "N" used in Great Britain. It's time to think globally! |
| Tomix Track Description Format (Kato is similar) |
| S = Straight, xxx = mm length, (part number, and quantity if not 1) |
| C = Curve, xxx = mm radius, (part number, and quantity if not 1) |
| X = Crossing, R or L = Right or Left crossing, xxx = mm length, -xx = degrees of crossing angle (part number) |
| P = Points (turnout), R L Y or C = Right or Left departure curve, Y-shaped, or Curve-on-Curve, xxx = mm radius, -xx = degrees of arc, (part number) |
| D = Double track; H = elevated viaduct track; SL = Slab track |
| Note: Tomix Fine Track numbers have the suffix (F). I have not included it in the lists below. |
| Basic Sectional Track System Parameters | |||
| The basic parameters of a sectional track system seem pretty obvious. They include the length of a standard straight track piece, the radius and arc of a standard curved track, and the standard spacing between parallel tracks. | |||
| Basic Track Parameter | Tomix Fine Track | Tomix Mini Rail | Kato Unitrack |
| Regular Track | |||
| Standard Straight | S280 (2 in 1022; 10 in 1092) | (uses S280) | S248 (4 in 20-000) |
| Standard Curve | C280-45 (2 in 1121) C280-15 (2 in 1124) | C140-60 C140-30 (2 of each in 1112) | R282-45 (4 in 20-110) R282-15 (4 in 20-111) |
| Standard Spacing | 37mm | 37mm | 33mm |
| Viaduct Track | |||
| Viaduct Standard Straight | HS280 (2 in 1072) | --- | S248V (2 in 20-400) |
| Viaduct Standard Curve | HC280-45 (2 in 1171) | --- | R282-45V (2 in 20-510) |
| Double Track Plate | |||
| Double Track Plate Straight | not made | --- | WS248 (2 in 20-001) |
| Double Track Plate Straight Incline | not made | --- | WS248 (2 in 20-003) |
| Double Track Concrete Tie | |||
| Double Trk. Concrete Tie Straight | not made | --- | WS248PC (2 in 20-004) |
| Double Track with Viaduct | |||
| Double Track Straight w/Viaduct | DS280 (2 in 1062) | --- | not made |
| Double Slab Track w/Viaduct | |||
| Double Slab Trk. Straight w/Via. | DS280-SL (2 in 1067) | --- | WS248V (2 in 20-401) |
| Fractional / Multiple Straight Track Sizes | ||
| These straight track sizes are basic fractions or multiples of the standard straight. (Other odd sizes are also produced and are discussed later.) | ||
| Fraction/Multiple of Standard | Tomix Fine Track | Kato Unitrack |
| Regular Track | ||
| 1/4-length | S70 (2 in 1024) | S62 (4 in 20-040) |
| 1/2-length | S140 (2 in 1021) | S124 (4 in 20-020) |
| 3/4-length | not made (use 1/4 + 1/2) | S186 (4 in 20-010) |
| Slab Track | ||
| 1/2-length Slab | S140-SL (2 in 1046) | not made |
| Viaduct Track | ||
| 1/4-length Viaduct | not made | S62V (2 in 20-440) |
| 1/2-length Viaduct | HS140 (2 in 1071) | S124V (2 in 20-420) |
| 3/4-length Viaduct | not made | S186V (2 in 20-410) |
| Double Track Plate | ||
| 1/2-length Double Track Plate | not made | WS124 (2 in 20-022) |
| 3/4-length Double Track Plate | not made | WS186 (2 in 20-011) |
| Double Track Concrete Tie | ||
| 1/4-length Double Trk Concrete Tie | not made | WS62PC (2 in 20-042) |
| 1/2-length Double Trk Concrete Tie | not made | WS124PC (2 in 20-023) |
| 3/4-length Double Trk Concrete Tie | not made | WS186PC (2 in 20-012) |
| Double Slab Track w/Viaduct | ||
| 1/2-length Double Slab Trk w/Viaduct | DS140-SL (2 in 1066) | WS124V (2 in 20-422) |
| 3/4-length Double Slab Trk w/Viaduct | not made | WS186V (2 in 20-411) |
| 4-length Double Slab Trk w/Viaduct | DS1120-SL (1070) | not made |
| Incremental Curved Track Sizes | |||
| These curved track sizes are greater or lesser radius than the standard curve by one or more increments of track spacing. (Other odd sizes are also produced and are discussed later.) | |||
| Multiples of Track Spacing | Tomix Fine Track | Tomix Mini Curved | Kato Unitrack |
| Regular Track | |||
| +3 | C391-45 (2 in 1128) C391-15 (2 in 1145) | not made | R381-30 (2 in 20-140) |
| +2 | C354-45 (2 in 1126) C354-15 (2 in 1144) | not made | R348-45 (2 in 20-132) R348-30 (2 in 20-130) |
| +1 | C317-45 (2 in 1122) C317-15 (2 in 1127) | C177-60 C177-30 (2 of each in 1113) | R315-45 (4 in 20-120) R315-15 (4 in 20-121) |
| -1 | C243-45 (2 in 1125) C243-15 (2 in 1143) | C103-60 C103-30 (2 of each in 1111) | R249-45 (4 in 20-100) R249-15 (4 in 20-101) |
| -2 | not made | not made | R216-45 (4 in 20-170) |
| Viaduct Track | |||
| +3 Viaduct | not made | not made | R381-30V (2 in 20-540) |
| +2 Viaduct | HC354-45 (2 in 1174) | not made | R348-45V (2 in 20-530) R348-30V (2 in 20-531) |
| +1 Viaduct | HC317-45 (2 in 1172) | not made | R315-45V (2 in 20-520) |
| -1 Viaduct | HC243-45 (2 in 1173) | not made | R249-45V (2 in 20-505) |
| Double Track Plate | |||
| +1/0 Double Track Plate | not made | not made | WR315/282-45 (2 in 20-112) |
| Double Track Concrete Tie | |||
| +4/+3 Double Track Concrete Tie Superelevated | not made | not made | WR414/381-45PC (2 in 20-181) |
| +4/+3 Double Track Concrete Tie Superelevated Easement | not made | not made | WR414/381-45PC AL-AR (1 each in 20-182) |
| Double Track with Viaduct | |||
| +5/+4 Double Track | DC465/428-45 (2 in 1163) | not made | not made |
| +3/+2 Double Track | DC391/354-45 (2 in 1162) | not made | not made |
| +1/0 Double Track | DC317/280-45 (2 in 1161) | not made | not made |
| Double Slab Track w/Viaduct | |||
| +7/+6 Double Slab Track | DC539/502-22.5-SL (2 in 1169) | not made | not made |
| +5/+4 Double Slab Track | DC465/428-45-SL (2 in 1168) | not made | not made |
| +4/+3 Double Slab Track | not made | not made | WR414/381-45V (2 in 20-541) |
| +4/+3 Double Slab Track Superelevated | not made | not made | WR414/381-45VS (2 in 20-544) |
| +4/+3 Double Slab Track Superelevated Easement | not made | not made | WR414/381-45VS AL-AR (1 each in 20-545) |
| Crossings and Related Short Straight Track Sizes | |||
| Once you get past the basics, things start to get more complicated. The size of crossings is influenced by the standard straight track length and/or the standard track spacing. The angle of crossings produced is related to curve arcs produced. Some short odd-sized straight pieces are produced to match one or more crossings to standard straight lengths. (Coincidentally, they also serve well to fill odd gaps in sectional layout design.) | |||
| Crossing or Short Straight | Tomix Fine Track | Kato Unitrack | |
| Regular Track | |||
| 15-Degree Crossing Right | XR140-15 (1322) | X15R (20-301) | |
| 15-Degree Crossing Left | XL140-15 (1323) | X15L (20-300) | |
| Note: The Kato 15-degree crossovers do not comply with the standard 33mm track spacing design; however, they create a 49.5mm spacing (1.5 standard). | |||
| 30-Degree Crossing | X72.5-30 (1321) | not made | |
| Note: This crossing is meant to be used with both tracks at 15 degrees, such as in the center of a double-crossover made from four turnouts/points. To understand its length see "Other Straight Track Sizes" below. | |||
| 90-Degree Crossing | X37-90 (in 1324) | X90 (in 20-320) | |
| Straight (= 1/2 of Track Spacing) | S18.5 (2 in 1324; 4 in 1099) | not made | |
| Straight (= 1/4 Straight - Spacing) | S33 (2 in 1324; 4 in 1099) | S29 (8 in 20-091) | |
| Straight (= 1/4 Straight - 1/2 Spacing) | not made | S45.5 (2 in 20-091; 4 in 20-320) | |
| Other Straight Track Sizes | ||
| The trigonometry of curved track arcs and straight track lengths dictate other straight track lengths, for use at angles other than 0 degrees and 90 degrees. | ||
| A straight placed at 45 degrees that is the square root of two (1.414) multiplied by a regular straight track length will project a length (at 0 degrees) and a transverse spacing (at 90 degrees) both equal to the regular length (equilateral right triangle). | ||
| A straight placed at 30 degrees will project a transverse spacing of half (0.5) of its length and will project a length at 0 degrees that is the square root of three (1.73) multiplied by that spacing (30-60-90 degree triangle). | ||
| General formula: A straight placed at X degrees will project a transverse spacing equal to its length multiplied by the sine of X degrees, and will project a length at 0 degrees that is its length times the cosine of X degrees. For example, the Tomix S72.5 straight listed below, when placed at a 15 degree angle, has a transverse spacing of 72.5 * sin (15) = 72.5 * 0.259 = about 18.5mm (half the Tomix 37mm standard track spacing). It has a projected length of 72.5 * cos(15) = 72.5 * 0.966 = 70mm (1/4 of the Tomix 280mm standard straight track length). | ||
| Straight (Length Basis) | Tomix Fine Track | Kato Unitrack |
| Regular Track | ||
| Straight (projects 1/4 Straight at 45 degrees) | S99 (2 in 1025) | not made |
| Straight (projects 1/4 Straight at 15 degrees) | S72.5 (2 in 1023) | S64 (2 in 20-030) |
| Straight (= 1/2 Standard Straight + 1/2 Standard Spacing) | S158.5 (2 in 1026) | not made |
| Viaduct Track | ||
| Straight (projects 1/4 Straight at 45 degrees) | HS99 (2 in 1075) | not made |
| Straight (= 1/2 Standard Straight + 1/2 Standard Spacing) | HS158.5 (2 in 1076) | not made |
| Turnouts (Points) and Related Track | |||
| In a similar manner to the table above, there is a relationship between the standard track spacing and the size of the curve, arc and length of turnouts (points). A turnout, along with a complementary curve to make a siding parallel to the straight track, needs to be sized to locate the siding at the standard track spacing distance from the main track. Unfortunately, for space reasons, the standard curve radius that is chosen typically does not work this way. The only exception is the Tomix Mini Points, where the 140mm radius 30-degree arc creates the standard track spacing of 37mm. This lets you substitute a turnout into any 140mm radius curve. Since Mini Rail was added to the Tomix N track product line well after the line was first designed and produced, this is either well planned or very lucky! The regular Tomix (and Kato) system therefore has a basic turnout with a curve radius that is not the standard radius, and that does not even fit into the incremental curve radius system. Therefore these turnouts create a need for a non-systematic curve radius to be added to the product line (and in the case of Kato N Unitrack, additional odd straight pieces and joiners). Please note that the Kato turnouts are technically not true #4 and #6 turnout designs, but these names are commonly used to identify them. | |||
| Turnouts & Related Track | Tomix Fine Track | Tomix Mini Points | Kato Unitrack |
| Standard Turnout | |||
| Std. Turnout Right (manual) | PR541-15 (1209) | PR140-30 (in 91082) | not made |
| Std. Turnout Right (electric) | PR541-15 (1241) | PR140-30 (1231) | EP481-15R (#4) (20-221) |
| Standard Turnout Left (manual) | PL541-15 (1210) | PL140-30 (in 91082) | not made |
| Standard Turnout Left (electric) | PL541-15 (1242) | PL140-30 (1232) | EP481-15L (#4) (20-220) |
| Curved Track to Match Turnout | C541-15 (2 in 1123) | not needed | R481-15 (4 in 20-160) |
| Straight to Support Turnout | not needed | not needed | S60R (tapered roadbed) S60L (tapered roadbed) |
| Note: Kato R481-15 turnouts require use of one of these two straights, plus a special regular or insulated UniJoiner (all included). | |||
| Additional Turnouts | |||
| Smaller Turnout Right (electric) | PR280-30 (1243) | not made | not made |
| Smaller Turnout Left (electric) | PL280-30 (1244) | not made | not made |
| Note: These small Tomix turnouts are 140mm long (1/2 standard length) and match the 280 standard radius. They can therefore be easily subsituted into layout designs. | |||
| Larger Turnout Right (electric) | not made | not made | EP718-15R (#6) (20-203) |
| Larger Turnout Left (electric) | not made | not made | EP718-15L (#6) (20-202) |
| Curved Track to Match Turnout | not needed | not made | R718-15 (4 in 20-150) |
| Note: The larger Kato turnouts do not comply with the standard 33mm track spacing design; however, they create a 49.5mm spacing, which equals 1.5 times the standard spacing. | |||
| Wye ("Y") Turnout (electric) | PY280-15 (1240) | (can use PY280-15) | not made |
| Double Crossover (electric) | PX280 (1247) | not made | 310mm (20-210) |
| Note: The Kato double crossover shares frogs and moving point rails with the R781-15 turnouts, but unlike those turnouts it meets the standard 33mm track spacing. | |||
| Double-Slip Switch Right (electric) | PXR140-15 (1245) | not made | not made |
| Double-Slip Switch Left (electric) | PXL140-15 (1246) | not made | not made |
| Curve-on-Curve Turnout Right (electric) | CPR317/280-45 (1248) | not made | not made |
| Curve-on-Curve Turnout Left (electric) | CPL317/280-45 (1249) | not made | not made |
| 3-Way Turnout (electric) | PRL541/280-15 (1261) | not made | not made |
| 3-Way Turnout (electric) | PLR541/280-15 (1262) | not made | not made |
| Note: Curve-on-curve turnouts permit longer clear straight sections for station platforms or storage sidings and yards. Right and left turnouts can be combined to make a curved crossover. These turnouts maintain the Tomix 37mm standard track spacing. | |||
| Other Track Sizes | ||
| Tomix recently released the curve listed below. It does not fit in the incremental radius pattern, does not relate to a turnout, and has an odd curve arc. It is intended to be used with two pieces in an "S" shape on one of two straight parallel tracks. In this situation it widens the track spacing from 37mm (standard spacing) to 55.5mm (1.5 times standard spacing) over a length of 210mm (3/4 of the standard straight length) to make space for an island platform or light tower. It can also be used as a large-radius curve, similar to the Kato R718-15 curve. | ||
| Other Track | Tomix Fine Track | Kato Unitrack |
| Regular Track | ||
| 605mm Radius 10 Degree Curve | C605-10 (2 in 1150) | not made |
| Multiples of Standard Track Spacing |
| Tomix (and Kato) station platforms, pedestrian overpass bridges, control towers, maintenance buildings, grade crossings and so on are designed to work with the standard track spacing or a multiple of it. Often the spacing must be 1.5 times the standard (55.5mm for Tomix N and 49.5mm for Kato N) or 2 times the standard spacing (74mm for Tomix N and 66mm for Kato N). These spacings can be made using track pieces available in the track system. |
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