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The Protofour Manual
Gauges for tracks and wheels



All prototype railways depend for their safe operation upon the maintenance of certain critical dimensions within accepted tolerances. The critical dimensions relate to the wheel tyre contour, the rail head contour, the spacing of the running and check rails, and the setting of the wheels on the axle. When any of the critical dimensions reach the tolerance limits, the component is changed and as this work is carried out in maintenance workshops and, in the case of track, fitted outside normal working hours its significance is not apparent to the casual observer. No doubt this is one reason why model railway dimensions are so rarely controlled and the causes of derailment so little understood. With the appearance of Protofour, the critical dimensions applicable to the full-sized railways were applied to the model, and Protofour railways consequently operate with prototypical reliability.

However, the tolerance limits of the critical dimensions which are very small even in the full-sized railways are virtually impossible to apply in the model if traditional ruler measurements are to be used. This means that another method of control must be utilised, and in Protofour all critical measurements are checked by means of gauges. The advantage of a gauge is that it maybe made by precision machinery to an accuracy of a hundredth of a millimeter, and components accepted by a gauge are therefore correctly dimensioned, while those not accepted are outside tolerances. By providing simple gauges to control the critical dimensions, Protofour enables the modeller, whatever his experience or lack of it, to achieve precision settings of his components without difficulty.

A complete amateur using Protofour gauges can achieve an accuracy at his first attempt that is far greater than modellers have been able to achieve using any other system of construction. This alone places Protofour modelling in a category of its own. The initial track and wheel gauges were made as individual units, but the advent of Protofour mainframes and the gauges that they required indicated that a new and standardised system of gauge assembly be used. Advantage was therefore taken to redesign the entire range of Protofour gauges and the result is beyond doubt the simplest and most advanced method of control of critical modelling dimensions ever to be presented to the railway modeller.


The Protofour Gauge System

In the following text, the gauge meaning the distance between two components will be referred to in lower case, while the Gauge meaning the unit provided to check the measurement will be given a capital "G". All Protofour Gauges are assembled on metric threaded rod, referred to as "M2" The Gauges consist of a spacer and bushes, with washers, nuts and, where necessary, a spring, mounted on the M2 rod to form a Gauge unit. The spacers and bushes are made from aluminium in order to prevent the accidental soldering of the Gauge to the work. The system offers greatly increased flexibility of use, as a non-standard track gauge may be catered for by replacing the spacers by those of appropriate value, leaving the bush dimensions unaffected. A table indicating the order of assembly of the Gauge components to produce the various Gauges is appended. (Editor note. Unfortunately not - too poor a quality to reproduce here.) The table also includes the Gauges required for locomotive mainframe construction and their use is described in 4.1.12. In this particular location the Gauges are used as construction jigs.


Critical Dimensions

The following dimensions must be controlled to ensure reliability of operation:





Schematic diagram showing the relation of the various Gauges to the track dimensions.
Schematic diagram showing the relation of the various Gauges to the track dimensions.


Wheel tyre and running rail head contours

The contour of the wheel tyre is highly critical in terms of trackholding ability. The most effective form not surprisingly that found on the full sized wheel, but it can only operate correctly when matched to the contour of the running rail head. Both these critical dimensions and contours are to be found in the appropriate British Standards, which have been used in the production of Protofour wheel tyres and rail. Therefore, Protofour wheels and rail are exact-scale reductions of the full-sized articles. The technical aspects of wheel and rail interaction are complex indeed, but it need only be noted here that the correct contours provide the minimal effective flange width and the correct running clearances. Any deviation from the prototypical forms is likely to affect the quality of the running. As the contours of wheel and rail are controlled during manufacture, it is clear that the use of Protofour components ensures conformity with the prototypical proportions and consequently the optimum performance. It has been the price of success that Protofour has spawned a number of imitators, and wheels and rail are appearing on the market with the suggestion that they are suitable for use with Protofour standard layouts. It must be stressed that ANY contour deviation, however slight, destroys the dimensional basis upon which the superlative running of Protofour is based. Therefore, IT IS ESSENTIAL TO USE ONLY PROTOFOUR WHEELS AND RAIL FOR PROTOFOUR LAYOUTS and no responsibility can be accepted for the results obtained with non-Protofour components.


Track gauge and gauge widening

It is a curious fact that modellers know the nominal value of the track gauge, which is variable, but rarely know the Check gauge and Crossing Flangeway, which are fixed values. The nominal track gauge is a spacing of the inside faces of the running rails which allows a certain lateral tolerance to the wheel pair. The coning of the wheel tread tends to centre the wheel pair on the track, so that the flanges in theory do not make contact with the rail faces at all. On the London Underground lines the Track gauge is 1/8" narrower than the 4' 8½" Standard gauge; modern theory suggests that clearances between the flange and rail should be reduced. However, the nominal Track gauge needs to be set with consistent accuracy, and for this purpose the Track Gauge (TG) is used. Fixed wheelbase vehicles such as locomotives present a problem when operating around curved track, as the clearances between flange and rail are reduced progressively with the reduction of radius of curve. To alleviate this problem, which results in binding of the flanges and therefore increased running resistance, not to mention increased wear of the wheel and rail, the Track gauge is widened proportionally to the decrease in radius.




Check gauge

The Check gauge is the distance from the running face of the rail to the outer face of the check rail associated with it. The function of the Check Rail is to prevent the wheelset from tracking laterally and striking the nose of a rail crossing (and perhaps taking the diverging road) by restraining the wheelset by contact with the rear face of the wheel flange. Check rails are also placed on curves below a certain radius to restrict the tendency of the wheel to climb the outer rail. The check rail is set in relation to the running rail containing the crossing, or the outer running rail, and not in relation to the adjacent running rail.


Crossing flangeway

The nose of a crossing and the associated wing rails are bolted together with cast spacers (or in modern layouts sometimes cast as a single unit) and so have a fixed flangeway dimension. This is 1-7/8" in the prototype. It is important to note that as opposed to Track gauge, the Check and Crossing Flangeway dimensions are fixed values. GAUGE WIDENING DOES NOT APPLY TO THE CG & CF DIMENSIONS. It is therefore clear that the flangeway between the inner running rail and the Check rail will be the result of the difference between Track gauge and Check gauge at that point, and only when track is gauged to the nominal setting will the value of the flangeway coincide with that of the crossing flangeway.


Wheel Back-to-Back gauge

It will be realised that a check rail can only function correctly if the distance from the rear face of one flange to the effective flange value of the opposite wheel is of the correct value. This is automatically ensured if the Back-to-Back dimension of the wheel flanges of the wheel pair on axle is maintained at the nominal value, and the wheel contour is that specified for the standards in use. This factor illustrates the danger of using non-Protofour wheels on a Protofour layout as the effective flange might be greater than the nominal value with the consequent danger of derailment at crossings, despite the maintenance of the BB setting within tolerances.


Protofour Track and Wheel Gauges Mk II

As stated in the Introduction the original Protofour Gauges (Mk I) have been replaced by the much improved Mk II pattern. A description of the earlier Mk I Gauges is given later.


TG Track Gauge

This consists of a TG spacer flanked by two CF bushes, flanked again by washers. The rails are held between the bushes and washers under spring pressure so that the Track gauge is held constant (Fig. 3), although minor variations in rail width (owing to curvature etc.) may be accepted. If it is accepted that virtually all curves on a model railway are to radii below the minimum value of the prototype equivalents, it is logical as well as convenient to apply maximum gauge widening in all cases where track is curved. To convert the Track Gauge for use on curved track (Fig. 4), a washer 0.2mm thick is inserted between the spacer and one bush. This is the Gauge Widening factor. It is desirable to maintain two TG and two TG+GW units ready for use when large runs of track are to be made. In order to set the CF at wing rails it is necessary to make a small modification to the Gauge (see below and Fig.7).

Setting the TG. The running rails are held by the washers and bushes under spring pressure.

Fig 3. Setting the TG. The running rails are held by the washers and bushes under spring pressure. The Crossing flangeway (but NOT the Check Rail flangeway) may be checked with either bush flange. (CF)

Fig 4. TG + GW. The Track Gauge has been converted to Gauge Widening by insertion of a 0.2mm washer (visible against the left hand CF bush). Its projection over the rail already gauged to TG will be noted.

Fig 4. TG + GW. The Track Gauge has been converted to Gauge Widening by insertion of a 0.2mm washer (visible against the left hand CF bush). Its projection over the rail already gauged to TG will be noted.



Fig. 5. Setting the CG. The Check Rail is held in one of the bushes and the opposite running rail inthe other. The Crossing Flangeway, but NOT the Check Rail Flangeway, maybe checked using either CF bush.

CG - Check Gauge

This is identical to the TG with the exception that a CG spacer is substituted for the TG spacer. However, note that NO gauge widening is applied to CG. In operation, one bush is placed over a running rail and the other over the check rail (right), as opposed to TG in which both running rails are held.


CF - Crossing Flangeway Gauge

The bushes used with TG and CG are of square form and the flange of the bush is the minimum value of CF. By placing the Gauge over the running rail and pressing a wing rail against the CF bush, the wing rail is automatically set at the correct distance to provide the correct Crossing flangeway.

The square section of the bush enables it to be identified easily, and allows the full depth of the rail, or only the running head, to be gauged using the pointed or straight edge of the CF bush as necessary.

To assist the setting of the CF at wing rails it is desirable to file a flat on the washer adjacent to the square CF bush, until the flat coincides with the circular collar on this bush. The use of this modified Gauge is shown in Fig. 6.

Note: Any CF bush may be used to check the crossing flangeway, but the check rail flangeway is never checked as it is a variable value. However, at diamond crossings or right-angle crossings there are two flangeways with wing rails set on both running rails of each road. In such cases the Nominal Track gauge is always used there is NO gauge widening and standard CF value applies to each flangeway. The Protofour TG offers both settings automatically.

Fig. 6. Setting the CF. The modified TG/CF Gauge is used to set the wing rail. Measurement of CF at the crossing is shown a) and b) with washer filed to clear the vee, c) with washer removed.

Fig. 6. Setting the CF. The modified TG/CF Gauge is used to set the wing rail. Measurement of CF at the crossing is shown a) and b) with washer filed to clear the vee, c) with washer removed.

Fig. 7. RB. The Back-to-Back Gauge used to check the setting of a wheelset.

BB - Wheel Back-to-Back Gauge

The BB setting is measured between the rear faces of the flanges of a wheel pair on axle. A simple cylindrical gauge is all that is necessary for the purpose but to allow easier handling the Protofour BB Gauge is provided with two additional flanged bushes and the assembly mounted on the M2 shaft. The bushes limit the penetration of the Gauge to the depth of the flange so that a false reading caused by the projection of wheel centre material proud of the tyre cannot occur. Non coupled wheels may be gauged at all points of the circumference by placing the Gauge against the wheelset and rotating it. This rotates the wheelset under the Gauge. Correct wheel BB gauge is achieved when the Gauge penetrates the wheelset easily but without play. (Fig. 7 above) No Gauge can check the factors responsible for wheel wobble as well as the human eye. If a wheelset is suspect, slowly roll the wheelset on a smooth flat surface and observe the rotation of each wheel in turn.



Switch Blade Gauge

Switch Blade Gauges

The only non-standard Gauge set is the Switch Blade Gauge which is used to assist the modeller in setting the correct gaps in a pair of switches when attaching the Turnout Operating Unit. The set consists of three clips (Fig. 8), one simply to hold a switch blade against its stock rail, while the other two are used to hold the remaining switch blade at the correct heel gap and toe gap. The use of these Gauges is described in Instruction Leaflet 4.1.7.




Protofour Track and Wheel Gauges Mk 1

The Mk I track and wheel gauges are now out of production. For the benefit of modellers who may obtain these versions the following notes are provided.

Mk 1 Track Gauge

Track Gauge Mk I

The inner faces of the Gauge claws constitute the gauging faces and rails held in the claws automatically assume the correct spacing. When soldering rail to the rivets, (see Instruction Leaflet No. 4. 1. 6.), only minimum lateral pressure from the soldering iron should be applied.

This is to prevent bending of the rail and consequent distortion of the gauge setting. The WIDER edge of the Gauge should be held over the OUTER rail on curved track as this automatically produces the required gauge widening. To ensure that rail is held upright, check that the Gauge slots are fully down to the rail head, and hold the Gauge firmly down to obtain proper contact between the rail and the rivet heads.

Mk 1 Check Gauge

Check Gauge Mk I

Note that CG is measured from the outer rail Gauge face or the vee nose and not from the adjacent running rail.

The flangeway between the check rail and the running rail varies according to the gauge widening and its value is not specified. The precision-made Protofour Check Gauge is designed to hold the check rail at the correct setting during assembly, or subsequently to check the rail position, without the need for measurements.

The Gauge should always be used with the screw-slotted head resting on the running rail on the inside of the curve adjacent to the check rail. The opposite end of the Gauge has a flat segment which is designed to clear the nose of the crossing with the adjacent flange resting in the crossing flangeway. The Gauge must beheld down firmly during soldering to ensure level rail tops and held, to minimise rail deflection, as closely as possible to the point of soldering. Recheck every check rail assembly after soldering.

Mk 1 Flangeway Gauge

CF Crossing Flangeway Gauge Mk I

The crossing flangeway, unlike check rail flange ways, is always a fixed value as it is closely related to wheel width and effective flange dimensions. The width of the flangeway is controlled in the prototype by bolting the rails together with spacing blocks.

In Protofour it is determined by means of a strip Gauge CF. When the crossing vee has been soldered into position and excess solder removed, the CF Gauge is placed against it and the wing rail pressed against the Gauge while it is soldered in its turn. When rechecking, the Gauge should enter the flangeway easily but should have no sideplay. The crossing flangeway and the check rail flangeway are not of the same value.

The CF Gauge should NOT be used for check rail flangeways, which are determined by the check gauge setting, and similarly, the Check Gauge should NOT be used to set crossing flangeways.

Mk 1 Back to Back Gauge

Back-to-Back Gauge Mk I

The Protofour Back-to-Back Gauge is a precision ground Gauge with parallel surfaces and is simple and adaptable in use. Correct BB gauge is obtained when the Gauge just slides between the wheel backs without sideplay. No force should be used when gauging, as this indicates an under-gauge condition and, either the wheels will spring together again when the Gauge is removed, or the wheels will be distorted and will no longer run true.

BB gauge should be checked at several points around the wheels as the setting of deformed wheels may well be correct at one point but not at others. Rolling stock and locomotive wheels may be checked while in place on the vehicles using one leg of the Gauge. The BB Gauge may be used to set locomotive wheels on axles as described in Instruction Leaflet 4.1.12.


Care and maintenance of Gauges

Protofour Gauges are precision tools and should be handled and stored accordingly. Great care should be taken to prevent damage to the Gauge surfaces.

Following soldering operations the Gauges should be cleaned thoroughly with spirit or other means to remove the flux which may have been deposited on them. They should be given a coat of silicone wax or machine oil and stored in a closed container such as a tobacco or pastille tin, together with a piece of vapour phase inhibiting (VPI) paper.

A piece of VPI paper is enclosed with the Gauges when despatched and they have an initial coating of silicone wax.

The Protofour Gauges enable the modeller to construct trackwork to a constant standard of accuracy without the need for ruler measurements. Furthermore, they enable modellers building layouts in different localities either to exchange stock or to combine the layouts with the knowledge that there will be no problems of dimensions or gauge variation. Protofour Gauges for track to other than standard gauge are used exactly as described above.