Process for fitting steel tyres to loco wheels

Author: Dave Gregson

The steel tyres are machined from solid drawn carbon steel tube. (Available in the north west, at a price, from TI tubes of Bromley Cross, 01204 354911) Machine the diameter one thou per inch less than wheel casting diameter (For example here where the wheel diameter is 7" tyres machined -7 tho.) Note the shoulder left on front face of the ring, this helps to retain the tyre in position and gives a more effective hold on the wheel centre. It also strengthens the wheel face against damage in possible derailments etc.

Wheel casting machined and set up ready for the tyre to be heat treated. This expands the tyre enabling the wheel hub to be fitted. The assembly is allowed to cool naturally and the tyre ring shrinks thus fixing the assembly together. Note the set up for heating the tyre in position and the bolt fitted in centre of wheel casting to allow easy handling and transfer of unit in direct line with the tyre when the correct temperature is reached. It is important that the tyre is heated evenly and that the temperature is raised to no more than black heat turning blue, approximately 475F to 535F. If the tyre is heated to a temperature any higher than required the process can have a reverse effect, therefore the tyre when expands it will stay at a larger diameter when cooling takes place. The use of inside callipers can be useful to determining the correct expansion before offering the wheel centre in place.

This view shows the ring shrunk onto the wheel and left to cool down slowly without any assistance. Note the blue colour of the tyre!

The wheel can now be set up in the lathe for the outside tyre to be machined to the desired profile. Note the small piece of newspaper clamped between the wheel and the mandrill, this prevents the work piece moving during the machining operation. Turning the profile is normal engineering practice i.e. slow speeds, fine feeds and plenty of coolant. The forces set up in machining the tyre will prove if the shrinking process has been successfully completed

This view shows front and back views of the finished process, clearly showing the tyres shrunk onto the wheel centres.

Retreading worn cast iron locomotive wheels using the steel tyre fitting process

Author: Dave Gregson

The principle involved is to replace worn out or badly damaged existing wheel sets on model steam locomotives, or to simply improve the adhesion factor to weight ratio by fitting steel tyres to the rim of the wheel.

The article is based on such an exercise replacing steel tyres to all the coupled wheels on the authors 5 inch gauge 4-6-0 B1 locomotive.

The process is very similar to initially fitting steel tyres, the only exception being that the wheels are fixed to the axels unlike the former as a result of which the wheel sets had steel tyres fitted before being keyed and pressed onto the axels. Therefore extra care must be taken in the machining and setting up process in order to keep the accuracy and concentricity reasonably accurate.

STEP 1 - Before any machining is attempted it would be wise to ensure that the wheels are firmly attached to their axels especially if you are unaware of the means which has been adopted, a simple solution is to pin the wheel to the axel shown in the picture below Photo1 this will reduce the risk of any movement during the machining process.

STEP 2 - The wheel set is then supported between centres in the lathe using a driving dog and catch plate. The first photograph below (Photo 2) shows a fixed steady supporting the axel to reduce chatter and also give more stability during the machining process. The second photograph below (Photo 3) shows finished wheel set.

STEP 3 - The next process involves manufacturing the steel tyres. This process follows the very same procedure as described in "Fitting Steel Tyres" and needs no further instruction. Photo 4 shows the tyres rough machined ready for the next stage of machining. Photo 5 shows the boring out of the centre ready for heat treatment before shrinking on the wheel sets.

STEP 4 - The next stage after fitting the tyres involves the final machining of the tyre profile, it is the builders choice which method is adopted; either included angle or flat finish across the tread of the tyre. A noticeable change in machining forces will be evident now altering from cast iron to steel and differences in machining techniques will be made obvious. Photo 6 shows machine set up and machining in operation, once again note the blue colour on the back face of the tyre as a result from the heat treatment and shrinking process. Photo 7 shows complete set of wheels fully machined. Photo 8 shows the wheel sets fitted back in the horn blocks of the B1 and ready for the road.