Notes on Small Locomotive Frames

The Live Steamer, May-June 1951

by George Murray

One of the first items generally acquired when building a small locomotives, is the material for frames. For the amateur machinist this may give rise to the question of what kind of steel to use? Experience in the construction of frames for two small locomotives leads me to advise the builder to use cold rolled steel-provided you have a way of getting it heat treated to relieve the stresses in the steel. The stresses are caused by the cold rolling operation compressing the outer skin of the steel. The writer has seen bandsaw cuts made with a blade less than a thirty-second of an inch thick, which opened up over a quarter of an inch when the saw had cut twelve inches into a bar of flat cold rolled steel in length-wise direction. To use such untreated bars for locomotive frames is to invite trouble, as the cuts which are made for axlebox slots will cause distortion. This may be overcome by the simple process of heating the bars to redness and letting them cool in the air. The advantages of cold rolled steel are: the flat scale-free sides and edges and the ease with which it may be filed, sawn or machined.

Hot rolled steel may be used for frames if cold rolled is not available or cannot be heat treated. The scale should be removed by a scraper, as the hard scale on hot rolled steel, dulls cutting tools quickly. It also may prevent parts such as cylinders, from making good contact with the surface of frames.



For the live steamer who has to machine the axlebox openings in his frames and has no machine other than the usual nine or ten inch bench lathe, the following method is recommended. First secure the two side frames together and rough out the frame openings and axlebox slots by whatever means are convenient. Generally these "means" consists of drillpress, hand hacksaw and considerable "elbow great". When the roughing out is done, mount the frames in the lathe as indicated in Figure 1, and operate on the sides of the axlebox openings as shown. The writer did a set of frames 26-1/2 inches long in an 18 inch between centers lathe by this method. The mandrel or arbor was a piece of 3/4 inch square cold rolled steel, the frames being 3/8 inch thcik. One end of this arbor had to be turned to No. 2 Morse taper to fit the headstock spindle, and was held in by a long 5/16 inch and through the headstock spindle and tapped into the end of the arbor. The other end of the arbor was turned round and revolved in the steady-rest which replaced the tailstock on the lathe. Facing of the sides of the axlebox slots by this method gives good results, the faces being square with the sides of the frames.

Some means of locking the pedestal tie bars to the frames, other than the securing screws, is advisable to prevent the axlebox slots opening out or closing in. A short cut method of doing this is illustrated in Figure 2. Clamp the tie bars to the bottom of the frames with a piece of tin under them and drill holes for the cross pins. Use a drill 1/64 inch under the final size and then ream out with the size to suit the crosspin. The bolts or screws which secure the tiebar to the frame should go through the cross pins to keep them from slipping out. Leaving the piece of tin out will permit the tie bar to clamp the crosspins securely.