On an Improved Turn Table
Proceedings of the Institution of Mechanical Engineers
ON AN IMPROVED TURN TABLE. I n the construction of Turn Tables three leading principles have been followed ; either the bearing has been on the centre only, with no bearings at the circumference, or with bearings a t the circumference and none at the centre; or a combination of these two modes has been adopted by allowing the weight to rest in part upon the centre, and in part upon the bearings or rollers at the circumference; this last construction has been most frequently adopted. Most of the
... dopted. Most of the turn tables first laid down on railmays were made to rest on fixed rollers, as Fig. 1 , Plate 29, for the sake of economy ; but although fixed roller turn tables are the cheapest kind in first cost, and were much used on the first railwsys made, live roller tables have been geiierally adopted latterly, from the greater ease with which they turn ;--as in the fixed roller turn table the weight bears on the axle of the roller, producing rubbing friction, but in the lire roller table i t bears upon the circumference of the roller, producing only a rolling action without any rubbing friction, except in the guiding ring. Some fixed roller turn tables have however of late been constructed, with much larger rollers than those formerly used, which has the effect of perceptibly lessening the friction; but these tables seldom continue long in good worlring order, in consequence of the rollers indenting the top table. This is an objection to ahicli all roller turn tables are subject, but those with fixed rollers most especially, from the top table always resting upon the rollers in these, in the same position, thus receiving the pressure always on the same points ; and as the amount of surface in contact between them is very small, (see Fig, 2 , ) thc whole m o u n t of surface in contact between the surface of the rollers and the top table being not more than three square inches, as shown, if so much, the rollers soon wound the under surface of the top table, so that the latter becomes indented over every roller. As soon as this takes place, considerably more power has to be exerted to turn carriages upon them, as the resistance to be overcome is greatly increased by the whole weight having to be lifted out of each of the hollows formed from the above cause.