Ingenious Gear-teeth Repair Methods
Page 57
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WFIEN a gearwheel has a number of teeth stripped it is usually regarded as damaged beyond repair. Efforts are made to obtain a spare immediately and, if such be not forthcoming, the machine involved is usually compelled to stand idle for a time.
Such, however, need not be the case, for it is often possible, by the exercise of a little ingenuity, .to make a good temporary repair, indeed, often a permanent one. The methods discussed below, however, apply mainly to gears not heavily loaded, such as timing wheels, power-take-off drives, and the like. It is rarely possible to make a worth-while repair in cases where heavy tooth, loads and high surface pressures are encountered.
Probably the best method of repair is to weld and build up new metal into the wheel, turn it up and re-cut the teeth. It done properly this makes a first-rate repair, even to gears comparatively heavily loaded. In some repair shops, however, it may occur that no milling machine is available for cutting the teeth. In such cases it is possible to obtain good tooth forms by the use of a sheet.metal gauge, which is first shamed to fit the good teeth.
Another popular method of tooth repair consists of filing off the broken teeth and drilling and tapping the gear face for a line of two or three hightensile-steel bolts, these being cut off short and filed to tooth shape.
The following method is novel and ingenious. It is done by making two saw-cuts in the wheel and removing a
piece of metal, half the width of the wheel, which embraces all the broken teeth aril an equal number of whole ones. This is then turned completely over so that the undamaged half-teeth go to take up the position previously held by the broken ones. The loose piece is screwed or riveted in place with packing behind it tocompensate for the metal removed by the saw.
It may be argued that as the wheel broke with its full face width in use it will not last long with only half the width available, and that the job is not worth doing. This is not the
writer's experience. Individual cases have to be decided by the man on the
job, of course, but it must be remembered that few gears strip in normal running. It is usually due to an accident, causing jamming, that breakage Occurs. In view of the safety factors commonly employed in vehicle work, therefore, the repaired gear is more than likely to stand up to normal work, and the repair is worth making. It can be further strengthened by pegs.
An alternative method is to saw along A and B (see accompanying • drawing) and to drill along C, in order to remove the whole piece of wheel carrying damaged teeth. A new piece is then fitted and held by screws inserted into tapped holes in the joints between the new and old portions. The teeth are machined or hand-cut as mentioned befcre. The main objection to this method is that it weakens the whole wheel when it is of a small size ; the fixing also is not over secure.
A most painstaking and ingenious method Nine to tne writer's notice some time ago. The mechanic responsible had, in this case, to deal with a wheel having 'nearly half its teeth stripped and a vehicle that was urgently wanted.
He put the wheel in the lathe .and, with a thin tool, parted it clean in two, He then turned the two half wheels around, as shown, and lined them up carefully, it being a helical gear. Finally, he riveted the halves together. It was done as a makeshift, but has now seen six months' service, for a new \thee' obtained has not yet
been put on. F.M.Y.