Renold Gears has manufactured the largest worm wheel in its history by cloning a worm gear currently operating on a coal-pulveriser drive at a power plant in the USA. The phosphor-bronze wheel is 2.4m in diameter and weighs in at just over four tons. It was manufactured to replace one that was coming to the end of its working life, but because Renold didn’t manufacture the original, the company had to ‘reverse engineer’ the tooth form.
This was achieved by taking an exact impression of the mating wormshafts thread profile in a perfect mould known as a slug. The slug was then despatched to Renold Gears’ factory in Milnrow, where it was measured using a co-ordinate measuring machine, loaded with special software created by Renold. This mapped the slug precisely and created a computer model of the original worm’s thread profile. From this model, Renold was able to manufacture a master worm and the tooling required to ‘hob’ the new worm wheel. After hobbing, the wheel was paired with the master and adjusted to get the optimum profile in order to create a perfect clone of the original worm wheel in the USA.