Chewed Gear

Chewed Gear
Originally uploaded by Phil_Parker

Sods law strikes again. I am trying to build this locomotive in a hurry and just when I think everything is finally going swimmingly I encounter a fundamental but rare problem. Model railway gearboxes have been around since the 1990's and by now are usually pretty good. Of course the gears themselves have existed since the beginning of time - archaeologists have unearthed many examples of "Romfordsauras", dinosaurs 72 times smaller than others with brass teeth and worm tails - and while there have been may of indifferent quality, modern manufacturing means a mesh is generally achievable with care.

I think these gears are from Ultrascale and they seemed OK when first installed. Thinking no more of it I pressed on and added the wheels and rods.

What followed were many hours of fiddling to try and get some decent running. Oil and grease on the various running surfaces seemed to help but only for a short while. I also noticed that the centre of the steel worm gear was discolouring - a strip appeared across it that first looked like rust but on inspection was brass swarf. Initially this was put down to normal bedding in but as you can see from the photo this was worse than I thought.

Checking where the tight spot was I wondered if I was experiencing a rare problem mentioned in Rice's chassis book - the grub screw on the axle was making the brass gear slightly oval. In desperation I whipped out the axle (not for the first time, practise was making me good at this unfortunately) and filled a flat in it so the screw could act as a "key".

At first I thought I'd fixed the problem but as the day progressed it became obvious that I hadn't. The gears seemed to be fine when run on their own but put a load on, such as the wheels, and they wouldn't self start. I could get things running by tweaking the wheels with my fingers but as soon as the power was reversed I had to tweak again. That's not what you want on a layout !

So, I need a new set of gears. My impression is that I had a set with duff, soft brass or a poor tooth profile. Time to hit the phone and see how quick I can get something delivered.