My friend Alan Powell bought an N guage layout which included a shed with a turntable.

When he first demonstrated that turntable I was gob smacked at the low speed and rock steady rotation it was capable of. Even in bigger scales the turntables I'd seen on various club/exhibition layouts rotated at unrealistic speeds or were very juddery or both. Here in N gauge was a turntable which had neither of these problems ... I wanted one.

The previous owner had kept all of the invoices and warranties for everything he had bought, and so Alan and I read through the contents of two box files until we unearthed the order for a 'slow motion' DC motor. It turned out to be a !2V DC Hankscraft motor which you can find here

That motor will turn increadibly slowly, down to 0.5RPM when unloaded. Of course an N guage locomotive on a turntable bridge constitutes a load so I've had to make do with 1RPM! Whilst the motor allowed for the slow speed rotation the turntable bridge juddered like every other turntable bridge I'd ever seen.

The judders were accompanied by a low frequency rumble, and then a high pitched squeal. Carefull observation showed it to be caused when friction between the runners at each end of the bridge caused drag, which builds up and then is suddenly released. Rotating brass runners at each end of the bridge eliminate almost all of the frriction which allows the bridge to roll around the base rather than drag across it. Two lumps of lead weight added beneath the bridge stabalise it and damp any vibrations. Pictures explains better than I'm able to in words: