TMNR axel bearings

TMNR was always built down to a price which is what made it unique – a mass produced garden railway system which whilst never cheap, was affordable to the rising middle classes in 1960s Britain.

As many components as possible were standardised across the range of locos and rolling stock and COTS – Components Off The Shelf – used wherever they could.

One of the purpose built items used on all the stock was the plastic – Deldrin I think – axel boxes.

These were either pre-greased at the factory or with some, a nipple was fitted to allow in use greasing. In either case, the steel axel very soon collected grit in the grease and started to abrade the plastic, quickly resulting in oval or worse axel boxes. Those TMNR sets used commercially – fun fairs, Butlins and so on – suffered especially badly and it is not unknown for axels to cut through the plastic boxes entirely!

In terms of restoring TMNR sets, some sort of replacement is obviously desirable, and at least one owner has manufactured and fitted roller bearing metal axel boxes to his stock. This is fine for battery or steam hauled use but obviously causes problems when used with two rail pickup! We obtained costings from a  couple of commercial firms and at 75p each these seemed OK – but not at the £2,500 required for the tooling…

We’ve been looking at solutions which would work with two rail systems – although we actually use battery locos on the LLLR – and have come up with a low cost ‘fix’ which seems to work.

This involves using a lath to cut out the axel box to accommodate a 12mm roller bearing, and also turning the axel down about 1 mm to fit. Doubtless it might be possible to use Imperial bearing shells to avoid the axel work but as we’ve also been mass producing axels it’s not a problem for us.

The bearing is a force fit, and after a year of use seems to survive quite happily.


Above shows a finished axel box, clearly showing the roller bearing, and the type shown on the box alongside.

Above here we have a used but still usable bearing shell, one with a roller bearing inserted and on the right a very badly worn on.

Lubrication is important and a factory fit solution is not really good enough – nor do we want to have to drop the axel sets to lubricate them, so fitting a 5 mm bolt screwed into a tapped hole cut in the dome of the box works well. Simply unscrew this and use a pressure oil gun to add lubrication a couple of times a year.

We use a generic bearing from Bearing Boys but doubtless many similar types would do equally well. Probably the biggest ‘problem’ is the need for a lathe which was one of the best investments we ever made for working on TMNR stock.

Bearing details:
Needle roller bearing NK12/12 = TAF121912
12mm x 19mm x 12mm
Dynamic load = 670KGF
Static load = 740KGF

See: http://www.bearingboys.co.uk/NK12_12_Needle_Roller_Bearings-5892-p

We’ve also been making new driver assemblies for power bogies with compatible COTS sprockets, chains and oilite bearing shells to replace the plastic ones – but that’s another story!