Wednesday, 16 January 2019

Tumbarumba Turntable - pt 1

The Tumbarumba Turntable.

Turning locomotives at the end of the Tumbarumba branchline was performed with a 60' turntable, large enough to take standard goods 2-8-0, C30T 4-6-0, and any C32 4-6-0 that happened to venture that way on tour trains.  It is also turned 48 class diesel electrics, although I just do not know if the CPH railmotors were turned for their favoured #1 end leading.

The turntable is a standard NSWGR 60' steel design, installed around 1921.  Manual operation.  Only one entry track, although the extension through the turntable was the home of the engine shed (actually a carriage shed), hopefully removed before 1970, as I have no space for it.

Tumbarumba Turntable, as I found it in December 1980. Yes, I know I have used this image before

Similar turntable at Cootamundra, photographed last year.  This supplied me with the details that my earlier picture did not

The model.

On the layout, the Tumbarumba turntable is going to be located right on the edge of the benchwork, close to the operator aisle. 
A ready to install model of the NSWGR  60 foot turntable is a made-to-order model from Anton’s Trains, and whilst I had already obtained one for Wagga, I had neglected to buy the turntable for Tumbarumba.   Antons turntable is  electrically driven, has multiple track aligning (which could suit a small roundhouse) and a full size pit.    If I was using an Antons turntable for Tumbarumba, the full size pit would have to be modified, as I am sure Tumbarumba only had abutments.

However, I like to challenge my skills, so, instead of buying, I thought I would make a turntable.  If I could emulate the prototype, and have a manual operation, then that would ease construction.

Construction starts

Over the years of not having a layout, I have been thinking about a turntable design, using a PC hard disk drive bearing for the central pivot.  And more recently, I came up with an idea of using rare-earth magnets for the alignment of the bridge with the end abutments.  So after buying a set of button magnets off the internet, I was in a position to start

Thank you should also go to AMRM, who had a plan of the steel 60’ table drawn by Alan Templeman (AMRM Issue 133 way back in August 1985).  The model railway magazine is a brilliant resource, and their on-line search function saves a lot of time.

an old harddrive bearing, after the case and metal disk platters have been removed. Note the pair of machine screws - the top of the bearing comes already drilled, and tapped

Hole saw cut hole into a piece of timber to accommodate the bearing depth


Bearing secured on timber with 3 screws


Brass turntable sides cut from scrap brass sheet, and assembled on a base of brass

View from above. Note the wooden block used to space the sides, and also maintain the joints being square

-          Brass turntable assembled on board for testing.

After securing the base to the bearing with the two screws the height at each end of the turntable bridge was tested with a makeshift pile of boards. It is vitally important that these align.  The harddrive bearing has ZERO slop.  I have added one of the two angled bases so you can tell what end is what 


extra brass added for the walkway, and an upper support brace has been added
-         Bulking up turntable pit 
Balsa framing

 Glue an MDF top with clamps. The top of the bearing pops through a hole in the MDF, and sits around 2mm higher.  Check to ensure the bearing still freely rotates.  The glue is intended to be permanent, so no more bearing adjustments are possible after this step
 Track assembly
Two 21cm (60 scale feet) of rail were cut, and assembled on PCB sleepers. Don't forget the electrical gap

-          Ring and Abutments.
 There are probably a lot of ways to construct these, but I chose a method that works for me with the tools, and material I had

I drew a circle using the end of the turntable as a guide, and then proceeded to glue on scrap blocks of balsa to act as the base for the future ring rail.  The balsa thickness was chosen so as to allow an assembled ring rail to fit under each end of the turntable bridge with not much spare space.
The gaps between the balsa blocks were filled with Aldi brand filler, and once dry, quickly sanded.  Painted concrete, with a ring rail above, any imperfections will look natural.  The bearing is only just visible, but looks OK.  The pit will also need to be filled with a slope matching the bottom of the turntable bridge.  Note the track now added to the top of the turntable - this is not yet secured.  The abutment timberwork is also missing, but I do have the track baseboard extensions down.

 Well, I think the turntable is about half done.  The magnetic alignment/locking is still to be fitted, and when I am happy with that, I will finish the track laying.  The pair of abutments will need to be completed,  the turntable will need finishing with a top cover, handrails, and some additional details.  Then painted.  The pit will also need its ring, and I have to arrange the electrical wiring to each turntable rail.  Of course, the pit has to be filled, and detailed too.  

Stay out of the sun.  Build a model, or read a model railway magazine.   Until next time.

Detail from Cootamundra  turntable.  A sign like this would add some spice to the fascia on the layout


  1. Great idea Rob. Just wondering what size hard drive? Was it an old 5.25" or a newer 3.5"?
    Also of note, I recall some utube video of the RTM 36 class being turned on the 60' sellars turntable at Nyngan. A tight squeeze!

    1. Hello David, the drive was out of an old windows 3.1 desktop PC, and fairly small in capacity (compared to what one gets today) - probably 40 megabyte. There were 3 metal disk platters, maybe 10cm in diameter, which I used as mirrors in the budgie cage 20 years ago. Finding a drive could be a challenge - maybe there are old PCs stuffed in garages that have a hard drive.