Turntable
A busy day at Butterknowle. Bert, the fireman, has just turned The Gaunless on the
nice new turntable and is taking a break, watching the boats down on the quayside.
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OK, the HLR only has tank engines, which are quite happy to run cab first, and so there really is no need for a turntable. Except that I thought one would make Butterknowle, the main terminus, look suitably important.
Also, there's a new first class observation carriage on the stocks at the moment (think shortened L&B). This really needs to be turned at the end of the line so that its occupants get a good view on the way back. As an aside, I've no idea how the prototype railway coped with this problem, although the L&B clearly never had the facilities to regularly turn their carriages, so I assume the passengers only enjoyed the view going one way. But my carriage will be a lot shorter than those on the L&B and will comfortably fit on a relatively small turntable, so the passengers might as well be provided with a good service. I've no idea whether this was ever done in reality; if you know, perhaps you'd tell me. But in the meantime, I'm happy to invoke the old adage; “This is my railway!”
Beyond all that, I just fancied making a turntable! And as, for once, I'd thought about it before the terminus was built, I was able to incorporate it as I went along, rather than try to add it as an afterthought. Now, I know that there are fine examples around of exquisite pieces of engineering, and some are available commercially. But applying my usual principles, I wanted to do it on the cheap, and I didn't want to spend weeks over it; railway time is precious! So I wanted a design that was quick and easy, and used mostly odds and ends that I already had. The whole job for under a 'tenner' would be fine.
Down to work
...a turntable built in a clay flowerpot saucer.
But enough of this rambling. Down to work. There's a picture in Railways in Your Garden which shows a turntable built in a clay flowerpot saucer. Which got me thinking, and paying a trip to our local garden centre. I returned home with a 15” (38cm according to the label) plastic saucer; quite big enough for any loco on the HLR. (Even a Roundhouse Vale of Rheidol or Accucraft Lyn would probably just about fit!) But these saucers do go up to about 20” (50cm) if you're running monster engines with great big tenders. Being moulded in plastic, it's perfectly round, and even has the centre point moulded on the bottom; how considerate!
Now, I think it was John Milton who said “Copy from one, it's plagiarism; copy from two, it's research.” So following his advice I also took a look at the turntable Peter Elliott has built from an old tea tray for his Brookwood & Amberley Railway, just down the road from the HLR. (See picture on the Visits page.) I had assumed that I'd have to start building a properly engineered table with wheels on a rail, but Peter's simply slides on the rim of the tray, which works to great effect. So a few decisions were made:
- The turntable bridge (the bit that goes round!) would be pivoted in the centre, but the weight taken at the rim.
- It would rotate on sliders bearing on a circular rail in the bottom of the saucer. Properly engineered wheels would be prototypical, but not really necessary, unless they have got to be visible. The added friction of a slider is probably no bad thing!
- The saucer would be permanently fixed in position, but the bridge would be easily removable and kept inside. (This meant that I wouldn't have to worry about using completely weatherproof materials for this part.)
- Turning would be done by hand, and alignment of the track would be by eye. This seems to be quite reasonable in 16mm scale, and certainly keeps things simple.
Making the turntable well
No, I don't mean that the turntable's sick (sorry!), but most turntables, of whatever form, do need some sort of circular hole to turn round in. By using a plastic flowerpot saucer, very little needs to be done except to add a rail for the bridge to run on, and provide a pivot in the middle.
I used a spare piece of brass bullhead rail in the turntable well. Happy coincidence here: rail is typically 36” long, which when divided by π (3.14157...) gives a diameter just over 11” — exactly the right size for a 15” saucer! But if you want it to end up in the bottom of the saucer looking reasonably round, you might find it a bit tricky, especially as you don't want to try soldering it together in situ in a plastic saucer! However, as with many such things, a simple jig is the answer, made from a spare piece of chipboard a little larger than the circle.
If you want to have a go, here's how I did it (click icon to expand/collapse instructions)
- Mark the centre point of the board and with a pair of compasses, draw exactly the correct sized circle. (Rail length divided by 6.283 gives the setting for the compasses. Come on, you remember the formula for the circumference of a circle: 2πr)
- Without changing the setting of the compasses, step off six divisions round the perimeter of the circle, then divide one of these in two with the compasses and step off six more divisions so that you end up with twelve equally spaced marks around the circle. I'm sure you'll remember doing that as well at school!
- Drill each of the twelve points, plus the centre of the circle, 4mm. The hole should be a push fit for a 4mm machine screw. Preferably, use a pillar drill to ensure that the holes are vertical.
- File a small groove across the top of each of twelve 4mm brass round-head machine screws. The rail will be located in this notch. Then push each one into a hole around the perimeter of the circle. If the screws are longer than the thickness of the board (their length doesn't matter very much) you'll have to support the board while you work so that the screws can be pushed right down.
- Bend a length of rail so that it more or less stays in an approximate circle. I just did this by hand. It doesn't matter if it's not too accurate, but avoid actually kinking it.
- Tin the top of each screw and the bottom of the rail at appropriate intervals. Also tin the rail at the ends. Then slip a rail joiner on one end of the rail, pushing it right on to the rail. [hlr_turntable03.jpg - Steps 7 nad 8]
- 7. Work round the circle of screws, soldering the rail to the top of each one, such that the ends finish up roughly between two screws. Make sure that the rail is curving at the correct angle toward the next screw before you solder. And make sure there's a good fillet of solder between the screw and the rail. Strength is more important than neatness here! I used my antique 65W soldering iron which coped OK, but there's quite a lot of metal involved, so make sure there are no dry joints as it's not so easy to fix later.
- 8. Push the ends of the rail into alignment and slide the rail joiner into position. Solder up solid.
- Mark the position of the rail join on the board so that you know exactly how the rail is aligned in case the holes aren't precisely spaced. Then remove the assembly and clean it up. If something comes adrift, replace into the board, and fix it.
- Using a hand drill, make a 4mm hole in the exact centre of the plastic saucer (Mine already had a moulding mark in the right place). Using this hole, fix the board to the underside of the saucer with a spare machine screw. Make sure that the top face of the board is against the bottom of the saucer so that the screws later align with the holes you're about to drill.
- Drill through one of the perimeter holes and put a screw through this hole too, to stop the board turning, then drill though all the other holes. Transfer the join mark onto the saucer and remove the jig.
- Open up the perimeter holes to 4.5mm to allow for a degree of expansion in the rail, and drill some extra holes for drainage. My saucer seemed to bow upward slightly in the middle, so I located the drainage holes around the perimeter, between the fixing holes.
- Insert the twelve screws now attached to the rail into the holes in the saucer using the join mark for alignment, slip on a washer and tighten up a nut on each one.
- The final task is to provide a pivot in the centre. You first need to select a suitable pivot shaft for the bridge. This shaft will be attached centrally to the bridge (see later). Drill a hole of a suitable size for your chosen pivot shaft in the centre of a flat piece of brass or aluminium. Using the shaft for alignment, attach the pivot plate to the exact centre of the saucer with a few more 4mm screws. Remember, this pivot will only be used for alignment; it will not need to take any of the weight of the bridge.
The turntable ‘bridge’
Once you've completed the well, you can concentrate on the turntable bridge. At this point you can really use whatever comes to hand out of your scrap box. Here's how I did it, but you can adapt to suit what you have available.
I started with an off-cut of (flat!) wood about 3” x ½”. Each end of the bridge will need packing to bring it to the correct height. When you're working out dimensions, remember that the height of the surface of the bridge must be such that the bottom of the rails are level with the top of the saucer. My saucer has a lip around the edge which will sit on the edge of a round hole in the concrete trackbase. The rails will just pass over it, with very slight packing under their sleepers, to align with the rails on the bridge.
I discovered that some pieces of aluminium roof truss from the old greenhouse were just the right height to go under the bridge and provided a suitable sliding surface. I also successfully experimented using blocks of wood with pieces of kitchen worktop edging strip glued to the underside to reduce both friction and wear. After some experimenting, I made the sliding surface at one end quite wide, but narrow at the other. This gave a sort of ‘three point suspension’ and eliminated the annoying wobble that my first attempt had!
Here is what to do to make one (click icon to expand/collapse instructions)
- Draw a line down the centre of your piece of wood. Use compasses to mark a radius at each end a little smaller than the inside dimension of the saucer at the height the bridge will be at. If, like me, you're going to add planking on top, you can afford to leave a good clearance.
- Cut the curved ends and shape the underside of the bridge to match the profile of the saucer.
- Add a strengthening block in the middle underneath the bridge (if it's not very thick) and, when firmly fixed, drill a hole at the centre point suitable for the pivot shaft you're going to use. If at all possible, find a pillar drill to do this so that the shaft is perfectly vertical. I used a 2” Meccano axle which is a force-fit in a 4mm hole and didn't need any further fixing. You might prefer to use a suitable Meccano fitting (such as a bushed wheel) screwed to the underside of the bridge to ensure that the shaft is vertical.
- Glue or screw appropriate packing pieces to each end as discussed above. You'll probably need a bit of trial and error, plus some fettling, to get them in the right place so that they correspond with the rail in the saucer without scraping on the side of it. Now is the time to make any adjustments, before adding track and finishing the ‘cosmetics’.
- So, cut a piece of track to the length of the bridge you've made so that the ends of the rails finish just inside the lip of the saucer and clean up the rail ends, leaving a slight chamfer on the inside faces. Then, making sure that the track is straight, place it in position on the centre line of the bridge and hold each end down with a suitable weight.
- Before you glue it down consider whether you need to drive straight across the turntable. If you do, the track on the turntable bridge must be absolutely symmetrical so that it aligns properly whichever way round it is, but it's not too difficult to get right by trial and error, marking the edge of the well and adjusting the track as you turn the bridge back and forth.
- I used transverse pieces of ¼” stripwood, a little wider than my widest loco, under the rails to support footboards and to disguise the unprototypical ‘sliders’. A further layer of ¼” stripwood packing and planks made from wooden coffee stirrers (or lollipop sticks if you prefer) brings the planking just below rail level. I used dilute India ink to gently weather the planking.
- I also added handrails made from bullhead rail uprights and coat-hanger wire rails. (Do use a simple jig to drill the holes for the rails, then they'll stay straight!) The uprights were Araldited into holes through both planking and supporting stripwood. You can, of course, get as carried away as you like with detail, but remember that this is meant to be a working turntable, operated by hands a scale 10 feet long! So it does need to be fairly robust.
You should now have a working bridge, albeit with no track on it, even if it's not very pretty at this stage. So next, it's time to fix the track in place. In practice, turntables don't usually seem to use sleepers. But for my purposes, it's much easier to keep the sleepers and just cover them over with footboards. You could spike the rails directly to the bridge structure, but if you're doing that, you're probably looking to use a much better engineered solution all round and won't be reading this anyway!
If you're still with me, all that remains to do is finish the bridge cosmetically. And at this point it really depends what you want your turntable to end up like.
Installing
How you install the turntable depends on your trackbase. I was using concrete here, so I used the saucer as a mould when laying it, making sure there was plenty of clearance below it. (But remove the saucer before the concret has completely gone off, else you'll neve get it out again!)
Don't forget that it's the perimeter that need supporting, not the centre. (So a suitably sized hole in a wooden base should be suficient without further support.) When the concrete was set, I fixed the saucer in place using copious amounts of transparent silicon sealant and then laid the track up to the ends of the rails on the bridge. The lip on the turntable saucer makes a useful edge when it comes to adding ballast, especially if you choose not to glue it down.
And finally
I'd hoped to make a turntable on the cheap (under £10 was my target). The main expense was the saucer, which will probably cost you five or six pounds. For me, the rest came from the scrap box and didn't show in the company's books. But even allowing for the cost of some rail and the brass screws, there should still be some change from that ‘tenner’.
The terminus at the other end of the line is very small (despite its large signal box!) with just two lines, each ending at the buffers. So there's no possibility of running round a train, which is a great disadvantage. Unfortunately, there's no room to add a run-round loop without ending up inside the conservatory. (Yes, I have thought of that - but the looks I got quickly dispelled any such ideas!) But there is room for a turntable at the end of the platform, and obviously that observation coach will need turning here too. So it looks like I have another turntable to make. I don't suppose there are many small narrow-gauge railways with the luxury of a turntable at both ends of the line but, like I said, “It's my railway!”