Fixtures and Fittings

While I'm not going to pre-empt the wagon model I'm currently having printed, I thought I'd show you the fixtures and fittings that will be needed once the model arrives.

While there is no real need to model the track, wheels and couplings when designing the model, I found it helps give a better sense of scale. It might even have helped me realise that the axle holes were too small in the first test print as I would have been able to see that the wheels intersected the model rather than sitting freely in the axle hole.

These models aren't entirely accurate representations (for example the coupling is slightly more rounded) but their bounding boxes are correct which means that if the modelled part fits the real one will. For reference all three are Hornby parts; an R600 single straight track section, narrow NEM style couplings (part number R8219), and 12.5mm spoked wheels (part number R8098).

In Good Company

I've recently spent some time (figuratively) crawling around under coal wagons inspecting their braking systems, in order to try and design a simple, but accurate, representation that I can add to my 3D printed underframe. One of the things I've discovered (two excellent resources are here and here) is that while the brakes on my model coal wagon worked so well that the wheels wouldn't turn, in real life they wouldn't have worked at all, as I fitted them the wrong way around.

By the late 19th century most wagons were fitted with a simple lever brake on one side only. The diagram shows the break lever (in red) in the off position. To apply the brake the lever was pushed down. This turns the shaft (blue) and connecting arm (green) clockwise, which in turn moves the two push rods and attached brake shoes (black) outwards and onto the wheels. As you can see this is a really simple, but effective, braking system. The one downside being that if you had to apply a brake to a run away wagon you might have to cross the track to get to it, which may well be bad for your health and well being!

The easiest way to solve this problem is to simply fit a completely independent brake system to the other side of the wagon, but with the brake lever always at the right hand end of the wagon (so it appears to always be in the same place no matter which side you view the wagon from). This means that when you view the connecting arms from one side of the wagon, the nearest turns clockwise while the one on the other side turns anti-clockwise as the brake is applied. This means of course that you can't simply connect the two brake systems together by extending the shaft (blue) the full width of the wagon.

To overcome this problem, and to allow either brake lever to be used to apply both sets of brakes requires a clutch mechanism (shown in yellow) and for the push rods and connecting arms to now be mirror images of each other. This works, because if you push down the far lever (which is the same as previously) then it now turns both connecting arms such that the push rods are forced outwards applying the breaks, but because of the clutch it has no effect on the other break lever. If, however, you push down on the near side lever then, via the clutch, it turns the shaft anti-clockwise applying the brakes on both sides.

Not only did I manage to fit the brake system wrong on the Parkside Dundas kits I built, but it appears that I'm in good company as neither Dapol or Hornby seem to model fully correct brake gear either.

Firstly, on the left, we have what I accidentally ended up modelling. Two independent brake systems, but with the connecting arms and push rods on the near side fitted the wrong way around. This means that instead of applying the brake when the near side lever is lowered, the brake shoes will actually move further away from the wheels, which clearly is wrong. Mind you, on the right, you can see how both Hornby and Dapol model the braking system. They go to the trouble of modelling the clutch to allow either brake lever to be used to operate both brakes, but then don't bother to model the wagon wide connecting shaft, completely negating the point of fitting the clutch mechanism. I'm assuming they don't bother modelling the connecting shaft because a) it is out of sight under the wagon and b) would possibly be quite fragile, but either way they clearly weren't aiming for accuracy.

So which version am I going to add to my 3D model? Well given that there will be no difference in cost, if I can work out a sensible way of modelling the clutch, then I'll probably model all three correct versions. This way I can print which ever I want depending on what time period I want them to represent. This is one of the main advantages of 3D printing over traditional manufacturing; there are no upfront cost to create expensive moulds, which allow us to print variations at no extra cost.

Using Lasers To Build Wagons

While I'm really enjoying this whole 3D printing thing I wish there was a UK based printer I could use. I'm currently printing my items via Shapeways and while their printing prices are fairly reasonable (and seem inline with everyone else) there is a €9 posting and packing charge to add to each order. In fairness to Shapeways this seems a common delivery charge for most of the printers when delivering outside the county in which they are based. This charge means it isn't worth ordering a single small model, such as my TPWS grids, as the postage cost would far outweigh the cost of the model. So each time I've placed an order it has included a number of items, and this time was no different. As well as test printing the mini TPWS grids, I also made two other, more experimental, prints.

I've finally hit on an interesting idea for a layout, one that has even got Bryony interested in the planning, but there are a number of pieces of rolling stock that I'll have to build from scratch. One approach would be to attempt to build rolling stock from plasticard and brass wire etc. but given my success so far with 3D printing I thought I'd give that a whirl first. Printing complete wagons, or at least the major components, will have the advantage that once I can print one wagon I can print as many as I need without having to spend any extra time.

Given that I managed to assemble a Parkside Dundas wagon so that the wheels wouldn't turn, I decided that the hardest part would probably by designing the underframe in such a way that the wheels would fit and turn properly. So one of the prints in my latest order was a simple wagon underframe.

As you can see the wheels do fit, and I promise they do turn quite easily; when weighted appropriately (sitting the mostly full bottle of liquid gravity on it) I can easily push it around my layout. I am, however, going to alter the model slightly. If you look closely you can see that the wheels are actually bending the model outwards quite significantly.

The problem is that while the model is wide enough to take the wheels I didn't make the holes for the axle deep enough. I'm not sure if this is really a problem with my 3D model or with the printing process. All the previous items I've printed have been using Shapeways Frosted Ultra Detail material. This material allows for the smallest of details to be printed, down to 0.1mm, but is also quite expensive (it's the most expensive of the plastics they support). As I wasn't trying to model fine detail but was simply checking rough proportions I printed this model in the cheapest material: White Strong and Flexible. Rather than printing by depositing plastic from a print head, this material is turned into a model using a process known as selective laser sintering or SLS; essentially using a laser to fuse a powder together to form the model. While printing in this way is cheaper it has a much lower accuracy, ±0.15mm, than the Frosted Ultra Detail material, ±0.025, and I'm wondering if this has made the holes slightly shallower than I intended.

Anyway as a test print, to make the postage and package costs worthwhile, I'm more than happy with how it turned out and I'm already working on refining the model ready for the next print run.

The West Coast Fiasco

Even, if like me, you have little interest in modern diesel or electric locomotives (I'm a committed steam era person) you can't possibly have failed to hear about the fiasco surrounding the awarding of the franchise to run the West Coast main line -- unless of course you don't live in the UK. Lets just say it's been a disaster from start to finish that has left the government owing millions of pounds to a number of large railway companies and we still don't know who will end up running the line in the long run. If you want all the details then the BBC have a pretty comprehensive write up of the whole debacle.

Although there is currently no end in sight to the bidding process, there is now a new company interested in bidding for the franchise; Bigjigs Toys Ltd. It's nice to see that there are still a few people in government with a sense of humour.

Just Because I Could

About a month ago I blogged about the Train Protection Warning System (TPWS) grids I'd had 3D printed in order to hide the light sensors I use as part of my scale speed trap. While these are tiny items (their bounding box is just 9mm x 13.12mm x 1mm), I decided, just because I could, to design a set of the smaller TPWS grids. These smaller grids are fitted to sidings, where the low speeds involved aren't conducive to the use of the full size grids (you get interference).

These mini buffer stop grids are really really small; their bounding box is just 9mm x 8.05mm x 1mm! Fortunately the tiny size isn't an issue for the 3D printing process involved and my test print was delivered today.

Those of you who have browsed around Penistone Railway Works, may well have been able to predict this blog post, as I'd listed these grids as "Coming Soon". Now that I've actually handled the printed model, if you are in need of some small TPWS grids, I'll happily sell you a set of four for a very reasonable price.

Penistone Railway Works: Open For Business

As you may remember I've recently become a convert to the wonders of 3D printing. First I printed a spark arrestor for an L&YR "Pug", and more recently I printed up a set of four Train Protection Warning System grids to hide the sensors for my scale speed trap. What I learnt from this was that, firstly, I'm better at building 3D models than I thought I was, and more importantly, that the results are actually usable. This has really got my creative juices flowing and I now have a bunch more ideas that I'm working on that will hopefully turn into more printed objects.

It seems a shame though to keep these models to myself -- I don't know if anyone else will find them useful but I won't know unless I make them available. So as of today Penistone Railway Works is officially open for business! Essentially this is just a shop front as Shapeways handles all the transactions, however, it provides a nice focus point and will allow me to branch out in the future to use other printers or manufacturing processes. Feel free to have a browse, and let me know if you spot any problems that need ironing out.

Hidden In Plain Sight

Whilst I was more than happy with the performance of the scale speed trap I built back in August, I wasn't happy with how it looked. Whilst most of the electronics can be hidden out of the way the light dependent resistors (LDRs) have to be on the track somewhere. Whilst I had chosen fairly small and flat LDRs they were still quite large and unsightly. To have any chance of hiding them I would have needed to place them below the sleepers which would have permanently covered part of the working surface. So if I want to add the speed trap to a nicely modelled layout I have to find a way of fitting and hiding the LDRs.

Fortunately it turned out to be easy to find LDRs that were a better fit to the track; the VACTEC - VT935G are a push fit between the sleepers and cost me just 70p each (with a pull-down resistor included) from oomlout. This just left the small problem of how to disguise the LDRs on a layout.

When I catch the train to work I have to cross the tracks to reach the Sheffield bound platform. Right next to the crossing is a signal and, as with many signals, it is fitted with a Train Protection Warning System (TPWS). A full TPWS consists of four grids positioned at set distances from the signal. Firstly there is an Overspeed Sensor System (OSS) which uses two grids a short distance apart to determine the speed of a train approaching a signal. If the train is travelling two fast then the breaks are automatically applied. The second half of the system is a Train Stop System (TSS) which consists of two grids next to each other positioned at the signal which are triggered by any movement of the train. You can find full details of how TWPS works at this interesting web page.

While a TSS would probably place the two LDRs too close together, using two separate grids as an OSS to hide the LDRs seemed like a perfect way of hiding the electronics in plain sight. Now PECO do make TPWS grids in the right scale, but when I looked into these I felt that they were a little chunky for my liking. In reality, from anything other than close to, the grids actually look more like a set of parallel bars as the thin ties aren't really visible. The problem is that modelling such thin bars at 4mm to the foot scale would result in very very fine plastic bars -- too fine to model accurately and as a result the are oversize on the PECO grids.

Having had some success with 3D printing, I decided to have a go at creating my own TPWS grids. The simple structure was easy to model and has printed really well. While I chose to leave out the thin tie bars completely, I'm quite happy with the look of the resulting grids, and they are a perfect size to hide the LDRs from view. Once the track is properly ballasted and the grids are painted it should all come together nicely.