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Saturday 14 November 2015

3D Print Experiments - Track Bases (BH rail)

Printing the bullhead rail track base was more problematical than the flat bottom rail base due to the oak key that protrudes from the rail chair on one side. It initially printed all over the place. The solution was in the the design rather than printer setup this time. It is too esoteric to go into details suffice to say it was a question of examining how and what was printed and then adjusting the design for simplicity of form to help the printer do its job.

In this photo I show the track base with a C&L chair (brown) for comparison. The C&L chair, being injection, moulded is finer and a more consistent form that is not easy to achieve for small parts in 3D printing where the plastic is extruded and layered.in free air.

We can see the variation that can result. The leftmost chair is quite acceptable but the one next door has lost a bit of form in the key. I wonder if extending the key might help but then I'll start seeing droop. Still scope for more experimenting but I may stick with this, providing batches are no worse, as it is barely visible at normal viewing distance.

Sunday 8 November 2015

3D Print Experiments - Track Bases (FB rail)

Trying to get more accurate track bed dimensions in 00 I previously spent a lot of time spacing out individual sleepers on Peco code 75, which does gives a more authentic look but the sleeper lengths are still inaccurate.

Now with a 3D printer to hand I wondered how easy it would be to make my own track bases to slide on to the rail. This would be quicker than setting individual sleepers and separate chairs. I focused on flat bottom rail and decided to set the sleeper height same as Peco so that the track was compatible with their turnouts.

The photo shows the printed parts (grey) with correct sleeper size and spacing for 00 gauge. i.e. sleepers 32mm* long and 8.8mm pitch. The dark coloured sleepers are Peco.

The CAD design was relatively simple. The sleepers were designed as joined pairs with integral rail base plates.

Optimising the printer was the difficult part but after a whole day spent tweaking this and that it finally came down to three factors. First to design the rail base plates a little meatier than Peco so that this minuscule part was substantial enough not to be malformed due to plastic fluidity. Secondly to heat the PLA plastic to 185C instead of the default 205C to stop the plastic 'leaking' and causing malformation and thirdly to vary the plastic layer height. The default is 0.24mm, which I retained for the sleeper but reduced it to 0.1mm for the base plates. The base plate clips are very small and need to be built up in very small small layers to preserve their form.

This unkind macro photo showing the rail 'clip' makes it all look a bit rough. The roughness is far less noticeable at normal viewing distance and when painted the lines shown in the top photo will be less prominent too.

Providing the clips have formed correctly they slide onto the rail easily and and hold it firmly.

* Is a 32mm long sleeper correct to scale? Well NO. in 3.5mm scale (being correct for 16.5mm 00 track gauge) a modern 8.5 foot sleeper scales to 30mm and in 4mm scale it is 34mm. To compensate for the narrow look of 16.5mm track when modelling everything else to 4mm the distance from the outer edge of the rail to the end of the sleeper is scaled in 4mm instead of 3.5mm giving a sleeper length overall of 32mm. Visually it looks right even though it is not true to scale overall.

Wednesday 4 November 2015

My Hornby Class S15

I wanted this class of mixed traffic locomotive for a very long time because it was common on my stretch of modelled line. Back in the 1980s I looked longingly at the DJH kit, which I think was the only supplier for an S15 in 4mm scale, but it was expensive and could not be afforded at the time.

Many modellers have craved for an S15 and it featured in published wish lists. Now Hornby has just released it, presumably in response to demand. My dreams have been fulfilled and I got one. It is the most expensive locomotive model I have ever purchased but costs well below the DJH kit, once the motor/gearbox and wheel set addons are taken into account.

I have already enhanced it with head code disks, cosmetic screw link coupling, crew and a Zero 1 chip. which fitted easily in the tender connecting to the DCC socket therein.

The accessory pack was tricky to fit, as usual. The front steps had to be set back further than designed so that the wheels did not interfere on my 800mm radius curves.

About making head code disks.

About making cosmetic screw link coupling.

About fitting a Zero 1 chip (class 700 but same idea),

 N15 and S15 (below) - Spot the Difference.
(one is green and the other black, Doh)
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