By The Devil, It's Big!

If you remember back a few months the initial motivation behind the 16mm scale Hudson Hunslet model came from a request to simply "scale up" the 4mm scale version I'd previously built. Well now I've finished it we can have a look at the two models side by side...

As you can see the 16mm scale version is an absolute monster in comparison! Either that or the 4mm version really is ridiculsouly small. To be fair I think both things are actually true.

If you've not been following along over on YouTube then there is a 25 part playlist documenting the iterative process to go from the 4mm version to the 16mm one which you might find interesting if you want all the gory details. If you just want the highlights then enjoy...

And if you want to build your own 16mm scale model then I'm making the 3D printed parts and the metal cowl available as a scratch aid kit. Full details are in the video and there is a link to a contact form in the video description where you can register your interest in one.

Somewhere to Sit

One bit of detailing that you couldn't see in the previous post was the inside of the cab.

Now I know it's not the best of photos but hopefully you get the picture. As you can see I've retained the original brake stand and wheel from the kit, but the rest is all new. The kit originally had a flor cut to look like wooden planks which didn't seem to match any of the real locomotives so I switched this to some chequer plate. I was intending to use the seat that came in the kit as once the driver figure is in place you can't see it. I began to have second thoughts on this when I found it was a little tall and the roof wouldn't fit because the drivers head was too high. I was just going to trim the bottom of the parts to lower it down, but then discovered that I'd manage to loose one part of the seat. At this point I thought it was easier just to make a new one that more closely matched the real thing even if it will be completely hidden.

Oh and before anyone comments that the brake wheel is wonky, I know. I took the photo with the parts just resting together. When I glue it in place I'll make sure it's right.

A Simplex for the Garden

Having shown little bits and pieces related to the 16mm scale Simplex locomotive I'm currently building I thought I should really show some photos of the locomotive itself.

The model is based around a kit, designed by Phil Sharples, that I bought from eBay. I say "based around" as the kit consisted mostly of laser cut MDF parts and as you can see there are quite a few parts on mine which aren't MDF. I'd already shown sandboxes (not fitted in the photos) in a previous post, but you can see I've also printed a replacement radiator as well as coupling blocks, bolt heads and chassis side frames. There are also a few other detailing parts that I've replaced or added which you either can't see in the photo or which haven't been fitted yet. I've also replaced the plastic wheels that came with the kit with some nice steel ones. Still quite a lot of work to do but it's beginning to come together nicely and the 3D printer is proving very useful in helping me quickly producing detailing parts as I go along.

Yet More Details

As at least one person spotted the sandboxes in the previous post are designed to fit on a Simplex locomotive. My original test print was designed mostly to check the shape and to see if the hinge would work. The next step was to finish the lids with the details seen on the real thing.

There appears to be two common types of lid, one showing the Simplex logo and one giving the company name, although I've yet to work out if there was any pattern to which was fitted or if it was pot luck. Looking at photos some have one of each (you can usually only see the front ones as the rear ones are often in shadow inside the cab) and some have two of the Motor Rail Ltd version. I think, now I've done the design work for both, that I'll go with one of each.

I received a few other comments about sandboxes, mostly people saying that they often contain anything but sand. Apparently they are a good place to store spare coupling pins or the starting handle. Also it's not unheard of to open one only to find a mouse nest.

Okay, so I'm insane, but the idea of a mouse inside one of them was too much to resist. Fortunately I didn't have to do much to achieve this as I found a nice model of a mouse on Thingiverse which I scaled down and printed. Because it was so small I printed it sat on a fake floor that would just slot into one of the printed sandboxes.

And with that I think the sandboxes are now complete.

Too Many Details?

I've heard people suggest that the larger modelling scales are easier as the pieces are larger and easier to see. I really don't think this is true. In my experience, and I've talked about this before, what tends to happen is that as the scale goes up you end up modelling smaller details that wouldn't be visible or possible in the smaller scales. I'm fairly certain that there should be a limit to this though, for my sanity if nothing else, but I'm still not sure where the line should be drawn.

Whilst I may not know where the line between sensible and ridiculous should be drawn, I think I've got quite close with the latest bit of detail work. I'm slowly gathering parts together to complement a 16mm scale kit I'm going to build and one of the kit parts I wanted to replace was the sandboxes. They aren't a particularly complex shape and I have prototype drawings so it was easy enough to produce some using my 3D printer.

So far so sane.... except....

Yes, I designed them so that the hinge would work, the lids would open, and they could actually hold sand. Now my problem is that I need to find some finer sand, but have I finally gone insane or is this a perfectly acceptable level of detail?

Spot The Difference

Alongside building the tiny OO9 model of the 10hp Baguley I've been looking through the parts for a much larger 16mm scale kit I'm going to build shortly. I'm not intending to give any hints as to what the kit builds into as yet, but instead I want to talk about bolt detail.

The kit is mostly laser cur MDF parts and the bolt detail (which is quite prominent) on the prototype is represented by circles etched into the surface of the part. Clearly this doesn't give any relief meaning that the details will mostly disappear under a layer of paint. Now there are obviously many ways you could add more detail. Some people use dots of glue, others use brass rivets, and you can of course buy plastic nuts and bolts that can be glued in place. All of those are probably easier than what I choose to do, but then I own a 3D printer.

Whilst many of the parts are too complex to replicate in their entirety and will need individual bolts adding as details, there are four pieces that fit at the corners of the chassis. These are just 18mm by 10mm and have five bolts on each. These seemed like a sensible starting point to check things like the size of the bolt head etc.

It didn't take long to draw these up and print out some test pieces. The first print I made is on the left. I printed this at the normal settings I use, which means each layer of the print is 0.05mm thick. Unfortunately as you can see (especially if you click on the image for a full size version) the layering is very pronounced on each of the bolts and it is very clear that they are made from multiple layers. To the naked eye the layering is less obvious but I fear it would be highlighted by painting and weathering.

So the next print I did is the one on the right, which was printed using layers just 0.02mm thick. The layering is still just about visible in the photos but I can't see it with just my eyes. The problem of course is that printing at 0.02mm instead of 0.05mm takes a lot longer. On a piece this small, just 2.175mm thick, the print time is increaed from roughly 12 minutes to around 27 minutes. While that's not a huge problem, if I was printing a much bigger model the difference would get quite significant.

I was especially annoyed with the longer print time in this case as the 0.05mm layers are perfectly acceptable for the main rectangular piece which takes up most of the depth. When printed at 0.05mm there are 43 layers in total with 32 of them being for the slab and 11 for the bolt heads. When we print the same piece with 0.02mm layers then there are 109 layers with 80 for the slab and 29 for the bolts.

Some of you may remember that back in April of last year, I discovered that the layer height specified in the files the printer uses is actually ignored and each layer is instead given it's absolute position above the bottom of the resin vat. On that occassion I used this to essentially double expose a single layer of the print in order to improve the result. Having moved on to using a different resin (specifically the Elegoo water washable black resin) I've not needed to continue using this trick, but I decided that the use of absolute positioning rather than layer thickness meant I might be able to speed up printing parts like these.

So I took the two files I'd produced and merged them. This resulted in a file with 61 layers where the first 32 layers had a thickness of 0.05mm and the final 29 layers had a thickness of 0.02mm. It took roughly 16 minutes for this file to print and the result is in the middle. Even under a magnifying glass this print is indestinguishable from the one on the right where all the layers were printed at 0.02mm but took ten minutes less time to print. I'm calling this a success.

The same trick should make it quicker to print some other pieces in the future where I only care about the layer thickness in certain areas of the model. For instance, any model printed with supports doesn't need the supports printing at thinner layer thickness, so the print time could be reduced by using 0.05mm for the supports and 0.02mm for the first layer of model upwards.

Mix and Match

As you may remember from a previous post, my son quite likes his Duplo and even uses it to build locomotives and carriages. What I don't think I've mentioned before is the large collection of wooden railway stuff he's also built up.

It all started when he was given this starter set as a present on his first birthday. There are quite a few different brands of wooden railway, most of which all use the same standards and so can be used together. That means the collection has expended rapidly with sets and pieces from Bigjigs, BRIO, John Lewis (although their range seems to have been discontinued), and a few of the wooden Thomas locomotives; after all we definitely needed a Toby the Tram engine!

As you can see with all these bits the layouts he can build (or he gets us to build) can get quite large and complex. One problem, that occurs more frequently that you might expect, is that you end up with an almost perfect layout but where you end up trying to join either two male or two female ends together. We do have some short pieces that do this, but because of the standard lengths of the track pieces often they won't fit. When you have two male ends to fit together there is no alternative to a piece of track with two female ends, but when you want to join two female ends there is another solution. You could just have a very short pin with two male ends without the need for it to actually have any track, and hence it will have no length when fitted but will hold the two track pieces together.

Given that it must be a fairly common problem for everyone rather than designing something myself I had a quick look on Thingiverse to see if anyone else had already done the hard work for me. It turned out they had so I just downloaded the model and printed a bunch out on my resin printer.

As you can see the connector pieces weren't the only thing I printed. While hunting for the connector I came across an even more interesting piece that allows you to use Duplo to lift up the track meaning we could build longer raised sections than before, which Toby thought was a brilliant idea.

Whilst I love being able to experiment with new models quickly on the resin printer it is exceptionally great for parts like this. I'm sure if they were available commercially they would cost a lot more than the cost of the resin I used. Plus rather than waiting for them to be delivered I'd printed all of those within about three hours of starting (I did two print runs as not all of that would fit in the printer in one go). They were all printed flat on the build plate as well so the only clean up was washing off the excess resin.

Top and Bottom

I'm still working on ironing out the kinks in using my new 3D printer. If you remember from last time one of the big issues was the underneath of the parts where the quality was terrible. It wasn't entirely clear why it was so bad so I've done some more experimenting.

What you can see in the photo is the underside of the Sand Hutton wagon chassis printed in three different ways. On the left is the original print I did which had the chassis parallel to all three axis of the printer and raised off the print bed on supports. The middle print was tilted slightly (only around one axis) but still printed with supports. The final print on the right was printed directly on the build plate with no supports at all.

As you can see all three prints have issues but the best one is the one printed directly on the build plate. This is true even if we discount the marks left by the supports. It seems that the resin essentially "sticks" to the cross beams and doesn't drain away as the build plate moves up (I'm guessing surface tension keeps it in place somehow). I was expecting this not to happen when the model was tilted but you can see that it still happens. The right hand print does show that I possibly don't need as many supports as I initially expected though, as the rest of the print is fine. I will need to raise it off the base plate though, so for real prints I'll still need some support structure, but I might have to be a little cleverer as to how and where they are attached.

I have had some better luck playing with the top surfaces of the prints though.

If you remember from last time, the other problem was not being able to see the gap between planks on horizontal surfaces.

The floor should be made of four planks, and the gaps between them should run left/right across the photo, but while there are very faint lines, they are not defined enough and would disappear under the lightest of layer of paint. I had an idea on how I might be able to "fix" this without actually changing the model.

Firstly I produced a much smaller test file; essentially printing just the floor planks and details straight onto the bed of the printer. This gave the following print

As you can see this is just the floor, and the plank gaps (which should now run up/down the photo) still don't appear particularly well. After applying my "fix" and printing the model again I got this

As you can see the planks are a lot more defined, the question is how did I do that?

I've been messing around with some open source software that allows me to view and edit the individual layers once a model has been sliced. What I spotted was that there is no overall setting for layer height within the file, rather each layer has a Z height position. A quick test showed that I could set this value to anything I wanted and the build plate would move to that position before exposing the layer. I videoed the test which shows the first few layers being exposed as normal and then the build plate going first to 50mm then back down to 20mm and then up to 60mm all without any issue:

It's a rather boring video and sorry you can't read the screen very well, my camera didn't seem to like focusing on the UV light -- the layers just tell you the layer number and the Z height.

So having figured out this was possible I set about trying to solve the issue of planks on a horizontal surface by doing essentially a double exposure of a single layer. The gaps between the planks on my test are a single layer deep (0.05mm) and two pixels wide. My fix was therefore to take the original layer (on the left) duplicate it, and then delete alternative planks on both layers to give two new layers (centre and right)

On my first go I gave them both the same layer height. While this seemed to work, gaps were more visible, it seemed that one set of planks was ever so slightly higher than the other. My assumption is that by using the exact same layer height I'd got a small amount of extra resin that cured on the second layer. So I set the second layer to be 0.01mm less than the previous layer (i.e. the smallest increment I think the printer can manage). The result was that the planks seem level with each other but the gaps are more visible than when printed as a single layer.

Each layer in the file also store the exposure time and off time so I was hopeful I could do other interesting things by editing the files (like longer cure times for certain layers) but it seems as if these settings are ignored and those in the file header used instead; at least that seems to be the case with exposure time.

Messing around with the files like this is certainly not straight forward, and you'd need to be careful setting the layer heights to ensure you don't try forcing a print through the bottom of the vat, or lift it up too high causing the second half to stick to the bottom of the vat etc.

Grey Resin

I've not had much time recently for modelling but today I set another test print running in my new 3D printer, not only to try it on a more detailed model but also to try a different resin. The default transparent green resin worked well but looks odd so I thought I'd try a more normal looking grey resin.

As you can see I printed the Sand Hutton Wagon which stalled because I couldn't get decent prints from Shapeways. On an initial look at the prints I was blown away. The crispness of the detail and the smoothness of the surfaces easily beats any prints of this model I've ever had from Shapeways. The underside of each part is deliberately less detailed due to the way they are supported while printing, but I can probably live with that. There are issues though.

First up, the floor of the wagon is missing plank lines. I'm guessing this is because the lines are quite thin, and unlike the sides of the wagon the whole floor surface is cured in one go, and the UV light has bled through enough to fill in the gaps. This could be easily fixed by widening the gaps ever so slightly.

A bigger issue though is the underside of the parts which is frankly horrid. It's all thick and bumpy. My feeling is that this is a combination of the grey resin being a little thiker so it doesn't run off as well when the layer is lifted, and that the part was printed parallel to the build plate. This means that when the layer lifted it held on to lots of the resin which cured slightly when the next layer was printed. It may be that the green resin would give better results as it seems to pour easier, but also tilting the model slightly so that the floor is printed in stages might also help.

So more experimentation is needed, but I'm getting there, and looking at the detail on the wagon sides, if I can iron out the teething problems the printer is going to be fantastic.

405 Nanometres

As most of you will know I like 3D printing, I've been a convert since I got my first print back in August 2012. One thing I worked out quite quickly was that while I really enjoyed designing the parts and receiving the prints (usually from Shapeways) I had no interest in having a printer of my own.

The main reason for not wanting my own printer was a simple cost versus quality trade off. All the printers I could contemplate affording couldn't get anywhere near the quality of the prints I could buy via Shapeways who could afford to buy very very expensive printers. Over the last year or so a couple of things have changed that caused me to rethink my stance.

Firstly Shapeways are no longer the friendly, open, and helpful startup they once were. Don't get me wrong they are still producing high quality prints, but they've made a number of changes to their platform that make it a lot less fun to use. First they hid the pricing formula and a lot of the related details which made it difficult to print items without them becoming more expensive than necessary. Then they increased the prices, with some models seeing price rises of over 30% and they doubled the shipping costs. Added to that they changed the website layout making it so much harder to simply order a print.

At the same time as Shapeways were doing their best to alienate their customers there was a significant change in the home 3D printer market. Until fairly recently almost all the printers that I'd consider affordable for home use were based around Fused Deposition Modelling (FDM); essentially a nozzle moving in three dimensions depositing melted plastic. Whilst these printers can be used to produce great models, they tend to be quite large, and the quality, especially on small details, doesn't match up with what I'm used to getting via Shapeways (the process there is also FDM but again it's the cost/quality trade off issue). An alternative approach to printing is to use light to cure a resin, often referred to as stereolithography. Traditionally this involved a laser and mirrors and was an expensive approach, but there are other ways of achieving the same result. One such way is often refereed to as Digital Light Procssing (DLP) printing, where the light for a single layer is projected onto the resin. Depending how this is achieved it can be done relatively cheaply while still producing high quality prints. More importantly it can be done cheap enough for home use.

As you've probably guessed by now I've gone and bought myself a 3D printer. Specifically I've bought an Anycubic Photon (best price I've found for a UK seller is Amazon, and they seem to have fairly regular offers on, I got mine for quite a bit less than the current list price in one of Amazon's "Lightning Deals"). The printer has a relatively small build volume (i.e. the maximum size of object you can print) of 115mm x 115mm x 65mm but that's plenty big enough for the models I usually print. The small size is actually an advantage as it takes up very little space (22cm x 20cm) on my desk. It works by using an LCD screen, at the bottom of the resin vat, to act as a mask for a UV light. After each layer has cured the build plate is moved up a tiny amount before the next layer is made.

This means that essentially the printer boils down to a UV light (with a wavelength of 405 nanometre), an LCD screen, and a single stepper motor (plus the control electronics obviously) making it fairly cheap to produce. Of course the approach does have some limitations. For example, the XY resolution is dependent on the resolution of the LCD screen, and the smallest detail you can produce is therefore the size of a pixel -- 47 microns in this case. Also with the LCD essentially acting as a mask there will be some bleeding of light which can make producing small holes an issue as they tend to close up slightly. So the question becomes how good can printers like this be for the price.

Well there is really only one way to find out, and that's to print something!

Okay I didn't just print one thing, but three things. Specifically I started by printing a sprue of 40 L&B roof finials as they didn't need any supports adding. I used the default settings with a layer height of 0.05mm and the finials look perfect; no obvious print lines and nice crisp details. Of course they are not the most complex or detailed parts so next up was the 6.5mm gauge chassis for the peat wagon I'm currently working on. This was a bit more involved as it required supports to be added. Even so it came out really well. A few lines on the print (possibly because of the orientation) and the fit of the wheels is ever so slightly tighter than I'd like but usable as they are. The final test print that I've done so far was the kit of parts for the K12 diesel loco.

This is a much more complex model with lots of parts requiring supports adding and a number of small holes and tight clearances (as it was designed to minimise the build volume to keep the price on Shapeways down). I altered some of the automatically generated supports which caused a few problems; the bottom of the buffer beams drooped downwards and half the power retaining clip is missing. Also the small slots for the etched parts to fit into are a little undersized. This seems to be a known issue with the printer and is probably a combination of light leakage on the LCD and the viscosity of the resin. There are a number of ways to work around the issue so it's not the end of the world. More importantly, I gave the part a quick waft of primer to get a better look at the details; I made no attempt to smooth the surface all I did was remove the supports.

Now this does highlight the drooping issue with the buffer beams but, look at the axle box detail, and how smooth the sides are! In this area, the print is better than the last print of this I got from Shapeways where I had to do lots of careful sanding around the axle boxes to remove the print lines.

All in all, I'm exceptionally happy with the printer so far. Yes I have work to do in order to fix a few issues (mostly around small holes and sorting out the best way of putting supports etc.) but I don't think it will be too hard to move to the point where I'm happy to use the prints for my own modelling. It might even be that I start printing parts for some of my kits as well. This isn't to say I'll never use Shapeways again as I'm sure I'll want to print in other materials (like brass and stainless steel) or I might decide that in some cases the prints from Shapeways are better for some reason (maybe something is difficult to support and print) but if nothing else I should be able to prototype new models a lot quicker and cheaper than before, and if nothing else I'm going to have lots of fun.