Friday, August 21, 2020

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.

Thursday, August 20, 2020

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?

Tuesday, August 18, 2020

10HP Baguley: Back a Few Steps

I finished the previous post on the 10HP Baguley by saying

In theory the next step should be adding a little filler and cleaning up all the joints before painting. Oh if life were only that simple!
which was because I already knew what happened next...

It turns out that when I originally soldered the cab back on, I'd not done it very well. Having trial fitted the chassis into the model I noticed that the back wall was no longer vertical. While trying to correct this it fell off and for some reason the floor came loose too. I took the photo after cleaning up all the parts ready ro reassemble everything.

Rather than trying, and probably failing, to solder the rear wall on again I instead opted to use some two part expoxy. I started by using the epoxy to fix the floor into the right place as this gave a much bigger contact patch to then make sure the rear wall was fully attached. I also decided to change the approach to couplings and so cut off the Greenwich couplings while the model was in pieces.

Once everything was back together it was time to start applying some filler and that brings us up to date. It's been about a month since I added the filler and I've still not got around to sanding it back as I've been distracted by other things. Hopefully I'll get back to it soon and then I can move on to painting it.

Sunday, August 2, 2020

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.