Saturday, 24 January 2015

Laser cutting again - clear miniature bases and 15mm sci-fi terrain

It's been a long time since we last spent time in the Boiler Room Studios, but it was great to be back there this weekend. And, of course, that means... laser cutting!

We've been painting a mixture of 28mm and 15mm (and 20mm) miniatures of late, so it made sense that the first job should be a load of clear bases for our minis. These discs are cut from 3mm thick clear acrylic, and each is 25mm or 12.5mm in diameter, with a 4mm hole this time. We got a batch of 4mm magnets off ebay - both 0.5mm and 1mm thick, so this seemed like the ideal opportunity to try some out.

Next job was to cut some "top layers" for our board game PCBs, so we have another set of six ready to take a graphics layer. Between cutting the acrylic and cutting the mdf, we removed the air assist from the cutting head and cleaned the lens with some isopropyl alcohol.

Whether or not this made the difference, we're not sure, but our board sections ended up about 1mm too large, all the way around (they were supposed to be exactly 8" x 6") but they are ever-so-slightly larger. Then again, we're only saying that our discs are 25mm and 12.5mm in diameter - they may also be slightly over-sized (though this would be much harder to confirm, since they're tens of times smaller than the size of a board section).

Maybe it's time to do some calibration with the laser and find out if we need to scale our  images for different material thicknesses (we've used both 2mm and 3mm mdf when cutting, so perhaps it's the difference in thickness which is causing the slight discrepency?)

Sadly, we'd already cut a full set of six board pieces before thinking to measure them against an actual PCB! Never mind - a bit of manual hacking will make these work for this newest set of six, but it's definitely something to investigate, next time we're down at the studio.

Before we'd noticed the size discrepency, we also set about cutting some 15mm sci-fi scenery. This is only going to get Grumpy Paul's blood pressure racing, but the actual shapes were designed some time ago, so it really was no extra work to dump a few ready-made images to dxf and cut them out.

The idea is to cut some walls from 2mm mdf and place some laser-cut shapes (carved from some 0.8mm birch ply) over one face, to give them a bit of detail to paint (rather than keep them all flat and use a sticker, as we did with our wild west buildings).

Coming off the laser, the cut-face appeared quite scorched. But simply putting strips of sellotape across the sheet allowed us to turn the laser-cut shapes over and see how clean and accurate the actual cutting was

By carefully prising the shapes off the sellotape, constructing wall sections of 1" and 2" lengths was relatively straight forward. The shapes were glued to the mdf using PVA glue, which allows time to move things exactly into position (superglue would give an instant fix, but it would be very easy to end up with mis-aligned shapes if we rushed this part!)

Where shapes didn't quite line up, a very light sanding with some fine-grit paper soon got everything nice and flush.

Now laser cutting a whole load of walls and extra detail might be good fun, but it's also pretty fiddly. The walls look fine even in a wood finish, but they would look superb with a coat of paint!

The previous photo shows where we got our next idea from - Paul's Linka moulds are great for making multiple wall sections quickly and easily. So we're going to make a mould from our wall shapes too. This means fixing the wall sections to a sheet of mdf. But before we do that, we need to seal the mdf with a coat of PVA glue (to make it easier to remove the silicone mould, once cast).

Then we gave the wall sections a wash with some 2:1 watered down PVA glue, just to seal the wooden faces, taking care not to obsure any of the finer details in the models. Then a Lego brick wall around the shapes sets up our mould framework

Rather than use modelling clay, we applied a generous bead of PVA glue between the bricks and the base, to stop the walls from leaking. Then, simply poured in the silicone and allowed to stand. While pouring the silicone into the mould, we kept on banging the table and jolting the mould, causing any air trapped inside the silicone to - hopefully - rise to the top, and capture all of the nice, fine details in the walls.

Given the number of air bubbles that came to the surface, we're giving serious thought to either sourcing, or finding someone with, a vacuum chamber. Most of these bubbles were probably introduced when we mixed the silicone with the catalyst/hardener, rather than during the pouring; there's no guarantee, but eliminating bubbles is one of the biggest problems with any kind of mould casting.

It's not only quite late now, but this silicone needs a good six hours or more to cure fully.
A few of us are off to play boules in Lancing in the morning, so this will probably get a good 18 hours or so to set, good and proper! Tomorrow we'll see how the mould turns out, and try casting a few wall sections from a bit of left-over dental plaster......