Quite a big update this week – the scope and rail are, bar more sanding and finishing, essentially complete.

The scope itself is made up of 6 individual parts – for ease of painting, I’m not attaching the front to the body yet as it has quite a significant overhang which will be impossible to get under if I glued all this together.  The above photo is everything just resting together.

I made a few adjustments to the model before I chopped it up for printing – I hollowed it out, so you can see through it from one end to the other.  My reasoning for this was that it would a) give me the ability to see through it, you know, like a scope, and b) it would be lighter and use less filament than if I printed it as a set of solid parts.  That said, I had to add some hidden features to help me with sticking it all together once it was printed.

Between the rear fluted part and the first part of the central tube, I indented the flutes into the body by about 2mm, so that I could press one into the other, which makes sure everything is lined up properly.  In the ends of all the other pieces, I cut 2mm diameter holes to a depth of about 15mm, which I figured I would be able to insert a clipped down cocktail stick to give the joint extra support, and also keep things nicely aligned.

While this seemed like a good idea at the time, due to me not taking into account the small tolerance of the final prints, the holes ended up being slightly smaller than the diameter of a cocktail stick, which led to me having to not only clip the sticks down to fit, but also file them down to get the diameter small enough to fit in the holes.  *note to self: remember the tolerance*.  Once I’d done that though, the parts stuck together perfectly, with very little gap.  I used a little filler to hide the joint completely and sanded everything down while the front section of the scope was printing.

I stuck the three parts of the front of the scope together in the same fashion, and then went to join the two parts together.  This is when another fundamental error on my part became apparent:  All the centre parts had six holes cut into them in the same locations all the way along, which meant that they could fit together at only six possible orientations.  With the cylindrical centre sections this was fine as it didn’t matter which way around the parts went together as the profile was the same all the way along.  The issue arose because the rear most part with the flutes could be fitted into its socket in ten different orientations, and because it had the side parts with the screws and the sight on top, it has a ‘correct’ way up, as does the front section as it has the scope cover and the front sight, which has got to line up with the rear one.  It turns out that in my haste to stick this all together (because I’m impatient…) I’d mounted the rear part a couple of orientations off from the rest of the piece, so that the holes in the front section didn’t match the holes in the end of the rest of the scope.  I could have just glued the parts together, but there was no easy way of ensuring that it was lined up completely right, and there really wasn’t much surface for the glue to get a good purchase on.  The solution I came up with was to print a small cylindrical tube part that I could slide into the end of one half of the scope and glue into place, and then attach the front part of the scope to that.  I named this part the ‘idiot joint’ in my honour.

The idiot joint in all its glory.

Around this time I also printed the attachment mounts in a couple of parts so the scope could sit in them and the top then placed over and glued in place when I am finally happy with the finish.

The next part to print was the rail.  For some reason, and I must have been tired, I decided that the best way to print this was to cut it up into sections no longer than 150mm (the tallest thing I can print in the printer, give or take) and print all the pieces standing up.  I decided to use the same method as with the rest of the scope to join them, e.g. cocktail stick supports, and this time made the holes a tiny bit larger so I wouldn’t have to file the damn things down again.

The massive disadvantage to printing them this way, other than the fact that if the head hits them too hard they could fall over, is that the grain of the print is essentially going across the part rather than along it, which means they are rather easy to snap in half, or in thirds, or quarters, especially if it doesn’t print properly in a couple of places…  In addition to this, because I’d forgotten to switch off support generation, it printed support material inside the holes at the ends closest to the print bed, to support the end of the hole.  Which proved almost impossible to remove.  After much swearing and snapping two pieces, I had to print a couple of bits again, which I this time printed laying flat on the bed, with no supports, which gave a much nicer finish and a stronger part overall.  I’m not going to reprint the rest of the rail as the remaining parts seem to be holding together pretty well.

I’ve learned quite a lot about what not to do and what to keep an eye on when modelling for 3D printing this week, and it also marks the point at which this project is going to be going on (certainly fabrication-wise) hold for the moment. – – Filament is at an all time low and I’ve got some other projects I’ve got to use it for, so I’m just going to concentrate on working out how I’m going to get the electronic functionality that I want and how I’m going to print the remainder of the rifle without using all the filament in the northern hemisphere.

More soon!

Part 1Part 2