Friday, 17 December 2010

Last piece(s) of the jigsaw

nophead kindly delivered the last pieces of my milestag gun housing today.These are the fittings and fixtures that make it work:

Here is the aesthetic flash supressor that fits on the end of the 20mm conduit barrel

The trigger fitted to the previously presented grip

The battery cover

The LED focus mount and aligner

The barrel alignment rings. These stop the barrel moving along the axis of the gun and the tabs are intended to stop the barrel rotating

These are 2 x LED diffusers not on the original CAD drawings. They are made from translucent PLA and are designed to fit in the end of the conduit barrel to mount and diffuse the muzzle flash LED

I started assembling the grip and breech this evening. I used #4 x 19mm self tap screws to bring the housing parts together. I had several problems with my design:

1. The holes the screws were to screw in to were too small. The self tap screws are imperial size #4 x 19mm with a diameter of 2.88mm. Some testing with scrap plastic showed that a hole of 2.5mm was best and I had to drill all receptacle holes to this diameter.

2. I had not sufficiently countersunk the mounting holes on the breech section. Subsequently the self tap screws did not protrude from this part. I had to increase the countersink depth by 12mm.

3. Several of the parts of this design require a 'sliding' fit. i.e. the trigger and the LED focus mount. I had CADed these to exact dimensions but RepRap seems to make things slightly bigger, and the ridges caused by the layer extrusion tend to interlock so these parts needed to be filed.

4. The small tabs on the barrel rings are meant to prevent the barrel from rotating but they are too small and will easily snap off. I need to thicken them up in the next revision.

5. The barrel and lens mount radii do not fit the 'perfectly' rount barrel conduit and lens. This is because RepRap extrudes layers of a finite size which results in a imperfect circle. The result of this is that the halves of the housing do not meet properly where there is a diameter between them (i.e. the barrel section, the flash suppressor). These parts currently require sanding. I believe that I need to increase the radius of these radii to fix this. Really need to do some empirical testing.

6. On several parts I had not allowed sufficient clearance for the head of the self tapping screws. A minimum of 5.5mm is required for #4x19mm screws.

Here is a picture of the assembled breech section complete with grip

And the LED focus mount in position

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