Quote:
Originally Posted by AndrewJ
Gday Julian
I have been following the evolution of these higher quality devices for a while, so have a good idea of what is possible commercially.
I was looking more at making stuff with astro sized threads built in using "consumer" 3D units. In theory, the machine should be relatively cheap once all the design problems re calibration etc get refined, but i doubt the govt would want these things in the wild.
Imagine being able to "print" a custom designed thin wall OTA for a refractor etc "in the shed" :-)
Andrew
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There's a few separate issues here - the physical capability to work in metal etc, the precision / repeatability of the manufactured parts, and what the government wants (or doesn't want).
Working in metal and other "serious" engineering materials is already "here and now", either through a commercial service, or through the still-emerging domestic technologies. When you think about it, the government can't stop this - the genie is already out of the bottle. There's no real philosophical difference between "additive" manufacture (3D printing) and "subtractive" manufacture (milling and machining) - and there's no way that the government could (or should) stop people from machining steel. The big game changer is that additive manufacture opens up all sorts of possibilities and efficiencies that subtractive manufacture stumbles on.
Accuracy and tolerances are a different matter - 3D printing currently tends to have relatively poor tolerances compared to milling / machining (but its improving all the time). If you wanted to make a gun, it would be a LOT easier to machine one than to print it using current technology! The optimal technology for home workshops will probably be a combination of additive and subtractive manufacture - e.g. design parts which can be built quickly and cheaply using additive manufacture, and can then be finished using subtractive techniques where high precision is required.
You will already see that part of the art of design for 3D printing is to recognise where the tolerances are likely to be poor by traditional standards, and design around it. This means recognising that building your part in horizontal layers will tend to make it stronger in the horizontal plane than the vertical axis, and designing and aligning your parts accordingly. Another example is that it is hard to get holes made accurately, whether they are vertical or horizontal. The trick is that you design holes to be somewhat under-sized and ream them out after printing; another trick is the classic RepRap "tear-drop" holes for horizontal holes, which allows them to be made without needing any internal support for the overhangs. If you need a mechanical anchor, you create a pocket (even blind pockets are trivially simple for a 3D printer to make!), and insert a steel nut, and it will grip a steel screw very firmly.
When it comes to "astro-parts" there are some parts which absolutely NEED very high stability and precision (I'm thinking of the whole optical train, motorised axis drive trains, etc), and others where overall precision need not be very high - here I'm thinking of accessory mounts and so on. 3D printing is already well suited to the latter, and I see no fundamental reason why it can't be used even for many high-precision parts, as long as you understand the materials and build technologies you are working with, and design accordingly.
For example, when you realise that a home-built RepRap printer can position the print-head reliably and repeatedly to just a few microns in 3 dimensions, you realise that very high precision can be achieved using plastic gears, rubber drive belts, steel threaded rods, and so on. The dimensional tolerances of the finished parts tend to be restricted by the shrinkage after placement, rather than the build-accuracy. You could certainly 3D-print the gear "blanks" for a drive train, but you might need to allow for the final milling and finishing to be done using conventional CNC machining or similar. (Even that's not necessarily true - the extruder on my RepRap uses a 3D-printed gear train which has had no post-processing or finishing whatsoever.)
(Somehow, we're a long way from a strictly astro-related thread, but 3D printing is another of my passions - and it fills in the cloudy nights very well!)