I am not too concerned with the challenge of casting the parts, but I’m not too mechanically experienced. Would aluminum casting all the printable parts make the Lowrider too heavy to function as its currently designed?
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I think someone did ask the question one or two years before but never got around doing it. 
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OK, two cents here…
Casting in aluminum I have given a bit of thought on. In PLA the parts work quite well. Upping the infill and walls makes it very stiff without adding a lot of weight.
For Aluminum casting, say lost PLA, the walls are very low as well as the infill on the patterns so quick print, the weight of the casting would be quite a bit more, about double a 80% fill, 4 wall PLA+ print, which I used. You would also have to build in the aluminum shrink percentage in the patterns. The biggest worry though would be air-inclusion causing voids and weak points in the cast parts/
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This is probably obvious, but you would need a lot of finishing work. For instance, the braces look to be simple parts ideally suited to casting, but there are lots of screw holes needed in three planes, and you’d have to machine the tube mounts to make sure they were perfectly aligned too.
I suspect that by the time you’d set up to machine all those axes, you might as well make them out of billet if that’s your thing.
There are lots of other details that would be problematic - through holes for zipties and belts for instance, and you’d have to work out how to maintain sufficient flex to allow bearings to be adjusted.
Intriguing though the prospect is, I think it would realistically be best with a complete redesign of the parts for casting efficiency.
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Some of the parts might lend themselves to a milling process to machine them, as opposed to being cast, and usually you can benefit from the stronger part being thinner than its plastic counterpart, however, sometimes the thickness is not just about strengthening the plastic, but also adding alignment surface, and this seems to be the case with the braces on the X gantry. The thickness of the brace not only helps with strength, but helps with the brace being aligned perpendicular to the tube.
In thinking about that vein, I wonder about the possibility of doing a CNC milling approach in making braces out of thick delrin. ???
All considered, the 3-D printing choice for the braces does seem like a very appropriate selection.
I did some looking at CNC milling the braces.
What I came up with was cutting out the outline, and edge jigs to hold the braces in turn with all 3 edges facing up, to cut the M5 holes for the screws. The 15mm thickness is close.to 5/8" so I think I could get the material.
Having the edges up would mean that it would be possible to get the sharp corners for the strut fittings. The only thing that I have some trouble with are the nut traps. I kind of figure that maybe I could do just the 2 sides, and epoxy them. Or just not do the nut traps and just epoxy… but it’s kind of the final hurdle…
Maybe an 18mm version would also be OK, but I don’t think I’d want to go down to 12mm.
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Why couldn’t you just tap the holes and not worry about adding nuts?
Good solution using Delrin or HDPE, but I’m probably looking at MDF or birch plywood. I’ve tapped those before, too, but never to try to rely on it long term, like more than a day or so.
Even the plastic is a bit dicey, since those materials tend to be low friction, the screws can back out under vibration and load. I suppose something like hot glue would make a thread lock if necessary.
I suppose that I did just thread tap M3 threads into my acrylic YZ plates on the LR3, so maybe weird to worry about that here. I suppose could use M5×20 screws then, same for the screws holding the beam to the XZ plates. Just need to make the openings about 4.25mm diameter instead of 5.1 to tap them.
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The design also relies a bit on the plastic being slightly compliant for the bearings. Aluminum wouldn’t have this, so they wouldn’t work correctly.
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