Re: 3D printing (Was: New early P&R steel.....)


Tom Madden
 

On Fri, Dec 20, 2019 at 08:30 PM, Dennis Storzek wrote:
..., can anyone tell me why SLA parts are oriented at an angle? Is it an attempt to change the angle of the overhangs so they don't need supports, or simply to provide more room for the supports?

Standard, "top down" SLA parts don't need to be angled - each layer is created atop the previous one. On "bottom up" SLA printers like the Form 2 each layer is created against the surface of the resin tray and has to be broken free of the tray surface after each layer is printed. Angling the part minimizes the area of the part in contact with the tray so it's always that joint that gives way and not the part as the build plate rises after each layer is printed. The CLIP bottom up printer uses a permeable tray and a process that keeps a layer of oxygen (?) between the tray and the part so it doesn't attach to the tray, but they (so far) have chosen not to serve the low end market.

Back to Tom's Shapeways Smoothest Fine Detail Plastic parts, is this a fused deposition process? One would think that some angular overhang would be possible, where each layer would project out less than half the width of the filament being deposited, and therefore be self supporting, like the overhanging bricks in fancy brickwork. If the underside of those handrail brackets would have projected from the vertical surface at a 45 deg. angle, could they have been built without the wax support and it's attendant track?
Fine detail is a jet printing process. I believe the jet printers Shapeways is using are 600 x 600 DPI X & Y, and at 16 microns per layer the Z is 1600 DPI. (3D Systems has 750 x 750 DPI machines with 13 micron layer capability, and 1600 x 900 but only for 32 micron layers.) In this process each individual dot/voxel has to have something under it so the wax is unavoidable. With standard SLA you can have unsupported overhangs of half the laser spot diameter from layer to layer but those layers are thicker - like 0.002".

Tom Madden

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