I want the possibility of home printing accurate parts in Polycarbonate, Peek, and Nylon, Abs and Pla along with flexible plastics becoming available. Perhaps a mod to print for lost wax (plastic ?) casting. Also for metal plating plastic parts using either conductive plastic or coating them with a conductive surface. I have seen a mods available for using it (i3) as a mill with a dremel (bit iffy IMHO). I just want a no nonsense printer where I can move the head and see very little error in scale and repeatability(<2 thou max if poss), with high accuracy for producing usable parts.
Why a prusa i3 ?. Popular printer, open source Cartesian design, all parts readily available. Fully customisable head/bed and parameters for all sorts of materials. Cheap to construct. Mature electronics/software easily serviceable without breaking the bank. Stand alone to print from SD card, via USB (Arduino 2560) or Wi Fi remote controllable using rpi and octoprint to monitor progress with any web configured device e.g. phone/tablet or desktop, including video output via webcam.
Why not a kit ? My take on it is that too many things about the kit designs (and prusa i3 in general) are inadequate for accurate smooth motion 3d printing. Mechanical conflicts in the design leading to poor performance and unsmooth axis movements. As an example, the X axis is a whole world of problems. The std design uses 4 lm8uu bearings and two fixed 8mm smooth rods. With just bearings and rod the bearings move smoothly and are a good fit. When clipped into the x carriage with a single rod major binding occurs. This is because the axial alignment is poor leading to binding with just one pair of bearings installed. The rods are not parallel, and the bearing spacing on the X carriage is different to the rod spacing, due to manufacturing tolerances. So moving the carriage is bending the rods. Additionally the X belt tensioner exerts force on the vertical z rods basically bending them to tension the belt

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Changes I intend include a solid mounting base (old granite kitchentop) to keep all axis in a fixed relationship, alterations in mechanical design to improve accuracy and stability (~ many kit parts would be unused), longer LM8LUU linear bearings replace bearing pairs to improve accuracy (no axial misalignment of pairs) and movement smoothness, upgraded stepper controllers (DRV8825 with 2*z drivers), higher voltage (24v) for steppers/bed and head giving better acceleration, with smoother control for the steppers and allowing the use of thinner flexible leads. A different heated bed configuration will precisely locate the bed glass and enhance thermal contact to the heater board, whilst cork insulation will improve warm up time and upper temperature. A moving bowden filament feed configuration to reduce the moving load on the X axis (weight of filament feed and motor is ~450 gms). I will use std prusa plastic parts where possible but upgrade to machined equivalents where design changes indicate.
Electronics using Arduino2560 R3, with Ramps 1.4 board, and graphic controller card, Marlin software, all powered by the usb cable.
picclock