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| picclock's modified i3 3d printer attempt |
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| picclock:
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 :drool:. 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 |
| nrml:
Can I suggest the following. 1. Acme lead screws for the Z axis - cheap and readily available on ebay. You can even order stepper motors with a long lead screw shaft built onto the motor to avoid flexible couplings. 2. Oilite bushings instead of LM8UUs. You can press them into a housing while mounted on the smooth rod to get a very accurate fit. I believe they are designed to 'remould' to fit the shaft when pushed into a suitable sized hole. They are less than 90p each. 3. Consider upgrading the Y axis and Z axis smooth rods to 10mm for greater rigidity. 4. Consider using these clamps to hold your smooth rods to the granite bed and Z axis frame http://www.ebay.co.uk/itm/SK10-Bracket-10mm-Linear-Rail-Shaft-Rod-Support-CNC-3D-Printer-SH10A-SK-10-/161839456593?var=&hash=item25ae622151:m:mzab4ZAhkOQPY6TBTK2-zJQ They will simplify your build for not much expense. 5. Consider a 240V silicone bed heater and SSR instead of the popular MK2 and Mk3. 6. Consider using these http://www.aliexpress.com/item/3D-printer-accessories-2GT-20-teeth-synchronous-wheel-pulley-wheel-Perlin-passive-idler-pulley-wheel-bore/32368752009.html instead of the usual bearing and washer arrangement. If you want to print reliably using materials other than PLA and ABS, an enclosed chamber (or even better - a heated chamber) is almost essential, which lends itself better to a corexy / Hbot or Delta design. I hope you don't mind if I chip in with other ideas / suggestions when I remember them. |
| picclock:
Hi nmrl In answer to your points. 1 I see no advantage over the M5 threaded stainless studding - if I encounter issues I will change but I intent to keep it for the moment. Not sure how they make it but its not rolled and seems to be very accurate pitch wise. 2 I have done testing with the linear bearings and am very satisfied with the performance. I have also found some advantage to using 3 in 1 lithium spray grease for their lubrication. 3 Had already considered 10 or 12 mm - but will see how it works out as std. Looks good atm. As I will be using a much lighter bed and bowden type filament feed the loads on the shafts will be less than normal. 4 Already making clamps. My clamp design will allow adjustment in all axis and I will use this to level the bed. Will show drawing with pictures later. 5 Considered it. Not happy with mains around. Std bed heater should be OK. 6 Not sure I see any advantage to this over the std bearing method. If I have issues will alter it as I have spare gt2 pulleys I could bore for a bearing. Have many other alterations to the std design which should improve precision and performance. Of course some of the ideas I have may not pan out, however time will tell. Best Regards picclock |
| nrml:
I find that the fit between M5 nuts and studding is very loose. I think there is a tiny bit of Z axis wobble where the nut rocks on the studding. I find that is not bad enough to ruin a print or even make it look bad on initial examination but it irks me that it can be seen on close scrutiny. My experiences with cheap linear bearings have been bad. They have been rough running even with grease, noisy, had a lot of play and they scratch the supposedly hardened smooth rods. Again, it doesn't seem to affect print quality too much mainly because I have tightened the Y axis belt as much as possible to compensate for the poor fit and I print at slow speeds. My hypothesis is that a toothed idler, toothed driving pulley and a tight GT2 belt is likely to behave like a worm gear drive, possibly improving positional accuracy. When I tighten the belt up really tight, I can see the teeth on the belt getting squashed against the idler bearing. This wouldn't happen with a toothed idler. I can't say for sure if this would actually make a difference or not but it is a cheap mod. All these are minor niggles, but I hope to address these issues when I rebuild mine in future. I am looking forward to seeing your adjustable clamps. |
| PeterE:
Good to see you getting started picclock! :clap: Will read carefully with great interest on your findings along the way. nrml, your comments both here and in my thread are valuable! Will see what I can apply to my build along the way. A few mods are already on the list. BR /Peter |
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