I've been working quite a few months at building a RepRap Prusa i3 and designed a frame I can build with 6mm thick MDF. I don't take credit for the design, this is simply taken and inspired from many designs already out there. I drew up a design in Autodesk Fusion 360, as I simply wanted something up that I could print, stick to MDF and run through a scroll saw, or perhaps even laser cut. I couldn't find any reliable laser cutting services in my area, so had to do it the hard, manual way.
I've been working on this for quite some time, and have finally finished my build, but facing a few frustrating issues, especially with the heated bed and ABS adhering to the heated bed.
Prusa i3 MDF frame on Autodesk A360
A short video of the machine can be seen
here on Youtube.
The build consists of the following major parts:
The frame is made of 6mm thick MDF, and I'm using GT2 timing belts for the X and Y axes, and a M5 threaded rods for the Z-axis, supported with a 8mm smooth rods.
I'm also using the latest version of Marlin firmware, at the time of writing this post.
I've been having some issues however and have a couple of questions:
Heated bed issues
The printer bed is finding it extremely difficult to maintain 110°C, in fact, I've never seen it higher than 110°C, even with a higher temperature setting in Pronterface. The bed takes about 10-12minutes to reach it's target temperature, for printing ABS, and that's when I'm covering it with a
sheet of ceramic fibre paper. I also glued a sheet of ceramic paper at the bottom of the heat bed, to try and insulate it a bit. My understanding is that the printer should easily maintain 110°C, even while the extruder fan is on.
Once I remove the sheet of ceramic paper, the bed temperature rather quickly drops and stabilises at 103°C. When the extrusion begins, and I'm lucky enough for the molten ABS to adhere to the Wanhao Build Tak sheet, temperature often drops to about 99°C and the job hangs and the bed never heats up enough to continue the print job. If it does, the print carries on for just a few seconds, until the temperature is down again, and the cycle repeats itself.
I'm not sure if this problem is due to the 12V power supply I'm using, are my cables too thin, is this an issue cause by the Rumba board, incorrect firmware configuration perhaps? I'm not sure right now to how many amps my power supply is rated to, but I made sure that it was more than enough, and think it's around 29A, but will update on that later tonight. I already replaced a previous Aluminium heat bed, that wouldn't even heat up to 70°C, and now the heat issues just carry on.
My opinion is that, the heatbed should easily be able to heat up to about 120°C, with plenty of buffer to maintain 110°C even when the extruder fan is on, ambient temperature is low, etc.
A question I also would like to ask here, is whether it would be better to opt for a MK2 heated bed, rather than using the Aluminium MK3 heated bed?
Molten ABS not adhering to the bed
When my print starts, even when printing the brim, the melted ABS doesn't stick to the Wanhao pad and it appears to happen in some places, and often quite randomly. Is this due to temperature not being exactly 110°C? Is this a side effect of the above problem? How tolerant would the ABS be to not sticking for lower temperatures like 105°C? Is it better to have a heatbed that is slightly hotter, rather than too cold?
I managed to print a 20cm calibration cube, and only once. From there I tried to print the calibration model found at
https://github.com/ahmetcemturan/SFACT/blob/master/calibration/_40x10.STL but the ABS sometimes simply refuses to adhere to the Wanhao pad. Is the problem with the Wanhao Build Tak pad? Should I opt for a different adhesion strategy? Kapton tape or glass with hairspray perhaps?
Extruder oozing even during retraction
Another problem I found was that the extruder keeps on oozing filament, even when retracting. Would it be a better option for me to opt for a direct drive extruder, rather than using a bowden setup?
Rebuilding the frame due to weaknesses
So with all my fiddling, I've managed to find loads of weaknesses in the frame, especially around the extruder, and other parts of the frame. I had to rebuild part of the extruder once, due to it breaking apart. And yesterday, a tiny MDF screw holder for my Y-axis end stop broke apart. The MDF simply isn't strong an reliable enough, and I've decided to rebuild with a stronger material like acrylic, or perhaps even laser cut out of 6mm Aluminium.
Looking forward to your suggestions and advice.
Edited 5 time(s). Last edit at 06/15/2016 02:48AM by josef.van.niekerk.