Monthly Archives: June 2013

New 3D printer

I’m building up a new 3D printer, a Mendel Prusa i3.  I ordered a mechanical pack from Greg Colbourn on the eMaker site that included all of the hardware, rods, nuts and bolts, bearings, motors and a set of flat parts in 6mm plywood.  I got a RAMPS electronics pack from the now-ubiquitous reprapdiscount, and was impressed by it.  It included hall-effect endstops and a neat LCD display, and a MK2A PCB heatbed.  I also got a 30A, 12V power supply.

I sanded down the plywood and finished it with some oil (and very handsome it is too) and printed off a set of Prusa i3 parts on my little eMaker Huxley in some nice silver ABS.  I think perhaps the Huxley has detected that it is fabricating the parts for its replacement, and is acting up a bit so a couple of the parts are a bit curled, but fortunately the design of the i3 parts is such that the squareness or flatness does not rely on a good bond to the bed.  Good work.

The mechanical parts went together with a minimum of fettling but I had to print some holders for the LM8UU bearings on the y axis.  These are designed to be simply zip-tied into some slots on the y-carriage, but I found that y-carriage itself collides with the y-axis motor at the far end of it’s travel.  Not by much, but a little, and enough to raise the bed a touch, so I modified the Y bearing holders from the i3-mini variant of the machine and that raises it a mm or so.  Bit of a pain because the hole spacing is so tight, but it works.

I like the three-point heatbed fixing / suspension system on my eMaker Huxley, so I went for the same thing on  this machine.  RepRapPro sell parts separately, so I got the aluminium heat spreader and the MDF insulator from them, along with the spring mounting hardware to go with it.  Of course, this system doesn’t use the four outer corner bolts like the i3 is set up, so I printed some extra pieces that bolt onto the y-carriage.  I lose some z build height, but it’ll do until I get an adapted y-carriage cut.

One of the most troublesome points of failure in my eMaker machine is the termination of the power electronics.  The Sanguinololu board isn’t great for the heatbed because the traces are pretty slim and I think the power handling is close to its rated limits.  That, together with _just slightly too little wire_ for the moving parts has meant that the cable to the heat bed has burnt out a couple of times.  I was determined to make a better job of the wiring this time around to avoid the froth of cabling that surrounds the Huxley.

To this end, I finally got some bootlace ferrules and made up a high-power wiring loom with with ferrules on one end (for screwing into the screw terminals on the RAMPS board), and fork or ring terminals crimped on the other end.  The fork terminals go into the screw-down terminals on the power supply, and the ring terminals are bolted into holes on the PCB heatbed.  I had to drill the holes out a little for that, but there is plenty of contact between the washers on the bolts and the traces on the bed, so it’ll be ok, and it has the benefit of being completely solder-free, and everything is disassembleable and replaceable.  This will make it less brittle, and more reliable.  I don’t know why more people don’t do this.  Soldering trailing wires onto moving PCBs is a really bad idea but this seems to be accepted practice on repraps.

Hot end is a lovely E3D, all-metal device.  Haven’t used it in anger yet, but it builds easily, heats up fast and squirts hot plastic out, and that’s what I look for in a hot end.  It came with a cartridge heater rather than a resistor.  I like it.

Finally is an extruder.  After being used to a bowden extruder on the Huxley, it seems weird to expect to fit a massive NEMA-17-toting extruder on the x-carriage itself, so I’m planning to eventually go with a bowden arrangement again.  It just seems more civilised.  However, E3D are out of stock of the bowden kit, so that’ll have to be a later development.  In the meantime, I’ve got the hardware for an MGS (metal gear system) extruder, and am printing up the RP parts for it right now.  The small gear on my old eMaker, Wade’s-style extruder has always worried me, and has always been deformed.  I just don’t like it, so I was pleased to see a metal system around.  I wonder if a direct-drive is better again, but I’m happy to wait to try that.