Richmond revealed

I was at one of Rob’s excellent rather useful seminars yesterday.  As it was about 3D printing, Rob asked me to say a little bit about my printer.  Having not prepared to do anything, I relied on some bits of video I found on my tablet.  Thinking about it, I realised that although this blog has quite a few posts about specific parts of the building process, there isn’t really a post just simply describing the printer.  So this is it.  I call it Richmond.

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It’s inspired by Johannn Rocholl’s Rostock printer, but the design is my own.  I wish I could blame someone else for the design flaws, but I can’t.  The basic design features three columns made of extruded aluminium section (bought).  Up and down each column runs a carriage (the pink bits), with spring-mounted ball bearings to make it run smoothly and without wobbling.   Rob printed these for me.  Here’s a close-up of one.

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The blue parts are modifications (printed by me) to add extra ball-bearings.  The original design simply had screw in the plastic which gradually wore loose.  At the right of the picture, you can see the fishing line which is attached to the carriage to drive it.  This loops around a motor-driven pulley at the bottom of the pillar and and idler pulley at the top, to make it move up and down.  The grey rods are carbon fibre, and join the carriage to the tool head.  The rods are in pairs, to keep them in a parallelogram shape – this means that the print head can move in three axes, but will never rotate.  The tool head looks like this from above: The translucent tube in the centre guides the plastic filament into the heated part.

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The print head looks like this if you happen to be underneath it (which I don’t recommend, because it heats up to 220 Celsius):

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The underneath view shows you the hot end – the part that melts the plastic and squirts it out through a tiny (0.3mm) hole.  The plastic filament is driven through the flexible tube to the hot end by an extruder, in which it is pressed against a rotating gear.  It takes a surprising amount of force to push the filament though the tube and the hot end.  Here’s the machinery that does it (with its operator):

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As usual, these components were printed for me by Rob, but they are not my design.  Rather, I downloaded the designs from thingiverse.  There is no sense in reinventing the wheel, especially when so much effort has gone into making it work well.  The plastic filament is taken from a reel, which sits close by on a home-printed stand:

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The filament drive is powered by a NEMA17 stepper motor.  Each carriage is also driven by one of these, mounted at the bottom of each column:

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Each motor has a printed pulley on it (printed and then machined with my printed lathe, in this case) which drives the Spectra non-stretch fishing line to move the carriage.  The filament is kept under tension by an adjusting screw on the carriage.  How much tension?  Until it goes ‘ping’ rather than ‘boing’ when you pluck it, that’s how much.  As an aside, it also makes an interesting Aeolian harp if you take it outside on a windy day.  Each stepper motor moves as finely as 3200 steps per revolution, so with the pulleys I have this means about 55 steps per millimetre of vertical movement.

Also mounted at the base of each pillar is an adjustable mount for the print platform (which is just a circle of glass from a local glass shop).  These are ugly and badly designed, but they do the job for the time being.  When I redesign the base, they will go.  Using three supports means that I can ensure the print surface is as close as possible to being perpendicular to the pillars.  This is important for ensuring good prints, particularly so for getting the first layer of plastic to stick to the base.  If the base is not level relative to the  and y movement of the print head, then it’s likely that the first layer will vary between being too thin (resulting in nothing but an impression in the masking tape) and too thick (resulting in a strand of plastic not actually stuck to the base).  Bear in mind that this means the print plate has to be level to within plus or minus a tenth of a millimetre over its diameter, and you’ll see why this calibration has been such an issue for me.

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The hardware is mounted on a box made out of plywood I had lying around, painted purple because I had a can of purple spray paint to hand.  On the front of the box is a basic controller interface – an LCD and a simple rotary/click controller. 

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The LCD provides status information about the printer, and a menu system to allow various parameters to be adjusted without using an attached PC.  It is possible to fit it with an SD card holder, which will allow printing completely independently, but I have no need for that.  The display and controller are driven by and provide input to an an Arduino Mega controller inside the main box.  The arduino is fitted with a Ramps 1.4 shield, which provides the stepper motor driver electronics and the higher power switching for the hot end.  The arduino runs Marlin firmware, which generates the stepper motor motions required to translate standard cartesian G-codes to carriage movements for the delta configuration.  The firmware also controls the extruder, monitors the temperature of the hot end, and drives the LCD.  The power supply driving all this is also in the purple box.  It’s a scrap supply from a PC, which provides handy 5V and 12V outputs, at high enough currents to drive the motors and the hot end.

Looking back, it doesn’t seem that complicated.  Makes me wonder why it took me so long to build.

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