Saturday, March 12, 2011

Beginning to come together...

I now have all the major components, with the exception of the all-important extruder assembly, ready. You'll have seen from previous posts that I completed building the x-axis assembly and mounted the motor and idler pulley. Not having made a decision regarding extrder type yet, I've just made a flat mounting plate (a square of 6mm MDF) which is attached to the 'x-bushings' using some plastic water pipe clips. This allows me to unclip the extruder mounting board when I need to.

I've gone with the high mount position for the electronics (Gen6). I see a double benefit to this. It presents the board where I can see it's status lights and get to the 're-set' button and connections easily (although when set-up I shouldn't need to be changing anything around), and secondly, the mounting board (6mm MDF) adds structural rigidity to the whole printer assembly. The printer isn't loose. In fact it's an amazingly robust construction. A lot of thought has gone into the design, with good use of triangulation. But there is no diagonal bracing in the 'horizontal - lateral' direction. The high-up mounting board for the electronics brings this bracing to the structure. The down side is it reduces visibility to the build platform. A good comprimise might be a 'perspex' piece.

See pict below for a visual on current build status:

You'll notice from the picture that there's a lot more has come together since I last showed a full picture of the printer, but you'll also observe that elements like the end-stops and all the wiring have just been loosely dropped into place. This was to establish good wiring layout and electronics board positioning. There is only the one board which controls the whole unit. That's the benefit of the Gen6 electronics, and I must admit the large mounting board is a bit of an over-kill, but as I've mentioned it's adding structural rigidity.

I was mightily confused about where the end-stops should be placed. (By the way, I got my motors and end stops with end-connectors fitted, so the wiring is of a delivered length -Mendel Parts. It seems to be spot-on. I should be able to hide excess cable length behind the mounting board and not get into cutting to length.) Sorry... back to the end-stop positions: I did a post and a sketch regarding this matter over on the RepRap forum and got great feedback there on where to place the end-stops on each axis.

I believe my sketch illustrates the positioning of the x, y and z end-stops in their min positions for this particular design - 'prusa mendel reprap/repstrap' so I'll reproduce that same sketch below for reference:

As a detailed aside...
I noticed from other posts that the z-axis coupling between the motor and the threaded rod is a common point of failure, where printed couplings are used. I got some help from a friend and had 20mm of the rod ends turned down to 5mm diameter to match the motor shaft diam. I then got a mild-steel bar drilled through with a 5mm hold and two 3mm holes drilled and tapped to take grub-screws to anchor the shaft and rod in place. I filed a small 'flat' on both shafts that the grub-screw tightens against. Here's a picture of that coupling:

That's it for now. The project is suspended for a couple of weeks as I travel for work. Thanks for visiting!

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