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I have an older version of the Rostock Max kit that came with two wire end stops and mechanical end switches. Unfortunately for me, those end switches seem to not deliver enough accuracy to resume a print after homing the printer. Now that I have switched over to the smoothieboard for processing duties, I want to convert my printer to use optical endstops to give me more accurate homing. I need a third wire on each tower and have been dreading the idea of disassembling each tower to run a wire through the center hole along with the other two wires that are already there.

Last night it hit me. I can use the extrusion itself as a ground wire. All I need is a bit of extra wire, drill, self tapping screws and six small round ground wire connectors. This way I won't have extra unsightly wires running up each tower and as an added bonus, the extrusion acts as shielding for the V and Signal wires to prevent unwanted noise from interfering with the long cable run. It works the same as the shielded guitar cables that I use.

Let me know what you think.

Don't know about the extrusions as grounding, but I once led 2 layerfanwires through one of the extrusions because the fellow I bought it from forgot that during his build. I managed with a lot of fiddling to pull them through the X tower, without any dismantling, using a very thin iron thread. But in retrospect I guess I ran a great risk damaging the already present wiring. I used some vasaline for better guiding. I would definately not do that again. Next time if needed I will make a seperate wireduct behind the Z tower I think...

Using the aluminum uprights as ground paths should work fine, just remember that they are grounded so you do not accidentally touch them with a hot wire and blow a fuse or worse.

Allow me to get on my soapbox for a second...

What I suspect you really want is high precision. Or, best case, high precision AND high accuracy. Take a look at this:

[img]http://kaffee.50webs.com/Science/images ... ision1.jpg[/img]

As you can see, high accuracy alone is going to give you bad results. High precision is what you need. Even if the trigger height is not accurate, you can can easily compensate for that in firmware. High accuracy with low precision is hit or miss.

... off soapbox.

On my V1 I actually run the endstop wires down the slot that the carriage wheels run in. They are twisted and I've never had a problem with this arrangement.

I thought I was encompassing both high precision and high accuracy by saying high accuracy LOL. You are correct. I want both high precision and high accuracy.

I have no plans to run other wires close to the extrusion other than the two wires encompassed within, so I should be OK in terms of shorting to ground.

I would recommend STRONGLY against using the frame as a ground for signal paths. On a wooden platform machine like these, the frames are floating antennae for all kinds of EMF rubbish. They're also exposed, so any oops moment electrically as you futz with the hot end is potentially going to toast something.

For a retro fit like this I'd be pulling all the cable out of the tower cores and running it up a conduit clipped and stood off one of the towers (z, most likely, so it's out of the way). If you can manage it, run power/signal/ground for sensors all together in a single shielded cable whose shield is pinned to ground at the RAMBO end and left floating at the top, then run it around the top teasing out the three wires for each sensor. Run your hot end sensors (thermistor/thermocouple, any probe switches) in another similarly shielded cable. And run power for fans, hotend etc in another set of shielded cable. Shielding means you can run 'em all up the conduit together without having to segregate them. Pinning the shield to ground at the RAMBO means all the grounds are the same and you don't turn the shields into antennae or create ground loops. Pulling it out into an external conduit makes it shedloads easier to modify later if you have that "Crap, I need another cable up there for my camera / laser / flux capacitor / whatever".