Proper positioning of Z endstop on McWire?

Hi, I'm building a McWire RepStrap machine and I'm starting to look at the z stage. But I have a question. I don't have an extruder right now and I think that at the beginning I'll be using a pen just for testing purposes. So I don't know exactly where to put the z axis endstop! I was thinking about
using only the MIN one (the one that catches when you are near the printing bed, is it the MIN one?). I have built some mechanical endstop modules with common microswitches. Is there a proper solution to my problem? If I understood it right this endstop should stop the nozzle when near the printing bed but if I change extruder or tool head than its calibration is now wrong...so what you do to solve this?

P.S.: I don't know if this is the best place in the forum to talk about that! Please move my thread if it isn't!

You're building a McWire? That is a very deprecated model that has all sorts of issues. I built one four years ago. While I got it to work decently, it was never a very good design. There are much better designs for RepStraps out there if you really don't want to buy a set of printed parts.

If you really want to continue building a McWire you won't find much support. Very few have gotten to the point of actually running decently. I think mine was somewhat of an exception, but I had to do a number of modifications to get it that way. Primarily, I modified it to run with belts instead of threaded rod.

Yes I'm building one! I started as a joke, but I've almost finished the mechanics and now I'm searching info about the endstops. I know McWire isn't perfect but, I've already done 3/4 of it so let's finish and try! ^^
You have experience with McWire you said, do you documented a buildlog or something (maybe a photoalbum) online? I'm using a threaded rods design but maybe I can learn something from your design. The most important question for me right now is how you positioned your Z-min endstop?

Endstops aren't required. you can run your printer just fine without them. You'll have to manually home and remove any homing gcode commands, and be extra vigilant for crashes until you know how your machine behaves.

I've been running without any endstops for about 10 months with no problem. I upgraded a couple things and just haven't gotten around to setting up the endstops.

I ran without a Z endstop because I couldn't figure out a good place to put it. Before each print I lowered the Z axis until it just touched the top of a flat dremel wrench that I had that had a known thickness. Anything with a known thickness will work. In the start gcode I had a G92 Zxx where xx was the thickness of the piece. Just make sure that your slicer isn't also including a G28.

Unfortunately I didn't do a good job documenting my build. You can see some pictures here though that may help: [reprapetc.blogspot.com]

Buback Wrote:
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> Endstops aren't required. you can run your printer
> just fine without them. You'll have to manually
> home and remove any homing gcode commands, and be
> extra vigilant for crashes until you know how your
> machine behaves.
>
> I've been running without any endstops for about
> 10 months with no problem. I upgraded a couple
> things and just haven't gotten around to setting
> up the endstops.

Mmm, I don't feel very confortable without at least 3 endstops. Are you using a McWire too?

NewPerfection Wrote:
-------------------------------------------------------
> I ran without a Z endstop because I couldn't
> figure out a good place to put it. Before each
> print I lowered the Z axis until it just touched
> the top of a flat dremel wrench that I had that
> had a known thickness. Anything with a known
> thickness will work. In the start gcode I had a
> G92 Zxx where xx was the thickness of the piece.
> Just make sure that your slicer isn't also
> including a G28.
>
> Unfortunately I didn't do a good job documenting
> my build. You can see some pictures here though
> that may help: [reprapetc.blogspot.com]

Mmm, thank you, so I think I can certainly live without a Z endstop, I'll take a look to your site, I see that using belts doesn't change the design so much. What's the movement speed with your design? I think it's also much quiter!

EDIT: how did you attach your stages to the driving belt?

Edited 1 time(s). Last edit at 09/06/2012 05:44PM by oniric.

I made a mcwire bot and I used optical endstops. With the optical endstops you can move beyond the min endstop easily. In such a way I was able to home to a position above the bed, then print several millimeters below the z minimum. Teacup firmware allowed this; I think Marlin does too if you are using that.

oniric Wrote:
-------------------------------------------------------
> EDIT: how did you attach your stages to the
> driving belt?

I just used a piece of aluminum angle bolted to the bed, and another aluminum piece bolted to that to clamp the belt. It was kind of a hack but it worked well.

The movement speed with the belts is much faster than with screws, however the X speed was limited because it also carries the Y carriage, and the whole thing is quite heavy. I think I was able to manage around 30 mm/s, which wasn't too bad. With screws you would be limited to a much lower speed. The printer was quite noisy with the original Gen 2 electronics since they could only do half-stepping, but when I upgraded to RAMPS when it first came out the sound was noticeably decreased by using the Pololu stepper drivers at 1/16th stepping.

I'm gonna certainly try pulley and belts now! At the beginning it seemed difficult to use and I wanted to stick to the original design but now I see using belts it's even easier to build the machine. Maybe it will cost a little more..but that's what you pay for quality Also I'll try 1/16th microstepping given that I'm using Pololu too! I didn't know it was quiter with that setting.