How to enable negative Z values?

[dtgriscom]

I'm using Repetier Host for OS X 0.56 and Repetier Firmware 0.91 to control a Rostock MAX v2, and am going through the calibration process. Problem: although it's extremely precise to find Z values using the paper-under-the-extruder trick, the printer refuses to go to negative Z values. So, if "Z=0" is too high then it's impossible to find out exactly how high.

Is there any way to convince Repetier Host or Repetier Firmware (I'm guessing it's the latter) that it's OK to go to negative Z values?

[Jimustanguitar]

You need to change this setting in Repetier (printer settings) and in the EEPROM to a higher number, find the correct height, and subtract what's left to get the final value.

Check out the manual for a full how-to.

[dtgriscom]

You need to change this setting in Repetier (printer settings) and in the EEPROM to a higher number, find the correct height, and subtract what's left to get the final value.

So, I need to, say, add 1 to the Z max length (thus shifting "Z=0" 1mm down), do my work to align Z=1 to the bed, and when done subtract 1 from the Z max length?

Seems doable, but round-about. There's no way to allow negative Z values?


Thanks,
Dan

[Jimustanguitar]

My experience has been to add 1mm to the length in both places, and then find the right height with a piece of paper. Let's say that the right height according to the paper trick happens to be at .2mm, you'll know to subtract that amount from your original value so that Z0 is dead on.

In other words, the subtraction bit that I mentioned is only because it's unlikely that you'll land on an even millimeter.


***edit*** This also depends on what firmware you're using! There is a new z-height feature in the 0.91 firmware that probably supersedes this process. You'll still have to change the setting in Repetier, but I believe that the new process takes care of the EEPROM bit. The manual knows better than I do. Always defer to Gene

[geneb]

Setting the Z zero point in the .91 firmware doesn't involve the host software at all, so I'm really not sure what you're trying to do.

g.

[dtgriscom]

Setting the Z zero point in the .91 firmware doesn't involve the host software at all, so I'm really not sure what you're trying to do.

I'm trying to follow the instructions in your manual to calibrate. Each time I adjust an end stop screw, I need to measure how far off "Z=0" is from the surface of the paper (on the glass). But, with the scripts as suggested, you have to make sure "Z=0" never ends up below the surface of the glass. And, that means that there's no direct way to measure the error; you have to guess, and make sure you guess short (to keep from hitting the glass hard).

I'd like to instead write the scripts to go to Z=1, and then use the manual Z adjustment buttons to move the print head down to touch the paper. I can then read the error right off of the host print panel, and can even whip up a spreadsheet that, given the geometry, will tell me how many factional turns to turn the nearest tower's end stop screw to correct. I also won't have to shoot low in order to save my glass. No, it won't be perfect, but it could cut the iterations by half.

(Let's say you want a factor of 1000 improvement in the error. Let's guess the eyeball method gets you 70% closer each iteration. Let's guess that the measured method would instead get you 90% closer each iteration. The eyeball method would take 5.7 iterations, but the measured method would take 3.)

But, I can't, because if the error is negative, and Z=0 is above the paper, then I can't measure how negative the error is. The restriction is in the firmware, because I can send raw commands from the host and they're ignored if the resulting Z would be negative. So, I was hoping there was an EEPROM flag or adjustment allowing Z to go negative.

The workaround Jimustanguitar suggested will work, but will require more thinking (ouch), and be harder to explain when I write it up.


More soon,
Dan

[JohnStack]

Dan,

I think I understand what you're doing - but in my experience, you're not going to get screw turns precise enough to do it.

My recommendation would be to use the manual. It's well written and works. I had to use Script 1 - 3 about four times before I nailed it. When I did, everything else was pretty dialed in. The only thing I noticed was that the base number Gene provided was different than mine - but overall, after some back and forth with the scripts and repeated screw turning, it worked fine. All in under an hour.

[dtgriscom]

Check out my new thread here outlining what I did to calibrate. It would be even easier if I could have adjusted the extruder to negative Z values.

... any ideas?


Thanks,
Dan

[dtgriscom]

I posted on the Reprap.org forums on this, and was told that the latest Repetier firmware has the ability to disable boundary checking, and so allow negative Z values:

Yes, the firmware prohibits it. The latest patch solves this. There you can do
G1 S1
to disable boundary check and
G1 S0
to enable it again.

This isn't in the 0.91 ROSTOCK MAX firmware, and I'm working on figuring out how to integrate the two.

FYI,
Dan

[mhackney]

Why would you integrate the two, just update to the latest release. There is no magic in the "Rostock MAX firmware". You are not going to violate any warrantees if you change, and frankly, you are not going to get any better or different support here or there if you update. Seems like a lot of work for minimal game. The newest Repetier has some great features - baby stepping for one. Once you take baby steps, there is no going back!

[dtgriscom]

Well, there is some magic in the Rostock MAX release: it Just Works on my machine. I tried installing the latest Repetier firmware on my machine, and just got a blank LCD for my trouble.

I'm sure the "magic" is pretty simple: it's just the MAX-specific configuration file (whichever the heck that is). So, I'm thinking to set up my own GitHub repository, forked from the Repetier firmware but with it pre-configured for the Rostock MAX. That way, naive users (such as me until now) will just be able to download and use it without having to worry about configuration.

Which file(s) should I migrate from the Rostock MAX release to my Repetier fork?


Thanks,
Dan

[Jimustanguitar]

https://github.com/seemecnc/Repetier-091-ROSTOCKMAX" onclick="window.open(this.href);return false;

[joecnc2006]

https://github.com/seemecnc/Repetier-091-ROSTOCKMAX

That's the one I use.

[Eaglezsoar]

Why would you integrate the two, just update to the latest release. There is no magic in the "Rostock MAX firmware". You are not going to violate any warrantees if you change, and frankly, you are not going to get any better or different support here or there if you update. Seems like a lot of work for minimal game. The newest Repetier has some great features - baby stepping for one. Once you take baby steps, there is no going back!

Can you explain (in layman's terms) what baby stepping does?
Googling the term brings up a lot about babies and stepping but very little regarding Repetier.

[mhackney]

You need to look at the Marlin or Repetier sites to get info on baby stepping. I am writing a little description for Repetier site. Basically...

Requires the LCD display
Enable babystepping in the firmware

To use, once you start a print you can move the hot end up OR down as it's printing using the knob on the LCD display. There is a new option that shows up called Babystepping that you use. This allows you to adjust the first layer height on the fly. You can go to -Z using this too so be careful!

[dtgriscom]

Why would you integrate the two, just update to the latest release. There is no magic in the "Rostock MAX firmware".

Well, yes, there is: the base configuration file(s), right?

You're using the latest Repetier firmware on your Rostock MAX, right? Would you mind zipping it up and posting it, or sending it to me? I'll then be able to compare it to the generic release and see what you had to change to get it to work. (It probably doesn't seem like a lot to you, but it would really help me get going.)


Thanks,
Dan

[joecnc2006]

Are all the latest updates from Gitt in the new .91 firmware which is on the SeemeCNC download page?
i.e.: smothed movement, probing etc.

[dtgriscom]

Well, I merged the ROSTOCK-MAX firmare with the latest 0.91.7 (plus a bit), and it works. And, the option to disable end stops indeed does allow moving below Z=0. But! neither the latest Windows nor latest Mac Repetier Host software displays negative Z values. So, I'm still where I was.


Oh, well...
Dan

[geneb]

...or better yet, back to the un-complicated method that works every time.

g.

[Eaglezsoar]

...or better yet, back to the un-complicated method that works every time.

g.

Gene, just to let you know, I used the calibration routine you put in the Orion Manual and in half an hour I had a perfectly calibrated printer.
Your routine works great without -Z's or any fancy whatchamacallits. Good job!

[geneb]

That's not my routine, Eagle. It's Andy's. He's the guy that has built every Orion that's gone out the door. I asked him to write his process up for me after I saw it in action at MRRF. I actually used it myself on Casper yesterday.

g.

[Eaglezsoar]

That's not my routine, Eagle. It's Andy's. He's the guy that has built every Orion that's gone out the door. I asked him to write his process up for me after I saw it in action at MRRF. I actually used it myself on Casper yesterday.

g.

Then my thanks go to Andy, imagine a process that is very effective, is not 14 steps long and contains no negative variables. Priceless.