Calibrating Mendel

I finally got my Mendel built, but I'm running into a ton of trouble trying to calibrate the thing. I can't seem to find any definitive guides that tells me what values I need to change to get this working. Every guide I've come across so far pretty much says to "print this model to calibrate" without actually telling me how to calibrate. When several dozen values with obscure names in both the firmware and the preference files are thrown at me, I'm sort of at a loss.

I tried to print the models found here:
[www.thingiverse.com]

I'm using the RepRap java host on a Windows 7 machine.

I tried to print the single walled test piece, but the model wouldn't print (the RepRap just stood at home and raised the z-axis, then told me its done). I tried to print the 20x20mm cube, and that actually printed. The result was a cube that's 27x27x10mm. Quite a ways off from perfect.

The issue is that when I move the axes manually through the software, they go almost exactly where they're supposed to. Setting X to move 20mm actually moved it 20mm. It's the same with the Z-axis as well, despite the model turning out to be a half the height of it's expected size.

So what do I do? I'm getting mixed answers online about what to change and where to change it. Do the values in the RepRap Java Host matter? Some say that those values are pretty much ignored by the machine, and that the values in the configuration.h file for the firmware must be modified. I'm also getting told that I have to change it in both, which makes absolutely no sense to me at all. The only values I can imagine would fix things is the (steps/mm) values, but my RepRap is moving at almost exactly the perfect distances when I move it manually and fails when I try to print.

Edited 1 time(s). Last edit at 06/05/2010 03:17PM by Katai.

If you are sending g-code to the firmware then the g-code commands are in mm, so the steps to mm conversion has to be done in the firmware and not by the host. Crazy, I know, but that is g-code for you.

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[www.hydraraptor.blogspot.com]

Another issue. When the Reprap starts building the cube, it's supposed to draw a square outline first, right? Because mine isn't doing that. It just sits in one corner and extrudes a blob, then does the zig-zag motion to fill the inside of the cube.

This is a guess, because I don't have a printer yet, but maybe that blob issue means something's up with skeinforge? Maybe you need to go and check your output from that, or the gcode (again talking out of my ass).

Some links (in case you haven't seen them)
Config_Axes
Config_Extruder

I remember a wiki page that had some pictures of the different extruder settings as a kind of how to for calibration, but I can't find it right now.

Katai Wrote:
-------------------------------------------------------
> Another issue. When the Reprap starts building
> the cube, it's supposed to draw a square outline
> first, right? Because mine isn't doing that. It
> just sits in one corner and extrudes a blob, then
> does the zig-zag motion to fill the inside of the
> cube.

That is part of cleaning the extruder nozzle. That is why on the stable mendel version there is a notch on the build platform. Are you using the reprap host?

Yes, I'm using the RepRap Host. I don't think it's cleaning the extruder nozzle. It extrudes this blob for each layer. The machine doesn't go anywhere near the notch in the build platform.

Make sure you have the correct firmware and re-download reprap host and dont touch any settings.
Then try.

And remember,dont just open the .stl file and hit print, you have to make gcode first.

You are saving the .stl to gcode file first right? I think we got strange results the first time too but we didnt remember to open the stl and "print to gcode file", then open the gcode file and print.

I don't see why that should make a difference to the printing using the RepRap Host software, as it is the same G-Code generated by print to file as used in the print to printer.

David

I agree that building a mendel printer which prints something is difficult but good calibration manuals are missing.
After my Mendel was able to print a rough form I adapted the settings in the firmware.
Then I constructed a writing pen holder which could draw on paper XY plane. I used a simple G code which was in fact a grid of squares (100x 100 mm)
The printer printed the squares and after measuring them I could correct them quite good. Now I know that the extruder nozzle is calibrated in the XY plane.
Using this method I thought makes sure that the influence of wrong temperatures, thicker or thinner threads of melted plastic have influence. Has anybody used the same method?
I plan to do this also for the Z direction. By the way I am still not happy with the print quality delivered by the Mendel.
Small details are messy and a vertical wall is has not a very nice smooth surface.
Also I wonder is there is a big difference between the g code generated by Repsnapper (which I use) of Skeinforge ?

Early on I followed this path. Host software with gen 3 electronics. 20mm cube barely looked like a cube if it would print at all. Errors all the time when trying to communicate between the PC and Gen 3, extruder jammed a lot... tried to manualy write gcode to debug...

I discovered the following:
Host software is poorly written and won't reliabiliy work with gen 3 - adopted newer code
Gen 3 is under powered and can't keep up with the 31mm/sec extruder speed - went to ramps
home made nozzles don't work - buy from makerbot or the like.

Result is no more fighting with the printer leaving more time to design better parts.

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