Z-Axis too high when printing

I'm finding that after zeroing the z axis when I start a print, it can start 1-2mm too high.
Firstly at the beginning of a print, when the carriage goes back to the x-axis, can this change the figures?
Are there codes to receive from the printer the z-comp value and the automatic bed setting values.

I'm not keen on using the z-probe having these problems, but have sent g92z0 and then used the probe to set the bed. Presumably I should set the bed manually. Does the probe just work out the difference and take it away from the set z figure or a probe figure? I'm sure things are getting complicated. By I have produced a 2 layer snowman !!!

Is it normal to get motor chattering/grinding on x at the beginning of the print? It seems to dislike going to the tab without obstruction. Just past it us smooth.
I really like the z-probing, but it seems awkward. A mechanical version would be good similar in position to the x tab, looked like a mechanical endstop, but gave variable readings.

Re x-axis chattering, try putting a bit of white tape on the x-axis homing tab. Also check that the x-carriage can slide past the Z extrusion - I had to file away some protrusions on my x-carriage.

I strongly recommend you use the manual bed levelling mechanism to get the bed flat - but you need three 16mm M3 screws to do this. Don't bother supporting the front two corners of the bed, just screw the heater pcb and heat spreader together here. After you have done that, you can do one of two things:

1. Use the z-homing and auto bed-levelling, but make sure there is very little sunlight or incandescent artificial light when you do this (and when you calibrate the G31 value).

2. Or put the nozzle at x=100 y=100, manually drop the nozzle until just above the bed, and send G92 Z0.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks. I think I'll have to take the manual option, I can do the white tape now.

The other problem, is that at times it prevents me from setting the z to zero and continues to report a plus or minus figure and ignores the G92 command. Any idea what does this?

@ Jamesr10, you'll need to edit the config.g to set you actual probe offset (if you haven't lready done so)

Ray

Quote
JamesR10
The other problem, is that at times it prevents me from setting the z to zero and continues to report a plus or minus figure and ignores the G92 command. Any idea what does this?

If you have already run bed compensation, then when you enter G92 Z0 it seems to apply the compensation and "correct" the value you set. Hopefully this will get fixed soon (I may even take a look at it myself). Also, there is a bug in older versions of the firmware whereby leading zeros after the decimal point get omitted, e.g. 0.02mm is reported as 0.20mm.

Edited 2 time(s). Last edit at 01/18/2014 07:10AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Well I've had some success. I put the white tape on but actually zeroed the x at z100. It went through silently. But basically I didn't run the bed levelling at all. So it allowed my g92 z value. But I'll want to sort it out.
Should the snowman be just 2mm thick? The outside doesn't ring falls apart, but it barely prints it. But it's a pretty reasonable success. There's hope!!!

So it doesn't actually keep the probe setting unless you put it in the config manually as well. Ok.
Nevertheless the probe is up in the air at the moment. I think manual setting is where it's at and then you can play with the probe.

Cheers guys. Gonna order some bolts. But it's a decent effort, thanks for the help.

Oh, my hotbed got up to 65 deg, so I turned it off for a couple of minutes near the start if the print. Can the software not act as a thermostat to control this better.

1. AFAIR the snowman is about 5mm thick. You can tell if the print has finished normally, because the bed moves the print away from the print head and the heaters are turned off.

2. The original IR probe is very sensitive to ambient light. Fluorescent and LED light are OK, bright sunlight and incandescent light are not. I have a prototype modulated sensor to alleviate this, and RRP are working on one too. Print head sagging also affects the calibration of the probe, and using the original nozzle mount, I found that my print head was sagging after a few prints.

EDIT: actually that snowman looks OK to me. Maybe I was wrong about the thickness.

Edited 1 time(s). Last edit at 01/18/2014 08:05AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks. I'd be interested to know about the snowman thickness. But I might have a go at an eggcup. It should be a bit of a clue as to whether there was anything wrong. I stopped it when the nozzle mount went back to x. I just have a energy saving bulb, which it fluorescent I think.
I know I fitted a 15mm laser cut ply disc which has a slot in it to balance the nozzle. The bearing was too small. So I'll be on the look out for sagging.
Anyway, thanks for the help.
It might be perfect by this time next week.

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Edited 1 time(s). Last edit at 01/18/2014 10:13AM by victors.

Hi JamesR10

If you upload snowman.g to [gcode.ws] you'll see the gcode rendered. If you look at the Model info, it says Model size is: 59.32x63.18x2.16mm (it doesn't count the first layer). So 2.4mm is right, not 5mm. It should be 10 layers, with 0.24mm layer height.

Just looked at the gcode for the first time. 0.85mm extrusion width! That explains why the hat doesn't infill properly... I'll have to get Adrian to reslice it. And put something less Christmassy, and more 3D (the snowman is a 2D extrusion) in as an example piece!

Ian
RepRapPro tech support

Well Valentine's day is next up then over to bunnies and eggs!

I thought that about Easter eggs. I tried out printing an egg cup to check the height, but fan base started getting caught, so looks like I might have to use some washers. Though I'm not sure anyone has said anything about the nozzle needing to be x about lower than the duct, I guess technically they should be parallel.