hot end sometimes scrapes

I don't seem to be able to stop my hot end dragging on my print, when it works well it just drags a little but sometimes the first layer will be basicly 0mm tall or the hotend will drag on highere layers so much that it stops the x carnage.

I am using a techzone Huxley but with RAMPS with marlin and a jhead (or a Chinese version anyway, but I seem to have got a good one). My software is mattercontrol

just doesn't seem to be consistent, sometimes I do the auto print levelling and everything works ok with only a little dragging and the next time I go to print it extrudes with the hotend pressed against the build platform! in this case I have tried winding the z stop up a bit and that helps for the first layer but the hot end ends up dragging a lot and sooner or later caused it to fail.

Sounds like it's putting out too much plastic, pictures of prints where it scrapes?
Have you properly calibrated your e-steps and extrusion multiplier?

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

I've measured the e-steps several times, not sure about the extrusion multiplier but that wouldn't be the cause of the hot end scraping against the bed on the very first layer. I think it may be more that perhaps my Z is not moving enough during a print. I've set the max z speed and I thought that was all I needed, could the current to the motor be too low and sometimes missing steps?

Edited 1 time(s). Last edit at 06/13/2014 08:55AM by mrkaras.

I haven't done any auto Z calibration, but from my ignorant knowledge it only helps on the print it is auto leveled for? I didn't think it was a solid set one time thing. In my personal, personal opinion, a well leveled and calibrated bed is superior to an auto leveled bed in reliability.
You would hear if your motor was skipping steps, even when the current was super low [basically nothing, but not dead zone of pot] it's always been really obvious to me my motors are skipping steps. I can hear it in another room [some lost sleep, but at least I could catch it before it wasted too much plastic]. Now other motors and setups may be different.
I would tune your bed manually and see if that helps. Could be a whole other problem, like I said, I've no real knowledge about auto leveling.

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

adjusting the current didn't seem to do anything, attached is a photo and a video, see the wobble as it hits and scrapes. in this case it was running off the 0 end of the bed because it had hit and lost its position

To me it looks like there is too much plastic coming out. Either the Z axis isn't going up as much as it should be, or there is too much plastic coming out. I have bed autoleveling. When setup properly it gives a first layer that is perfectly level and at the correct height. You definetly will have to calibrate Z axis steps whether you use autoleveling or not.

Edited 1 time(s). Last edit at 06/14/2014 04:04AM by TheTechnicalNoob.

I'll see what I can do to reduce the amount of plastic coming out, perhaps the extrusion multiplier as mentioned earlier. I have already calibrated the Z axis steps and hen I manually move it up 10mm I can measure that it is in fact 10mm.

only one run done so far, but I set the extrusion multiplier to 0.7 and it looks like it might be OK. and possibly the bed scraping part may be related to where the z is at the start, I read somewhere about somebody having differences where the end stop was already engaged, not sure but perhaps its related to my problem too.

You can use the M119 command in the pronterface command line. It will report back the status of the endstop swithches (closed or open). I manually spin the rods on my printer to lift z a bit when I think the z is too low, so I can see what difference it makes.

I just realized I got this squashed hole, doesn't that indicate z is not moving enough? reducing the flow does seem to help with the hitting but I'm thinking it may not be the right solution given the shape of this hole? when I press the button to move 10mm it always does and there seems to be no backlash or free play with the motor so I don't see how this can happen. I had noticed a previous print seemed shorter than I expected but didn't have a measurement of what it should be so weren't sure.

I have manualy spun the z axis up in the past but I try to avoid it because that tends to unscrew things and the bed get out of level in relation to the X

Edited 1 time(s). Last edit at 06/15/2014 09:38AM by mrkaras.

Don't worry about the hole until you have the rest working ok. The way your prints currently look you can't determine if the z-axis is working correctly or not.

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I have the same problem and I also have a Huxley. My problem seems to happen because some parts seem to get much higher then they should; see attached picture to see what I mean.
I have tried different temperatures but nothing helped. This is PLA b.t.w..

Might this be the same problem as OP?

Edited 1 time(s). Last edit at 06/21/2014 03:23PM by roady001.

Quote
roady001
I have the same problem and I also have a Huxley. My problem seems to happen because some parts seem to get much higher then they should; see attached picture to see what I mean.
I have tried different temperatures but nothing helped. This is PLA b.t.w..

Might this be the same problem as OP?

The lifting at the corners that you are seeing is due to too little cooling. Try a big fan blowing while printing, and it will go away.

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Mike Anton
[manton.ca]
[laserlight.wikidot.com]

Confirmed: Indeed cooling fixed the curling problem.
Also, I noticed the x-axis belt was getting more slack than it used to be, causing slipping to occur much more easily. I tightened the belt, added cooling and now my problems are fixed.