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Foolproof way of starting a print?

Posted by alanbattersby 
Foolproof way of starting a print?
February 03, 2014 05:12PM
Hi,
I am having problems starting off my prints with the first layer using the standard 0.24 layer height. After that everything seems ok. I have mechanically levelled the bed using m3 x 20mm bolts as described on the web-site. I follow the instructions to set the head height as written on the website but do not seem to be able to get the printer head set correctly. My eyesight plus a fairly dark environment is not up to seeing when there is a small gap between the head and the base. So I I test by lowering the head until I can just pass a 0.5mm shim under the head, then set the height to 0.5mm. When I do this the head tends to be too low and the extruder stepper stutters and produces a blobby output. If I set the head height to 0.2 mm when touching the shim (to give me 0.3mm wiggle room) then the first layer does not stick. What should I set the head too, is this really critical?

Alan
Re: Foolproof way of starting a print?
February 03, 2014 05:22PM
Heat the bed to operating temperature, then level the bed mechanically or automatically or both. Heat the nozzle to 180C and wipe off any PLA sticking to the bottom if the nozzle. Then put the head at X=100 Y=100. Put a sheet of 80gsm copier paper under the head, lower the head until it just grips the paper quite firmly, then do G92 Z0. [Or you could use your shim at this point.] Then raise the head a little, then print.

The only time I had a recurring problem with the first layer sticking, it was down to using a different make of filament.



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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Foolproof way of starting a print?
February 03, 2014 05:35PM
Hi Alan - I normally print things with a footprint of around 50-60mm diameter, placed centrally on the bed, and I set zero on my Z using a piece of paper (0.1mm thick) lowering the head until I start to feel dragging. I then used to remove the paper and lower the head a further 0.1mm (which worked OK) but now use the fan buzz feeling (I think ormerod 168 pointed this out, but I may be wrong) - and lower it until I can feel/hear the fan vibration as I drag the paper - I then leave that as the home height and this works very reliably. I do the Z zeroing at X=100, y=100, since most of my printing is within 30mm of that point.

I think even with good eyesight it's hard to tell when a shiny thing is just about touching another shiny thing with another shiny layer below that smiling smiley

I don't normally use bed compensation (and haven't used the z probe for quite a while) and wondered whether these may interfere - but I did do manually bed compensation today followed by zeroing using the buzzing method above, and printed a 185 by 155 object (I was quite surprised to be able to get it to print, I definitely needed the compensation to help me out without rebuilding the bed!) It did blob a little on the first perimeter (slicer wouldn't let me add my default skirt, since it would have gone outside of the print area), and the first solid layer was uneven in places, but the unevenness averaged out after a couple of layers.

Also I chickened out on this print and used PLA instead of ABS, and got no curling whatsoever at the corners - I was very impressed, if not shocked that the machine did so well.

Ray
Re: Foolproof way of starting a print?
February 03, 2014 06:05PM
Ive actually noticed that my prints differ from using the web interface and prontrface.
on prontrface i was using the paper dragging method and everything was fine, but now when im using the web interface i done exactly the same as normal but the first layer is too high (0.24) and wont stick.

What i do now is the same paper drag as always, then lower by 0.2 and zero there. When i print they stick perfectly and the nozzle doesn't drag on the bed.

I suppose that i am printing my first layer at 0.4 height which i could probably set in slic3r?
Re: Foolproof way of starting a print?
February 03, 2014 06:14PM
The output from slic3r tells the printer to lower the head to 0.24mm (or whatever first layer height you have set) at the start of the print. So you really want to set Z=0 when the head really is touching the bed, or is even a little lower (i.e. the bed is lifting the head slightly) so that the head is a little lower than 0.24mm when the first layer is printed and you get a nice squished first layer. That's why when I lower the head. I wait until it grips the paper firmly (which is typically 0.1mm lower than when it first starts gripping the paper) before defining that as Z=0. Alternatively, you could set Z=0.1 or 0.15 when the head just grips the paper.



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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Foolproof way of starting a print?
February 04, 2014 08:24AM
Thanks everyone the paper trick worked a treat.

Alan
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