I have a problem with dark globs at the start of a print.

3D Printing
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I have a problem with dark globs at the start of a print. As the hotend heats up, a little material oozes out. When the printer begins to print, that ooze is pushed to the side and sticks to the nozzle. It cooks dark and is usually deposited somewhere on the perimeter of the print. Sometimes I can scrape I off before it does harm but some day the hotend is going to catch my hand when I am doing that.

Makerfarm Prusa i3
J head 0.4mm
PLA (285) and ABS (225)

2

A lot of the ‘professional’ printers have a ‘priming’ series of steps to get the nozzle clear and primed and any boogers out of the system before it starts to print parts. Some hang the nozzle off the side of the build plate, some draw a long line around the perimeter…you might try adding a brim to your part

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I do print with a skirt but that only catches the glob sometimes. My last print accidentally had a skirt that used about 10cm of filament but it was too flat to catch on. I think the last big glob was dropped on the 3rd or 4th layers around a hole inlay.

Two ideas I thought of are to heat the hotend with z=-.01 to clog it up. The other was to start off the edge of the bed and try to scrape it off. I am not sure either of these are good ideas or will work.

An interesting thought, what about scraping the nozzle on a fine soft Brillo pad (can’t think of the real name right now…), like one would tin a soldering iron.

4
  1. Use a pair of needle nosed pliers to pinch the extruded extra filament off.
  2. Always print a “brim” it’s called in CURA. Others call it a “skirt”. This keeps the print from warping and let’s the nozzle get rid of any globs without an effect on the actual print.
    That’s what works for me.
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@Richard_Turnock A brim and skirt is different. A brim is attached to the part, a skirt is not, thus a skirt is probably what @Matt_Harrington wants in this case (unless you also want the extra adhesion that a brim provides).

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That won’t be a problem to solve, extrude a little filament before you print. And if it blocked frequently you should change a nozzle.

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i do a skirt and usually two passes and if theres junk still on it usually comes off when i use a file one the outside of the print to scrape off the hairs etc that are on the print

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@Oystein_Krog , yea I figure a 1 layer skirt and a brim will be similar in their ability to dislodge globs, but i can put the skirt far from the object.

@Alex_Cam , I’m not sure who you are replying to. Are you suggesting that one of these methods could result in a jam?

As a followup, I made a few adjustments that appear to be helping. I cleaned the bed real well, lowered the z a tad, and removed the default slic3r code that raises the z after homing and before heating.

I am hoping that, now that my printer is attached to a rigid surface, the z won’t go out of tram as often and this fix will continue to work.