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What is backlash in 3D printing?

Nov 15 2015
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The cause

Many problems with printing in 3D stems from backlash. It is caused by anything that introduces some looseness, play or springiness in the x and y axes.

In the image below you can see gaps between the perimeter lines, often also between perimeter and infill and between the infill itself. You can see that the infill lines are grouped in pairs. This is a typical sign of backlash.

What often happens is that one tries to increase the extrusion to cover up the holes caused by backlash. This will cause some serious over extrusion of around 15%. In the image below you can see that the perimeters are more or less ok, but the infill is completely over extruded in a bid to cover up the gaps.

The solution

To solve the problem, first lower the extrusion to the point it doesn't over extrude the infill. Grab hold of the x motor and wiggle the (unheated!) hot end with your other hand. Do you feel any play? Any springiness? You can tighten all the nuts, the belts to the point it gives a high pitched sound when you fiddle with it. It may be that the printed idlers break. Try finding some more solid objects on thingiverse or replace it with brass. I've done the last and it hasn't failed since.

Now grab hold of the y axis motor and wiggle the print bed. Also wiggle it up and down. Beds with three mounting points for easy levelling are susceptible for up and down motions as they are not well supported in the two corners where the triangle of the mounting points has just a single mount. This can be solved by buying a really flat and solid aluminium y-carriage. Make sure you get it in as level as possible and use auto bed levelling to level it completely. Also tighten all the nuts on the y carriage, make sure the mount is solidly in place. It often comes loose if no loc-tight or nyloc nuts are used.

After you've made sure everything is as tight as possible, you can try calibrating the extrusion multiplier again. This time the infill lines should be nice and evenly spaced. At this point infill and perimeters should be equally well covering the previous layer.

Some thoughts

It could be that there's some significant excessive extrusion noticeable in the corners of the infill. This can be caused by a few things.

  • The bed bounces up and down at every direction change of the bed, the unsupported corner dips and comes up like a spring motion. In the image above you can see this effect in the corners of the object, the lines are squiggly. This gives the nozzle more room and less resistance and extrudes depending on the height of the bounce of the bed.
  • You may need to calibrate Vxy-jerk setting. If you print at speeds significantly faster than this speed setting, the corners will be printed slower. Since the nozzle pressure can't change instantly, it will extrude more in the corners. If the nozzle can keep moving at the same pace or close to it, it will extrude more evenly in the corners.
  • Slic3r 1.2.8 and 1.2.9 have an issue with thin walls of about 2mm. The gap infill may extrude too much filament causing it to build up layer after layer. Use Slic3r 1.2.7 or earlier for correct gap infill.

Last changed: Nov 15 2015 at 7:12 PM

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