Backlash!

Even if your printer is supposed to print “right out of the box,” chances are there is a thing or two you are going to have to adjust if you want to dial in perfect (well, near perfect) prints. For me, it was backlash.

Backlash is the result of play (or “slop”) between the gears, threads, and belts of your printer. It is unavoidable, as these meshing parts need a little extra space between them so that they can move–without that space, your printing would literally grind to a halt.

The problem is that this space is going to vary a bit with manufacturer’s tolerances and if you don’t account for it accurately, your prints can come out looking pretty bad. Fortunately, figuring out where your trouble is and adjusting for it is not really that difficult.

In the x-y planes, your print is effected by backlash in the following way: your printer’s software instructs the hot-end to move to a location while depositing material–the printer spins a rod, which turns a gear, which then moves a belt. If the hot-end is moving in one direction, things are usually fine because there is constant pressure from, say, the gear onto the belt… problems generally arise, however, when the software asks the printer to change directions and there is some amount of play (space) between the meshing surfaces that the software hasn’t accounted for.

The result is that the first part in the sequence will move a little without actually touching the next part in the sequence. Granted, this is a small amount of movement but it is enough to effect the final result… the movement of the hot-end is different than the software directed and the material doesn’t go exactly where it is supposed to.

Problems with backlash are most easily identified on circular items. Notice above (left), on my first printed part (a light switch dimmer knob), the separation/deformation at 5 and 11 o’clock. On the underside (right), note how the cylinder is much more oval than it should be, again slanting downwards at 5 0’clock and upwards at 11 0’clock.

When printing a circle, your printer changes direction twice through the x-axis and twice through the y-axis. My printer seems to print circles in a counter clock-wise direction and so, if it starts printing the circle at 3 o’clock, my printer pushes the print-head towards the back through the y-axis and to the left through the x-axis. Once the print-head reaches 12 o’clock however, it changes direction for the first time (in the y-axis only), opening up the possibility that the space between the gears and belts will open up space between the printed plastic beads being laid down by the hot-end.

Again, you will change direction four times in a circle, in one plane at a time. You will change direction in the y-plane at 6 and 12 o’clock and in the x-plane at 3 and 9 o’clock. Any deformities due to backlash calibration errors will present just after these changes in direction are supposed take place…

I found that the problem was most easily identified in the backlash calibration test print (above) where you can really start to visualize the hot-end being “instructed” to change y-axis direction by the g-code at 12 o’clock but actual execution is not realized until it reaches about half-way to 11 o’clock–opening up the relatively large gap you see as the hot-end was allowed to run in a straight line across the x-axis during the backlash moment. My particular printer was mis-calibrated in the y-axis only, if it had been mis-calibrated in the x-axis as well you would have seen gaps like those shown above at both 2 and 8 o’clock as well.

Addressing this issue was a relatively simple, albeit a trail-and-error process. I just needed to tell my printer how much slack to account for. An important note… it will help if you can discover (online or through contact with the manufacturer of your printer) the ranges within which the correct settings will probably fall (the ranges will probably be different for each axis). This will give you some parameters within which to estimate your changes.

I went to M3D for help with my Micro printer and this is where I found both the ranges and a downloadable test print (in .stl format) so that I could gauge both the degree of my problem and my progress as I made adjustments. I think that the test file might be of help on any printer, though I imagine the setting ranges will probably be different for every manufacturer’s printer.

My first attempt closed a good part of the gap (above left) but it took a couple more tries to get to just the right settings (above right) and a near perfect circle. Ultimately, I was pleased how easy this was to address. I simply downloaded the test print, printed it, and gradually increased the amount of backlash my settings were accounting for until the gap had completely closed. It only took four prints, including the first test print.

One other note; I only had to adjust my y-axis settings but it is possible that you may have to adjust both or make changes to one only after adjusting the other. I would suggest making changes in only one axis at at time, adjusting the setting that appears the furthest out.

So there you have it. When I first noticed my printer had this issue, I wondered if I had damaged it during set-up or if it needed to be sent back and serviced. After about 10 minutes googling “I can’t print round circles,” and discovering my problem lay in the backlash settings, I was completely relieved. And I really was pleased how easy it was to adjust. I hope your adjustments go as smoothly.