Dimensional Accuracy Biased Too Big XY

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Maxparker72
Posts: 5
Joined: Tue Apr 30, 2019 10:41 pm

Dimensional Accuracy Biased Too Big XY

Post by Maxparker72 » Tue Jul 09, 2019 11:47 pm

Hey Guys!

So, I have a second hand Lulzbot mini and I am still trying to get familiar with the printer. First, I do want to ask opinions on calibration/what to check since it's second hand. Secondly, I am puzzled by a recent experiment I performed. I printed 12 20mm test cubes and recorded their actual dimensions with calipers in excel. My goal was to find an average dimensional error so I could determine my printer's accuracy (eg: my printer can print to +/- 0.15mm). Instead, I found that my printer was pretty consistent but not accurate. My X axis was biased too large while my Z is biased too small. It might be easier to take a look at the screenshot I attached to see what's going on. I'm curious if this is normal, just my printer, all lulzbot minis, or if there is something I can tweak physically or in software.

I appreciate the help. Thanks!
Attachments
Screen Shot 2019-07-09 at 10.49.54 PM.png

nopick
Posts: 1010
Joined: Mon Sep 09, 2013 11:14 am

Re: Dimensional Accuracy Biased Too Big XY

Post by nopick » Wed Jul 10, 2019 6:48 am

For the X and Y, I would start with an extruder calibration. Over extrusion will produce a part larger that the design size. Make sure you are actually extruding 100mm when you command a 100mm extrusion. Adjust your ESTEPS value to correct over or under extrusion. If the extruder is moving the correct amount of filament, you can tweak the flow rate for a given filament in the slicer. Here is an info page about adjusting steps per mm from terminal commands if you don't have an LCD display on the Mini. http://marlinfw.org/docs/gcode/M092.html

Your Z measurements look pretty good. For my purposes, I wouldn't worry about it. If you want to try to dial that better than what it is, I would suggest getting X and Y corrected and see what happens to Z. Z steps per mm can also be tweaked with M092 but you might find yourself chasing the mechanical limits of the machine.

Keebie81
Posts: 114
Joined: Sat Dec 20, 2014 12:53 pm

Re: Dimensional Accuracy Biased Too Big XY

Post by Keebie81 » Fri Jul 12, 2019 4:48 pm

The issue is the mini 1 and taz6 and lower all use 100.5 steps/mm on x and y. It should be 100, the mini2 uses 100 now.

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