An Honest Review of the Mbot Grid II

My Background: Retired tool and die maker, Model railroad hobbyist. I purchased the Grid II figuring that it would a nice tool to build structures for the model railroad and right from the start nothing but problems, most I might add I have solved. The unit I received was poorly constructed in that a lot of the hardware was never properly tightened the extruder heads were loose on the carriage, the X axis belt was never properly tightened, the offsets in X and Z weren’t properly set causing many problems and the X axis limit switch wasn’t working properly as the wires connected to it were severed under the heat shrink. In stead of using the leveling routine I used the jog mode and a digital drop indicator in this manner I can get the build plate to within a couple thousandths of an inch I can’t get it perfectly level as the build plate has a couple thousandths bow in it when I checked it on a granite inspection table at a machine shop using a digital height indicator. I only use the leveling routine for the last part to set the extruder height which I use a 1 thousandths feeler gauge. The offset from the Z axis limit switch to the height of the extruder tip to the build table is 1mm, so I set the Z axis offset to .8mm seeing that the extruder tip is .4mm I figured half of that or .2mm would be a good starting point and it has worked out very well.
Types of filament: I’ve found that PLA works out extremely well, but ABS is total waste of time with out a heated build platform. I found that right at the 2mm print height the ABS would start to curl and the extruder would knock the print off the build table every time.
Durability of the unit: As it stands right now I’ve run 3 x 2.2kg spools of PLA through this printer and signs of appreciable wear are very apparent on the guide bushings for the Y axis there is 25 thousandths of play in them which playing havoc with the clearance of the extruder tip to the print as it moves around.
Accuracy: According to the sales pitch this unit should be capable of holding a .1mm tolerance which my world is 4 thousandths of an inch. Just before sitting down to write this review I printed 2 objects and gave it a fighting chance by slowing down the feed rates and using the highest quality print setting. The results are as follows. A 1/2 inch cube, X measures at .510, Y measures at .510 and Z measures at .493. The second shape is a 1 inch octagon 1/2 thick, the results are as follows. Measuring across the flats, .994, 1.002, 1.002 and .990. The 1/2 thickness ranges from .488 to .497 .
Summary: Until they start producing printers with direct drive lead screws in all axises and sintered bushings and get rid of the plastic bushings and rubber band drives mechanisms your pretty much looking at a moderately expensive toy, which is OK, as it does make decent prints as long as you know where to cheat in the dimensions.
Just my 2 cents worth which is about all it’s worth.

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