X, Y, Z Axis details - Part 1

A project log for Monoprice Select Mini Electro-Mechanical Upgrades

Endeavoring to build upon the existing fanbase work of this $200-ish printer.

Michael O'BrienMichael O'Brien 08/26/2016 at 02:510 Comments

Note 1: I capitalize "X-axis", "Z-height" and the like for legibility when scanning/skimming; pedants can hate me later.

Note 2: This is part one where measurements and construction details of the mechanical structure are listed. Idealistic modifications are in Part 2.

Disclaimer: Due to human error but mostly manufacturing tolerances, the following apply.

Hey, the title for the project is 'Electro-mechnical' so it's about time I make good on the latter half, no? Before anything can be modded, we need to have a close look at what the mechanical structure is and then adjustments can be made from there.

So the M200 printer went through a couple of revisions more likely than not. We know that the electronics were built to a cost and possibly the hardware was too. There haven't been any major problems that result from it's industrial design, but is there evidence of slimming the cost of parts?

I want to bump any and all of the 3 axis to larger dimensions so this Mini can print larger than mini, so lets take a closer look at the axis construction. The Z-axis & A-axis are where we have custom parts that if you irreparably damage, you'd have to buy a new printer or hope someone can print replacements, which no one has dropped into CAD yet. We have graphite composite for these pieces to assure rigidity and thermal resistance; especially since the X-axis motor mounts to the Z-axis carriage. This latter portion I'll touch on after listing a few details of the linear shafts used.

There are 7 shafts, 2 belts, and 1 threaded rod that are responsible for the physical movement of the printer, excluding eh extruder. Here are their details:

Stock Z-axis

The Z-axis carriage has space for 3 linear bearings, all of which are LM6LUU's, which are basically 2 LM6UU's stacked end-to-end. Two of these bearings are sitting closest to the printer bed to provide additional riidity as this is the natural fulcrum of the A-axis arm. The third is by its lonesome self near the Z-axis limit switch. For the front two, the composite has a thickness of 17-17.75 mm and the rear has a thickness of ~20 mm.

The mounts for the shafts are relatively simple pieces of steel with press-fit hex stand off nuts. Their purpose is to prevent radial movement of the shafts. There is a rattle in the printer since there is no axial play prevention from the mounts. If you look closely though, the front mount brackets have a width of about 9 mm. However, the rear mount brackets has a width of 11 mm. Given the symmetry of these differences and the Z-axis carrier, I'm willing to bet that an 8 mm rod was used in the back at some point in the design and they just never adjusted the carrier's mold.