Lead Screw Top Mount for Aluminum Extruded Printer Frames

There's quite a bit of controversy over whether it's beneficial to use a rigid top mount for FDM printer lead screws.  While, IMO, the short answer is solidly “no”, there are situations and setups that can benefit from having a top mount.  If your lead screws are not perfectly straight, and all three points of contact, the motor end, the X axis carrier, and top mount aren't in perfect alignment over the entire length of the lead screw, binding will occur and may cause Z banding or other obscure artifacts in your prints.  I say that because there are those who think mounting the top of the lead screws solidly to the frame is some kind of “silver bullet” fix for Z banding, while it certainly is NOT.

While a stock Creality Ender 3 comes with no upper lead screw mount and tends to print nicely without banding, adding a second lead screw corrects a multitude of sins, but can introduce Z banding especially towards the top of the Z axis, which is perhaps why most 2nd lead screw kits for the Ender 3 come with upper mounts for both lead screws.

Since most of my machines that have been upgraded with a second lead screw by using mostly 3D printed parts, I decided to model the style of upper mount that works best for me in most configurations.  I modeled this after the upper mount that was included with the single lead screw Tronxy XY-2 Pro.  This style upper mount sells on Amazon, typically from $6.00 to $9.00 a piece.  Meanwhile, it could be printed and completed for less than $1.00 in material, screw hardware, and bearing.

These are designed to use 68ZZ bearings with an ID of 8mm, OD of 16mm, and thickness of 5mm, but will work perfectly with the sealed 688-2RS bearings as well, either of which can be bought in bulk for less than 50 cents per unit.

In addition to the bearing, each of these mounts will require two M4x13mm screws with 4mm T-Nuts for connecting the mount to the frame, and two M3x20mm screws with M3 nuts for securing the bearing seat.

These will print as modeled in the STL files without any need for supports, although, I prefer to print the bulk of my printer upgrades with 100% infill, and of course did so for both pieces of this mount.  I print these in PETG, but so long as you're not using your machine in a heated enclosure, they should work fine printed in PLA.  If you are printing in a heated enclosure, Nylon, ABS, ASA, or PC would serve you better than PETG or PLA.

In a perfect world, Z stepper motors with permanently fixed lead screws would pair nicely with these upper mounts, but in my world, a world where I prefer not to sink outlandish amounts of money into my machines, I like to begin with a perfectly straight lead screw and use RIGID 5mm to 8mm couplings.  I've played with love joys and flexible couplings, even flexible couplings with an 8mm ball bearing within the flex, but I've found rigid couplings, like those shipping with the stock Ender 3 tend to work best for me.  Your mileage may vary…