Printrbot Simple, 300mm Y Axis-No Sag!

Author: iamjonlawrence, published on 2014-02-09

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Upgrade your Y axis to 300 mm (12″) or more or less, GT2 belt drive, and eliminate Y-Sag in one mod…

  • I upgraded to 300 mm capacity here only because I had a piece of 8 mm rod 915 mm (36″) long and didn’t want to waste it. Not to mention “just because I can.” I am currently only using 150 mm to reach the edge of my 6″ heat bed, but have run it all the way out and it is extremely stable over the entire distance. Rod & belt lengths can be adjusted to whatever you dare. Only requirement is that the lower rod is 50 mm (2″) longer than the top.
  • Increased linear bearing centers from the stock 24 mm to 64 mm. What this means is 3x the overhang possible, effectively eliminating Y-sag common to the Simple. I was surprised at how solid the Y axis is now.
  • Designed to hold stock wooden direct drive extruder. Not tested with aluminum DDE.


  • 95 mm x 95 mm print area
  • The ability to print FLAT without edges lifting
  • Well calibrated printer
  • GT2 20 tooth belt pulley. 18 tooth will not clear bearing
  • Z axis Hex nut to measure 1/2″ across flats
  • Y/X axis at 90 degrees.

2014-02-19, REV.B: Added ZScrewMount for printers purchased after 10/23/2013 where they changed the Z screw assembly. Also changed Z Endstop Extension to a better design.

2014-03-17, REV.C: Modified Z nut mounting to accomodate ACME nut. Uploaded new version of ExtendYPlate.stl as ExtendYPlateRevC.stl.

2014-03-23: Uploaded front plate for 2014 Simple fan and aluminum extruder. “ExtendYFront2014AlExtruder.stl”

2014-03-24: Uploaded front plate for 2014 Simple, Fan, Aluminum extruder, and Cable management. “ExtendYFront2014AlExtruderCable.STL”

2014-03-25: Updated “ExtendYFront2014ExtruderCable.stl” to “ExtendYFront2014ExtruderCableRevA.stl” which includes mounting for a bolt on fan duct extension. Also uploaded “ExtendYFanDuct.stl” as the extension piece for the fan duct.

2014-04-02: Uploaded a version of the front end for the 2013 Simple that includes a side mounted fan like the 2014. “ExtendYFront2013Fan.slt” Use with “ExtendYFanDuct.stl”

2014-04-07: Uploaded a version of the rear end that allows the use of identical length rods. With this rear end the rod lengths need to be at least 175mm longer than your desired stroke.

2014-04-14: Uploaded an updated version of the end stop flag RevA. This will allow you to insert the belt thru the flag and remove some of the belt vibration.

2014-04-17: Uploaded an updated version of the front end for the aluminum extruder that includes some extra supports. “ExtendYFront2014AlExtruderRevA.stl”

2014-05-11: Uploaded a version of the rear end that uses a clamp to secure the rods, and allows the upper rod to pass thru, so equal length rods can be used. “ExtendYRearClamp.stl”

This design was inspired by kingfuroy’s Modified Simple

Feedback is strongly encouraged.


  • Drill out the 8mm rod holes to clean up. Do not drill thru. I actually used a 5/16″ bit (didn’t have an 8mm) and just wiggled it a bit to oversize the hole to 8mm-ish. The rods press in nice and tight.
  • Reuse Z stop screw & mounting blocks.


  • Install extruder end of GT2 belt before mounting extruder. It is really difficult to reach afterwords.
  • To locate the drive pulley, slide the pulley on the shaft but do not tighten the set screws (grub screws). Thread the belt and just hold tension by hand. Slide the axis by hand and the pulley will spin on the shaft and locate itself. Tighten the screws to lock it in.
  • To get belt length correct, thread belt thru machine and thru rear tension block. Mark where the belt exits the rear tension block and cut belt 10-20mm past that point to give enough length to fold over. Slip belt off 608 bearing. This will give you enough length to fold on your mark and insert belt back in tension block.
  • Don’t go crazy tightening the bearing block screws. Just snug them up. The part geometry will hold the bearings with very little screw force.
  • Use “M208 Y300” or “M211 Y300” to increase preset limits. If neither of these work you may need to flash your firmware with the “Marlin Unified V2” firmware then use “M211 Y300”. Follow the guide published by Printrbot at:

License: Creative Commons – Attribution – Non-Commercial

Tags: Extension, GT2, Printrbot, Printrbot_Simple, Sag, Simple, V2, Y, Y-Sag