The i2 contains a radical change to the Z axis, and a new controller board - the Sainsmart 2 in 1.
The Z axis motor is now positioned inverted underneath the power supply and drives the right Z axis threaded rod with a closed loop pulley. In turn, that right Z axis threaded rod drives the left Z axis rod with another closed loop belt. As with the i1, the two threaded rods remain in physical sync eliminating bed leveling problems.
The pulley on the Z axis motor is 16 tooth driving a 20 tooth pulley on the threaded rod, a 4:5 ratio reduction. The threaded rod is an 8mm with 1.25mm travel per rotation. With the 4:5 reduction, each revolution of the stepper motor results in a 1mm lift on the Z axis. The beauty of this is that the Z axis can run all the way down to 0.005 resolution while moving only full steps on the stepper motor totally eliminating microstepping from the Z axis resolution. No matter what the layer height is, it will always be in full step increments, guaranteeing that all layers will be exactly the same height, which microstepping can not guarantee.
Usually I would run from a Sainsmart product. But the 2in1 is actually "Betterthanramps". It has screw-in terminals for the motors, which means wiring can be cut to exact length. I crimp non-insulated 18 AWG ferrules on the wires for connection. The 2in1 is 1/32 capable with DRV8825 steppers. Although DRV8825 can be used on a RAMPS 1.4, the RAMPS itself does not actually support 1/32 stepping while the 2in1 has the 2 extra jumper pins for 1/32 stepping. The board is compact, with the arduino and ramps built into one board. I have 5 of these running and have to admit - Sainsmart finally did something right (in spite of little documentation). Another plus of this compact board is that I can place it 10mm away from it's mount plate allowing the fan air stream to pass over the top of the board and exit behind the board, thereby cooling the traces on the back of the board (4th picture below).
The i2 also has an LCD controller, the compact AZSMZ LCD. This is produced by the same guy who offers the AZSMZ controller with the 32 bit processor (a $53 Smoothie) He is a pleasure to work with and welcomes suggestions.
START i2 Pictures:
END i2 Pictures
The concept behind the OneZ is the elimination of bed leveling problems inherent in Cartesian designs. Instead of using a so-called "auto-bed leveling" scheme I decided to eliminate the cause of level creep - the inability to keep two Z motors in sync. NEMA 17 motors are not manufactured to Hadron Collider specs for $70,000 ea, they are manufactured a thousand miles up the Yangtze River by a guy with an 8th grade education for $8 ea. That's what we want. Consequentially, all NEMA 17 manufacturers publish the Error Rate for their motors. While that rate is small, it accumulates on a printer. Indeed, so-called "auto-bed leveling" techniques increase the effect since they are constantly moving the Z motors across every layer. The solution - One Z motor physically synced to two rods.
OneZ has only one Z axis motor. That motor runs the left threaded rod through a pillow block at the top. The top of that rod has a pulley mounted that engages a GT2 timing belt to run the right threaded rod. The right threaded rod has a pulley mounted on top and is held in place with a pillow block top and bottom. 8mm threaded stainless steel rods with nylon nuts was used because 2 acme screws required too much torque, heat and sound for one NEMA 17.
The BOM is located HERE . It contains links to parts ordering, a print version and a clickable PDF version. The SKP files are in a ZIP that contains an assembled file and a file for just the OpenBuilds rail framing. The rails in the SKP are the correct lengths for the build. The rails file has bolts attached to the rails where 10 5mm threads must be tapped and by moving one of the Z upright rails you can see the purpose of the 6mm access hole drilled 10mm from the bottom of both upright rails. Another ZIP contains the STL files. Another ZIP contains the Marlin Ramps Firmware for Arduino 1.6.5.
This is a completed build. The finished product (below) and the beta version (further below) are now printing parts for more OneZs for sale on Ebay & Amazon. It takes about 30 hours to print a OneZ. These two, plus a BldrBot are running 24 hours a day with prints lasting out past 7 hours, with no leveling creep on the OneZ and OneZ Beta (with I could say the same for the BldrBot and OrdBot).
The Printer has an 8inchX8inchX7inch build area with a tidy storage size of 16.5" wide, 15.5" deep, and 16" tall (with handle, without slip-off spool post which can be placed on either side).
Oh, yeah, and that extruder knob on the motor is now a MUST have. The extruder is an E3D knock-off that has the aluminum fin body inner hole resized to 4mm so a 4mm OD PTFE tube runs from the MK8 drive gear to the top of the E3D barrel creating a smooth channel for flex filament. Adding filament is a simple matter of stuffing it down the top PTFE tube in the adjustable lever then rotating the knob - it threads itself. Twisting the knurled bolt head sticking out of the lever can adjust the spring tension for flex, ABS, Nylon and PLA filaments.
OneZ gets it's name from it's most unique feature - only motor for the Z axis while maintaining the stability of two bearing guides for the Z axis. Reduction to one Z motor eliminates need for auto bed leveling.
- Build License:
- CC - Attribution NonCommercial - Share Alike - CC BY NC SA
Reason for this BuildTarget: an easy to assemble, compact Cartesian printer that retains a level bed once it has been set.
Inspired byQU-BD OneUp and my own BldrBot