Mostly Metal Servo CNC

thingiverse

Introduction When I first embarked on my project to build a CNC, I scrutinized existing designs. I examined Mostly Printed CNC and OX CNC closely, but I wasn't fond of installing and tightening so many bearings or V wheels. So, I designed a CNC based on linear motion ball bearing and smooth rod instead. Design Objectives and Decisions: My design objective was to create a DIY 3-axis CNC that is relatively stiff with no need for drilling holes in metal for assembly. I also wanted it to be compact and low-profile. Therefore, I decided to use a moving gantry design and 40mm x 20mm aluminum extrusion for the gantry structure. For an additional challenge, I opted to use servo motors for this project. I chose a low-cost 370 size geared motor with a hall sensor rotary encoder. Since CNC require much more torque than typical 3D printers, I selected leadscrews instead of belts to further gear down the motor and increase torque. Completed Project: Initially, I planned to use two Y-axis motors, but synchronizing them has been tricky. After testing the CNC with just one Y-axis motor, I found its performance satisfactory for routing wood. The motor has sufficient torque to break a 1/8” milling bit. Unfortunately, I broke one by forgetting to switch on the rotary tool before running the gcode. The Z-axis plunged the milling bit into the wood, and when the gantry moved in the Y-axis, the stuck milling bit was broken in half. Below is a recording of the CNC cutting wood at actual speed: https://youtu.be/HnzwKwf-6_s The Y axis flexes when the Z-axis motor pushes the rotary tool into the base. I'll be replacing the smooth rod with SBR10 linear rail for added Y axis strength. ======================================================================= March 27th 2017 Update: I've replaced the Y axis with SBR10 linear rail and SBR10UU linear bearings. I've updated the photos and STL files to reflect the new design. Using SBR10 linear rail has allowed me to align the Y axis leadscrew much better than before. I've added a tab at the side of the Y axis motor holder and the lead screw bearing holder so that when pushed against the SBR10 linear rail, the lead screw is parallel to the rail. As the leadscrew is now better aligned, I've been able to add a second Y-axis motor on the right side. The jerky motion with two Y-axis motors in the first design was due to misaligned leadscrews, not synchronization of the 2 Y-axis servo motors. This revised design has improved the Y axis and Z axis stiffness. Parts for the Build The printed parts are shown in green in the attached drawings. All other parts listed below were purchased online: Parts Quantity LM8LUU x2 8mm rod (132mm) x2 10mm rod (300mm) x2 SBR10 linear rail (500mm) x2 SCS10LUU x2 SBR10UU x4 SK10 x4 T8 leadscrew (100mm) x1 T8 leadscrew (300mm) x1 T8 leadscrew (400mm) x2 T8 leadscrew nut x4 Motor coupler x4 370 size geared motor with encoder x3 2040 aluminium extrusion (170mm) x4 2040 aluminium extrusion (266mm) x2 90 degree bracket (Single width) x6 90 degree bracket (Double width) x2 ======================================================================= April 30th 2017 Update: This third iteration of my Mostly Metal Servo CNC is finally stiff enough to mill aluminum. It can mill through a 2mm thick alumium with a nice finish. https://www.youtube.com/watch?v=i8By9_Nfgq4 https://www.youtube.com/watch?v=ixt_-YsAor8 I will be uploading the revised Z-axis design once I have time.