After all the interest I received on my MPCNC foam cutter at Flite Fest East 2017 and my article about it, I wanted to see how inexpensive a machine I could build. This machine is loosely based on the LowRider CNC from Vicious1.com. My version is simpler in that the y-axis rails are fixed and the lightweight z-axis has the needle cutter integrated.
The 3D printed parts and a drawing of the side plates for this machine are available on www.thingiverse.com/thing:2520214. I milled the side plates on my MPCNC, but they could be cut with a jigsaw, router, and a drill using the printed template.
Mount the bearings to the y-carriage as shown. The four inner bearings use 1.5 in bolts and the eight outer ones use 1.25 in bolts.
Here is the detail of how the flywheel mounts to the motor.
Insert the t-nut in the rear section of the z-carriage. I used servo screws to secure it.
Completed z-carriage. The spacing on the needle cutter is set for a 2212 1000kv motor. A motor and ESC can be purchased for $15.99 on Amazon.
8 mm rod can be used for the z-axis rails, but in the pursuit of inexpensive, readily available parts, I chose 6.5 in 5/16" bolts and cut the heads off. The heads can be left on without any issues. I did have to grind the bolts a bit in one spot that was thicker than the rest of the shank. I chucked it in my drill and used a file and 600 grit sand paper until I was happy.
Here is the assembly of the z-carriage onto the y-carriage. Mount the stepper on the top plate. Mount the threaded rod to the stepper using the pineapple coupler or similar. Insert the z-rails into the top bearing of the z-carriage, then the lower y-carriage mount, then the lower z-carriage bearing. Apply a thin coat of lubricant on the rails. Finally thread the rod into the t-nut to mount the top plate with #6 screws and captured nuts. There is a provision for a bearing on the threaded rod, but it is not necessary for this short movement.
Next, cut your 3/4" conduit to length. It needs to be 5" longer than the width of your table. To cut 20" x 30" foam board, you need at least a 27" wide table. I used a 32" door for a table which gives me a 25" cutting area on the y-axis. Ikea sells a table top that is 59" x 29.5" for $30 that may work. Insert the conduit into the tube carrier. Mount the stepper to the x-plate. The belt guide consists of the 3D printed part (not shown) two bearings, and two washers mounted with 1.25" bolts and lock nuts. The rollers are mounted with 2.5" bolts with a lock nut on both sides of the plate to clear the belt.
Insert the tubes through the plate, slide on the y-carriage ensuring that the belt attaching holes are on the same side as the servo, then the other plate and tube carrier. The tube carriers are secured to the plates with 2" bolts and lock nuts.
The drive belts for the y-axis are zip tied to the carriage. The x-axis belts are fastened to the edge of the table at each end however you like. I am using spring clamps for now.
To assemble the needle, feed the end of a length of 0.025" or 0.03" music wire into the needle holder and put a 90 degree bend on the end in the center. Mount a small bearing (8mm or 10mm) on an m3 screw with a lock nut.
Press the bearing into the needle holder.
The needle holder is then screwed into the first hold from the center of the flywheel. Then use a screw and nut (if necessary) in the outer hole on the opposite side of the flywheel to balance it. The needle guide is a 0.035" MIG welding tip threaded into a 3/4" block of wood. The wood has a 5/64" hole from the top surface down to the MIG tip. I enlarged the hole at the top slightly. The wood serves as an isolator. Without it, the metal guide gets hot enough to melt the plastic. I added some cooling fins to my guide, but they are not necessary.
Cut the needle to length so that it is flush with the guide in the full up position. If you then dress the tip of the needle to a conical point, you will get better cuts.
For more information on the needle cutter, see the long running forum thread started by dj4linux.
For electronics, I use a Ramps 1.4/Arduino with LCD controller. You can use whatever you like, but this setup will let you run gcode files off an SD card without being tethered to a computer. I use the Marlin firmware configured for the MPCNC available at Vicious1.com. This configuration tricks the controller with a fixed hot end temperature, so you don't need a thermocouple and don't get min-temp errors. I am using a servo tester to control the cutter, but it can be driven from the Ramps board with gcode commands.
For a power supply, I used a Dell DA-2 that was being thrown away at work. They are 220W 12VDC, have a long cord so the brick can lay on the floor, and are available for ~$10 on eBay. Just cut the PC connector off and connect the blue wire to ground (you could add a switch). There are three sets of white and black wires. I used one pair to power the ESC, and the other two for the board.
Here is the parts list. There may be a few random items like zip ties that are missing.
|60mm urethane wheels||6||$19.50||https://shop.vicious1.com/collections/lowrider-parts|
|GT2 belt||6 m||$11.97||https://shop.vicious1.com/collections/lowrider-parts|
|16 tooth pulleys||4||$8.76||https://shop.vicious1.com/collections/lowrider-parts|
|M3 x 10mm screw||12||$1.88||Lowes|
|M3 x 20mm screw||3||$1.00||Lowes|
|5/16 lock nut||32||$4.70||Lowes|
|5/16 threaded rod||1||$1.05||Lowes|
|3/4" electrical metallic tubing||1||$7.24||Lowes|
|2212 1000kv brushless motor and esc||1||$16||https://www.amazon.com/Hobbypower-1000kv-Brushless-Multicopter-Quadcopter/dp/B00E7LG85O/ref=sr_1_1?ie=UTF8&qid=1507433610&sr=8-1&keywords=2212+brushless+motor+1000kv|
|12vdc power supply||1||$10||eBay|
Comparison with the MPCNC
Pros: This machine ends up about $50 less than what I spent on my MPCNC. The savings are in one less stepper, half the bearings, and about a quarter of the hardware. This machine can be easily removed from the table, or just pushed to the side with no rails, the table can be used for other projects. The MPCNC takes up quite a bit of space.
The x-axis can be extended without the issue of sagging rails for cutting longer materials.
Cons: This machine is dedicated to the needle cutter, or a pen/vinyl cutter. The MPCNC can use a router or spindle for cutting and carving wood.
The side plates require some accurate cutting, which is easier if you already have access to a CNC machine.