I've just completed building a 4th axis attachment for the Zen 0712
that I think is accurate, inexpensive, and can be easily duplicated by the serious DIYer. The major elements are readily available, more or less off the shelf. The headstock, tailstock, and chuck are manufactured by Taig.
The first carving was a logo design on a 1.25" diameter piece of Ash hardwood using a 1.0mm endmill. CAD/CAM was CorelDraw/Cut2D, executed by EMC2 with the stepper motor connected to the Y axis. Note the handwheel on the Y-axis leadscrew shaft to manually position the table under the cutter on the centerline of the workpiece. It's not necessary, but an added convenience.
Here is a video
of the unit in action: http://youtu.be/Y0c5UMKyQl4
Elements of assembly: Headstock/stepper motor mounting plate
(not actual size. See DXF file below
) should be cut from rigid material, ideally aluminum, but PVC, HDPE, acrylic, etc. should suffice. The plate serves as a drilling template for the four mounting bolts to secure it to the headstock extrusion. I drilled and tapped mine to receive 10-32 cap screws, but any similar size should be fine.
Here is the DXF file:
The dovetail way upon which the headstock is mounted and the tailstock is positioned is made from the same PVC material as the CNC router itself. 45 degree cuts were carefully made on a table saw for a fairly tight fit. The way is centered on a .5" piece of MDF onto which was applied a few coats of varnish to seal it from moisture. The original PVC table was used as a drilling template for mounting screw holes. Alignment of the way on the table was done by moving the cutting head along the entire length of the X axis. The way piece's edge was set against the bit at each extreme, clamped into place and then drilled through and finally screwed to the MDF table.
_______________________________________4TH AXIS ATTACHMENT Bill of MaterialsCarter Tools
- Taig distributer. Nick will give a 10% discount
Headstock 100-00... $63.90
Tailstock 1150........ 39.50
Faceplate 1035....... 14.90http://www.cartertools.com/catalog.htmlThe Carter Tools catalog lists various chuck options other than the faceplate with 3 and 4 jaw chucks in the $60-$70 range.Hubbard CNC Inc
. Ebay store
Timing Belt 50T pitch 0.20 width 3/8 in. ............................... $5.49
Pulley 10T pitch 0.20 bore 1/4"............................................ 5.99
Pulley 40T pitch 0.20 bore 1/2" .......................................... 19.99
...(bore to 5/8" for headstock shaft)
Stepper Motor 120oz 1.8 deg 1/4" shaft Shinano Kenshi NEMA 23 ... 21.50http://stores.ebay.com/HUBBARD-CNC-INCBrent will combine shipping fees to minimize cost, but follow the online instructions.
CSI is another source for reasonably priced steppers:http://www.circuitspecialists.com/stepper-motorTOTAL
: $171.27 plus shipping and misc. hardware.
_________________________________________________SETTING UP THE GCODEThe 4th axis stepper motor is plugged into the stepper motor controller socket where the Y axis motor is normally connected, so the Gcode is generated as if it were carving on a flat surface. Instead of the axis moving laterally, it rotates in this configuration and the design/image/cutting path is "wrapped" around the cylindrical surface.
The cylindrical workpiece is measured with a digital caliper. The diameter is 1.246 in.
To find the carving area, the circumference is calculated
= 3.14 * 1.246
= 3.914 inches
Length of workpiece = 4.5"
Enter surface area into Cut2D, import CAD .dxf file, generate tool-paths.
Gcode option: CNC Wrapper
, a Windows program designed to automate the process of converting 2D/2.5D Gcode for 4th axis indexing. Only $20. The program includes a handy surfacing feature which prepares roughed cylinders for final carving.http://www.cncwrapper.com/
Set up EMC2 dedicated config. file Y axis with revs-per-inch, pulley teeth (10:40), number of micro-steps.
Revolution per inch = 1/3.914 = .2554[Edit: corrected 40T pulley bore to 5/8" vice 3/4"]