An Inexpensive 4th (Rotary) Axis

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An Inexpensive 4th (Rotary) Axis

Postby Sparky » Tue May 31, 2011 6:09 pm

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.
4thAxis1.jpg


Here is a video of the unit in action: http://youtu.be/Y0c5UMKyQl4

Elements of assembly:
4thAx1.jpg
4thAx1Expl.jpg
4thAxMotorPlate.jpg
4thAxMotorPlate.jpg (25.93 KiB) Viewed 12944 times

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:
4thAxMotorPlate.dxf
(22.98 KiB) Downloaded 459 times


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 Materials

Carter Tools - Taig distributer. Nick will give a 10% discount
Headstock 100-00... $63.90
Tailstock 1150........ 39.50
Faceplate 1035....... 14.90
http://www.cartertools.com/catalog.html
The 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 ... 21.50
http://stores.ebay.com/HUBBARD-CNC-INC
Brent 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-motor
TOTAL: $171.27 plus shipping and misc. hardware.
_________________________________________________

SETTING UP THE GCODE

The 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
C=pi*D
= 3.14 * 1.246
= 3.914 inches
Length of workpiece = 4.5"
Enter surface area into Cut2D, import CAD .dxf file, generate tool-paths.
4thAxCAM.jpg


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"]
Attachments
4thAxEmcConfig.jpg
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Re: An Inexpensive 4th (Rotary) Axis

Postby GMezzacapo » Wed Jun 01, 2011 10:21 am

Sparky, as always, very nice project. Do you have a part list? Thanks

Gianni
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Re: An Inexpensive 4th (Rotary) Axis

Postby Sparky » Wed Jun 01, 2011 11:57 am

Thanks Gianni, I'm working up a parts list with sources and will add it to the initial post above along with some assembly notes.
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Re: An Inexpensive 4th (Rotary) Axis

Postby johntech » Thu Jun 02, 2011 7:09 pm

Sparky wrote:Thanks Gianni, I'm working up a parts list with sources and will add it to the initial post above along with some assembly notes.


Are you going to start production soon? :P
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Re: An Inexpensive 4th (Rotary) Axis

Postby Sparky » Thu Jun 02, 2011 7:51 pm

johntech wrote:Are you going to start production soon? :P

Yeah, I'm retooling the plant for mass production as we speak! ;)
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Re: An Inexpensive 4th (Rotary) Axis

Postby johntech » Thu Jun 02, 2011 9:35 pm

Sparky wrote:Thanks Gianni, I'm working up a parts list with sources and will add it to the initial post above along with some assembly notes.


Is that metal strip in the X direction the base for the whole assy that screws or bolts to your table? Now that my 12x12 is working properly I may give it a shot!!

Thanks for sharing!

John
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Re: An Inexpensive 4th (Rotary) Axis

Postby Sparky » Thu Jun 02, 2011 9:59 pm

Yeah, it's the base and can be removed as a unit. This dovetail piece (way) that the headstock and tailstock attach to is PVC at the moment. It seems adequate since there's no movement along it except to position the tailstock when needed. I'd prefer and probably will soon go with aluminum or steel instead. Milling a piece that size myself is a bit of a challenge at the moment, but I'm working on it. But for carving hardwood it's quite rigid enough and the cuts are very clean and accurate.
I had tried using an aluminum U-channel set into a slot in the MDF table as a track for the tailstock, but quickly abandoned it in favor of the tried and true old school dovetail scheme.
The rotary axis opens up a whole new area of possibilities and besides, it's cool to watch it in action.

By the way, on a stock 1212 there may be issues with inadequate clearance under the bit, that is the Z axis will probably need to be raised a few inches, or at least the spindle raised some. This subject has come up before and Xin suggested adding blocks to raise the gantry. There was talk of plans for this mod, but I haven't seen it posted. Shouldn't be too difficult though. On the 0707 and 0712 which I have, you can simply raise the Z carriage up to the next series of screw holes to increase the height above the table.
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Re: An Inexpensive 4th (Rotary) Axis

Postby johntech » Fri Jun 03, 2011 3:34 pm

Sparky wrote: .............The rotary axis opens up a whole new area of possibilities and besides, it's cool to watch it in action.

By the way, on a stock 1212 there may be issues with inadequate clearance under the bit, that is the Z axis will probably need to be raised a few inches, or at least the spindle raised some. This subject has come up before and Xin suggested adding blocks to raise the gantry. There was talk of plans for this mod, but I haven't seen it posted. Shouldn't be too difficult though. On the 0707 and 0712 which I have, you can simply raise the Z carriage up to the next series of screw holes to increase the height above the table.


I was wondering about that if it would be too low. I was trying to come up with a way to raise up the X axis supports so I would have more travel and be able to cut thicker stock. Looking into remounting the lower Z axis bearing differently to be able to add more clearence there.

So basically everything I need is listed in the above diagrams and parts list? How are you driving the stepper? Did you just tap in to the Y axis to run the new motor?

Man Sparky I was just thinking....... if you took your same setup and instead of a lathe chuck turn it 90 degrees like a platter then you could engrave or mill things in that plane... but then you would need to have another controller or just use the Y and Z axis"s ... hmmmm

Something I ran across a while back for the experimenters out there ..... check out this site http://www.stepgenie.com they sell a chip for about $6.00 that will controll a stepper motor with 4 HEXFETS and a couple current limit resistors. They have a demo board with the chip and HEXFETS with some demo software for $25 I think the HEXFET's are about a buck each and are good for 100 volts at 28 amps ( with heatsinks of course). Here is the info about the chip http://www.stepgenie.com/StepGenieSpec.pdf incase anyone is interested.

John
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Re: An Inexpensive 4th (Rotary) Axis

Postby Sparky » Fri Jun 03, 2011 4:02 pm

johntech wrote:I was wondering about that if it would be too low. I was trying to come up with a way to raise up the X axis supports so I would have more travel and be able to cut thicker stock. Looking into remounting the lower Z axis bearing differently to be able to add more clearence there.

So basically everything I need is listed in the above diagrams and parts list? How are you driving the stepper? Did you just tap in to the Y axis to run the new motor?

Yeah, I'm pretty sure I didn't leave anything major out. I hope to be able to offer the two fabricated pieces (motor mounting plate and way) sometime in the near future, but that would be weeks off at best. June is pretty much booked with other activities away from the shop, but I may make up a t-shirt that reads "EAT, SLEEP, CNC" or "I'd rather be CNCing" just to express my sentiments.

To drive it I just unplug the Y stepper and plug in the rotary stepper in its place. I'll eventually add a switch for convenience.

Raising the gantry seems like the best option, but then I can't spring for a 1212 to be sure. Since the rotary axis doesn't need to pass completely under the carriage, it should be possible to fabricate a spindle holder bracket to extend it forward and higher enough to clear the workpiece and chuck or faceplate.
johntech wrote:Man Sparky I was just thinking....... if you took your same setup and instead of a lathe chuck turn it 90 degrees like a platter then you could engrave or mill things in that plane... but then you would need to have another controller or just use the Y and Z axis"s ... hmmmm

I may need to scratch my head some on that and mull it over, but it seems that wouldn't add a capability that doesn't already exist on that plane under the normal basic mill configuration.
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Re: An Inexpensive 4th (Rotary) Axis

Postby p38nut » Mon Oct 22, 2012 1:57 pm

Pulley 40T pitch 0.20 bore 1/2" .......................................... 19.99
...(bore to 3/4" for headstock shaft)

Can anyone verify the 3/4"? I believe that it should be 5/8"

Thanks. Mike
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