DIY CNC Router, cutting BMX chain sprocket, Part 1: Pocketing

I wanted to make one for my nephew. Not having bike in hand, and not knowing the crankshaft and boss diameters, I decided to do a test piece.

I'm using OneCNC XR3's high speed toolpaths for roughing, and traditional toolpaths for finishing. The cutouts for the spokes were pocketed to prevent the slug from jamming and binding the bit or stalling the steppers.

Material is 1/4" mic-6 aluminum tooling plate, but the real one will be 3/16" 7075.

I ran out of WD-40, so I ended up using Cabot's Lubri-Tascon, which I feel worked way better than WD-40! I was able to achieve a nice finish on the pocket floors.

For more information on my machine, and for other DIY CNC videos, check out my channel:
http://www.youtube.com/user/AtienzaLouie?feature=mhum
or my build thread in teh CNC Zone:
http://www.cnczone.com/forums/diy-cnc_router_table_machines/122070-one_thing_...

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[AtienzaLouie]

Get or make the most ridgid machine possible, with the most powerful spindle practical. If you can afford it get a benchtop mill like SyiL. If you are building a first, I'd recommend high-ridgidity aluminum extrusion for a frame, to make things easier. Try to use as much bolt-on stuff as possible to minimize machining.

[151tdawg]

ok so if a person got into cutting such things what would you recomend for a machine for a beginner??? this is open to anybody!!!

[AtienzaLouie]

@151tdawg Sorry if I missed this... My first machine was based on plans from solsylva.com. My first videos are of that machine. There are different sized machine plans available. CNC Zone is also a valuable reference...

[camiphone]

I want to get into doing aluminum but have never tried it. Is there any tips you could offer to a beginner? :)

[AtienzaLouie]

The keys here are: 1) using the largest doc means you're using the SIDE of the endmill which cuts more efficient than the bottom, which also means less wear and less heat; 2) more doc means the workpiece is closer to the collet, meaning more ridgidity, 3) the right speed and feed so that you make chips that draw heat AYAY from the bit, and the chips should be hot to the touch; 4) lubrication to prevent galling, and 5) use a toolpath that doesn't bury the bit; use half doc for profiling....

[AtienzaLouie]

For pocketing, if you decrease the doc, you can usually safely increase the radial doc (or stepover). This can be seen in the center hole pocket versus the spoke pockets. Once you have your speeds and feeds for a particular bit then it's all proportional, more or less, for other sized bits; i.e. for a 1/8" bit, I'd decrease everything but the spindle rpm by 1/2, and adjust from there. Also whenever possible, it's better to helix in than plunge.

[AtienzaLouie]

@camiphone Read up on teh tool manufacturer's recommended speeds, depths of cut, etc. Adjust them to the ridgidity of your machine. I'm pretty close to the recommended feed, though using a shallower doc and radial doc to accomodate the ridgidity (or lack thereof) of my machine. Always use a lubricant when cutting aluminum. Use stub endmills whenever possible.

[AtienzaLouie]

@camiphone I used OneCNC XR3 Mill Advantage, but since upgraded to XR4 Mill Professional. I used their HSM (High Speed Machining) toolpaths which allow for more tool engagement without "burying" the bit, during pocketing operations...

[camiphone]

What software have you used to program the cut paths?