Copper sign

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Copper sign

Post by JohnP » Thu Feb 25, 2016 7:13 am

As a first "real" project, I decided to mill a simple sign for my wife's business out of MDF, plastic and finally copper, as a way to learn about the various limits/capabilities of my new SO3. As expected, I learned as much about my limits as I did about the machine's capabilities :roll:

What did I learn?
  1. The machine won't think for you! If you tell it stupid, it will. Happily!
  2. What works for wood, won't for plastic; what you think you learned from them won't apply to metal. Except, after you make all the same mistakes on each, you realize it does.
  3. CNC calculators like GWizard have a steep learning curve if you are ALSO learning machining and CAM at the same time. Use one anyways! It is cheaper than broken bits.
  4. Double stick tape works well as a hold down.
  5. Double stick tape is a horrible hold down. It sticks too well for fragile plastic, and it is a pain to remove from the finished objects.
  6. The SO3 needs a better hold down mechanism than "attach things directly to the provided waste board".
  7. Cutting salvaged copper plate is difficult - it isn't really flat, it has work hardened sections, and unless you have bits to spare, requires a wet coolant/chip removal system.
  8. For the copper milling, I used between 3 and 7 IPM, a 0.015 to 0.02" cut depth and a carbide 2F 5/32 endmill at the Dewalt611's slowest speed. I should have used a 1/8" endmill and a roughing pass.
  9. Cleaning up plastic and MDF chips is too easy; I didn't worry much about enclosures or dust shoes - and now I have copper chips *everywhere*!
  10. There certainly is an art to optimizing job run times - an art that I'm just learning! So many variables, so little time :!:
  11. Using a work coord system (WCS, aka G55, G56...) made it easy (and routine) to re-home (with limit switches) and re-run milling passes after bit changes.
  12. I used Illustrator, VCarve and bCNC - I couldn't have done this project with the limited feature set of just CCreate and CMotion.
  13. Don't start a job with only one bit. It WILL break halfway thru the job. (see point #1)
  14. The distance to a store that stocks the bits you need is dependent on how soon you need a replacement bit.
Oh, and the last important take-away? I still love my Shapeoko3!
MDF prototype
IMG_3404.jpg (9.21 KiB) Viewed 3241 times
Plastic prototype
IMG_3405.jpg (12.11 KiB) Viewed 3241 times
IMG_3430.jpg (12.54 KiB) Viewed 3241 times
Shapeoko 3 #1322 - Dewalt 611, limit switches, drag chain and cable dressing

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Re: Copper sign

Post by Atonwa » Thu Feb 25, 2016 10:57 am

Great first project, thanks for sharing. I agree on all your points :lol:
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Re: Copper sign

Post by WillAdams » Thu Feb 25, 2016 11:56 am

I think it could've been done in Carbide Create and Carbide Motion --- just would've required a few workarounds.

Great write up! Added a bit to the wiki so as to add it: ... _a_Machine

Certainly a big change from when we were struggling to puzzle out how many M5 washers the machine needed: ... f_ShapeOko

Also, nice logo, sign and project!
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Re: Copper sign

Post by JeromyReno » Thu Feb 25, 2016 10:10 pm

killer first project

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Re: Copper sign

Post by atrueresistance » Fri Feb 26, 2016 5:03 am

Nice job. It looks really good. I've never used gwizard, is it worth the cost?
JohnP wrote:
[*] I used Illustrator, VCarve and bCNC - I couldn't have done this project with the limited feature set of just CCreate and CMotion.
Well done, bCNC is the best.
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Re: Copper sign

Post by JohnP » Sat Feb 27, 2016 4:12 am

GWizard has a 30 day trial, so you can use it for free on a real project and make up your own mind.

As an example of how I used it, I did about an hour of googling cnc milling copper and aluminum posts for speeds and feeds, and found (surprise) mostly a clustering of shapeoko wiki references. The suggestions were "all over the map", with high and low spindle speeds, high and low IPM feed rates, youtube videos with great motivational drama, ...

I started with an ad-hoc web consensus: 12000 RPM, 15 IPM, 0.05" cut depth with a 5/32 2F carbide bit. The job ran about an hour before the bit was too dull to plunge cut anymore.

Realizing I didn't know what I didn't know, I re-read much of Bob's great cnccookbook compendium of cnc lore and sprung for G-wizard's trial.

Clicked on "Shapeoko3 / 611", copper alloy, 5/32" carbide endmill ... and saw "min RPM too high for cut". Hmmm
clicked on generic CNC instead, and it suggested a ~8000 RPM, 4 IPM setting with a 0.01 to 0.015 cut depth with conventional milling (not climb cuts)
At 12000 RPM, the program suggests (in red) that I'm going to be exceeding the spindle's HP capacity at any non-zero feed rate (at least that's how I interpret the output...)

Learned that I wan't anywhere close to the sweet spot, and that there was more than 0.004" of bit deflection - which explained the chattering.

I continued the job with a 3-4 IPM 0.015 cut depth at the low end of the DW611's speed range. I also used a manual lube spray for chip clearance, and the 2nd bit lasted 6 hours (with about 3x-4x more material removed) It failed the same way - it got too dull to plunge cut because I flaked out on the lube at the end. Since I was now out of 5/32 bits, I finished the job the next day with a 1/8" straight bit as a rougher, and then re-ran the final g-code section with one of the "dull" bits fully extended to clean up the edges.

Was it worth it (assuming I was paying for it instead of free-trial'ing it)? It probably saved me the cost of a bit on this job (~$25 new or ~$7 to resharpen since I didn't break it), so if I use that as a completely unscientific benchmark, I'd need to save $80 worth of bits a year; if a bit == a project, that means if I use it on 4-6 projects a year, I break somewhat even. But that's not all the cost savings - I have a limited hobby time budget, and the time spent googling for web consensus comes out of that bucket. If GWizard saves me an hour per project, that's a whole day of making chips instead of flattening my butt on a chair.

Yeah, a lot of hand waving and questionable budget balancing rationale in the above; but hey, at least I'm better at it than <insert your least favorite presidential candidate here - there's lots of them to choose from> :-)

As for bCNC / CMotion...

I was a bit harsh - I probably could have done this with CM/CC if I was willing to spend more time compensating for missing features that are already in bCNC and VCarve. My comments about limited hobby time come into play here as well - I spent 2 days trying to do things that took 20 minutes to do in VCarve/bCNC, and I'll never get those days back...

bCNC isn't perfect, though. On Win10, it loses the feedback connection from grbl after the first couple of minutes; the control panel stops updating (no path progress, no DRO updates, but g-code keeps getting sent out...) and a python file I/O error stack trace in a window when exiting...

Shapeoko 3 #1322 - Dewalt 611, limit switches, drag chain and cable dressing

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