CNC relief on a curved object

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Hi all, I am hoping you lovely peeps can help me deciding whether to purchase the Snapmaker 2.0 now or better wait for further developments. I am new to CNC machining so forgive my incorrect lingo.

The objects I work with are sections of metal parts from car panels, which are covered with anywhere between 35 to 200 layers of paint in different colours (see cross section image bottom left). The paint layers vary in thickness from 10-40 microns thick. The metal on which this all sits is around is 600 microns.

If at all possible, I would like to CNC on these curved shaped pieces, for example as shown on the sculpture in the picture - top left and close up at the top right. With this piece (20x5x1cm) I carved into the paint layers manually with a handheld rotary tool (Dremel), which took me about 40 hours, just for the carving alone. I am hoping to be able to do other pieces and shapes with the Snapmaker 2.0, resulting in more geometric and precision shaped cuttings, and more importantly, saving me time and my sanity!

For the cutting / carving itself, plunging a couple of millimeters deep seems to be no problem for the Snapmaker, or any CNC machine for that matter, but is it also possible to ā€˜shaveā€™ off say about 5-10 microns at a time, over a distance of a few centimeter? In other words, peeling off layer-by-layer, tapering down (as in bottom right in picture)? I currently do this with handheld (power) tools or by hand, but with the layers being as thin as a human hair, it doesnā€™t take much to cut too deep and expose the next layer.

Thereā€™s a lot I have to learn! So far to prepare and get into it I have installed Luban and Fusion 360 on a Mac. I did find a similar question in this forum:

(Using CNC for 3d Objects)

But here I got stuck as things are still a bit over my head. I donā€™t fully understand the relation yet between the software packages, what all the ā€˜codesā€™ are, how to overlay the tool path over the 3D scan data etc. but first and foremost I try to understand if this is possible at all before I spend my hard earned money.
In summary my most burning questions are:

  • Which ā€˜point cloudā€™ file format is the best and how to import it into Luban
  • How does Luban know (or how do I let it know) the position of my object on the board - angle, height etc. so it starts at the right coordinates?
  • The pieces I use donā€™t have complex shapes so I guess a simple 3D scan app will do the trick like Qlone, Scandy Pro or Heges. Trnio is also an option I guess.
  • or
  • Is there a way the CNC module (in combination with a camera or sensor) can pre-scan the stock / object on the table, which seems (to me) an obvious feature to have, also for ā€˜flatā€™ objects, which arenā€™t always perfectly flat. Or is this an add-on / feature yet to come?

Totally understand if my question either donā€™t make much sense and or are in the wrong order but any pointers much appreciated!

Many thanks!

Marc

ps 1. on my website are more works with the same material www.marcvellekoop.com

ps 2. happy to help anyone here with questions related to (automotive) surface finishing, sanding, cleaning, prepping, paint application, polishing etc. Metal and composites are my forte, wood less though but ask me anyway.

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Hello, interesting post!

I think that the Snapmaker may not be the solution you are looking for though. Setting aside any issues creating the toolpaths you require, the machine has a minimum step size of 40 microns on all X, Y and Z. Added to that, backlash could affect the accuracy.

It seems to me like we are comparing and analogue process (your work with a Dremmel) and a digital method- CNC. Iā€™ve been making PCBs using the CNC and the only way I found of making it work is to mount the stock on a sprung base and mounting a bearing around the cutting tool to press down on the work as it moves through the workpiece. By setting the height distance between the tip of the bit and the bearing to the required depth of cut and then setting the toolpath to move the tool further than required, I can achieve a really shallow cut. I hope I explained that properly, maybe the video will help. :slight_smile: Obviously, Iā€™m engraving a flat surface, not curved like yours.

If you do find a way to do this I would be very interested to hear about it.

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Hi, thanks a lot for your answer, itā€™s good to learn about the 40 microns minimum step size! I might have to wait for a newer and hopefully more accurate version, or look for another brand. Perhaps just a CNC unit, I donā€™t need the laser engraving and 3 print modules anyway. Still a bit baffled as to why the bed is moving and not the frame with module on the tracks, seems a bit odd (to me) but surely thereā€™s a reason for that. Anyways, many thanks for your help! Stay safe:-)
ps. love your solution with bearing and sprung base!

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The Snapmakerā€™s main selling point is its ā€œtriple threatā€ nature, and itā€™s not going to be as good at any one thing as a single-purpose machine of comparable price. So yes, if you only need the CNC, youā€™re likely better off with a dedicated CNC machine.

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Cheers, yes looks like I better look further and find a dedicated CNC unit.

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@MarcoV Thanks for the comments!

One of the reasons the bed moves is that the height required for 3D printing means that moving the gantry back and forth would lead to all sorts of problems.

Alan

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Got it! Thanks again AlanšŸ•ŗšŸ¼

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@albutch a late question with regard to your pcb engraving method: What type of bearing is that exactly that youā€™re using? Is it a thrust bearing? Iā€™m trying to find a place to buy one like these but having trouble identifying the exact type of bearing it is.

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Its a bicycle crank bearing. They are 37mm diameter which suited my purpose just about right.

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Great, thanks!
That makes finding the right ones a lot easier :slight_smile:

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Evo-S - Mekanika ā† take a look at their site, it is not cheap but will probably fit all your needs, itā€™s a pretty good machine saw it on video of a YouTuber called MpoxDE he introduced the SM as well :slight_smile:
MEKANIKA Evo-S | Profi CNC FRƄSE als AnfƤnger? (Erfahrungsbericht 2022) - YouTube