Anyone doing subtractive?

Discussion in 'Tool heads & ToolChanger' started by Joe Pomo, Jun 7, 2020.

  1. Joe Pomo

    Joe Pomo Well-Known Member

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    Just curious what is out there?

    I created a dremel + flex-shaft tool and got a decent surface finish on some PETG coupons.

    I printed them with a .8mm nozzle and milled the surface at ~0.2mm stepover, using 0.5mm depth of cut increments and 5mm/s feedrate. I don't know what the RPM was but it was set to ~"5" on the Dremel.
     

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  2. Paul Arden

    Paul Arden Well-Known Member

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    Cool, what did you use for toolpath generation? Were you just relying on bed adhesion to keep the part in place while milling?
     
  3. Michael Pearson

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    Awesome!! How are you calibrating the cutting head?
     
  4. Joe Pomo

    Joe Pomo Well-Known Member

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    Yes for the Bed adhesion. I kept the bed hot (~70C) during the milling and haven't had a problem with these small coupons.

    For the toolpath, I've just been writing the Gcode by hand, but I want to find an easier way. One option I'm looking into is Fusion360's CAM suite. The Diabase H-series printer uses fusion for tool-path generation. I'm 99% sure that printer is Duet-based, I just haven't figured out how they reconcile the printed part/"workpiece" coordinate systems.
     
  5. Joe Pomo

    Joe Pomo Well-Known Member

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    Hey, do you mean for offsets? I just treated the spindle as an extruder for setting the offsets (G10, etc.)

    For XY offsets, since I can't use the vernier scale method, I followed these instructions from twitter for using a Webcam/Microscope:
    https://twitter.com/brendonbuilds/status/1180608246735888390
     
  6. Nicholasav

    Nicholasav Member

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    Very cool. I haven't begun that part yet, but am going to use the attached as step one of this process. The plan is to use our injection grade resin via pellet extruder to produce a fitting, then ream the ID for a smooth finish. For the reaming tool, the idea is to use a printed "mold" to grab the fitting before reaming.
     

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  7. Joe Pomo

    Joe Pomo Well-Known Member

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    Awesome, I like it! What do you plan to use for a spindle to hold the reamer?
     
  8. Nicholasav

    Nicholasav Member

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    I'm not really sure yet. Because the ID size will be fixed per part, I was thinking about just using a shaft coupling and doing a belt drive from the stepper. I'll definitely post more when I get further along... I probably should have waited, but as everyone here knows projects can be exciting. :)
     
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  9. 1013D

    1013D Active Member

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    Very Nice.
    If you can get the slicer to automatically mill the exterior after every layer, the cutting forces should be very small and produce very fine parts....May want to look at an air grinder type tool for higher RPMS so you can use small diameter ball cutters.
     
  10. Marcus Mendenhall

    Marcus Mendenhall Well-Known Member

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    This (high speed cutter) might not work too well. Plastics melt into a gummy mess with high-speed tools. You probably have to go annoyingly _slowly_ to get a good finish. The point about very light cuts it probably correct, though.
     
  11. Joe Pomo

    Joe Pomo Well-Known Member

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    So, it took me a second to realize you are attaching the pellet extruder to your Toolchanger.

    How do you manage the added mass of the tool

    ...and do you have a hopper, or are you using some other system to feed pellets?
     
  12. Nicholasav

    Nicholasav Member

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    So far, the mass does not seem too great for the tool changer, though I would wager it exceeds rated specifications (does anyone know what the max weight per tool is? I had trouble finding anything but fairly casual information in a blog post). I haven't made any attempt yet to print at high speeds, and suspect some modifications will be necessary to do so.

    The first picture shows the hopper -- because the parts in question are small, the material weight is negligible. I will probably upgrade to some sort of feeding system, eventually. The extruder OEM (www.mahor.xyz) has a very nice looking feeder, but without drying. The hopper was printed with PP. Mounts were done with Formlabs Tough resin.

    When I get further along I will definitely share more information in a more appropriate thread, I don't want to derail yours too much.
     
  13. Joe Pomo

    Joe Pomo Well-Known Member

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    Update: The dremel spindle is working well, and I built another spindle in the likeness of one of these:
    https://hackaday.com/2014/08/03/brushless-dc-motor-used-for-high-speed-cnc-spindle/
    but still untested...

    Previously, I mentioned that I would need to reconcile separate coordinate systems for printing followed by milling. This is not actually the case as long as both the slicer and CAM software use the same coordinate origin (I'm using Prusa Slicer). I'm running RRF 3.1.1 on Duet 3 and I use this post-processor found on the Duet forum: https://github.com/mwinterm/fusion_post/tree/master/DuetCNC

    Keep in mind that this and other post-processors may automatically create Start and End code for your tool-paths which may require editing to work with your particular machine. (For instance, I didn't want the printer to home at the start of the milling tool-path because the printed part was still stuck to the buildplate, etc.)

    Curiously, while my T1 extruder tool (hemera) is offset with respect to my T0 (also a hemera), the dremel spindle tool required offsetting from T0's datum (i.e. the tip of the Omron z-probe). Trying to offset the spindle from T0 resulted in an incorrect offset. I don't know why this is, but I'm sure I'm just over-looking something.


    Overall, the software workflow is pretty much nailed down. This is a work project, and I won't be able to share more photos for several weeks, however, low-load milling appears to be possible with the TC.
     

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  14. Greg_The_Maker

    Greg_The_Maker Administrator
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  15. W1EBR.Gene

    W1EBR.Gene Well-Known Member

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    Will the tools run with a Duet 2 ?
    Now I am excited about this !!!
     
  16. Greg_The_Maker

    Greg_The_Maker Administrator
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    i was done with a standard ToolChanger & Motion System setup, which uses Duet 2.
     
  17. Joe Pomo

    Joe Pomo Well-Known Member

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    I may have missed it, but are you all planning to provide firmware configurations for your set-up? the blog mentions using an ESC to drive the BLDC but I'm curious about what outputs you used on the board + macros ....do you switch to CNC mode for the spindle...etc.

    And nice work, btw!
     
  18. Greg_The_Maker

    Greg_The_Maker Administrator
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    Have a look at the codebase, there are examples on there | https://github.com/AndyEveritt/ASMBL

    I'll post the config from the ASMBL machine next week.
     
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  19. W1EBR.Gene

    W1EBR.Gene Well-Known Member

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    @Greg Holloway , if you want to try "smoothing" TPU, I suggest starting with something slightly abrasive, like a dremel hard felt tip that would normally be used with a polishing compound, but in this case you use it dry ( I have erased layer lines in TPU using a dremel tool with a hard felt tip; this was for making toys that a child could throw and would not break )
     
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  20. W1EBR.Gene

    W1EBR.Gene Well-Known Member

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    @Greg Holloway , what's the smallest milling bit size that you found will still work? I am wondering about extruding small (12mm O.D.) Nylon-CF gears and then cutting the teeth with the milling bit.
     

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