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How fast is "fast"? [Leadscrew Poll(ish)]

Discussion in 'CNC Mills/Routers' started by Batcrave, Feb 2, 2020.

  1. Batcrave

    Batcrave Journeyman
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    Question: What (rapid, G0) speed & acceleration settings do you like to run on your (leadscrew-based) Openbuilds machine?

    Backstory:
    I've been troubleshooting some frustrating intermittent stalls lately on my Lead, and there's at least a slim chance that motor tuning may (or may not) be a contributing factor. My machine's not exactly standard issue and just dropping in someone else's settings isn't going to solve anything, but I realized I don't have any sense for what sort of settings anyone else runs with on these Openbuilds machines, and thought it would be interesting to compare notes and see what everyone else is doing - what's "normal", what's cautious, and what incredible and unsafe speed records have you set before accidentally launching the spindle into the living room.

    As a starting point:
    I've got a half-width Lead 1010 with OB-standard 8mm/4-start screws, 185oz/3A NEMA 23 steppers (almost OB-standard), and driving it with a Gecko G540 and 36V/10A power supply. I'd been running around 200ipm rapids, with acceleration around 25-35in/s/s depending on axis and how brave I was feeling at the moment.

    So... what's your machine, and how do you run it?


    (Don't take mine as a recommendation, btw - I'm dragging around a horribly heavy spindle which makes hard acceleration harder. Also, that whole "stall" problem)


    -Bats
    (apologies to anyone who was hoping for a multiple choice poll - there were just too many options to keep straight)
    (also, apologies to anyone expecting it to be in Polish)
     
  2. Wallied

    Wallied New
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    Check ooznest's documentation. They have suggested sttings for GRBL, and if I remember correctly, they suggest a feed limit of 2500mm/min (about 100 ipm) and an acceleration of 150 mm/s^2 (6 i/s^2).

    That being said, I run a rather modded 750x1000 Workbee, and my current settings are a feed limit of 8 m/min (320 ipm) for X&Y, 4 m/min for Z, and acceleration of 750 mm/s^2 (30 i/s^2). These are at 4x microstepping.

    My drivers support up to 256x microstepping, but the feed has to go down accordingly due to the maximum pulserate of an Arduino Uno (about 30 000 Hz), which on a 8mm/rev screw brings us to 8/(4*200)*30000*60 = 18 m/min to be divided between the axes. On 8x microstepping it would be only half that and so forth. I have tried mine at 20m/min without problems, but that's too much for my liking already, and I didn't dare go higher. And for acceleration I stalled at 15m/s^2, instead of staying close to that, I decided to stick to a lower and less violent setting.

    And again, these on a rather heavily modded Workbee, so I don't suggest going straight to high settings like these.

    Regards, Will
     
    Peter Van Der Walt likes this.
  3. Batcrave

    Batcrave Journeyman
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    I'll have to check those out - I always forget that their docs go into a lot more depth on some topics. That said, that sounds awfully slow (both the feed and accel) - but it looks like their stock PSU for the Workbee (and, I think OB's, before the BlackBox) is only 24V, which is going to limit things.

    The G540 runs 10x microstepping (the "full-step morphing" it uses for higher speeds confuses the math a little, so I'm going to pretend it doesn't exist) and I've got Mach 3 set at 65kHz (their tests say the PC should be solid to 100kHz, but I didn't have any reason to push it), so - spindle weight aside - by that equation my 200ipm is in pretty safe territory (especially with the Z generally set more cautiously).

    Yeah, I'd tested some pretty frightening speeds (I think I hit 800ipm with 2Gs acceleration at one point, although it obviously wasn't sustainable), but even aside from stalls, those sort of settings made the Lead sound/feel like it wanted to fly apart. I didn't want to even think about what sort of damage it would do if I crashed while carelessly jogging along at that sort of speed - or what would happen if one side of the gantry stalled while the other kept screaming along. :eek:

    Not to get too far off topic, but any interesting mods? Just the electronics and (presumably) bigger power supply, or have you done structural/mechanical work on it too?


    -Bats
    o/~ It's my tooopic and I'll go off if I want to... o/~
     
  4. Giarc

    Giarc Master
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    I like 2500 mm/min. It works for all woods and plastics I normally cut. If the wood is harder, I just turn the rpms up a little bit. Aluminum is the only thing I cut where I slow it down significantly.
     
  5. Alex Chambers

    Alex Chambers Master
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    Those Ooznest settings are only starting settings (for those who don't know where to start) - you can faster than that if you want to experiment. Like @Giarc I find those settings fine for what I do so haven't bothered changing them (and I am lazy).
    Alex.
     
    Giarc likes this.
  6. Wallied

    Wallied New
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    To clarify, I never cut anything @ 8.000 mm/min, at most @ 4.000 mm/min, and when I do, it's a very light cut. The fast feed limit is for the rapids. I tend to run long programs, often measured in hours. In those scenarios rapid movements end up being a significant chunk of the duration. A chunk that I readily am willing to cut down some. Add to that the fact that I most often actually do the math for feeds and speeds when programming instead of using the same settings for most everything.

    And Batcrave. Yes, the most significant mods are on the electronics side, but a couple I'd mention are having filled my extrusions with 12 mm mild steel and epoxy and tensioning the screws instead of compressing. The machine weighs a lot more after the added steel. Luckily I don't need to move it often ;)
     

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