G2 and G3

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  • July 29, 2018 at 2:08 pm #11064
    DrewHamilton
    Member

    Hi,
    I’m having some issues with my TinyG outputting straight lines instead of arcs when I send it G2 and G3. As far as I can tell, this does not happen every time. I am sending these to a small Sherline lathe. I have successfully turned a bigger radius (R0.3655) on the end of a small brass part, but the Tiny G seems to be turning other G2’s and G3’s into G1’s or potentially just utter nonsense moves. My current theory is that this happens below a certain R value, but I can’t say for sure. My chordal tolerance was set at 0.01″, I dropped this to 0.001″, and later 0.0001″. The minimum arc segment length ($ma) = 0.004″.
    ChiliPeppr is loading my geometry and everything looks correct.

    Is there a minimum size for geometry with the Tiny G. I’d like to be able to turn pretty small little radii.

    July 29, 2018 at 2:40 pm #11065
    DrewHamilton
    Member

    I did a little further testing. Here is some test code I ran. The Tiny G ran all of the arcs perfectly except for the last 3. Instead of running these, it skipped straight from line N7 to N11 and made a rapid move back to X3 Y0.

    N1 G20
    N2 G0 X3 Y0
    N3 G3 X2.293 Y0.076 R0.5 F5
    N4 G3 X1.5 Y0.0 R0.4 F5
    N5 G3 X0.939 Y0.0 R0.3 F5
    N6 G3 X0.539 Y0.0 R0.2 F5
    N7 G3 X0.342 Y0.0 R0.1 F3
    N8 G3 X0.186 Y0.0 R0.08 F2
    N9 G3 X0.106 Y0.0 R0.04 F0.5
    N10 G3 X0.066 Y0.0 R0.02 F0.5
    N11 G0 X3 Y0

    July 29, 2018 at 3:03 pm #11066
    cmcgrath5035
    Moderator

    tinyG does have limitations on some G2 and G3 moves.
    It has implemented rather strict check for arc start and end points based on gCode specifications.
    Is this manually generated gCode, or output from a CAD to gCode translator?
    Are you in inch mode or mm mode? MM frequently works better. All tinyG internals are in mm, inch commands and data are converted first into mm, with some inevitable loss of precision(its 8 bit math).

    the CP display on screen is essentially a gCode plotting package and does not include the rules checking that goes on within tinG

    July 29, 2018 at 3:32 pm #11067
    DrewHamilton
    Member

    I am in inch mode.

    That last snippet of code was written out by hand. I had trimmed off past the 3rd decimal place to see if it helped. Just recently I tried running a few more tests that were mathematical exact endpoints:

    G0 X3 Y0
    G3 X2.3000 Y0.0000 R0.46098 F5
    G3 X1.5000 Y0.0000 R0.40 F5
    G3 X0.9000 Y0.0000 R0.30 F5
    G3 X0.5000 Y0.0000 R0.20 F5
    G3 X0.3000 Y0.0000 R0.10 F3
    G3 X0.1020 Y0.0000 R0.099 F2
    G3 X-0.078 Y0.0000 R0.090 F0.5
    G0 X3 Y0

    I tried this with both 3 and 4 decimal places, and it still fails to run anything with a radius under 0.1″, which tells me there is some setting somewhere that prevents radii under that specific value from being cut.

    I have tried every possible combination for $ct and $ma (chord length and minimum arc length) and these do not have any effect.

    July 29, 2018 at 3:54 pm #11068
    DrewHamilton
    Member

    So, I tried converting this GCode to mm, and it turns out that was the issue. Very small arcs need to be in mm, or there will be errors finding the equation for the arc, I’m guessing. I was able to trace arcs with a radius of 0.1mm with no issue. It’s a bit of a pain in the neck having to convert units, but it will work for my application.

    This code worked:
    N1 G21
    N2 G0 X76.20 Y0
    N3 G3 X58.420 Y0.0000 R8.890 F200
    N4 G3 X38.100 Y0.0000 R10.160 F200
    N5 G3 X22.860 Y0.0000 R7.620 F200
    N6 G3 X12.700 Y0.0000 R5.080 F200
    N7 G3 X7.620 Y0.0000 R2.540 F200
    N8 G3 X2.620 Y0.0000 R2.500 F200
    N9 G3 X0.620 Y0.0000 R1 F50
    N10 G3 X-0.380 Y0.0000 R0.5 F25
    N11 G3 X-0.580 Y0.0000 R0.1 F12
    N12 G0 X76.20 Y0

    I hope this helps someone having issues with:
    1. TinyG not cutting arcs.
    2. TinyG small arc problem
    3. TinyG G2/G3 problem
    4. TinyG mm inch conversion problem.

    July 30, 2018 at 5:10 am #11069
    cmcgrath5035
    Moderator

    Good news!
    Thanks for the summary

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