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IndustryArena Forum > OpenSource CNC Design Center > OpenSource Software > Initial moves on CNC job varies from time to time
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  1. #1

    Initial moves on CNC job varies from time to time

    Hi,
    I am using GRBL and UGS, and Fusion 360 for CAM, and i am making my very first chips as we speak.

    I have not installed homing switches or Z probe switch yet. I just jog my way to roughly the XY position where i have put my origin in the model and GCODE, then I do the old paper slipping trick for setting the Z height. Afte that, I set all my axes to 0, and press start.

    the funny thing is that sometimes, the spindle moves slightly up and over the workpiece before it moves in XY direction to where it will do its first cuts. This is what i prefer!
    Sometimes though, and more often than not, the spindle start moving directly towards the location for the first cuts, without moving up and over the workpiece at all. It's snapped one of my precious little Proxxon end mills already. i can prepare for it though, because the visualizer in UGS shows me that the first move only involves XY movement.. that's when I zero the Z axis a little higher to avoid crashing. If the stock had any bumps or raised parts though, it would be unavoidable, i believe.

    What i don't understand is what on earth am I doing differently from time to time to "achieve" this, and am I doing it in CAM or UGS, most likely??

    Thanks for any response.

  2. #2
    Registered
    Join Date
    Nov 2012
    Posts
    142

    Re: Initial moves on CNC job varies from time to time

    As I try only using open source software I'm not familiar with how Fusion 360 does things, but the "traverse height" (the minimum Z height to which the tool must rise before doing any non-milling movements) is a distinct concept any CAM processor keeps track of and should let you set as you wish. As such, Fusion 360's CAM (g-code output) processor should let you set it, and you should be mindful of what you set it to, for every project. In this particular case, there are pretty much only two possibilities: either you're unaware of this setting and some of your projects get generated with some default traverse height that is too low or zero, OR the UGS sender, for whatever reason, decides to rip the relevant lines from your g-code (not as outlandish as it sounds - senders routinely mess with the g-code before sending it to GRBL eg. to remove comments or replace arcs with many small linear segments etc. although in this case this removal would be a bug). The easiest way to decide where the problem is would be to load your g-code into a simulator BEFORE ever trying it with UGS, to see if the heights are correct or not. There are a number of these available for free (very useful to see what will happen even when bugs are not involved) - just search for "Basic CNC Viewer", "NCSim", "NC Corrector" or "CAMotics"...

  3. #3
    Member
    Join Date
    Jul 2017
    Posts
    212

    Re: Initial moves on CNC job varies from time to time

    blinklight is correct ..i would imagine its in your cam toolpath program and not UGS..UGS just reads the gcode and then sends that to your machine....you can also open your gcode file in notepad or word pad and see if it shows a Z movement at beginning or not..if its not there the issue is your cam software

    if the z movement is there and your machine is not moving up in z then for some reason UGS is messed up/communication issue

  4. #4
    Member
    Join Date
    Jul 2017
    Posts
    212

    Re: Initial moves on CNC job varies from time to time

    here is a simple GRBL gcode file doing an engraving toolpath with z lift ups

    T1
    G17
    G20
    G0Z0.2500 lift up z .250 to start
    G0X0.0000Y0.0000S16000M3
    G0X2.9941Y4.8417Z0.2000
    G1Z-0.0600F25.0
    G1Y4.8800F50.0
    G1X2.9910Y4.8592
    G1X2.9855Y4.8298
    G1X2.9734Y4.7875
    G1X2.9625Y4.7599
    G1X2.9487Y4.7300
    G1X2.9421Y4.7176
    G1X2.9238Y4.6875
    G1X2.9159Y4.6761
    G1X2.9434Y4.6811
    G1X2.9657Y4.6871
    G1X2.9755Y4.6905
    G1X2.9819Y4.7115
    G1X2.9872Y4.7379
    G1X2.9914Y4.7727
    G1X2.9938Y4.8155
    G1X2.9941Y4.8417
    G1X3.1129Y4.8409
    G1Y5.7566
    G1X2.8797
    G1Y4.9468
    G1X2.8788Y4.9190
    G1X2.8755Y4.8882
    G1X2.8697Y4.8571
    G1X2.8608Y4.8257
    G1X2.8484Y4.7945
    G1X2.8322Y4.7639
    G1X2.8121Y4.7349
    G1X2.7882Y4.7082
    G1X2.7613Y4.6848
    G1X2.7321Y4.6651
    G1X2.7016Y4.6493
    G1X2.6704Y4.6372
    G1X2.6392Y4.6286
    G1X2.6082Y4.6229
    G1X2.5775Y4.6198
    G1X2.5481Y4.6189
    G1X2.5118Y4.6195
    G1X2.4838Y4.6212
    G1Y4.5776
    G1X2.5375Y4.5684
    G1X2.5881Y4.5613
    G1X2.6365Y4.5563
    G1X2.6876Y4.5526
    G1X2.7414Y4.5504
    G1X2.7980Y4.5496
    G1X2.8554Y4.5510
    G1X2.9062Y4.5550
    G1X2.9500Y4.5613
    G1X2.9864Y4.5693
    G1X3.0153Y4.5785
    G1X3.0368Y4.5879
    G1X3.0512Y4.5965
    G1X3.0600Y4.6036
    G1X3.0671Y4.6114
    G1X3.0753Y4.6238
    G1X3.0842Y4.6423
    G1X3.0931Y4.6677
    G1X3.1011Y4.7002
    G1X3.1074Y4.7399
    G1X3.1115Y4.7865
    G1X3.1129Y4.8409
    G1X3.2317Y4.8401
    G1Y5.8755
    G1X2.7609
    G1Y4.9487
    G1X2.7602Y4.9272
    G1X2.7579Y4.9054
    G1X2.7539Y4.8843
    G1X2.7481Y4.8639
    G1X2.7404Y4.8444
    G1X2.7305Y4.8258
    G1X2.7186Y4.8086
    G1X2.7046Y4.7929
    G1X2.6888Y4.7791
    G1X2.6714Y4.7674
    G1X2.6528Y4.7578
    G1X2.6331Y4.7502
    G1X2.6126Y4.7445
    G1X2.5914Y4.7406
    G1X2.5696Y4.7384
    G1X2.5473Y4.7377
    G1X2.5164Y4.7383
    G1X2.4863Y4.7400
    G1X2.4566Y4.7429
    G1X2.4275Y4.7470
    G1X2.3974Y4.7523
    G1X2.3650Y4.7592
    G1Y4.4802
    G1X2.4586Y4.4613
    G1X2.5193Y4.4510
    G1X2.5737Y4.4434
    G1X2.6261Y4.4379
    G1X2.6809Y4.4340
    G1X2.7381Y4.4316
    G1X2.7979Y4.4308
    G1X2.8303Y4.4312
    G1X2.8614Y4.4324
    G1X2.8910Y4.4343
    G1X2.9192Y4.4369
    G1X2.9459Y4.4403
    G1X2.9712Y4.4444
    G1X2.9949Y4.4491
    G1X3.0171Y4.4545
    G1X3.0379Y4.4606
    G1X3.0571Y4.4672
    G1X3.0748Y4.4744
    G1X3.0911Y4.4821
    G1X3.1058Y4.4903
    G1X3.1192Y4.4989
    G1X3.1312Y4.5079
    G1X3.1419Y4.5173
    G1X3.1518Y4.5275
    G1X3.1612Y4.5387
    G1X3.1701Y4.5512
    G1X3.1785Y4.5650
    G1X3.1865Y4.5801
    G1X3.1939Y4.5966
    G1X3.2008Y4.6145
    G1X3.2071Y4.6339
    G1X3.2127Y4.6546
    G1X3.2176Y4.6768
    G1X3.2219Y4.7005
    G1X3.2254Y4.7255
    G1X3.2281Y4.7520
    G1X3.2301Y4.7798
    G1X3.2313Y4.8091
    G1X3.2317Y4.8401
    G0Z0.2000 lifts up z .200 to go to next move

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