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  1. #31
    Quote Originally Posted by jimbowley View Post
    I'll probably go back to 16 microsteps giving a max feed around 2300 as I don't think I'll be needing 4700 mm/min.
    Be aware that this will put more stress on the parallel port as your needing twice the pulses to travel same distance no matter what the speed so your open to missed steps if the PP struggles at higher feeds.!
    Don't think of MS in terms of increasing resolution because in reality at this level it doesn't really it has bigger affect on smoothing the motors. But it does come at a price by putting the system under more stress. With machines running external motion control cards this isn't an issue but it can be trouble some for PP driven machines. Esp if using cheap drives and Bob's etc.!

  2. #32
    I'll leave it at 8 then, and enjoy high speed rapids over my 60x60mm workpiece :)

    2 new drivers arrived today. Everything now appears to be working. I took one of the dodgy ones apart and the heatsinking was poor - blob of paste covering about 25% of the surface area. A nicely ground bit of aluminium plate between chip and heatink, but it had been chopped leaving a burr which lifts the end!

    Before I do any sustained work, I think I will take my good ones apart and ensure a good heatsink connection.

    Also spotted one very poor solder connection, so there is a posiibility of fixing the bad ones.

    I did take the goods ones apart, and made sure the heatsinking was good. The 2 replacements, and the one original that worked had smaller (but flatter) heat sink pads than the faulty ones. Indicating that the design is at least evolving! The pad edges still needed a clean up though, and the paste was still only 20% coverage.
    Click image for larger version. 

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    Last edited by jimbo_cnc; 08-09-2014 at 11:01 AM.

  3. #33
    So what was causing the faults / resets when jogging from the keyboard ? did you change the breakout board ?
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  4. #34
    2x faulty Tongka M542 drivers. It would appear that the original BOB is OK.
    Last edited by jimbo_cnc; 30-08-2014 at 11:31 PM.

  5. #35
    YAY! first cnc cuts done.

    Another Mach3 mistake though. I set Z high and ran the gcode in free air, double checking the x and y extents weren't going to hit the vice. But the way I stopped mach3, set Z zero and then started again meant that it re-started mid code. Instead if doc 1.5mm with my 3.2mm cutter, it plunged to 9mm and started pocketing. The noise wasn't too bad, I only stopped it because the pocket was filling up with 15mm long strands of swarf all standing up and filling the pocket.

    So I went back to line 0 this time and started again, much quieter.

    At least I know that cutter is good for more than 1.5mm doc !

    feed was 800mm/min, RPM 11500 (need to adjust my vfd as that's the max I can get)

  6. #36
    Somewhat risky for a newb like me to have metal screws in the work area, but I took a chance. All went well until I hit the z-axis limit switches (piss poor planning) in the middle of my job. In the confusion I did the same as before, started the job mid program but I'd done a goto zero. I should have noticed it was heading off inthe wrong direction but I wasn't ready ready to pounce onthe stop button.

    The tool scored a direct hit on a holding down screw.

    Hopefull no damage to my spindle.Click image for larger version. 

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    All seemed to be going well but I've got one concern. The third pocket, is undersized slightly eg 13.85mm instead of 14.0mm in the long axis direction. Does that indicate missed steps?

    I ran it again at 70% feed and another sliver got taken off one face, so now 0.10mm undersize rather than 0.15mm.

  7. #37
    I think I understand the undersize problem on long axis, I think it comes from slack on the long axis bearings. I can feel slack when I rock the gantry back and forward (on top of the flexibilty).

    The setup is SBR20 round supported rails with matching bearings. I don't suppose they are adjustable? or maybe I can buy adjustable repalcements?

  8. #38

    Quote Originally Posted by jimbowley View Post
    Somewhat risky for a newb like me to have metal screws in the work area.
    whenever I'm not sure if everything will be OK I put some styrofoam on the machine (with doublesided tape) and add a mechanical stop to the z-axis just before the tool touches the machine bed. This way you don't need to worry about breaking anything even if things go completely wrong.

    2D / 3D CAM Software and CNC controller:

  9. #39
    Quote Originally Posted by jimbowley View Post
    The setup is SBR20 round supported rails with matching bearings. I don't suppose they are adjustable? or maybe I can buy adjustable repalcements?
    Some of the SBR20 bearings have a little grub screw in the bearing housing which will let you take some play out but still not good ideal.

    Unfortunately this is what you get with these low spec machines so you either accept and work around or start going down the upgrade route which soon gets you to the point of diminishing returns. Problem is you quickly get to the point where the machine structure becomes the weak link and then you may as well just start a new build as it will be cheaper and probably easier.

    Wrecking cutters and material is just part of the learning curve and after a few cutters and sheets you soon start paying more attention to what the machines doing and reacting quicker. To be honest even now after running millions of lines of G-code if I break cutters it's nearly always from clipping something like a screw or clamp on way to home or some fixture offset.
    One of the common Gotcha's for new users is when the machine goes homes or Rapid moves to some point on table it doesn't always take the route you expect. This is true when moving two or more axis at same time to a point on table. The motion planner will interpolate the path and move at feed rate so all axis arrive at same time.
    So what happens is that while you think it will clear clamps because at the commanded feed rate for that axis it would be no where near the clamp the planner actually slows or speeds up that axis to ensure all axis arrive at same time. This catches many out, esp with Z axis because when retracting the other axis are moving fast because they have a long distance to travel but the Z axis gets slowed right down to ensure they arrive at same time. So the cutter doesn't clear clamps or material like you'd expect..!! . . . . . . This is why you should have Safe Z enabled in Mach3 when homing but in G-code it doesn't apply so can Catch you out if code is produced this way.!

  10. #40
    Well inspection of the linear bearings revealed that one grub screw was loose, and one was missing. It may have shaken loose but I couldn't see it on the floor.

    Quick tighten up (no idea how tight to do these so I just pinched it up) with M6 screw inserted for the missing grub screw. And now the slack has gone

    The flexibilty remains, but that can be managed.
    Last edited by jimbo_cnc; 04-09-2014 at 10:36 PM.

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