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  1. #1
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    Oct 2013
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    Backlash inconsistent

    I have been checking the backlash on my router and found that the feed rate affects the amount of backlash. At a slow speed, 100-500 mm/m, I get around .1 to .18 mm backlash but at a feed rate of 1000 to 10000 mm/m I get 0.0 to 0.02 mm. I get this result whatever distance I move, 1,10,100 or 500 mm. What reading should I use? I normally cut wood at 2000 to 3000 mm/m so I’m inclined to have no backlash compensation. What would you recommend?

    Cheers
    Calum

  2. #2
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    Mar 2015
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    Re: Backlash inconsistent

    I assume you measured the backlash by measuring dimensions of the part. If you run at different feed rates, the cutting forces are different. This results in different flex (machine, router bit, etc). The flex adds up to the backlash. The two combined results in parts having wrong dimensions.

    It is easy to compensate for backlash because backlash is "always" the same. Compensate for the flex is quit difficult because flex depends on the cutting forces.

  3. #3
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    Re: Backlash inconsistent

    Sorry I should have added that the backlash was measured using a 1 metre long optical scale that I use to tune my stepper motors, there is minimal load. I go past the reference point the move forward, zero the gage then move forward a set amount the go back to the zero point and observe the backlash on the gage.

  4. #4
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    Re: Backlash inconsistent

    I suspect:
    • if you measure at 10 mm per minute and at 3000 mm/min, the difference will be larger.
    • if you measure in the mid of the router table or at the side, the difference is larger in the mid of the table.
    • If you reduce the acceleration a 100 times, the difference will be less.


    If so, the sag of the belt or spindle is causing the problem.

  5. #5
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    Re: Backlash inconsistent

    Haven’t tried changing the acceleration that may be worth trying. This is not belt driven it’s rack and pinion.

  6. #6
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    Re: Backlash inconsistent

    It is possible, the deceleration causes the backlash to "disappear" at higher feed rates. This is possible if the drag/friction in one direction is higher than in the opposite direction.
    You could measure the backlash from Y- to Y+ and from Y+ to Y-.

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