no slower feedrate possible

Hello everyone,

I use the repetier host with the repetier firmware to controll my DIY-Laser/Plasmacutter.
The Hardware ist an ArduinoMega and a RAMPS-Board.

The slowest feedrate for Plasmacutting is ok, but for lasercutting (of black paper) i need very slow movements.
(My Laserdiode is not very strong).
Every change of the "G1 Fxxxxx" has an influence in the movement speed, but at a certain point (approx. G1 F<400) there is no slower speed possible.
I assume there is somewhere a minimum-speed-setpoint.

Has someone an Idea to solve my little problem?

Thanks

DomiMa

Yes, there is a minimum speed or acceleration will start with a first step that is way too long, so it is to solve a mathematical problem with explicit integration. The part is in Printer.cpp:

    float accel = RMath::max(maxAccelerationMMPerSquareSecond[X_AXIS],maxTravelAccelerationMMPerSquareSecond[X_AXIS]);
    minimumSpeed = accel*sqrt(2.0f/(axisStepsPerMM[X_AXIS]*accel));
    accel = RMath::max(maxAccelerationMMPerSquareSecond[Z_AXIS],maxTravelAccelerationMMPerSquareSecond[Z_AXIS]);
    minimumZSpeed = accel*sqrt(2.0f/(axisStepsPerMM[Z_AXIS]*accel));

As you see, you can influence it with a different acceleration. Or you set it simply to a fixed value and ignore the jerk at acceleration start.

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Hi repetier,

thank you for your answer. It solved my problem.
Reducing the acceleration of "Printing" from 1000 to (ridiculous) 5mm/s² and "Travelling" 1000 to 50mm/s² allows me now feedrates of 100mm/min.
At slower feedrates the problem comes back again. But 100mm/min is fine for me.

Thank you so much.

DomiMa

I am trying to convert my 3d printer into a laser cutter/engraver/etcher. I am using the same electronics as you, Arduino mega, ramps 1.4 and I'm using marlin. How do you connect the laser to the ramps board? Also are you able to have the laser be power % control or is it just simply on/off. What software do you use to give you the proper g code to?