Advice on setting print area correctly



  • Hi all, I am hoping someone can provide me with some advice/guidance.

    I have managed to get my Duet 2 WiFi working fairly consistently now, despite my lack of understanding causing various problems. However, I am really struggling to understand how I can configure it to work correctly with my current bed dimensions.

    I am using the frame from my original printer (Geeetech prusa i3 pro b) but despite trying different options in the configurator or adjusting my config.g file, I cant seem to work out what I need to do to get the dimensions right.

    My print area should be 200x200x180mm, but using these values doesnt seem to work. When I move axes I often get strange results (moving X to 200 takes it only halfway across the bed for example). When I send an axis to the extent of its printable area, the coordinates shown in web control do not correspond with what I was expecting (for example again, X maxima is about 335 of whatever units web control is showing me, rather than the 200 I am expecting)

    I am sure this is all to do with me not understanding how to set the correct steps per mm (I am using e3d high torque motors for X, Y and both Z axes - have tried to calculate steps per mm but I am not sure if they are correct), and not understanding how microstepping affects everything, but I am baffled and could really use some help

    Is anyone able to explain (in terms a simple man like me can understand) how to correctly set this up?



  • Can you post here your config.g file?

    Is this the stepper you are using? https://e3d-online.dozuki.com/Document/wiwQjVSQdCLQT44I/MT-1704HSM168RE.pdf

    Do you know how many teeth your X/Y stepper's pulleys have? (e.g. 20? 16?, other?)





  • @Harrynice As others have alluded, It does sound rather like you haven't set the steps per mm correctly. A common mistake is to calculate the steps per mm for a 1.8 degree motor but then use these for 0.9 degree motors, which effectively will give half the travel distance (because 1 revolution of a 1.8 degree motor requires 200 full steps but i revolution of a 0.9 degree motor requires 400 full steps).



  • @zapta hi, yes that's the model. Will post up my config.g as soon as I can get to it. Thanks!

    #edit - added config.g - hopefully you will be able to spot where I am going wrong?config.g



  • @deckingman yes, I started with this issue not realising the difference, but have since set the configuration for 0.9 degrees. Problem is I am not entirely sure what the other settings should be - I am using 6mm (is that the belt pitch?) gates powergrip gt2 belts, the motor spindle is 5mm, but I don't know how many teeth to specify!



  • @Harrynice said in Advice on setting print area correctly:

    @deckingman yes, I started with this issue not realising the difference, but have since set the configuration for 0.9 degrees. Problem is I am not entirely sure what the other settings should be - I am using 6mm (is that the belt pitch?) gates powergrip gt2 belts, the motor spindle is 5mm, but I don't know how many teeth to specify!

    Hi,

    You know where in the config file to specify the steps per mm, correct?

    Just command a move of a known distance, say 200 mm, and measure how far it actually moved. Let's call that distance D.

    Then multiply the existing steps per mm by (200 / D) and use that for your new value steps per mm value.

    Repeat as needed to get the correct movement.

    Frederick



  • @Harrynice said in Advice on setting print area correctly:

    @deckingman yes, I started with this issue not realising the difference, but have since set the configuration for 0.9 degrees. Problem is I am not entirely sure what the other settings should be - I am using 6mm (is that the belt pitch?) gates powergrip gt2 belts, the motor spindle is 5mm, but I don't know how many teeth to specify!

    6mm is the belt width which is unimportant. The motor spindle size is also unimportant. gt2 usually means 2mm pitch which is the most common size. So if we know the pitch (distance between teeth) then all we need is the number of teeth on the pulley and you can count these. The most common sizes are 16 teeth and 20 teeth.

    Once you know the number of teeth on the pulley, then you can easily calculate the steps per mm. As an example, let's assume its 20 teeth. The pitch is 2mm so we know that 1 revolution of the motor will be 20 (teeth) x 2 (mm pitch) = 40 mm. For your 0.9 degree motor, we also know that I revolution is 400 full steps. So 40 mm = 400 full steps therefore 1 mm = 10 full steps. We then multiply this by the micro stepping (usually 16x) and end up with 160 (micro) steps per mm. If it was a 16 tooth pulley, then 1 revolution would be 32mm. Divide 400 (step per rev) by 32 (mm/rev) and we get 12.5 full steps per mm. Multiply this by 16 and we get 200 (micro) steps per mm.

    Hopefully, you should be able to calculate the steps per mm for any size pulley with that information - you just need to count the teeth.


  • Moderator

    xy_steps_per_mm = (motor_steps_per_rev ∗ driver_microstep) / (belt_pitch ∗ pulley_number_of_teeth)



  • @deckingman OK - I know that I have both 20 tooth pulleys and idlers, so used your calculation and have set 200 steps per mm for X & Y. The Z axes use 300mm threaded rods/leadscrews with an 8mm pitch, which via the configurator states steps per mm of 800.

    So, I set these values and what do you know? My endstops have stopped working :). For some reason I am now getting a G28 X error (failed to enable endstops). Perhaps I will meet you all in my next question post?

    However, testing using M564 H0 shows that my axes are now all moving the distances I was expecting them to, and so I thank you all once again!



  • @Harrynice No worries. Start a new thread with your new problem. Include the board type and firmware version as well as your config.g file and perhaps your homing files.



  • @deckingman not to worry - managed to resolve the issue 😊


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