nanoDLP

I have never used a top down printer but i guess you set the start position manually according to the level of resin . So from that i guess you will need to "tell" the printer that that = Z home ( or zero)
CW just starts normally and relies on you having manually homed the printer ( or in your case manually set the start point
So if that logic is true then i guess in your start of print job G code, you need to set the Z to zero with the gcode command G92 Z0 
You might also need to make sure the printer is using relative coordinates

Hope this helps

Always tricky when i haven't any experience with top down printing. What sheild are you using. Im intrigued by your statement " i have my shield set to Zero at Bottom" I presume you mean the bottom of your vat?? and this is just to prevent the build platform trying to lower beyond the bottom of the vat ??
It can all get quite confusing with the actual direction of the stepper ( wiring), firmware stepper direction and firmware home at min or max as well as homing direction. 

Option 1 From your recent post in the "After each layer section"  first line i would try changing the "+" to "-"
so >>>     G1 Z{[[LayerPosition]]-[[ZLiftDistance]]}
Worth a try !! ( on a dry run if possible)

Option 2
You might just reverse the stepper by changing the wiring . Its all down to perspective !  WHen you press down your platform should move "down the model" ie the print head (print effect / work point) gets closer to the base layer Try to think of it from the print head & model perspective rather than the physical direction of the platform
Example in a standard Prusa i3 Y axis The print head wants to go away from us to effect a + Y movement but the bed actually moves towards us! 

PS What patched Marlin are you using ? Can you share it or post a link to it ...Thanks

Cheers
Phil
( im big my name is Phil and i currently live in SIngapore hence bigfilsing ( old gamer tag) :-) )

Last edited by bigfilsing (2017-03-11 06:22:09)

Youre welcome. Glad it worked out

Good news and bad news :-)  Bad news = im no expert but learning through research !  Good news is i have a few ideas. To start with take a look at this video which i believe shows a similar setup to what you are trying to achieve >> https://www.youtube.com/watch?v=osoOQjE … yF&index=8
The video at least confirms our previous logic that down = "down" the model and should actually move the platform up in the resin vat.
From what i can see you should try changing your syscall calc for movement from Layer position to Layer thickness so>>  G1 Z{[[LayerThickness]]-[[ZLiftDistance]]}
You may need to change the "-" to "+"
You might also want to control the speed by adding the F variable at the end... see below

Example on my KLD LED 1260 " bottom up" printer i have in the "after each layer" section
M107 ; Turns off the LED light source
G1 Z[[ZLiftDistance]] F200 ; Lift printhead out of resin at F speed
G1 Z{[[LayerThickness]]-[[ZLiftDistance]]} F200 ; move printhead back into resin at Fspeed and by the layer thickness  minus the lift distance ( creating a negative Z movement)
[[Delay3]] ; wait for resin to settle before printing next layer

Hope this helps

Last edited by bigfilsing (2017-03-14 04:36:26)

Thats strange ...Couple of comments
1/ It stopping at layer 240 might be due to your setting for Z height. It is odd but the Z height is expressed in pulses ( rather than mm) Trying increasing that and see if it gets further.
2/ Both the operands "+" & "-" are supported according to the info page so i cant figure out why yours isnt moving !  Basically it should be at one postiion then lift then go back to a position that is the same + or - the layer thickness.
3/ During a print you should be able to go to terminal and issue an M114 gcode which should report back its current position so you can see at least where the machine "thinks" it is

You are welcome . It just so happens that your issues coincide with my experiments . I had it all working with my top down a few months back but "lost" the SD card somehow. Now im back at reconfiguring from scratch

Z height >>For example i have my Z height at 192000 ( which in my case equates to 120mm of travel)  Why this is expressed as pulses is a mystery to me but there's bound to be a good reason for it
If you set the pluses in the setup screen you can then see what actual distance is by going to the calibration screen and looking under "Platform information"

I too get the erratic movement of the Z axis when in the Z calibration screen. Not sure of the issue there ...probably the stock firmware jerk and acceleration settings . Regardless the motion during a print is fine

Last edited by bigfilsing (2017-03-15 13:48:05)

Dejavu  You will have to excuse me for waiting on the celebrations till the test print is complete :-)

Last edited by bigfilsing (2017-03-16 02:45:20)