DEFAULT_AXIS_STEPS_PER_UNIT Above 999 - T8x2 Leadscrew

Hello,

I need help setting up a new Marlin firmware. I have built a 3D printer (prusa) 18x18x18 custom made... I am using lead screws for all axis (XYZ)...They are not the 4 start 8mm (8mm per turn) but they are T8x2, 8mm single start (2mm per turn) my initial values for the DEFAULT_AXIS_STEPS_PER_UNIT should be:

#define DEFAULT_AXIS_STEPS_PER_UNIT {1600,1600,1600,94.4962144}

I typed those values into the firmware and everything uploads fine, EXCEPT the X and Y axis values show as 600 instead of 1600. The Z axis shows as 1600.00 just fine...

I tried the M92 command (M92 Y1600.00 Z1600.00 X1600.00) followed by the M500... the reply is OK and "settings stored" but when I look at the LCD, it says 600 instead of 1600 for the Y and X axis.

To make sure: I typed the command M92 Y800.00 Z800.00 X800.00 which is half of my steps and should give me half of the distance... I move the axis 100 milimeters using the "move axis menu" and I get 50 (that's what I expected using half of the values)

When I send a M501 command, it reads

Stored settings retrieved
Steps per unit:
M92 X800.00 Y800.00 Z800.00 E94.50

So I know the values for the X and Y that are less than 999 are being stored and used correctly.


I again typed the commands M92 Y1600.00 Z1600.00 X1600.00 followed by the M500 to save the 1600 values into the X and Y...

I checked the settings that I just saved and I get:

Stored settings retrieved
Steps per unit:
M92 X1600.00 Y1600.00 Z1600.00 E94.50

but the X and Y axis don't move correctly as if I had stored 1600 per axis... it moves as if it stored only 600.

The M501 command shows the 1600, but the LCD only shows 600.

Any number that I type above 999 for the X and Y on the DEFAULT_AXIS_STEPS_PER_UNIT only the last 3 digits are saved... Example if I type #define DEFAULT_AXIS_STEPS_PER_UNIT {1200,1200,1200,94.4962144} and when I look on the LCD the X and Y only show 200... The Z would show 1200 though.

Any ideas?

I am using a MKS base 1.4 with 1/16 microstepping.


Thank you very much for the help

It would make no sense to limit steps to 999 as an integer can go to 32000. The LCD however has limited space so they may limit the numbers shown to 3 digits.
Did you test movement at the 1600 steps, it could be set right but only showing the last 3 digits.
The reason for the limit is at 1000 steps per mm you would need 50,000 steps to only go 50 mm/second which is to high for the mega250 marlin was programmed for.
To go 100mm/s at 2mm/rev = 100*60/2 = 3000 rev/minute which is too fast for most steppers. This is why multi start rods are needed.

George

Thanks for the reply.

When I set at 1600 it only shows 600 and behaves as if it was set to 600 as well. I got those leadscrews T8x2 because I wanted to print slow but very accurate large prints (time wasn't a concern on the design)

I guess I will have to switch the T8x2 for the T8x8 four starts

I wonder if there is any way to change the microstepping so like 1/8 so I could use 800 instead.. but I don't have any manuals for this MKS board I have here...

Thanks


Marcos.

Thanks for the replies...

I ended up switching to 8mm 4 start leadscrews... much better.


Thanks for all the help


Marcos.