Help with steps/mm

[czucker 0]

Hi,

I am in the process of cobbling together an Ultimaker2 build platform for my UM Original.

I've been able to find the aluminum plate and linear bearings.

However, it seems that I'm going to have to switch to an 8mm 2mm pitch lead screw like on the UM2.

Can anyone help me out with the settings that I will need to change in the firmware?

Is it as simple as changing the steps/mm from 200.0*8/3 (UM Original) to 200 (UM2)?

I've looked through the configuration.h file and I'm not really sure what I'm looking for.

Thanks,

Chris

 

[Dim3nsioneer 361]

It's actually 200*8/8 but you got it... depending on which Marlin version you're using you don't even have to recompile the firmware; you may just use a M92 command (and an M500 to save it).

If you build a heated bed, you have to change the settings for the heated bed and the bed temperature sensor as well.

 

[anon4321 16]

You need to change the third value in the DEFAULT_AXIS_STEPS_PER_UNIT define in Configuration.h

#define DEFAULT_AXIS_STEPS_PER_UNIT {78.7402,78.7402,200.0*8/3,760*1.1} // default steps per unit for Ultimaker

The values are X, Y, Z and E and the formula is using the Z value as an example:

200.0*8/3

200 - full steps per rev

8 - number of microsteps

3 - pitch

 

[czucker 0]

Thanks for the replies. . . . I'm a touch confused though.

So far as I can tell, since I'm not changing the stepper motor all that is changing is the screw pitch (and diameter). It is going from 3mm to 2mm.

Wouldn't that mean I need to enter 200.0*8/2?

 

[anon4321 16]

Hmmm, I'm a bit confused too.

I believe 200.0*8/2 would be correct for a 2mm pitch.

I think the confusion is because you mentioned like the UM2 which appears to have a 2mm pitch BUT it is a quad helix screw so the effective pitch is 8mm.

But I'm not 100% sure so wait for someone else to confirm.

Or you could just try 200.0*8/2 and have the platform move 2mm. The screw should rotate once.

If I'm correct about the UM2, it would only rotate 1/4 of a turn.

 

Is it as simple as changing the steps/mm from 200.0*8/3 (UM Original) to 200 (UM2)?

 

[anon4321 16]

Pretty sure about the UM2. Even though the pitch is 2mm, there are four helices. Using the controller to move 8mm only results in one revolution. So it has an effective pitch of 8mm.

Actually, looks like the correct term is lead. The UM2 screw has a lead of 8 and a pitch of two.

http://en.wikipedia.org/wiki/Screw_thread

So the formula is really:

The values are X, Y, Z and E and the formula is using the Z value as an example:

 

200.0*8/3

 

200 - full steps per rev

8 - number of microsteps

3 - lead

 

So use the value of the lead in calculating the steps per unit.

 

[czucker 0]

Okay, got it. I didn't realize that about the UM2. That makes more sense.

Thanks a lot for walking me through this. I was even able to find a 4 start rod and nut to match the UM2.

So it'll be 200*8/8 (or just plain old 200).