Z-Axis Homing difficulties

My Z-axis is having a spot of trouble. I'm retrofitting RAMPS to my Makerbot Cupcake, and this is the last bit I need before it works.

If you're looking at the front of the machine, the Y-MIN endstop is at the back, the X-MIN endstop is on the right, and the Z-MAX one is near the top.

The X and Y ones work just fine, the problem lies with the Z-homing. I issue the command, and Z homes first to get out of the way. Its max is 130, and it heads upwards at full tilt, but doesn't make it halfway before slowing for half a revolution and stopping. It moves the same distance each time, and doubling the max to 260 doubles the distance it does go, but neither one brings it the 13 centimeters or so it needs to actually home. I have a sneaking suspicion that my steps/mm are WAY off, and that the machine thinks it's homing more than it is, which is why it cuts off early.

I've tried disabling the software end-stops, and messing with the steps and homing speed, all in Configuration.h, but to no avail. Any advice?

to the best of my knowledge your X min should be on the left or you prints will be a mirror image ( mirrored on the y axis)
Z should home to min ( print nozzel slightly above the print bed)

I don't understand what you mean by "Z homes first" I assume you mean when you press " Home all axes" Which ever way Z should home towards the print bed ( Z min endstop)

In pronterface
When you press Y + the bed should move towards you
When you press X + the hotend should move to the right
When you press Z + the hotend should move up

Good luck



Edited 1 time(s). Last edit at 06/18/2013 11:27AM by bigfilsing.

bigfilsing Wrote:
-------------------------------------------------------

> In pronterface
> When you press Y + the bed should move towards you
>
> When you press X + the hotend should move to the
> right
> When you press Z + the hotend should move up
>
>

On my machine and on all the industrial CNC's I've operated Y+ is away from you, therefore X and Y both home in the - direction X to the left and Y towards you, with the firmware for my Reprap Z homes in the - direction too (towards the bed).

This is different in professional industrial machines where Z homes at the extreme of + (at the top) that way it doesn't risk crashing on the bed,.

Keith

Keith
I think the difference is CNC is a subtractive process whereas 3D printing is additive . That account for the Z axis

I think you have your relative XYdirections the wrong way round but because you have flipped both X and Y your models turn out OK
Tell me when you print does is print as per the orientation seen in the Cura "view" for example ??

Phil

The rule is to think of the tool's motions from the perspective of the table. If you don't keep that perspective, it can seem that some machines move opposite from others, depending on whether it is the tool or the table that is actually moving. Sitting on the table, Y+ is the tool moving to the back of the machine, and so on. That would be the table moving forward in the machine, or the tool moving back in the machine.

Sorry, I was thinking back to front with Y, the table moving towards you makes it Y+ because relatively the hot end is moving away. With the CNC I operated all axes were on the one tower so would move away for Y+ and to the right for X+ and upwards for Z+.

It's not really a matter of 3D being additive and CNC's being subtractive as all the directions are taken care of with the coding, we would write all our own coding (no slicing programs) by moving the head/cutter end to the relative positions and take the position of all 5 axes including B & C, thus the only relavance of whether Z went up or down was what was necessary for cutting in the right place.

The reason that Z homes at the top is as I said, to ensure it doesn't crash into the bed in case of a limit switch failure, the cutting heads are very expensive so are to be protected above other machine parts.

Keith