Calibrate Z homing and maximizing bed size

My Ormerod is in great shape right now, thanks to a lot of helped on this forum. Especially from dc42.

However, two things still bother me.

1) Home all + auto bed compensation almost works without any manual labour. The only problem is homing Z where the nozzle is too close to the bed. Maybe 0.4 or so. Therefore, I always to Home all, then set Z to +0.4 and reset Z0, before doing auto bed comp. Is there a way to fix this in a configuration file? I'm running a late version of dc42's firmware.

2) The other issue is bed size which isn't used optimally. I guess I have to configure where all end points are somehow since the don't correspond to the edges of my bed atm. Is there a manual of some sort on how to do this?

Hi,

1. What I think you are doing is using the stock IR sensor, homing Z in the corner, running 4-point bed compensation, and then finding that in the centre of the bed Z=0 is below the surface of the glass. Is that correct?

If so, it's because the acrylic X arm may wave a little under the weight of the head, and/or the sideways force exerted by the Bowden tube varies along the length of the X axis. These factors cause the head to drop slightly in the middle of the X travel, which gives the appearance that the glass is bulging in the centre. Here are some fixes/workarounds:

(a) Use my IR sensor, then you can do Z homing ni the centre of the bed, and also use 5-point bed compensation.

(b) Replacing the acrylic X arm by DaveK's aluminium one may help.

(c) Or just reduce the G31 Z parameter by 0.4mm to allow for the difference between the corners and the centre.

2. If you are using my homing files then you should use the M208 S1 command in config.g to define the X homing position, and on the Ormerod 2 the Y homing position too. On the Ormerod 1, define the Y homing position by the regular M208 command. If you are using the RRP homing files then you need to adjust the G92 commands in homex.g, homey.g and homeall.g to define the homing positions.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Sorry, I should have been more precise. I'm using your IR sensor. I'm doing Z homing in X100 Y100 (and 5 point bed compensation) and I already have the aluminium X arm from DaveK (which is great btw!). Also, I have a piece of white paper below the glass bed. An attempt for better Z homing way back. Can I safely remove that since I'm using your IR sensor? Maybe it's causing issues?

Or does that mean I'm left with (c)?

2.I'm using your firmware with SD files from your branch so I assume I'm using your homing files. Will have a look at that later tonight. Thanks!

Edited 1 time(s). Last edit at 08/18/2015 12:47PM by bitfield.

Quote
bitfield
Also, I have a piece of white paper below the glass bed. An attempt for better Z homing way back. Can I safely remove that since I'm using your IR sensor? Maybe it's causing issues?

DC42's sensor can have problems if you have white paper under it or a reflective glass bed (i.e. A mirror), even the shiny aluminum heat spreader can cause issues

This is from DC42's blog about the mini sensor, which is the same as the hot end board in terms of IR height sensing (I think)

Quote

The sensor works on most print surfaces. However, when using a glass surface, the sensor reading will be affected if there is a very strong reflection from the back of the glass. For this reason, mirror glass is not suitable. If there is a bright aluminium or white plate underneath the glass, then we recommend that you either paint it matt black, or place a sheet of black paper or thin black plastic under the glass.

On a side note, has anyone put the mini IR board on the Ormerod 2 with the acrylic heat spacer? I'm considering going this route vs the full hot end board, hoping to mount on the carriage. I'm using the acrylic spacer for the Aux fan mount, so using the older hot end duct with the DC42 mounting holes isn't really an option for me.

What does Z-1 mean in M208 X-8 Y0 Z-1 S1 ?
Nevermind, I get it. The minimum accepted Z value.

Edited 1 time(s). Last edit at 08/19/2015 02:32AM by bitfield.

I'm not entirely sure how I should set M208.
I want Y0 to be defined as my current Y8. X0 seems to be fine already.

My current config looks like this:

M208 X214 Y210 Z200					; set axis maxima (adjust to suit your machine)
M208 X-8 Y0 Z-1 S1					; set axis minimum (adjust to make X=0 the edge of the bed)

Should the last line read M208 X-8 Y-8 Z-1 S1?

Edited 1 time(s). Last edit at 08/19/2015 02:39AM by bitfield.

Quote
bitfield
I'm not entirely sure how I should set M208.
I want Y0 to be defined as my current Y8. X0 seems to be fine already.

My current config looks like this:

M208 X214 Y210 Z200					; set axis maxima (adjust to suit your machine)
M208 X-8 Y0 Z-1 S1					; set axis minimum (adjust to make X=0 the edge of the bed)

Should the last line read M208 X-8 Y-8 Z-1 S1?

Yes. Setting Y-8 in that command tells the firmware that the lower limit of movement in the Y axis, and the point at which the low-end homing switch triggers, is at -8mm. After doing that, check whether you really can move to Y210 in the positive direction, and reduce the Y210 parameter in the first M208 command if not.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].