Z axis homing question and rotary encoder issue

I'm currently half way through the build of a prusa i3. Its my first go at a 3d printer but i still thought i could shop around and reduce my costs over a kit

the configuration is....

Alloy plate frame/ hotbed support
stretched gregs/ wade extruder
J hotend 0.35mm
resistor heater
epcos 100k thermistors
Mk2a hotbed
HP server power supply (bridged the 12v inputs on the ramps board)
arduino Mega
ramps 1.4
smart LCDcontrol panel
Marlin 1.0.0.5
pronterface
slic3r

work done so far....

moded server power supply / bolted to frame
built all the mechanics /motors in / belts on/ bearings in
arduino on
ramps board in (no stepper drives in yet)
power supply conected and tested
marlin firmware configured (to the best of my ability) and uploaded
hotbed led/resistor on / thermistor on, connected to ramps and tested coming up to temp (ir gun) (controlable from pronterface)
J hot end on / thermistor on, connected to ramps and tested coming up to temp (ir gun) (controlable from pronterface)


my next step was to add the home (end) stops...
looking at the printer, the x axis is placed on the left had side... the Y at the back

so first question...

???? Can i place the z axis home stop at the top of the printer so that it homes at the top then steps down to the hotbed?????? will this work with marlin firmware? What do i have to change?

second question.......

I have the smart lcd/sd/rotary encoder board from www.geeetech.com

in configuration.h i enabled this board (and board 33 for the Motherboard) and in the Pins.h i uncomented rapms1.3 compatability

the lcd works.. the sd card initialises and i can sed files to it from pronterface... when i press the rotary encoder the lcd swaps from the information screen to the menu but turning the rotary encoder does not select different menu items.

i clipped a logic analyser to all the pins on the encoder and i'm only getting an output (pulses) on one of the pins when i turn the knob... I get pulses on a different pin when i press the knob in ....



any thoughts? is this broken or is there a configuration issue in the firmware ive missed.


thanks in advance

Ade

IR heat guns are not a good idea for calibrating this stuff. They are set up for a very specific emisitivity from the target. They also have a beam area that may or may not be ideal for your target. The thermistors normally used are 1% devices. They (probably) are >3X better than your IR thermometer.

The settings for X, Y, and Z homing will allow you to set the home position to either the bottom left or top right on your Y carriage. The Z normally does not require any modification. The X and Y both change sign to do this.

There may be a tweak for the rotary encoder on your board. Mine (different board) works fine without a lot of firmware fiddling.

hi...

Thermistors... yip.. i know they are better... but only if they are working... the IR proved that... not accurately ... but....



so...


" The settings for X, Y, and Z homing will allow you to set the home position to either the bottom left or top right on your Y carriage. The Z normally does not require any modification. The X and Y both change sign to do this. "

Ummmm...

Can I home to

the left on x

the back on y

the top on z

then have the co-ordinate system work as normal (not home at 0,0,0 but step to this )




also... i have only ever used one rotay encoder before and it had two pulsed outputs that were out of phase with each other... so it knew what direction the knob was being turned... is this the same!!!

You can home anyplace on the 4 corners of the printer. There are only two locations where the coordinate system works out to allow you to print on the printer after you have homed. Two corners give you a positive Z with a standard file, the other two corners give you a negative Z with a standard gcode file.

so i'm guessing from your comments that ...

the machine has to home at 0,0,0.... and that the work coordinates 0,0,0 and the machine co-ordinates 0,0,0 have to be the same place....

is that correct?


A.

You can set the end stops for max rather than min. If you set them for min, then yes, all of the 0,0,0's are the same. You offset from that 0,0,0 to center the print up. You can also decide to run without end stops and manualy center the X and Y. Then your print could be centered at X=0, Y=0.