Setting Extruder to Bed Clearance on a Wilson II Printer

I had to replace the extruder nozzle on my WIlson II printer. The new nozzle
was a little longer than the original and there is 0 clearance between the nozzle
and the bed. I need to adjust this distance but don’t
know what the best process is to do this. Essentially I need to know how to
set the Z-axis home position on this printer. Running the “Auto Home” function
on the printer doesn’t seem to work…?? Any comments/suggestions would be
appreciated. My “slicer” is Simplify3D and setting the Z-axis offset doesn’t seem
to change or help??

so you gotta move your Z axis to the new “zero” (actually a little above the bed, how much of a little depends on your printer), then set zero using

G92 Z0

Then save that to firmware using … M500? Can’t remember that part dang it.

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I have a workaround to make the printer usable (physically lowered the bed).
G92 didn’t seem to work and in my troubleshooting, my bed stopped
heating! The gremlins are out…! Any way, now with the bed, I checked
the power to the bed (assume it should be 12V) and it reads 0. Checked
the printer power supply and there is 12V to the PICA board. It looks like
the BED HEATER is driven by a rather LARGE (physically) MOSFET.
Don’t know much about MOSFETs however measuring voltage at each
of the three legs find two at 0 and the third with a constantly changing
voltage between 4V and 6V. Seems odd, but perhaps this is normal.
In any case I would expect one of the three legs to be at a constant 12V
and none were.

I either have a bad BED or BAD PICA card. I would think if it were
a bad BED I would see 12V at the BED terminals - but I don’t. This leaves
the PICA as the culprit…

Your thoughts??

It’s Marty Rice’s PICA Shield board? That’s what I have on my Mendel90 (I have the 24v version).

Are you measuring the bed terminal voltage while it thinks it’s heating? Yeah should be 12v.

Try measuring the same on the hotend output terminals on the board while it’s heating and see what you get.

If it’s a bad board you may be out of luck, there was a recent thread … somewhere? maybe? where a user was saying Marty’s stuff was disappearing off the net. ETA: you could probably get some help from the Electronics folks here putting a new MOSFET on the board if you want to try to fix it.

The board is Marty’s RAMP. Its looking like the RAMP is bad since there is no power to the board when attempting to “PREHEAT FOR PLA”… Marty has taken down his forums which would have been a good source for parts and/or ideas. I have an OLD RAMP board… there was an issue with it but the issue
was NOT with the bed. I’m going to install it and if the BED heats, I’ll know its the board… then the
next hurdle, as you said, will be finding a replacement!! (BTW, the MOSFET appears to be surface
mounted and the back of the module is bare and I think soldered to the board - would be a bear to

There are several stand-alone MOSFET drivers on AMAZON that would probably work. Unfortunately I would prefer to have a schematic of the RAMPS card before introducing a module that may draw more current than the board is designed for.

Ah that’s too bad, the documentation was on the site where is forums are.

Post a pic of the board please.

I’ll be at the space tomorrow night if you want to bring that board up for me to look at.

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Sure… time and place??? On the MOSFET device shouldn’t I find 12v on one of the three leads?

I’ll be in the Vector area tonight around 6:30 and I’ll try to remember to wear my DMS instructor name tag.


Dumb question - is the fuse intact?

yep… good thought though…the hot end gets hot. Don’t think it draws the current the hot bed does… Steppers all work… Have found a source for the RAMPs card and have ordered one … but would sure like to know has gone bad…

BED HEATING PROBLEM SOLVED - There was either a COLD solder joint at the bed connection or some high resistance at the slip-on crimp connector
at the board. I removed both wires (black and red) and replaced
them both with fresh wire and new crimp-on connectors. The bed now heats as expected… Now, on to a new issue (maybe from swapping out the PICA board)
but AUTO HOME drives the print head (X axis) into the right support.
One step at a time… appreciate your comments…

AUTO HOME drives the print head (X axis) into the right support.

Start by checking your axis dimensions and offset settings, in Marlin, and make sure (M503) they match what’s in the firmware.

Getting lost in the Marlin software. M503 returns some values that look decent. Is there some where
in that code that defines the “home” position? My goal, I would assume, would be to move the print head to be centered between the vertical supports, the bed centered front to back and the z-axis maybe 100mm above the bed. This, to me, would be the “home” position. The other thing I need to find/set is the maxstop positions - this should prevent the head crash. You know of any web site that would be a good tutorial on setting-up 3D printers??

Resolved all the issues and things seem to be working – just can’t get the z-axis adjusted.
Using PREPARE-MOVE-ZAXIS I lower the printhead to Z=00.0 as indicated on the LCD panel.
It will not let me move it lower than Z=00.0 which is OK… but, where does the machine get the
Z-axis lower limit?? At 00.0 the nozzle tip is still 1mm above the bed. Obviously when it starts
to print the filament goes everywhere because it isn’t close enough to adhere to the bed.
M503 returns “M206 Home Offset X0.0 y0.0 z0.0” Is it acceptable to raise/lower the bed to get the clearance I need?? … Suggestions welcomed!!

The z axis length is set in the firmware - in Marlin it’s in configuration.h - 200 mm for example.

When the carriage triggers the Z end stop, it thinks that’s Z=200 (or whatever value is configured). If you want to move farther, adjust the Z length and recompile and upload Marlin. Or you may be able to tweak the axis length with a Mxxx command.

Thank you so much. I very much appreciate your patience. One
more question. I know the MARLIN code defines Z-axis positions. The slicer (S3D in my case) allows Z-axis modifications. The g-code is created without respect to the MARLIN code. I assume the MARLIN code just reads and executes the g-code… so, what effect does this have on the settings in the MARLIN configuration file? Also does the g-code G29 bed level command change any of these or does it just determine the “squareness” of the bed and create offsets to the MARLIN settings compensate for an uneven bed? I
assume a positive offset moves the head AWAY from the bed.

After getting what I think is a good combination of the physical position and
the Z-axis settings, I am still unable to get a print. The initial layer is not sticking to the bed (glass pane). I’m going to test the heat of the bed/glass later to confirm the thermistor is working appropriately…

G29 has different functions depending what what type of automatic bed leveling is specified in the config.h. Most likely, you are using bilinear leveling, which creates a mesh so that the first few layers follow the contours of the bed. On a glass pane, I highly recommend using hairspray or an elmers glue stick. Simplify3D and other slicers create gcode based on what firmware you have selected. By default it is Marlin, but if you want, you could select it for reprapfirmware or other firmwares.