Wednesday, September 2, 2009

Pictures of the rebuilt Bertha now a CNC

Note Big Berthas PSU's and microstepping controllers are on the shelf under bertha thought I would get Bertha working before going bigger.

I'm having trouble with the Z end stop / home using EMC2 on Ubuntu 8.04 with emc 2.3.0

When trying to home the Z Axis I get a problem with this message "home switch inactive before start of backoff move"

I first tried to use EMC on this little 3 stage machine

I put this project to one side thinking it had a faulty embedded micro switch.
For Bertha I decided to use infrared opto end stops as used on a reprap 3D printer.

Picture of all 3 Opto endstops Z then Y and X at the bottom note the fully shielded USB cable going to Z.
X and Y home exactly as expected on the bigger machine as the did on the tiny machine however Z will only some time home mainly giving the fault condition message "home switch inactive before start of backoff move"

I re wired the opto swich with Shielded cable ( an old USB lead) as I suspected stepper motor noise could be giving false readings I also decoupled the supply with high an low value capacitors for high and low frequency noise.

Neither of these fixes solved this problem Im not quite sure where to investigate next.

The Linux is Ubunto 8.04 from the CNC install CD from this site so the EMC version is 2.3.0 the mother board is an ITX Gigabyte Atom as it has a parallel port.

All ideas and suggestions welcome.

Is there a file that you can adjust the sensitivity of the hysterise on the home switch?

Is this a known issue with the mother board Im using.. ?

Is there a way to de-bounce the Z home switch in SW?

A picture of the Works in side the top box..

I get 30mm/s travel on Bertha using a 10mm 2mm pitch trapezodial drive shaft if I run it faster which it can do I get a tolerance / friction vibration from the Nylon corner blocks on the 8mm bar.

A front view or contol pannel view

Yes it is tuly amazing the things I can build in Migdes Kitchen.. and get away with..


  1. Nice blog. I tried to leave a reply on Linuxcnc's forum but had a login issue on this computer.

    There is a debounce feature to desensitize EMC's response to RF on the limit lines. Take a look at the manual (pdf copy found on every EMC install or at

  2. Thank you ~ ooops think I have fallen over with a RTFM problem. looking now

  3. Wow impressive, have you been able to mill anything with it yet ??????

    On de-bouncing you can do it using discrete components like this

    Worth a look at.

    Hope this helps.



  4. Yes well it had a 24 hour unintentional soak test using a pic to gcode file that turned out to be 220,000 lines of G code.. Opps.. I stopped it after 117,000 Gcode lines.
    Midge was not too happy about the constant noise it made tho..

    It will be making the all the mounting holes for the linear Slide bearings on Big Bertha once I figure out how to write the G code for drilling.

  5. Yes I meant to say the problem was solved, by increasing the size of the plastic IR blocking tab, after chasing many red herrings.

    Switching noise caused by vibration from the stepper drives The tab needed to be 1/4" bigger to eliminate the problem.