Thread: Yet another gantry CNC router.
Just thought I'd post a picture of my almost complete router. Works well on aluminium although it generates far more filth than I expected which is causing problems with limit switches.
It uses a HSD liquid cooled spindle and overall I am very happy with it.
CAM workflow is: Draftsight -> LibreCAD -> DXF2GCODE -> OpenSCAM (sanity check) -> LinuxCNC.
All open source and avoids any Microsoft products.
Very nice little machine well done!
Are you getting swarf in the limits switches or are you having false e-stops? Noticed you have a single energy chain so are running stepper power and limit signal lines together.
Out of interest, what is the electrical set up - is that the box just out of shot at the top of the picture?
Yes the enclosure contains stepper drives, VFD, contactors etc.
The problem is due to swarf and I conclusively proved this last night. Should be easy to fix though.
One other big mistake I made was to wire the limit switches into the stepper driver enable line to remove drive on whichever axis has tripped it. This leaves drive to the other two and as it is the z-axis which stops, x and y are free to bury the cutting tool into my work piece which is reasonably catastrophic. You live and learn.
I'm pretty sure Dean runs without a lower Z limit switch for similar reasons you have mentioned above. I also ran without limit and Z home switch for a while as I kept getting false e-stops (longest cables, direct into BoB), but my 24V upgrade should sort that out. You'll have to decide what you are comfortable with.
You could locate the 'lower' limit switch right at the top near the stepper motor housing, then connect a long upside-down 'L' shaped bracket to the Z axis so that when it gets near the bottom the bit of the 'L' which sticks out comes down and presses the top of the switch. This might look a bit untidy but its an option and is well out of the way of the swarf.
If you've been following the recent build logs you'll see some useful circuit diagrams for wiring limits etc. which avoids the problem you mention above. Once you get the bugs out (which is normal by the way!) I think you have a nice little machine there.
Been meaning to ask (as I'm about to do the same) - did you finish the top of the bedplate yourself on another machine or did you have it polished? I can't see machining marks or witness marks at the extremes of travel so I'm guessing you haven't leveled it using the cnc machine?
There is not a lot of point in my opinion of having any limit switch on the bottom of the Z axis as you always have different length tools in the collet etc (so how can you set it) . Also if any limit is tripped the machine should be set up to stop all action on all axis as you will have lost position. ..Clive
Absolutely agree. Now that I have seen the affect of two axis still running. Problem with using the enable line is that it fails very quietly. I only figured the problem out because the z-axis status LED on the stepper drive was solid and the other two blinking (status enabled and ok). I blew all the cr@p off the limit switch and all three LEDs started flashing. I had lost z position and tried to save the job but forgot to home the z again (after clearing the fault). Suffice to say it all ended badly.
The bedplate is 12mm ecocast. It is mounted in a way that I can adjust in situ then clamp it tight. I use a digital indicator mounted in the spindle and have achieved a parallelism of +/- 0.05mm across the table.
I didn't like the finish on the ecocast as it showed every little touch (just wiping swarf left marks) so I used a scouring pad + WD-40 to buff if to a uniform bright finish. This can be achieved every time I want to give it a quick polish.
I am undecided about z-limit. Will have a long look tomorrow.
Isn't it designed to hard stop? I design Z axis so that it looks it would fell from bearing rails, but in reality at a certain moment the ball screw would stop it up or down so the drive will trip if we come to that.
So i agree with all, no switches are needed. Plus you have software limits. Plus you are with Lunix so no excuse on part of software.
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