I have been working on projects with very tight tolerances and some take 2 or 3 days to build. My problem is I can not turn off my unit between tool path changes or repairs, some which take many hours, due to losing my exact location. I have to wait until I am done with said project before I turn off my machine.
I have read that I am damaging my step motors keeping them sitting for long periods with the machine on, But I have no choice and at 25 dollars each I have decided to get spares and keep them handy for when I have a failure.
Can you please offer an upgrade to limit switches that do not re-calibrate after shut off and or setup a system where the machine goes into rest mode without needing a re-calibration on wake up.
Also I think it re calibrates on stop after a pause as well. I am not sure on this but if you make a mistake you have to let the toolpath finish or if you pause and stop, you force a location re-calibration?
If you shut down the steppers, there’s no way to guarantee position wasn’t lost.
Can you explain this?
I was told that the magnet switches do not need a re calibration between shut downs.
I may be totally wrong, I just know I can not turn off my machine without re calibration of x and y and that ruins anything I am working on.
Are you referring to homing? Or “initialization” in CM?
Doesn’t matter what switches you use.
Some say that the proximity sensors are more accurate or precise or repeatable, but I don’t know that anyone has quantified that. The stock switches are pretty good. A step up to high precision limit switches would add a significant cost.
I can not stop mid project and re set my x and y, everything will be off by a small amount. I very carefully tried so many times, I got a blank end mill to reduce random offset by end mill flutes. I secure the touch probe so it does not move when touched. I was under the impression that a set of magnetic switches would cure that by keeping my x y information between machine startups. So if I shut off the machine, I turn it on and my work piece x y is still in memory?
I could be totally wrong here…
the x yz of your work piece is stored in persistent memory. these are relative to the machine zero (e.g. the homing place)
HOWEVER once you turn of the power to the steppers, the machine can move freely and this means it does not know anymore where it is compared to the homing place. the easiest where you can see this is that the Z axis immediately moves down (if you don’t have an HDZ). The only way to get back to a known place is to home… and then it knows where the work piece is again. HOWEVER, homing comes with an inaccuracy…
Sorry I am new to cnc, will magnetic switches fix my issue or no? And is a screen saver not possible?
I do have a HDZ…
How large is the offset/positioning error you are seeing between two homings / on your parts?
Browsing older posts, it seems like there are cases both of people getting as high as 1mm repeatability error, while others saw much lower error, with stock switches. Some of us have upgraded to proximity switches but I agree with @neilferreri that there has been very little actual data reported about exactly how much more precise they are.
There are mechanical things that can explain differences from one machine to the other too, so it’s hard to come up with a definitive answer.
I am brand new to this so I can not say it is not somehow user error. I would see 1 mm or close to that differences randomly on x and y but never exact. I gave up weeks ago trying to re home mid projects and am strictly on a do not turn it off mid project, if the power goes out your screwed system.
However I can cut jigs and flip and switch 30 tools and never have a problem as long as I do not re home.
When/if you have some time between projects to have another go at checking this homing/repeatability problem, it would be interesting I think, you should be able to get (much) better than 1mm. For the long run you don’t want to be stuck to leaving the machine on for hours…
If you later decide to consider upgrading to prox switches, this thread has a couple of interesting (and recent) references for buying them
To start with, the error is going to be up to 1/2 the step distance (1/20mm) — when the machine starts up it’s at a full step position by default — one way to make this startup positioning more consistent is to pull the machine fully into the corner opposite the homing switch and to pull the gantry flush against the endplate — @edwardrford called this “poor man’s homing” and it worked pretty well back before homing switches became the default.
Another possible source of error is the activation range of the switch — not seeing a spec for that at:
so I’d call that negligible — so the question should be is where the 8.4mm operating position falls in the 0.05mm microstep distance. I don’t think aluminum or steel or Delrin stretches or shrinks appreciably at room temperatures, so that effect should be discountable?
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