How to repeatably break the Z limit switch on an HDZ

Just for the record: the fact that the Z axis does not stop when hitting the switch when retract is set to something higher than the available remaining travel, is because the limit switches are intentionally ignored DURING a job, to prevent false positive detections (people would be about 9000 times madder that their 15 hours 3d carve was ruined due to a false limit switch detection near the end). And since there is no such thing as a perfect filtering/robust signalling (not without a lot of complications), false detections cannot be ruled out. So it’s a design choice, it’s debatable, but it’s the least of two evils, at least this is my understanding of why things are setup like this (and what a number of previous threads on this topic highlighted).

I for one would vote that switches be ignored only after the initial retract move.

One can enable soft limits (and/or even hard limits), but you need to know what you are doing, and it does not fit very well with the fact that CM has its own internal soft limits, so overall it is not recommended.

My $0.002: it’s just easier to double-check that your retract height is consistent with the available Z travel.

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The switch, although a good switch, is simply in the wrong place. There isn’t enough overtravel in the switch to accommodate how far the axis (all of them) can move before hitting the physical stops. This is why they fail. You can also break them by pushing them past the “click” with your finger while trying to test an axis, or manually moving the axis into a stop. The switches are just plain mounted 1-2 mm too close to the edge on the entire machine (you can look up the total safe travel, and acceptable overtravel in the switch spec sheet). They’re great switches, but they don’t have the internal overtravel to manage where they’re mounted.

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That seems to be consistent with the manufacturer’s data sheet for the switch family, 2.7mm overtravel.

I guess I’ll be continuing to mis-mount mine until those brackets for the proximity switches are available and I can switch over.

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Thx Julien,

I understand the noise problem with using the switches as limit, we’d need to do a whole load of de-noising for that to be remotely near the right balance.

With regard to the soft-limits though, Carbide can’t be the only machine that it’s best not to slam into the end-stops, is there any more reading / info you could point me to on how the soft limits work in GRBL and why they’re not a good idea with CM pls?

Phil,

I have got quite quick at soldering them :wink:

There’s a thread where the part numbers and digikey / mouser sources are discussed if that helps?

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About those soft limits, here’s a great post from @neilferreri

EDIT: and I mention this because he educated me on the fact that soft limits WILL address this retract crash (I initially thought they wouldn’t)

The fundamentals are on the GRBL page here

As to why CM has its own internal soft limits instead of using GRBL’s ones… I…would need to go and read about that in old posts and…I’m in a tunnel, I’m losing you…brzzzz… :slight_smile:

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Thx Julien,

There seem to be a few informative threads with the right search string.

I guess I could choose to see this as another straw on the pile of excuses I’m building to go to the dark side and CNCjs…

But more seriously, I think it’s worth spelling out to HDZ users that it is possible to physically damage to the home switch just by exceeding the retract limit until there’s a fix with either proximity switches or a mount that’s within the allowable overtravel from the vendor. It might save support some postage on new switches for starters. From experience I know how frustrating it is to not be able to continue because you can no longer initialise your machine after mashing the Z home switch.

The fix being something like “If you are setting a high zero for a tall workpiece or an ‘air cut’ be very very careful with your retract heights in your CAM software and make sure you’re not going to hit the Z limit” - or do what I have done and file off the locating peg on one side of the switch and make the position check a regular maintenance item.

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Why not just go simple and add a hard stop? Looks like a longer Z stepper bolt just might work.

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Yeah,

I was reading a thread yesterday on mycncuk where a guy 3D printed the secondary wipers for his HiWin rails out of a flexible filament and I was thinking that printing a “bumper” for the Z travel might work quite well for a softer and less switch-mashing impact.

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Incorporate the switch overtravel limit into the hard stop bumper that is also the switch mounting bracket that swings out of the way instead of breaking. :smiley:

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The solution in my case, (I broke one about 2days after installing the HDZ and never got a replacement)
Was to make a simple aluminum bracket to hold one of my $0.25 lever arm switches I had on hand. It’s worked fine ever since. And it has overtravel of probably 10mm before it will break or even move… I don’t use fusion, so that was not my problem… I’d bet you can find similar with same hole dimensions.
While the oem switches are not cheap, as I’ve mentioned before, they are VERY Fragile

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Having looked at the problem for a while I thought that the shave the pin off the switch idea was probably not likely to be generally acceptable to other HDZ owners, I also wanted to keep the very repeatable precision Omron switches (I’ve used Omron before and their stuff is Japanese quality for the most part).

I have implemented a simple rubbery buffer instead which allows the Z to home but provides a soft landing when the GCode sails past the disabled soft limits and heads for a home switch mashing hard stop. This is only until I can replace the whole lot with proximity switches as a permanent solution;

Two layers of the 3mm thick neoprene rubber stuck together and cut to match the shape of the Z stepper mount, that’s approx 6mm or 0.25 inches (which is how much more than the 2.7mm allowable the HDZ over-travels);


This is then stuck to the bottom of the Z motor mount where the top of the moving Z carriage otherwise impacts it, next to the home switch;

During homing there is still clearance with the switch in the normal position and the homing appears to work normally, however there is not sufficient compression in the rubber to allow for switch crunching over-travel, probably also a bit better for the ballscrew to take a soft landing on the physical travel limit;

It’s not very pretty but it’s simple, cheap and works.

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Very cool hack, I like the simplicity.

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I would love to see an official Carbide3D “solution” to this problem. I have an HDZ which has worked fine for hundreds of carves since I installed it, but a few weeks ago on the initialization sequence it crushed the Z limit switch. I wonder if the switch went bad before the initialize causing the Z to crash on the sequence but who knows.

I wonder if the inductive homing switch retrofit which is supposedly coming “soon” will resolve this.

One would certainly hope so, if it doesn’t I’ll just be making my own brackets for the proximity switches.

I’ve also yet to find anything more specific than “difficult to diagnose support problems” as an explanation of why soft limits are disabled with CM, I’d like to hear from anyone who’s actually had soft limit problems about what they are pls.

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I suppose it wouldn’t hurt to experiment with soft limits. I turned soft limits on since I have my custom Suckit retrofit and found the Reduced X Travel HDZ settings conservative. Just jogging, within inches of my soft limit set points would prompt a pop up alert about over travel. I thought it was predicting steps when jogging using Fast speed but it was more limiting (during jogging) than the Reduced X setting, so I just toggle between the Full X during large projects/surfacing and the Reduced X when I‘m being more cautious.

I may do more testing now that the Z-axis homing switch issue has been brought to my attention. If I go through all of my spare switches, I’ll migrate over to proximity switches.

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the prox switches work quite well… no internal switch parts to break even if you bump them.

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Is there a tutorial or video on wiring the proximity switches.

Brown to +5V, Blue to Ground, Black to your switch input.
This is assuming you have 5v proximity switches with that color scheme (all I’ve seen until I saw the connectors on the C3D switches)

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Try it? As Trump says “What have you got to loose?” (to convince people of color to vote for him in 2016). :wink:

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