Z axis falls on one end when I cut power

I’m finding that, when I hit ‘Stop’ on my LCD panel or turn off the power, the -X end of my rails falls down very quickly, but the +X end doesn’t move. Some searching seems to suggest that both ends falling down slowly is normal? Even if it’s normal, it seems like a bad idea, especially if I don’t have software control of my router. . I’ve tried playing with the tension of the slots that the Z rails slide through, and other minor adjustments, trying to either get both sides to fall or neither, but that seems to have no effect. Not sure where I should be looking to find the cause.

Is it really standard to just have the whole gantry crashing down when you cut power? I’m new to CNC stuff, but I’ve got a few friends who are mechanical engineers and they thought that this sounded weird too. I haven’t done much testing yet but it seems like my whole system is working pretty normal, so unless I’m putting a ton of extra stress on the +X end’s Z motor it seems like it should be possible to have it stay in position…

The right way to solve this is have the machine park itself at the end of a job, return to 0,0,0.

Your machine able to fall on it’s own is a good indication your tensions are set well, one side or the other depends on where the router is.

Which stop though? Maybe this is an issue with the TFT sending M84 on a stop. I think you’ve mentioned this before, Ryan.

1 Like

Yeah it could be but if your ending gcode says go back to 0,0,0 and then it powers down nothing happens.

It is only an issue when ending “above last position”

Except 0,0,0 would depend on what part I’m making, wouldn’t it? I don’t really want to be drilling a hole in my table and then having to precisely position all my parts relative to that or something.

That’s the thing though, it doesn’t depend. If the router is on the -X end, the -X end falls. If the router is in the middle, the -X end falls. If the router is on the +X end… the -X end very slowly falls. The +X never falls, even if I apply a bit of pressure to the router sitting on that end.

The stop button on the LCD control. Only one I have right now.

I’m not running any gcode yet, just playing around with the LCD to do some testing.

Yes, but 0,0,0 will never be on your part unless you use it as a center location. As for the hole in the table your Zero should never be lower than a 1mm or two below your table surface, you have full control of router depth before you start.

It also does not matter, it is not a qualifier. If you axis moves up and down when powered everything is as it should be. If it bothers you the tension is slightly off or the screw is not lubed, any sort of little thing causes that. What is does when powered off is not really a thing to worry about.

You should not be using that unless there is an emergency. Everything is controlled in CAM/gcode.

When you do this should all make more sense.

Maybe I’m misunderstanding something, but my idea of the workflow would be, I get a piece of material. lets say a piece of paper for simplicity. I have gcode that wants to draw a border 1/2" from the edges of that paper, and then a design inside it. So my home needs to be positioned relative to somewhere on that piece of paper doesn’t it? Or am I supposed to manually position the paper near some arbitrary hole in the table where the home is and rely on my precise, sub-mm precision by hand to do it?

So, since one side holds itself in place when powered off, and still seems to move up and down okay, then it should be safe to adjust the other side (somehow) to also hold itself in place then? There’s no risk of stressing the motors as long as they’re physically moving fine still? And no risk of the two Z motors moving slightly different amounts since one has more resistance? Plus, if only one side is falling, aren’t I putting a ton of stresses on the assembly? It’s supposed to be at 90 degree angles, but if one side is 8" higher than the other it’s going to be all out of whack

I’m only using that when I have an issue like the tool running into something, not in general use. It’s just an example of one of the two ways that I’m running into where the Z axis falls down. But, since it is an emergency thing… Isn’t that exactly the case where you don’t want your still powered on tool to come crashing down? Say I’m an idiot and put my hand in there, then I hit stop, and now the whole thing comes crashing down on my arm? If there’s an emergency and I need to e-stop the machine, it should stop, not collapse.

From my understanding that is how the lowrider responds to power off. Both sides should drop I believe. Sorry If you hit the RED button router off and all work is lost. If its bad enough for that its gone anyway never put anything soft and blood filled near the blade if you have to put guards in place or a box

Once you start running geode you can pause and it will have the affect you are looking for but you will need a separate such for the router

1 Like

No it does not have to. I know what you are getting at but you are just kind of over thinking it. 99% of the time where your material is makes very little difference. You will usually be cutting inside the sheet of paper leaving plenty of room for hold downs on the side. Those times you leave a side as a reference than you can easily do that as well. I promise once you use it a couple times this is a non-issue.

No and if they do you will know right away. Like I said if they are both moving up and down you are fine. No where in the instructions does it say anything about dropping on power down.

Yes, that is why you do not do that. You have your ending gcode at 000. That is a one time thing and that is in the instructions, maybe even the milling basics page.

Your Z axis should in reality never be more than about 3/4" above the material. You are worried about an odd thing that could happen but where are you planning on getting a 8" bit? I think 1.25" is as long as you can get commonly. So 2.5" max off the surface. The side plates no longer have bottom wheels so they can easily handle a 2.5" lean if some super odd random thing causes that.

Not sure what to say about that. when you kill the power it is coming down.When you kill the power the router should also be killed. at that point if you have your hand under it…

There is nothing you can do other than over tension it to keep it up. If this is really a major concern for you please build a MPCNC.

P.S. Never ever ever leave you machine alone. Be sure you can get to a power strip or E-stop to kill all power in case of an issue. I am sure you were joking but once you kill power nothing on your body should ever be near the machine. Carbide bit do break and send shrapnel flying, eye and ear protection are not optional.

So I’d like, preferably, to either get both sides to fall down, or neither side to fall down. Do you have any pointers on where to look on the YZ assembles regarding this? There must be something not quite aligned but I’m having trouble finding it

In most use cases I have for this, I’m going to be doing cuts with multiple different bits, probably on both sides of the material, and I’m probably going to have the material pre-cut to its proper external size, so aligning everything is super important. That’s why I noted the 1/2" border on the paper. I’m not cutting a piece out of the paper/material, the edges are equally important.

The best I can figure for this right now, I’m probably going to have to put a few alignment points in my material at known, human measurable positions, then make special gcode commands to move the tool to those spots, so I can get my material lined up, then clamp it down and run the actual gcode. Unless there’s a better way?

If you’re cutting on something that you’re not cutting out (like carving a pattern on a cabinet door), then you will most likely want a food external reference. In that case, a fence at X and Y would let you have a good starting place and having zero off to the left somewhere is pretty easy.

But I don’t do that. This is my work flow.

I always start my LR at the front of the table, all the way down. I give each screw a small twist to zero out any tension in the couplers. I pull the machine against the front, which I know is square.

I then power on the machine and use the electronics to jog to the starting position, which may be on my workpiece.

I zero everything and run my gcode. At the end, the machine just waits for me (up to something like 10 mins).

I turn off the router and use the electronics to drive it back to a safe spot to put it down.

There isn’t any stop or estop that is for real safety. The machine isn’t stronger than anyone and you need to keep loose clothing and digits away from the router. No button is going to be fast enough in a true emergency.

The reason for an estop would be to try to salvage your work. In that case, the stop button sucks. Use a power strip for your controller and router and power them both off at the same time. The stop button is really for 3D printers and is more of an “ah crud, I forgot XYZ”. But I also don’t think it should be sending M84. I believe that is a setting in the ini file and can be fixed.

1 Like