X Y axis s going out of square due to the dual Y axis rails

I’ve just done my first few carves and noticed this behavior as well. I’ve tried using spacers which help some, but is there a way we could simply add a homing switch to the Y2 side so that when you home the machine it fixes this automatically? Seems like a simple and logical solution, but only if the x-controller supports it somehow.

Have not done it, but I guess you could just wire the two switches in series to accomplish that. No need for an extra connection or modified firmware, just some basic skills working with electronics. You might destroy your limit switches, though.

Adding a homing switch to Y2 won’t accomplish anything since Y1 and Y2 are slaved and actually unaware of each other.
With a 2nd switch on Y2 in line with Y1 will just make Y1 travel past switch point until Y2 switch is triggered.

What you can do is add a spacer screw or similar that act as a hard stop for Y1 / 2 so before each time you power the CNC up you push them up against these two, once power is on they will stay locked relative to each other.

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Yeah I figured they were slaved. It would be nice if the X-controller could slave them until one hits a homing switch and then move the second until it hits it’s homing switch and then reslave them. Oh well…

I suppose I could add stops on both Y1 and Y2 sides up top since the homing switch is on the bottom. Then just push it up before turn it on. Then it could still run it’s homing sequence moving down to the Y1 homing switch stop. I may give that a whirl.

That is what I do, I have reference points I use to align Y1/Y2 - then power up/home.

That’s a limitation of GRBL. GRBL is only a 3 axis system so the “slaving” of the axis is not done via SW but is done via hard wired electrical connections.

If you step up to MACH3 and a Gecko or similar driver, you can get this functionality.

But otherwise, just make some spacers, pull the gantry to the spacers before power-on, and then power on. See my “jig” I made to accomplish this above.

To me, it wasn’t about accuracy. It’s about setting them the same offset everytime so if I put down a piece of wood and it takes multiple power cycles to finish the toolpaths, it’ll always be the same alignment, even if its slightly off.

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most people just use their tall clamp bases to set the Y axis gap against the front bracket. Whenever I’m doing a high precision cut, I’ll usually align a v bit against the top or bottom of my workpiece and run the X-axis back and forth to straighten the workpiece to my Y axis.

Unfortunately this is probably the biggest weakness in the X-Carve design, but it’s inherent to all belt driven systems. The truth is, once you get accustomed to it, it isn’t that big of an issue.

I wouldn’t say ALL belt driven designs. Just those being driven by a three axis control system.

Again, you can step up to MACH3 (presumably also LinuxCNC and others) and get this level of control to square the gantry using switches in MACH3. You just have to have 4 axis control with one axis slaved, which is a GRBL limitation.

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Curious, but how would any belt driven system not get out of square, assuming they use separate steppers? I understand you can use switches to recalibrate, but if you’re using separate steppers, it’s possible to get out of square at any moment during a cut, at least, to my knowledge.

Well you qualified your “all” with an “assuming use separate steppers” after the fact. Therefore, by your statement of an assumption, all doesn’t apply if you’re only using 1 driven side or your belt driving the center of the table moving with a single belt.

There’s plenty of belt driven options that don’t cause an out of square condition. You were just not stating your assumptions when generalizing all were a problem. Do I agree it’s a deficiency with the Xcarve not being able to self correct due to GRBL? Sure. Is it the “biggest weakness in the X-Carve design”? No where close. The Z axis, the 6mm belts, the 24V stepper supply, the Vwheels, the Y axis rails not supported.

In addition, if you properly tension your belts and Vwheels on an Xcarve, you can keep it from going out of square. There’s been plenty of times that I’ll carve 5-10 quick signs, power off for the day and come back the next day and not re-square and everything is fine. It’s about symmetry between axis. I just normally square mine just out of habit.

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while it’s powered it isn’t really any issue (assuming no belt failures), because both motors are being simultaneously driven. same signal, same torque.

but truth be told, nothing is immune to the problem, just varying degrees of resistant to it. just depends on your precision needs. It can still happen on rack and pinion systems and even acme rods and ball screws… although the latter aren’t going to give as much. an outside bearing track (XY plane) can be added in some cases to limit it further and encourage self correction.

Sorry, I just assumed we would be speaking about the design in question. I agree the Z is another big weakness. I’m not familiar with any CNC machines that use a shaft to bridge the Y axis, but I assumed that would be one of the solutions.

Not true. Crank down the Vwheels or severely loosen them to the rail on one side and see what happens. Or have the belts at vastly different tensions and see what happens. You’ll lose steps on one side and not the other.

In a perfect world, if this truly matters to you, when you calibrate you should check both sides and ensure both side’s steps/mm are the same so they are moving the same. If your goal is to maintain square, you should have both sides be moving the same distance given the same steps. Adjusting whatever needs to be adjusted to fix this would bring them “in sync”.

I would think, and this is a big assumption on my part because I’ve got no personal experience, if you’re using a 4 axis system each axis could have an independent steps/mm or equivalent configuration so they both move the same distance and you could calibrate each side since each axis has its own independent step pulse generation. I don’t know how true that is but I personally think that is a logical feature to have.

Am I missing Phil’s comments? I can see responses to him but not the comments. Is this because he was banned?

I have read this thread, re-read this thread, and read it again.

I can’t even count the times I have pressed “Yes, Abandon” to the response to my pressing the “cancel” option when typing in a post to the thread.

Lots of speculation and very little hard data.

For now, I think I’ll just sit on the sidelines and enjoy the show.

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I’ve never liked Elvis…

Yep.

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I included the assumption of basic tuning/maintenance, but yes there are a few more factors that can affect belt systems than others .

Hi Haldor!

Firstly, thank you for all of your invaluable contributions to this forum- you’ve saved my bacon on numerous occasions!

Secondly, I’ve been thinking about this method a lot, and was wondering if both Y1 and Y2 both had “homing bolts” to snug the side rails up against before powering on the X Controller (and thereby locking their positions with the motors), how would the limit switches then work?

If the gantry/side rails assembly is hard up against two Y axis bolts on the operator side of the machine, they would block the limit switch for the Y axis, which is also at the operator side of the machine.

Are you suggesting to place the bolts at the back of the machine instead? As always, I’d really appreciate your insight here.

I’d love to see some pics or a diagram of this setup, if you’d be so kind? I’ve been suffering from ‘trapezoidal gantry syndrome’ for two years now, and I’m ready to throw my machine in the trash.