Mach3 / KX1 Erroneous Limit Switch Detection

This topic has 7 replies, 5 voices, and was last updated 21 May 2026 at 11:33 by Steve Withnell.

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15 May 2026 at 09:37 #848270
Steve Withnell
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@stevewithnell34426
My setup is as shipped by ArcEuroTrade some years back. Dell desktop running XPSP3 and the locked down version of Mach 3 that came on the disk. Vectric Cut2D has coped with everything I’ve done so far, which has been fairly wide ranging. This set up has never missed a beat so far.

This week I set out to do a very simple job, a small instrument panel ten 5mm holes for LED’s and then engrave the LED function underneath.

The engraving job triggers an emergency stop from a false limit switch detection at random intervals. I discovered that the software debounce settings ‘as shipped’ was set to 0, and this has never been an issue. Anyway I’ve upped that to 6mS and the fault remains, sooner or later the engraving job triggers a false limit switch detection.

I’ve waggled all the drag lines to the switches with the machine running and I can’t force this problem.

Next step will be to put some decoupling caps on the inputs to the Mach3 PCB, but I don’t have a schematic or annotated photo of the USB version of the Mach3 control board.

I understand this issue is well documented in this and other forums, but my searches don’t pull anything close.

Any ideas please?
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15 May 2026 at 10:45 #848285
Jim Guthrie
Participant
@jimguthrie82658
Just a note on what happened to me a month or so ago. With pretty well the same setup as you having purchased the KX1 from Arc Euro with the bundled Cut2D.

I was cutting with a 2mm slot drill and all was well. I then had to change to a 0.5mm slot drill to finish off some small details and I started to get intermittent limit switch operation. After a bit of consternation, the cause dawned on me.

I normally work with a 18mm spoil-board on the table but in this case I had opted to work with the workpiece clamped directly to the table. I use an ER25 collet to hold my cutters. With the longer 2mm cutter in use, there was no problem, but with the shorter 0.5mm cutter, the machine was hitting the Z limit switch when lowering to do its cutting.

This was hidden from me since I use an auto height setter which is about 25mm tall, so auto height setting with the shorter cutter was no problem.

I don’t know how you are holding your cutters, but if you are using an ER style collet, then there’s no way shorter cutters can get anywhere near the table surface.

Jim.
15 May 2026 at 11:52 #848296
Steve Withnell
Participant
@stevewithnell34426
Hi Jim,

That was my first thought, I was using an engraving cutter in a collet chuck, so close to the Z limit, even with a 6mm spoil board. So I reset the whole thing around a 50mm thick spoil board and it made no difference. The cutter path is now well within the machine limits and the problem continues. It’s quite random, sometimes it won’t complete a character, then it will complete six.

The status is ‘Limits STOP[Ext-Movement Info]’

Just now, the machine wouldn’t reset without multiple attempts and moving the axes manually would trigger it. Now it’s been running for about 30 minutes without issue, so quite hard to diagnose, I’ve been stood watching the diagnostics panel, but its hard watch without blinking for long periods 🙂 not seen even a flicker on the limit switch indicators.

Thanks

Steve
15 May 2026 at 12:26 #848306
Keith Petley
Participant
@keithpetley53472
Hi Steve,

I converted my KX1 to run Linuxcnc and in the process traced most of the electronics.

The USB card is a Leafboy77 AKZ250, details still on their website here:

https://leafboy77.com/?page_id=25/#downloads

As well as the schematics the manual is quite useful as it gives explanations of the inputs and outputs.

The following pictures are the pinouts as I traced them ( I couldn’t find a way to easily post a pdf ).

Keith
16 May 2026 at 16:29 #848461
Steve Withnell
Participant
@stevewithnell34426
Thanks Keith, good stuff there.
16 May 2026 at 16:43 #848462
Robert Atkinson 2
Participant
@robertatkinson2
Some things to check:

Loose connection or connector affected by vibration

Limit switch worn

Electrical interference

Can you run a couple of test cases, one with no cutter and the spindle turning and one with no cutter and the spindle not turning?
The first to rule out vibration and the second to reduce possible electrical interference.

Robert.
16 May 2026 at 18:02 #848469
Keith Rogers 2
Participant
@keithrogers2
Hi Steve.

I’ve had similar problem with my mill in the past.

Easily cured by running the driver test that’s within Mach 3.

If you haven’t done that I suggest you try it, it may sort it out.

Keith.
21 May 2026 at 11:33 #849052
Steve Withnell
Participant
@stevewithnell34426
Thanks, I wasn’t aware of that. It does seem to be only the engraving job that forces the issue. I ran a two hour pocketing job on a chunk of H30 with a 6mm cutter and the mill never missed a beat.

I’ll run the driver test and see what that reveals. I’ve also noticed there is no ferrite on the USB cable, I have some chunky -31 toroids so I’ll add a couple of those into the set up just in case it’s a PC end issue.
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