So, I have nearly finished the assembly of my X5SA Pro… Although I was prepared to use shim steel in order to get everything square and accurate, I was not expecting to use multiple washers to fill in the gaps caused by some manufacturing issues
But my big issue is the missing Z axis limit switch… Maybe the inordinate amount of spare nuts, bolts and screws, but I have double checked and I have not missed anything. I have read and re-read the destruction book, and there is nowhere any mention of a z axis limit. This will be further confirmed when I start connecting everything. So the question would be to any other owners of this machine… Is there any capability to add another limit switch, and if not, how have you solved the issue?
If there is no loom capability for a limit switch, I am considering adding a microswitch to the place obviously made for a Z axis limit, and using that to cause a 4 pole relay to break the A and B sides of both z-axis motors… Are there any better options?
If the Printer has bed levelling then it does not really need a Z limit because the sensor in the printhead is used instead; as both the limit switch and as a bed mapping probe when needed.
Edit: A quick websearch later and yes; it has a ‘touch’ bed levelling sensor. So that is being used in lieu of a physical switch at the top of the frame and associated wiring & complexity.
I accept there is a levelling sensor, and I must admit to being quite excited to try this. After all, my first printer was a MK1 replicator, made of laser cut plywood and a bed size of about 2 square inches and nothing else… Even my last FDM printer was nothing special and needed the bed to be manually adjusted… So this auto levelling sounds good…
But (you could tell that word was coming couldn’t you ), on every CNC machine I have ever worked on, there is always a hard limit switch… I would feel more comfortable knowing that if it all went mamories upwards, I will not damage the x-y axis
If the sensor is reliable then it won’t be an issue. These machines are based on common RepRap and OpenMake components so adding a switch yourself is easy (physically), bupotentially tricky from a software/config perspective (depending on your IT skill level).
This is typical of machines at this sort of price-point, it’s a simple engineering/production compromise. A more sophisticated machine or one with heavier construction may well take a more (Belt aand Braces (*)) approach, but that will reflect in the price.
(*) The American translation is ‘Belt and Suspenders’ but that sounds really silly in my native UK English for… reasons.
It all depends on who is wearing the suspenders…
If it is a nice librarian type with long blonde hair, then suspenders are fine… If it is an overweight slob holding up his trousers, then there would be an issue
But if I was to say that the printer is made of aluminium, and the colour is black, then you should be able to guess my native language
And if that does not help, then if I were to say I went to Ilkley Moor bah tat, then you would even get my county…
My IT skills are ok, but not brilliant. I first learned programming in the days of Z80 processors and direct hex input… We thought that BASIC was for lazy buggers. Then I had a 30 odd year break from software (I went down the hardware route and joined the navy as an RO), before learning Arduino IDE. But the idea of a hard limit is that it does not run through software. Therefore if all fails it still prevents a crash… So the idea being that I use a microswitch running 24v through the NC contacts, feeding a 4 pole relay. If I connect the A and B coils of each stepper through the NO contacts of a 4 pole relay, then I have a fully working hard stop, with no software requirements at all… Regardless of software errors, motherboard crashes or logic lock-ups, the hard limit would still work…
While my SK-Tank kit came with hardware for a Z limit, the kit manufacturer recommended against using it. So I didn’t hook it up at all, and just use Z probing at the head.
My Qidi X-Max 3 has no separate Z sensor at all; it likewise uses the probe on the head.
A limit switch is just a position sensor. And the Z probe is just a position sensor. On a 3D printer, it is not normal for any of the limit switches to be “hard” because they are used for homing. They are soft in the sense that they are interpreted by software. (It’s the same on my CNC router, where honestly I ran it for a long time with no limit switches and no homing and just set work coordinates where I wanted them.)
In fact, my Qidi X-Max 3 doesn’t even have independent switches to measure X and Y. It takes advantage of “sensorless” homing; the stepper driver just senses the back-emf when hitting the hard, physical limit and stops.
In general, 3D printers have motors that trade off power for speed and responsiveness (low inertia) and if they run into a limit, they are not nearly powerful enough to break the hardware.
Now, the two z motors on your Tronxy could, if not kept in sync, rack your bed support. On my X5S, I replaced them with a motor and a long gt2 belt loop so that one motor ran both sides and stayed in sync. But no limit switch is going to protect you from racking the bed anyway.
I got lucky with my Tronxy X5S; the frame components actually went together very square, which was why when I gave up on most of the printer and started over, I was able to reuse the frame.
In the end, I did include my own limit switch modification.
It does not run through the controller, it is purely a hardware failsafe. Just a microswitch and a relay to stop A and B coils of each of the Z axis motors.
As far as the controller is concerned, there is no hard Z axis limit. And I hope never to have to find out if my modification actually works. the only indication I have is an LED. So there is no change to the existing wiring loom.
The z-probe is still the primary method of height control.
It may be overkill, but it makes me feel more secure…
That’s basically unplugging the steppers while running, which is… a great way to destroy the stepper motor drivers.
If you really want a hard Z limit, use it the switch to cut the input power, rather than suddenly interrupting the stepper coils. You’ll get the same protection, but with less potential for damage.
