Has anyone bought one of these edge finders?

[curiosity22]

Hey G'day folks,

Has anyone bought one of these, do they work ok? Anyone got one to work with UCCNC?

It seems cheap enough to buy for the heck of trying one?!?1

cheers,
Steve
https://www.aliexpress.com/item/1005003579161396.html

Similar Threads:

• Need Help!- Best and most accurate edge finders?
• Electronic edge finders
• Electronic edge finders - any recommendations?
• Edge finders and techniques.

[RCaffin]

I have several touch probes, so of them quite accurate.
Frankly, I never bother with them.

I have had as much joy with a 6.00 mm carbide rod and a feeler gauge, a combo I do use all the time.
I have also used a simple battery/LED arrangement when either the rod or the object can be isolated. 5 um sensitivity there.

Cheers
Roger

[curiosity22]

Hey Roger,

Thanks for the info, I was looking at buying one to fiddle with. I wouldn't mind trying one out to see if it can point cloud an object more for curiosity than anything else. Due to the odd shape of many pieces of timber that I use for carving, was thinking it might find a centre or corner without my having to recite my family history each time as well lol. Do they work within UCCNC?

Cheers and avagreatday.

Steve

[RCaffin]

Well, at least a touch probe is good for measuring the flatness of the mill table. Mine drops off about 10 um on either side (E & W) : warping I suspect in the casting after the T-slots were machined.

Now, software for a touch probe. The problem is that while a human can handle a touch probe in just about any situation with no trouble at all, a general purpose routine for driving one automatically can take several pages of g-code. I have many versions from the web. And even then, some situations get missed.

Can UCCNC handle one? I don't know as I use Mach3, but I would be a bit surprised if it could not. Getting a touch probe to work with a cheap Chinese pulse engine will be another matter: many of the Chinese engines are a shade minimal. This can be hugely painful.

So while I have several 2D and 3D touch probes (some MYOG), and I have even made extra ruby-tipped styluses for them, I very rarely use one. Too much bother. Sorry about that. (Yeah, drilling into tiny ruby balls is great fun.)

Cheers
Roger

[whodwho]

I have one of these and it is actually really well built especially for the price, it was smaller then I thought it was going to be. I have used it for normal edge finding and point cloud mapping.

I am using it with a GRBL controller on a small bench mill, they are available both NO and NC and 5-24v so I don't see why you shouldn't be able to get one to work.

I mapped a BMW M20 piston which has a complex domed crown with an offset dish and it did well (pic is first test on a flat top piston). I ran it at 1mm points and it gave decent resolution but could of probably used a tighter pattern around the valve pockets which I believe you can do smaller higher resolution areas and merge the point clouds.

I did have an issue with it at at first. On the first run it stopped half way through, I tried again and it stopped again. I looked into it and it has a silicon dust boot that is a bit stiff and countered the return spring, I removed the boot and has been good since.

Tripod type probes have inherent inaccuracies but are easier/less expensive to make and are good for most generic non high precision uses.

Touch probe accuracy – Frank's Workshop

[RCaffin]

re Frank's tests
I don't know what sort of touch probe he was using, but it was appallingly BAD.
0.3 mm variation around the circle? The mind boggles!
His results suggest that
* the probe was badly built - asymmetrical
* the stylus shaft was really floppy
* the spring holding the disk down was far too stiff.

Probably all of the above.

Try:
MYOG and Repair Touch Probe Styli

Cheers
Roger

[Rubes]

I have one...actually had to replace it twice due to crashing, so glad I didnt do that with an expensive one.
It seems pretty accurate after you take the time to center the tip. I adjusted the tip to less than .0005 runout.
Not Aerospace quality, but good enough for me.

[whodwho]

Hey Roger, sorry if I posted a bad article... 8^(

I honestly didn't review it, I knew there was an accuracy concern with the tri point probes depending on the orientation of the triangle and the edge and did a quick search for something that 'touched' on the subject.

Glad you mentioned the spring, I didn't want to fix the issue with the original one mentioned with increasing the return spring pressure to counter the boot. With removing the dust boot I used a lighter spring from a ball point pen (same diameter) with less stiffness to aid in trying to help with the tripped point to help with accuracy. It seemed to help with surface probing as the stylus didn't deflect as far when triggering.

Thank you, I will review your post and see if I can apply to the mentioned probe 8^)

[whodwho]

I have one...actually had to replace it twice due to crashing, so glad I didnt do that with an expensive one.
It seems pretty accurate after you take the time to center the tip. I adjusted the tip to less than .0005 runout.
Not Aerospace quality, but good enough for me.

Curious, did it do more damage then just a stylus replacement?

[Rubes]

Curious, did it do more damage then just a stylus replacement?

First crash was an over travel event so just damaged the stylus. But I bought a whole new unit as well as a new stylus. Second crash was a straight down plunge and busted the PCB and another plastic piece inside.

[whodwho]

I could see an opps in the z travel doing some damage. Fortunately the closest I have gotten was forgetting to connect it up and seen it didn't trigger when it touched an edge and hit the panic button in time! 8^)

[curiosity22]

Hey Roger G'day,

Cheers for that mate.

Speaking of Mach3, your not a mach4 user? I heard and read such great things about Mach4 for a long while, the discussion has sorta disappeared.

As for the touch probe, I went and ordered one I'm just to curious as to how quickly I'll hate it or fall in love with it. It won't be the first dollar I've thrown away in pursuit of curiosity. I'm happier to loose around $100 to try one out than pay a few hundred and find its not for me.

It's not much more than ye gods 8 lettuce heads lol.

Cheers,
Steve

[RCaffin]

No, I have not (yet?) made the transition from Mach3 to Mach4.
Yes, Mach3 has a few deep ineradicable bugs, but they are known and I go around them.
And I can program macros with crystal basic fairly easily.
So, right now, it's a case of 'why change'?

Cheers
Roger

[phomann]

The biggest issue with this probe is that it is a N/O configuration. I’m not even sure how they achieve that. As discussed the probe shaft has 3 rods that sit between balls closing the circuit until the probe tip is hit, lifting it off the balls breaking the circuit.
Presumable they invert it with an open collector transistor output or the like.

The problem is that Mach3 or other software doesn’t know when a N/O probe is not plugged in or there is a break in the wiring.
Normally, when a probing routing is executed the first thing it does is check if the probe is active and if so it informs the operator and does not run the probing routine.

With a N/C probe, if it is not plugged in, or has a break in the cable, the input is reported as active, stopping the probing routine from executing. With a N/O probe, in this situation, the routine is run, destroying the probe tip or worse.

My advice is don’t buy a N/O touch probe, find a N/C one.

Cheers,

Peter


Sent from my iPhone using Tapatalk Pro

[RCaffin]

The problem is that Mach3 or other software doesn’t know when a N/O probe is not plugged in or there is a break in the wiring.
Normally, when a probing routing is executed the first thing it does is check if the probe is active and if so it informs the operator and does not run the probing routine.
Well, yes, but no.

Mach3 does not directly sense the signal from the probe. Rather, the signal first goes through the Mach3 input SW buffering, where the Active state as seen by Mach3 can be set to represent either a HI input signal or a LO input signal. This is controlled by the settings in the Config/Port&Pins page, down some distance.

The same applies to the Home and Limits inputs. You can set them how you want. The Step and Dir outputs can also be set to be Active HI or Active LO, as you wish. Which means that if find that an axis motor goes in the opposite direction from what you want, you can reverse it by flipping the Dir output setting, again in Ports&Pins.

If you are using DC servo motors you can do the same reversing thing by swapping the motor wires. You can also reverse the direction of a 4-wire stepper motor by reversing ONE pair of the windings: only ONE. (Either one: it does not matter.)

On the other hand, Mach3 can be confused by a disconnected NO switch IF the electronics do not cater for this, which can be tricky. Having the equivalent of a NC switch is safer in this case. My probes do not have this problem as they have active outputs rather than NC/NO ones. For this reason.

Cheers
Roger

[phomann]

[I]

Mach3 does not directly sense the signal from the probe. Rather, the signal first goes through the Mach3 input SW buffering, where the Active state as seen by Mach3 can be set to represent either a HI input signal or a LO input signal. This is controlled by the settings in the Config/Port&Pins page, down some distance.

Cheers
Roger

Hi Roger,
The Mach3 software buffering has nothing to do with the problem I’m identifying with N/O input devices.

There is no was to tell if a N/O device is connected to a controller’s input.
It is why all safety system devices are configured as N/C.
This includes limit switches, home switches, Estop circuits, etc. Touch probes should also be wired as N/C for the same reason.
Whether Mach3 sees the input as Active Hi or Active Lo is irrelevant. It is to do with the circuit connectivity.

With a N/C circuit, if there is a circuit failure it will present to Mach3 as active (regardless of whether Mach3 sees it as Active hi or Lo). This notifies the operator of the failure.

I would never wire a system with any switch input (home, limit,Estop, probe) as N/O. It is just not safe.

Cheers,

Peter


Sent from my iPhone using Tapatalk Pro

[Rubes]

The difference here is that the NO description is kind of inaccurate or being mis-understood.
If you go to the link provided, it states NPN-NO. You could read that as NPN Normally Off.
It is NOT a simple open or closed switch.
This can be connected to have such a "probe present" detection by placing a pull down resistor on the controller board so that if not plugged in it looks like a closed switch which would cancel the probing function.

[phomann]

Hi Rubes,

A N/O switch and a NPN transistor ARE the same thing in this circuit. They both pull the iProbe output line to 0V when the probe is activated.

Your Pulldown resistor would only work if the breakout board did not have a pull-up resistor on the input. If it did then the pul down resistance was a factor greater than the boards pull-up resistor. In that situation, it would probably keep the input lol (active) even when the probe is plugged in as the probes pull-up is 10K ohms.
Assuming that there are no pull up or pull down resistors on the breakout board inputs, you could use a 100K pulldown to achieve what you are saying.
That said, I don’t know of any breakout boards that don’t have Pull up or down resistors on inputs.

It would be much easier to get a probe with N/C output.

Cheers,

Peter


Sent from my iPhone using Tapatalk Pro

[RCaffin]

It is why all safety system devices are configured as N/C.
This includes limit switches, home switches, Estop circuits, etc. Touch probes should also be wired as N/C for the same reason.
Whether Mach3 sees the input as Active Hi or Active Lo is irrelevant. It is to do with the circuit connectivity.

I suggest that what we have here is a 'dispute' between modern electronics and last-century engineering. Engineering used to rely on big 10 (or 20) amp safety switches to break the power circuit. That worked, then, but it is not the best way to do this today. These days we rely a lot more on computer control and modern electronics.

Moving on to a touch probe, I have to ask whether we should be still relying on last-century techniques or whether we should move into the realm of electronics. That does not mean the problems of distinguishing between a missing touch probe and one with a LO output are gone. I note that a lot of touch probes these days include their own electronics, often within the body. Instead, I suggest it would not be unrealistic to ask that a touch probe should, these days, be a four-wire device: Gnd, +5V, Signal AND a 'probe present' signal. Modern I/O interfaces do not have the older desperate limits on the number of I/O pins available.

OK, in the meantime, compromise has to be made, to distinguish 'missing' from 'Active'.

Cheers

[curiosity22]

LOL I had a good belly laugh and will have to remember "I suggest that what we have here is a 'dispute' between modern electronics and last-century engineering".

I think I can use that comment in a lot of circumstances well said.

Thank you to everyone for your input I am much better educated and have learned something.

Cheers,
Steve