Problems with synchronising spindle for screwcutting

I am configuring a lathe using a Mk3 board and PlanetCNC software. I believe that I have correctly connected and configured everything, but I cannot get the spindle to synchronise for screwcutting. Each pass starts in a different place.

I am using a 100PPR spindle encoder, belt-driven from the spindle via 1-1 pulleys. I have AB and index pulses connected to the CTRL port.

When I turn the spindle slowly by hand, the spindle speed is shown in the display (so I believe that the encoder AB pulses are correctly wired) and I see the Index LED on the IO panel flash once per rev.

The speed display appears to be correct - spindle speed shown is within a few percent of the set speed. On the "Spindle" settings page, I have set PPR=100, Index PPR=1, and debounce to 0. I have tried "Spindle RPM" and "Sync Signal" with all combinations of "From Index" and "From Encoder" without this making any difference.

I have tried to read through the "Settings" section of the manual (copy which came with the software distribution dated 2022/07/25) but I see that there are at least one or two parameters in the Settings dialogue that are not described in the manual. Specifically, under Settings->Program Options->Speed, there is an entry for "Sync Speed" and I have no idea what that does or if it is relevant here - but it sounds as if it might be!

I particularly want to use this CNC lathe for screwcutting so I am getting very frustrated...

Thanks in advance for any help or comments,

Brian

(In case it is relevant, I am generating toolpaths using Fusion 360 and the PlanetCNC turning post-processor. This appears to generate G33 commands for threading.)

I am still exploring this problem. I have found the setting that specifies where the screen spindle speed readout is derived - Set Speed, Index, or Encoder. I get a stable (apart from a small variation - not sure if this is an encoder signal issue or if the speed does change slightly) result from if I use "Encoder". However, if I use the Index signal, the speed readout is all over the place - completely random numbers from very small to over 30000 - and I know that my lathe can't manage that!

Looking through the manuals, the Planet CNC web site, and the settings screen, I see that there is a "Debounce" setting under Spindle->Encoder but the manual says that this is a setting for "encoder signals" but the web site guide to encoder wiring says "Index". Which is right? I shall try playing with it tomorrow - I have had enough for one day! I can imagine that if there is not a steady index signal then screwcutting sync is impossible. However, I would appreciate any comments from anyone who has gone through this process.

Surely I don't need to go to the lengths of installing opto-isolators, etc?

Thanks,

I tried playing with the "debounce" setting and setting it to 5ms helped the speed readout jitter a little, but not very much. I then tried selecting "Invert" for the encoder index signal, and suddenly the problem went away. With the spindle free-running (i.e. not cutting) there is a fluctuation of around 0.1% or less in the speed readout, so 500RPM might flicker slightly by +-0.3. That seems pretty good to me. I am using the index signal to drive the screen speed display.

I then tried screwcutting and I am now getting what appears to be reliable spindle sync, taking successive passes at 300RPM.

I have no idea if anyone is going to read this, but it might come up on a search and help someone in the future.

I was just preparing response for you. I'm glad that you solved problem.

I'm guessing that the TNG board wanted a longer index pulse and inverting the input turned a short pulse into a long one! I'm surprised as the index pulse is no shorter than the quadrature pulses, but I have no visibility of the input circuitry or pulse detection method used. Important thing is that it does now seem to work.

Pulse must be longer than debounce. If you set debounce to 0 then pulse can be very short.

I have the same problem which no matter what signal I use, encoder or index, the rpm reading is all over the place. I'm using MK1 software, no debounce or invert encoder signal here. I tried invert and fast option for index and reverse for the encoder. None of them works for me. What else could I try?

Opto isolate encoder from controller, use good power supply for encoder and properly shielded cable. Make sure you use high speed optocouplers.

My lathe use servo motor 80ST-M02430 as spindle. I noticed when I enable the spindle motor the interference happens. Not only to the encoder, but sometimes also disconnects the communication between mk3/4 board to the software. What could the interference come from and how should I solve it? I do use shielded encoder cable, should I also connect the shielding layer to the GND on the control board? I'm currently using common cathode connection method, does it matter it I change it to common anode method?

Do you have filter and/or isolation transformer for your servo driver? Check your driver user manual.

Hi,
is the servo drive direct off-line? That is to say is it powered by 230VAC direct from the mains supply? Such servo drives are very VERY common but they have an issue
in that they 'pollute' the mains supply with harmonics that result from how the rectifiers inside the drive work.

At the very VERY least you need a two stage EMI filter on the AC input to the drive. If the drive is particularly troublesome then you need a line reactor in addition to the
EMI filter. These devices are to try to contain the harmonic energy to the servo drive and prevent that energy getting onto the local supply where it can upset of much more
sensitive electronics devices, your controller for instance.

VFDs are the same. I was having the occasional fault when I was pushing my spindle hard. I fitted an EMI filter and it helped, but when I made and fitted a line reactor I've never had
a spindle induced noise issue ever since.

As an example, this is a two stage 16A EMI filter:

https://nz.element14.com/schaffner/f...sis/dp/1191381

Craig

I'm trying optocoupler connection. It's NPN encoder to PNP optocoupler. When optocoupler is connected to the controller board, on IO panel, it shows ABZ all green. Is it normal, should it be all red instead? I tried inverse option for encoder and nothing changed.