Lathe Threading - Spindle & Axis Sync (Resolved)

[hebs]

The video linked shows my slow test result:

https://www.dropbox.com/s/gr6ef8mukwyv6 ... 5.mov?dl=0

In summary:
It appears that each successive pass shifts a little. I understand that a G76 multi pass threading cycle could do this normally with an appropriate angle but I am using a G92 threading cycle, so this shouldn’t be the culprit.

I have shielded the hell out of the encoder signal and it appears to be a consistent error shift, so I am inclined to discount noise as the problem.

Perhaps my encoder Is off by a handful of counts meaning that it shift by the same amount each pass?

It is 2500 counts per quarter => is 10,000 counts per rev which is what I have setup in Acorn (and checked with a laser tachometer - off by about 5%)

I may do some calculations and adjust the encoder counts?

Can anyone suggest anything else?

Many thanks

Keith Hebs

[martyscncgarage]

Thank you for posting the pictures!

You're encoder is incorrect at least from a voltage standpoint. Clearly on the label it says 9-30VDC
Acorn puts out 5VDC which seems to be more typical.

I suggest you replace the encoder. +5VDC Line Driver/Differential required. 1000ppr is sufficient for a spindle encoder.
Info video from Keith on encoder requirements:


Marty

[hebs]

Thanks Marty,

Can you recommend a specific encoder or supplier that can handle 6-7,000 rpm.

I have been through several ‘ebay’ encoders already but they struggle past 2,500 rpm even though they are specc’d to cope.

[Dave_C]

The noise issue may not be external! In my case it was cross talk on non twisted pairs of wires.

For encoders to run at the frequencies that we run them at, we need shielded twisted pair wire. I actually sent my encoder to Centroid and they tested it with no faults but when I put it on the Lathe it would not cut threads.

The ONLY thing I changed out was to put Centroids encoder and wire on. It has worked perfectly ever since without any issues. I can thread as fast as the material can handle. 600 RPM no problem!

So wrapping the cable may not be helping!

Dave C.

[hebs]

Dave,

Are they still selling the centroid encoder? I can’t seem to find it.

[cncsnw]

Centroid does not brand their own encoders. They are usually Dynapar or Quantum encoders.

Go to https://www.centroidcnc.com/centroid_di ... oller.html and search/scroll down to "DC Servo Motor Encoders". You could use any of the 2000-line encoders shown there.

Those are all hollow-shaft flex-mount encoders. If you want a solid-shaft encoder, go to Automation Direct. Their TRDA-2E1024VD, TRD-S1024-VD, or TRD-N1024-RZVWD would all work.

[hebs]

Thank you everyone for the help. I have been through a few wrong (and cheap crap) encoders now. I am in the UK, so ordering from the US is a little tricky.

I believe that RS422 is the same as a line drive differential output, therefore I think this is what I need.
I am sorry for asking people to check my shopping list but I need to ask:

https://uk.rs-online.com/web/p/motion-c ... s/9189086/

Seems to fit the specs, despite not having a twisted pair cable? Perhaps I could solder on my own?

[cncsnw]

Yes, that will probably work.

I would cut the supplied cable off at 6" or so and install a plug (either DE9 or C-Grid, just to be consistent with Centroid typical practice and documentation); then run a shielded twisted-pair cable the rest of the way.

However, there is a good chance that it will work fine just using the supplied cable.

[hebs]

I was really hoping to post details of my success but sadly not!

Ordered the new encoder, machined a new mount for it, got the new encoder, broke the GT2 pulley belt, ordered a new belt, fitted the new belt, tried to turn a simple M10 thread and got the same results Gutted!

The only thing that I have left to try is a fully shielded twisted pair cable - just using a straight fully shielded cable.

Totally at a loss. Perhaps I have some serious noise issues? I have fitted EMI filters to each separate circuit in my cabinet so not sure where else to look?

[martyscncgarage]

Can you post a fresh report?