Need help with lathe threading

skunkworks wrote:

if you think your encoder setup is correct - are you sure your Z axis scale is correct?
 

Yes, X and Z move exact distances, no issues there.

That is the reason I'm here, I've tried so many things without making any progress, I figured the experts here might point me in the right direction. It's probably something simple I'm not seeing.

Have you verified the encoder scale?
Make a mark on the spindle and then start linuxcnc and look at signal spindle-revs. It should be 0. Rotate 1 full rev by hand, spindle-revs should be 1 or close to 1.

Metal wrote:

...
I'm using an encoder that have 60 pulses per revolution, phase A, B, and Z
...
The problem I'm having is,   If the spindle is rotating above 120 RPM the thread pitch is off ...
...
It seems to me with the encoder I'm using I should be able to use much higher RPMs,
...
 

If this means that thread pitch is right below 120 rpm then something is most probably wrong with the encoder.
Care to share more info about this encoder? I usually see encoders with much higher than 60ppr. (BTW there is no Z phase on any encoders, you are most probably referring to the Index signal) 

JPL wrote:

Metal wrote:

...
I'm using an encoder that have 60 pulses per revolution, phase A, B, and Z
...
The problem I'm having is,   If the spindle is rotating above 120 RPM the thread pitch is off ...
...
It seems to me with the encoder I'm using I should be able to use much higher RPMs,
...
 
If this means that thread pitch is right below 120 rpm then something is most probably wrong with the encoder.
Care to share more info about this encoder? I usually see encoders with much higher than 60ppr. (BTW there is no Z phase on any encoders, you are most probably referring to the Index signal) 
 

Here is a link to the encoder I'm using www.ebay.com/itm/123868112309

That encoder has "NPN" or open collector outputs which
need external pullup resistors.

Do you have stiff pullup resistors on the A and index outputs?
(say 1K or even 470 Ohm to 5V)

PCW wrote:

That encoder has "NPN" or open collector outputs which
need external pullup resistors.

Do you have stiff pullup resistors on the A and index outputs?
(say 1K or even 470 Ohm to 5V)
 

No, I did not do that.
I may have some laying around, so I will try to get that done today and report back.
Thank you guys!

OK bear with me guys, I'm by no means an electronics guy but can solder stuff and in most cases get by with basic understanding of what I'm trying to do.

That said, I found a couple of 800Ohm resistors and soldered them in this configuration.
 

I did another test cut and I did not changed the spindle rpm and it cut in the same grove as last night, which is the wrong pitch.
In other words, adding resistors did not make a difference.

Here is a screenshot of my signals on the hal scope
 

Here is how I'm connecting it to BOB (minus the B signal)
 

I didn't realize you were using that type of BOB
Those should work with NPN outputs without pullups
(as the inputs are pulled up by design)

Can you plot with a bit faster sweep speed so the edges can be counted a bit better
(and perhaps at a higher speed that should result in counting issues)

PCW wrote:

I didn't realize you were using that type of BOB
Those should work with NPN outputs without pullups
(as the inputs are pulled up by design)

Can you plot with a bit faster sweep speed so the edges can be counted a bit better
(and perhaps at a higher speed that should result in counting issues)
 

OK, this is running the spindle at 400RPM
I hope this is what you're asking for
 

 
 

Hummm, something seems to be wrong with phase A. Looks like it is skipping pulses all over the place...