This just a rounding issue with the display of the axis DRO and the fact that you have a low step resolution. If you have 10,000 steps/inch you'll never be accurate to 0.0001" (ten thousandths). It has nothing to do with the actual SmmothStepper HW.

Seriously folks getting your shorts in wad because a DRO shows a 0.0001" discrepancy is ridicules. 99.999% of the machines that folks have on this forum can't resolve down to a ten thousandths of an inch. Also 99.99% of folks here do not the equipment to accurately measure a ten thousandth of an inch. You'll have loads more variation in your part from tool deflection, tool wear, your machine heating/cooling, etc than 0.0001" !

I suggest the people that are worried about this have a look at some of the big names in machining and see what their positioning accuracy is, for example I just looked an Okuma MD series which by all accounts is a very nice machine, positioning accuracy is plus/minus  0.000120"

Hood

Edit
HASS VF11, first one I looked at from them, positioning accuracy plus minus 0.0003

This just a rounding issue with the display of the axis DRO and the fact that you have a low step resolution.

Echo the above.....

Millmaster, Step and direction, no encoders, just plain Jane machines here.

I know how you feel  as i gave been playing around with the an indexer / rotary and when it shows some fraction of 45 deg like 44.9987 it becomes an motional issue..........practicaly it's meaningless....but wanted  to have more exact display so bumped the gearing and now I am non-emotional.  But it's still may be meaningless depending on what your doing with it. 

Off to the sideline,
RICH

Hood,
I have a smoothstepper on a bridgeport style mill with the fourth rotary axis.
millmaster

Jeff and Rich
Can you explain why the DRO rounding issue disappears when I run the mill through a parallel port instead of the smoothstepper?

Rich
Just curious (seeing as you do not have display issues) what are your step settings for the axis on your machines with the smoothstepper?
millmaster

millmaster,
On the lathe the X axis is 12700 steps / unit and i get that silly .0001" difference with the PP or SS.
 It means nothing,  and there is .0003 or 4 backlash anyway and there is nothing that can be done to eliminate it.

All the other axes on the other machines are over 20000 and never had a DRO problem. I am currently not using the SS since i got a new pc, can swap very easily if i wish. Thus i  haven't even tried the latest SS plugin.

What i remember from what someone posted  some time back on the DRO rounding, if the dro display was changed to show 10 places + you would see how things are being rounded. If a number was rounded, that small difference would be added to the next move .....don't take this as an absolute statement and it was some time ago and may be out of context. So no i can't tell why that is happening as it's beyond my understanding of the details. Greg would need to be the definitve source on the rounding manner for his HW.

Are you loosing a step / pulse ( .0001").....A friend came over with a custom built piece of electronic equipement ( borrowed from his workplace lab ) when we were investigating something on threading, i don't have anything that will measure a single lost step electronicaly. I doubt most folks do.

For position / mechanical movement i do it opticaly as it is easier only because i have the equipment to do it and it is much better than any indicator .
RICH

Hood,
I have a smoothstepper on a bridgeport style mill with the fourth rotary axis.
millmaster

Yes, so even if it is a real error rather than just a display issue you are never going to see it or be bothered with it.
 I do agree it was at first an annoyance seeing it, as I  see it on the lathe at times, but for me it is 0.0001mm which makes me think it is a display issue as that is 0.000003937"
 I think there is a good chance if you increase the digits displayed after the decimal in your DROs you will see the 9's go further back.

Hood

when we were investigating something on threading

This had to do measuring  how many pulses were sent to the stepper as compared to output pulses from the index
relative to triggering the axis move. The electronic device measured to so many parts per million of pulses and could
add, subtract, or totalize the pulses from three or four inputs.It was used because,even very high end ditgital scopes are not
as good as that device / it's a custom counter. So you could see the affect of something put in line and compare and see if a pulse was lost. Something proved with pulse counting, was how belt tension and allignment can create a non movement ( call it backlash in the timing belts) of the axis which you would think was due to the ball screw or bearings when in fact it was lack of belt engagement to the pulley and even had an effect over time period ( small but real ).  So where's that lost ( for lack of a better word ) pulse relative to display and  mechanical movement can be get very complex. I'll leave the details to those that know what they are doing and just accept at times that all is well. Again i find out how stupid i am when i get into the expertise or discipline of another.

Not trying to curtail your quest for answers, just sharing experience FWIW,
RICH

I disagree with Jeff about it not being a problem with the smoothstepper, if I run the machine with the parallel port I do not see the leading and lagging on the DROs, when I run the machine with the smoothstepper then the DROs do not match the g-code hence the .0001 lead and lag which leads me to think there is a issue with the smoothstepper. Can you shed some light on that Jeff?
I have three other NC machines, 2 machines have MicroKinetics controllers and the 3rd has a Centroid control, none of these machines have a lead or lag issue, the DROs on them match exactly to what the g-code that is being run at the time (makes for easier troubleshooting g-code issues when things appear to be going sideways), it is just the smoothstepper setup that gives mismatching readings between g-code and DROs, if it was a rounding issue wouldn't other controllers do the same, everything still points to the smoothstepper being the culprit which I think could be made right.

millmaster

There is no doubt that the issue is in the SS and the reason you see it with the SS and not the PP is that when using the PP Mach puts the numbers in the DROs, when using the SS it tells Mach what to put in the DROs.
 Obviously if this issue is not present with Quad outputs then it is the way the SS does things with step/dir only.
Whether its a real position error or just a DRO error I dont know but as said above due to me occasionally seeing it and it just happening to be 0.0001 when I use mm makes me suspect it is a DRO issue, annoying from a visual point of view but no way a problem with the machining even if it was a real error.
 If it can be fixed then I am sure Greg will get round to it but it will be low on the list I suspect.

Hood

Finally someone admits that there is a problem with the smoothstepper. Now how do we get it fixed?? Why would any problem with the smoothstepper be low on Greg's list?? I see Greg is a moderator for this forum why can't he come on the forum and explain everything from the problem to a fix?

millmaster