the display of the axes, does not indicate the exact distanc

[DakotaSport07]

1.0mm on axis (X), display reads 1.0000. STEP PER UNIT = 320

1.0mm on axis (Y), display reads 1.0007. STEP PER UNIT = 320.76984763

1.0mm on the (Z) axis, the display reads 0.9994. STEP PER UNIT = 322.19287045

Hi!

(PS: I'm a new user of the UCCNC software recently so maybe it's me who set it wrong or forgot to set some parameter).

My question is… Why does the axis display not show the exact distance ask?

Example: I request a displacement of 1.0mm on the axis (X),
but the display shows a displacement of 0.9998mm.

The result obtained is different depending on the axis.
1.0mm on axis (Y), display reads 1.0007
1.0mm on the (Z) axis, the display reads 0.9994.

This also happens in step mode.
If I adjust to get a 1.0mm step in the "JOG PANEL"
also the display shows the same deviation. Let (for the X axis) be 0.9998.

This discrepancy between the motion request and the result obtained, occurred after having calibrated the axes, using the automatic axis calibration function, included in this software.

I noticed that if I indicate a step per unit without decimal in the "STEP PER UNIT" box, the result is correct.

Next question...After having calibrated the axes, should we make new settings to re-calibrate the software?
(Or something else?)

thank you in advance for your help!

[cncdrive]

Because your steps per value of the axis makes it impossible for the axis to step to that coordinate.
The motor can move the axis only to multiplication of the steps.
For example if your steps per value is 100 then one step is 0.01 units and so if your home position is 0 then your axis can move the 0, 0.01, 0.02, 0.03 etc. your axis cannot move to for example 0.015

[Battwell]

you may find- if you are using the same gearing per axis etc that you are measuring something wrong. ( as your numbers are very similar.)
always measure over the largest distance available.
(or better, calculate exact steps motor to gearing)
if you measure over a small distance any error is multiplied over long distance.
if you measure over maximum travel distance, any error is divided at small distances.

[DakotaSport07]

Because your steps per value of the axis makes it impossible for the axis to step to that coordinate.
The motor can move the axis only to multiplication of the steps.
For example if your steps per value is 100 then one step is 0.01 units and so if your home position is 0 then your axis can move the 0, 0.01, 0.02, 0.03 etc. your axis cannot move to for example 0.015

OK, agreed.
I didn't know that.
Thanks for the information.

[DakotaSport07]

you may find- if you are using the same gearing per axis etc that you are measuring something wrong. ( as your numbers are very similar.)
always measure over the largest distance available.
(or better, calculate exact steps motor to gearing)
if you measure over a small distance any error is multiplied over long distance.
if you measure over maximum travel distance, any error is divided at small distances.

Hi! Thank you for your comment!

Yes I know that it is better to measure over the greatest possible distance, but I do not have what it takes to do it with the maximum precision. I don't have a specific standard.

Regarding the difference in pitch/unit obtained between the axes, it would be caused by the fact that the Chinese ball screws are not all identical. (I learned this on a forum.)

The motors are mounted at the end of the shaft.

Please. If it's not a problem, can you recalculate for me if I have the correct pitch, and set my stepper drivers correctly?

The ball screws are 16 X 5,
Motors are Nema 23 57BYG250C 1.8 degree,
The stepper drivers are DM542s, which I set to 1600.

What is Dip switch number 4 on the stepper drivers for?
I don't know their usefulness.

“Just to discuss and explain how I proceeded…
I measured my displacements using a digital linear dial indicator of 25mm stroke with a resolution of 0.01mm.

I reset the comparator to zero for the start, I ask for 25.0000 mm, and the axis moves 25.00 mm on my dial indicator. (I know, its not a long trip).
I have to deal with.
The repetitiveness seems very good to me.
I repeated the procedure twenty times minimum on each axis, and the displacements requested are always respected. I still have my 25mm and the return is still zero.

PS: It's the display that intrigued me by not indicating exactly 25mm, but if its just the display that's missing 0.0001 to 0.0006, I'll let it be.

Thank you so much!

[Delco]

you may find- if you are using the same gearing per axis etc that you are measuring something wrong. ( as your numbers are very similar.)
always measure over the largest distance available.
(or better, calculate exact steps motor to gearing)
if you measure over a small distance any error is multiplied over long distance.
if you measure over maximum travel distance, any error is divided at small distances.

Hi! Thank you for your comment!

Yes I know that it is better to measure over the greatest possible distance, but I do not have what it takes to do it with the maximum precision. I don't have a specific standard.

Regarding the difference in pitch/unit obtained between the axes, it would be caused by the fact that the Chinese ball screws are not all identical. (I learned this on a forum.)

The motors are mounted at the end of the shaft.

Please. If it's not a problem, can you recalculate for me if I have the correct pitch, and set my stepper drivers correctly?

The ball screws are 16 X 5,
Motors are Nema 23 57BYG250C 1.8 degree,
The stepper drivers are DM542s, which I set to 1600.

What is Dip switch number 4 on the stepper drivers for?
I don't know their usefulness.

“Just to discuss and explain how I proceeded…
I measured my displacements using a digital linear dial indicator of 25mm stroke with a resolution of 0.01mm.

I reset the comparator to zero for the start, I ask for 25.0000 mm, and the axis moves 25.00 mm on my dial indicator. (I know, its not a long trip).
I have to deal with.
The repetitiveness seems very good to me.
I repeated the procedure twenty times minimum on each axis, and the displacements requested are always respected. I still have my 25mm and the return is still zero.

PS: It's the display that intrigued me by not indicating exactly 25mm, but if its just the display that's missing 0.0001 to 0.0006, I'll let it be.

Thank you so much!

The problem with only doing it over 25mm is if its really 25.05mm ( actually hard to get within 0.05mm visually ) then when you do 250mm then it will measure 250.50mm , therefore 2500mm will actually be 2505.00mm . A large error. Easier to get it accurate over the largest distance you can so that at smaller distance the error is less . ie if you did it over 1000mm but it was actually 1000.5 ,very easy to get within 0.5mm then over the 25mm its actually 25.0125mm so a very small error in magnitude .
That being said doing it over 25mm is a good way to get you into the ballpark before you use the calibration tool over a larger distance to gain the acurracy.

Units are whatever you decide , then issue a gcode command to go from metric to imperial and visa versa.

[wmgeorge]

But UNCNC does not recognize G20 or G21 to switch from Imperial or Inches to Metric or vs versa. A mm unit is different from a inch unit when it comes to moving the axis. If I have a project on the router 27 x 8 x .750 inches if that is in metric there will be a difference. The software is Metric.

Units are whatever you decide , then issue a gcode command to go from metric to imperial and visa versa.
Delco

[ger21]

But UNCNC does not recognize G20 or G21 to switch from Imperial or Inches to Metric or vs versa

It's just not that simple to implement. Even in Mach3 it's recommended to use separate profiles, as sooner or later you'll end up with a machine crash, from something that was missed in the G20/G21 implementation.

[wmgeorge]

Yes, I am going to try Soft Limits Again in Mach4 but decided to just give up on the Inches thing and since all my files are in VCarve Pro just use the Mach3 mm post processor or UNCNC one if its there. Thanks again Gerry and the others for answering my questions!