[Alex__]

Hello,

For an inexpensive CNC machine I am planning to use C7 spindles for all axes. While these are far less expensive than ground C5 spindles one disadvantage is that the pitch can vary quite significantly over the length of the spindle. Can the PlanetCNC software/controller compensate this error? I have seen that other CNC controllers can use a lookup-table where the actual measured pitch (which varies over the length) is stored and then used to compensate during movements. At first glance I did not find such an option in PlanetCNC and am not sure that the API offers such a function either.

Did I overlook something or is there a possibility to achieve this functionality?

Best regards,
Alex

[PlanetCNC]

PlanetCNC does not have this functionality.
But if sub micron accuracy is important to you then screw compensation will not solve anything.

[Alex__]

Thanks for the swift reply.

I am indeed not chasing sub-micron accuracy. On the other hand, the standard C7 grade is specified with a 100 micron error over 300mm and additionally I am not certain that the specification is followed to the letter by every manufacturer. So if there is a software option to cut this in half without spending a factor 5x for C5 grade that would be rather attractive.

Sub micron we leave to the professionals with temperature controlled workshops and all the bells and whistles required.

[PlanetCNC]

C7 has +-50u/300mm,
C5 at 300mm has +-25u with 20u fluctuation.

Accuracy grades C0 to C5 are defined in the linearity and the directional property, and C7 to C10 in the travel distance error in relation to 300 mm.
(in accordance with the JIS standard JIS B 1192 (ISO 3408))

There are much more important things on machine than C5/C7 selection.

[Alex__]

C7 has +-50u/300mm,
C5 at 300mm has +-25u with 20u fluctuation.

Exactly, the error window is 100 micron for C7 and approximately half that for C5. Sorry if my wording was not as accurate.

There are much more important things on machine than C5/C7 selection.

Oh yes, there are a huge number of considerations that are going into a machine. So if there is a software possibility to reduce this number by one that can be much easier than a mechanical change. Often though, as for example with backlash, my personal opinion is that this can only be solved mechanically and no amount of compensation can provide a completely remedy.

So if PlanetCNC would offer pitch compensation as an option that would certainly be useful as this can not really be implemented in a post-processor for g-code but has to live in the machine controller.