C-Axis (Angular) and sprockets configuration..

First off let me tell you that what I have works, i just don't know why.

[Edited - Nevermind - I cannot count - the jack outer sprocket is 30 teeth not 40 - The math works]

On my XZC lathe, i have the following mechanical on my "C" axis.

Stepper motor (200 steps/rev)
Driver (Half stepping enabled) - so result is 400 steps / rev)

I have sprocket w/chain setup as the following:

Motor (10 teeth) - > Jack outer (40 teeth) with same spindle Jack inner (10 teeth) -> Lathe spindle (18 teerh).

By my calculations:

400 Steps / Rev * 4 (first reduction) * 1.8 (second reduction) gives me 2880 steps / revolution

So 2880 / 360 (degrees) gives me a scale of 8
When i enter the scale = 8 in the .INI file - and i tell it to run from G0 C0 to G0 C360 it overshoots by quite a lot.

When I change the scale to "6" - it is spot on.

Why? What am i missing?


Here are the relevant portions from my .INI file (I think):

[AXIS_5]
TYPE = ANGULAR
HOME = 0.0
MAX_VELOCITY = 360.0
MAX_ACCELERATION = 1200.0
STEPGEN_MAXACCEL = 1500.0
SCALE = 8.0
FERROR = 1
MIN_FERROR = .25
MIN_LIMIT = -9999.0
MAX_LIMIT = 9999.0
HOME_OFFSET = 0.0

[TRAJ]
AXES = 6
COORDINATES = X Z C
MAX_ANGULAR_VELOCITY = 360.00
DEFAULT_ANGULAR_VELOCITY = 36.00
LINEAR_UNITS = mm
ANGULAR_UNITS = degree
CYCLE_TIME = 0.010
DEFAULT_VELOCITY = 9.50
MAX_LINEAR_VELOCITY = 95.00

cts1085 wrote:

G0 C0 to G0 C360 it overshoots by quite a lot.
When I change the scale to "6" - it is spot on.

I have a similar situation. but even more.

I have five axes on the machine. fifth - the rotary axis.
the simple move from 0 to 180 blows this axis to 202, and then back to 179 and then 180.
even if you move just one degree, axis still overshoots and returns.

why?

Would it be possible to post a picture of the setup? in my case I was really worried about backlash and devised a chain tensioner that keeps the chain seated in the socket - it may be that this is your issue.

please help me calculate the SCALE value for B axis.

there is a stepper motor 1.8 degree step running in the half-step mode
it wears a pulley, with the number of teeth - 18.
the shaft of the reducer also has pulley, with a number of teeth 23
reducer has a gear ratio of 1:80 (passport, ie pdf)
pulleys are connected by a belt, that is, the stepping motor rotates the reducer

just how to calculate SCALE?

Yes, all think so.
SCALE = 113.58024691358
But Linux CNC thinks differently, or more precisely
SCALE = 123.828938408304 (about)
As you have guessed, if there was a question, then it is not that simple.
What could be wrong?
The gear ratio of the gear unit is engraved on its body.
Number of teeth on the pulleys I recounted many times.
The step value?
or there is some other variables that affect LinuxCNC?

andypugh wrote:

What scale number are you using?

now SCALE = 123.828938408304

andypugh wrote:

What would you expect to see?

I expect that when command G0B180 B axis is rotated at 180 degrees. But this does not happen, if the SCALE = 113.58024691358

my INI: