Re: [Emc-users] using Screw Comp file are values interpolated question

[Gene Heskett]

On Tuesday 02 October 2018 19:24:50 robert - Innovative-RC wrote:

> Does any one know if the points inbetween nominal values are
> interpolated or not in a screw comp table?
>
> ie if i have 10mm nominal and 20mm nominal with correction values.
> would say 15mm travel become an interpolated value for screw comp?

IIRC yes. The file method is intended to improve the accuracy of screws, 
and not normally needed with ballscrews and  ballnuts. lincurve, the 
loadable module does this also, but can be cross coupled to do an x 
correction according to z position. but needs an offset module to hide 
the difference from LCNC.

Otherwise the correction is seen as a following error so the offset 
module puts the correction in going to the motor, and takes it back out 
of the motors feedback.

This is how I am improving the turning accuracy of a 70 yo Sheldon 11x36 
that has some bed wear just in front of the spindle. I took readings 
every 1/4" and made a curve out of that for a first approximation by 
mounting a .0001 dial to the toolpost, bringing the tailstock up and 
putting the dials finger on its barrel, then took a reading as I used 
the carriage to push the loose tailstock down the bed, the theory being 
that since it rides a different vway on the rear of the bed it s/b 
straighter. This then was cherry picked for high points in the deviation 
and applied to the lincurve modules set points.  So now its only about 2 
thou out, where it was nearly 10 thou out at the start. Now I have a 
laser setup to fine tune that under construction.  The laser itself s/b 
done today, but the camera and some python code are yet to be built.

My AC in the garage has died, so that, if I can get it out of the window 
and onto a worktable, I'm 84 with a bad back, may occupy me today.  Its 
already 77F at 10 am local, and forecast to be a record breaker today.

Something in the control panel has died, and it even runs intermittently 
when turned off, but doesn't cool. All the rain and humidity from 
Florence froze it up into a solid block of ice a month ago, so I expect 
I'll find a bad transistor or a failed capacitor in the control board.  
I am a C.E.T. so if I can get my rusty thinker working again, I s/b able 
to fix it.  No help from Frigidaire of course, its 6 or 8 years old. And 
this time of the year, all the window units have been sold off at fire 
sale prices already to make room for Christmas stuff. Gr.

> i had a look in motion.c , control.c and command.c
>
> but i was unable to decide for my self maybe someone thats more able
> to read and understand the code can tell me for sure.
>
> i did see a slope value get worked out in command.c
>
> /* calculate slopes from previous entry to the new one */
>
>
> thanks, rob
>
I hope my rambling is of some help.

-- 
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 


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Re: [Emc-users] using Screw Comp file are values interpolated question

[Jon Elson]

On 10/02/2018 06:24 PM, robert - Innovative-RC wrote:
Does any one know if the points inbetween nominal values 
are interpolated or not in a screw comp table?


ie if i have 10mm nominal and 20mm nominal with correction 
values. would say 15mm travel become an interpolated value 
for screw comp?



Yes, the correction is interpolated between specified points 
in the comp table.


Jon


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[Emc-users] using Screw Comp file are values interpolated question

[robert - Innovative-RC]

Does any one know if the points inbetween nominal values are 
interpolated or not in a screw comp table?


ie if i have 10mm nominal and 20mm nominal with correction values. would 
say 15mm travel become an interpolated value for screw comp?



i had a look in motion.c , control.c and command.c

but i was unable to decide for my self maybe someone thats more able to 
read and understand the code can tell me for sure.


i did see a slope value get worked out in command.c

/* calculate slopes from previous entry to the new one */


thanks, rob



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