Problem with creating a curve line with precise coordinates

[assen_pandov]

Hello,

I'm trying to create a curve line 61cm with exact coordinate points...  I need precise coordinate on each 16,5mm.

If I use the spline the line doesn't pass on the exact coordinates even if I give tolerance 0.0000.

When I convert it to poly line and  put high precision the CNC struggles to do smooth curve..

If I do it directly with poly line and after that give a "curve fit" should it be better?

Those are the coordinates I need:

0,5.884	0,29.603
7.5,5.504	7.5,29.944
24,4.723	24,30.626
40.5,4.108	40.5,31.235
57,3.502	57,31.800
73.5,2.899	73.5,32.325
90,2.422	90,32.784
106.5,1.991	106.5,33.193
123,1.558	123,33.575
139.5,1.212	139.5,33.892
156,0.944	156,34.139
172.5,0.695	172.5,34.373
189,0.484	189,34.568
205.5,0.326	205.5,34.705
222,0.185	222,34.837
238.5,0.073	238.5,34.941
255,-0.006	255,35.006
271.5,-0.064	271.5,35.059
288,-0.098	288,35.091
304.5,-0.110	304.5,35.102
321,-0.098	321,35.091
337.5,-0.064	337.5,35.059
354,-0.006	354,35.006
370.5,0.082	370.5,34.914
387,0.200	387,34.802
403.5,0.351	403.5,34.660
420,0.536	420,34.469
436.5,0.775	436.5,34.256
453,1.058	453,34.003
469.5,1.375	469.5,33.675
486,1.781	486,33.306
502.5,2.292	502.5,32.850
519,2.780	519,32.331
535.5,3.377	535.5,31.765
552,4.105	552,31.115
568.5,4.777	568.5,30.402
585,5.555	585,29.635
601.5,6.500	601.5,28.791
609,6.935	609,28.374

Can someone suggest me the best way to do it simple, smooth and accurate ?

Thanks in advance

[Kent1Cooper]

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@assen_pandov wrote:

.... If I use the spline the line doesn't pass on the exact coordinates even if I give tolerance 0.0000. ....

---

It does for me:

I put your coordinates into a file that I called junk.txt, in a place where AutoCAD knows to look.  They came in one XY pair per line [I had to remove blank lines between coordinate-value lines], so the file is like this:

0,5.884
0,29.603
7.5,5.504
7.5,29.944

....

[I hope that's the right sequence, and not straight down your left column and then up the right, or something].  Then:

(setq file (open (findfile "junk.txt") "r"))
Command: SPLINE

Current settings: Method=Fit Knots=Chord
Specify first point or [Method/Knots/Object]: (while (setq pt (read-line file)) (command pt))

and ended with Enter to conclude the Spline command, and (close file).

The Spline does pass exactly through those coordinates.  Do you perhaps have the Method option set for Control Vertices rather than Fit Points?

[assen_pandov]

Sorry i put two curve lines... take just one column..

[assen_pandov]

for example on coordiante 370.5,0.082 it passes on 0,0868 .. and it's same with almost all the points..

[Kent1Cooper]

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@assen_pandov wrote:

Sorry i put two curve lines... take just one column..

---

That makes a difference to the result:

but not to the fact that it does go through those exact coordinates, and therefore to the question -- what is the Method option set to in your Spline command, if that's how you're doing it?

[assen_pandov]

method fit points (I paste all the coordinates and give tolerance 0.0000) but still when you zoom they don't pass on exact coordinates

[Kent1Cooper]

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@assen_pandov wrote:

method fit points (I paste all the coordinates and give tolerance 0.0000) but still when you zoom they don't pass on exact coordinates

---

I tried it by just pasting in the list, rather than with the AutoLisp read-the-file approach, and it also goes exactly through those locations.  I don't have any idea why it would not work for you, unless maybe you're in a UCS other than World Coordinates.  Can you post a drawing file with your results?

[Patchy]

I couldn't get them to go through the points neither, they are off by a hair of a flea

Your cnc can handle that.

[Kent1Cooper]

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@Patchy wrote:

I couldn't get them to go through the points neither, they are off by a hair of a flea

....

---

Even in your posted drawing, they do go precisely through those coordinates.  I select the Polyline, hover over a grip until it locks on, and look at the Coordinates display, here at the second vertex from each end:

     

The coordinates agree down to the full 8 decimal places it can display.  I checked a variety of them [not every one], and all agreed exactly.  Where are you seeing them being off?

[Patchy]

I see it when I zoomed in really close.

The point goes thru but the spline is off a little bit.

 

[assen_pandov]

Sorry was driving, will try to post a file or a picture, but I'm new and I will check how to do it now..

This curve is for a speed skating template..even 0,01-2 makes a difference of the desire result..

[Kent1Cooper]

Okay, so it's not a question of fit points not being at the right place, which is what I had assumed.  That kind of deviation appears to be the nature of Splines generally, though I'm not sure.

[assen_pandov]

You did poly line or spline? 

[assen_pandov]

Do you think if I do poly line and put "curve fit" can do the work? or will not be smooth enough?

[Kent1Cooper]

I did a Spline [see my first Reply].

[assen_pandov]

I'm sorry for the stupid question, but how can I do my coordinates more precise and I'm using auto cad 2018, should I always safe the file in older version?

[assen_pandov]

If I change "arc and smoothness circle" to "1" is really off, if I put it to 20000 it's closer.. should I leave it to 20000?

[Patchy]

Have you actually use the file with cnc yet? many don't read splines, they read arcs and polylines

So does it make any difference where it show on the screen and the coordinate points is what matter.

[assen_pandov]

Well I tried it on poly line, but it wasn't with the best result, I tried to put it more accurate with coordinate point on each 1,5mm but it was too much and then the CNC was cutting it was stopping on those point and make small wholes in the metal... so I realise that small steps is not working well

[Kent1Cooper]

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@assen_pandov wrote:

.... should I always safe the file in older version?

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Does it come out more precisely in older versions?  [The drawing you attached has the same issue when opened in 2019 that I have here.]