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- Does anyone know the formula (s) used for making a...

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05-03-2012 05:15 AM in reply to:
hayalexj

**Without arcs I can't make ellipses**, unless I use hundreds or thousands of small lines from a CADCAM program - which can't be parametric and the reason I'm looking for some formula(s)!

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05-03-2012 05:31 AM in reply to:
norm77

Why wouldn't the formula for hundreds of short lines be parametric?

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05-03-2012 05:43 AM in reply to:
hayalexj

Parametric programming for me and the machines that I take care of is always written manually. Who wants to manually write a program with hundreds or thousands of calculations & lines of code for a machine that at the end of it, and expect to have not made any errors in the program, let alone the crazy amount of time required to do it???

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05-03-2012 02:36 PM in reply to:
norm77

Surely whatever code you have to write would allow some kind of loop such that you just tell it to run the calculation say a thousand times?

You said that you needed a formula that could be calculated in Excel and Excel would not require you to work out each tiny line individually! If you must insist on using inaccurate arcs then you could use the coordinates generated by the accurate formula as the start, end and midpoints to plot arcs.

You said that you needed a formula that could be calculated in Excel and Excel would not require you to work out each tiny line individually! If you must insist on using inaccurate arcs then you could use the coordinates generated by the accurate formula as the start, end and midpoints to plot arcs.

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05-04-2012 05:41 AM in reply to:
hayalexj

hayalexj wrote:

Surely whatever code you have to write would allow some kind of loop such that you just tell it to run the calculation say a thousand times?

You said that you needed a formula that could be calculated in Excel and Excel would not require you to work out each tiny line individually! If you must insist on using inaccurate arcs then you could use the coordinates generated by the accurate formula as the start, end and midpoints to plot arcs.

**I feel like I'm not being listened to. I cannot program ellipses - therefor I have to program arcs. I need formula(s) that can replicate a pellipse from AutoCAD, which requires knowing the start, end, and radius of each and every arc.**

**I've been writing parametric programs for many years for CNC routers, which require formula(s) in order to make them!**

**-Norm**

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05-04-2012 06:43 AM in reply to:
norm77

You "cannot program ellipses - therefor" you should program many lines.

For the record, it's not the best way to do it, but you can just use the trammel formula to generate the three points for each of the arcs.

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05-12-2012 11:05 AM in reply to:
norm77

Norm,

Can you explain how you use autocad to 'program' the cnc machine? Does the cnc machine understand an acad drawing? I presume if it does, then it only 'understands' certain drawing element types (ie arc, lines, but not ellipses).

If what i just said is incorrect, can you explain it a bit more, especially when you say it needs 'formulas'?

I think AGX may be able to help you if I could understand your needs a bit better.

Thanks

John

studioDIGITALresin.

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05-14-2012 04:11 AM in reply to:
norm77

This may not be any help to you, but it happens that if you offset an ellipse in AutoCAD it becomes a spline. So if a spline would be of more use than an ellipse just offset it a certain distance, erase the original ellipse then offset it back.

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05-14-2012 04:45 AM in reply to:
norm77

I doubt it that if the CNC machine cant work with Ellipses, then it wont understand splines. This is a complete guess ;-)

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05-14-2012 06:17 AM in reply to:
hayalexj

I write Gcode programming - my options are only lines and arcs, and the routers do not accept drawings of any kind (no CADCAM on machines). I have limited number of variables so even if I wanted the daunting task of calculating and writing formulas for hundreds of lines, and even with looping it wouldn't work (program space issues then).

When I program any line - I need the X & Y axis location for the start and end points of that line. When I program arcs - I need the X & Y axis start and end points as well as either the radius or the X & Y axis location of the center of the Arc in relation to the start point. I'm not 100% sure, but I don't think that using the Trammel formula **" on 3 point arcs" (which I didn't think of using it that way)** will work because of having to find either the arc's center or the radius.

Basically, I need to enter the Major axis, and Minor axis sizes into 2 variables, and be able to calculate the start, end, and radii of a set number of arcs to mimic an ellipse *or pellipse*. This is why I said that excel can be used in programming. Enter 200 in one cell and 350 in another, and then calculate with formulas the arcs that would make up a quadrant (other quadrants can be mirrored).

A Pellipse in AutoCAD is great because each arc flows into the next because the ending angle of one arc is the starting angle of the next, and there are only 4 arcs which simplifies the calculations required (when you have the formula). I understand how the Pellipse is made (see picture posted earlier in this thread), but I don't have the formula(s) to complete it.

-Norm

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