Helical Curve Inacurate?

Genius
Genius

Hi All,

 

Can someone please explain why the Helical Curve feature produces different results when the same input is used.

 

To get the angle I need I put a quick little spreadsheet together to give me the height, number of turns and Pitch from a specific angle.

 

To get a 21° angle 184mm high I need a pitch of 282.19mm and the number of turns will be 0.652 on a circle of 234mm Dia.

 

2017-02-18_15h55_36.png

 

Below are a number of screen shots showing the results from three different ways to produce the same thing in the Helical Curve command. First the one that produces the incorrect result "Constant Pitch" Note that the actual length of the curve is 205.23mm yet the dialog box says 184mm

 

2017-02-18_15h52_07.png

 

Now lets produce the same thing using "Compound" Note that all the inputs are the same as for "Constant Pitch" yet the resulting curve is the correct height.

 

2017-02-18_15h53_13.png

 

Finally "Variable Pitch" again the same inputs yet again the result is correct at 184mm.

 

2017-02-18_15h53_38.png

 

Am I missing something or is there a genuine issue here?

 

6 REPLIES

Re: Helical Curve Inacurate?

Solution Partner Phenom Solution Partner Phenom
Solution Partner Phenom

Hi Neil,

answer is: a genuine issue.

 

It is already logged to dev.

 

Ota

Re: Helical Curve Inacurate?

Genius
Genius
Thanks once again Ota. I trust that this error has not caused anyone undue issues with peoples design.

Neil...

Re: Helical Curve Inacurate?

Phenom
Phenom

Hi @ota_poul2 - digging up an old post but I came across this issue today in ST9 MP10 and remembered this thread.  You mentioned it had been logged already - do you know if this is fixed in ST10? Seems like it is the kind of thing that would have also been fixed in an ST9 maintainance pack if so.


Thanks,

Alex

Re: Helical Curve Inacurate?

Honored Contributor
Honored Contributor

Hi @Alex_H

 

 

taking a look into the MP2 readme shows an entry regarding helical curves.

Should be tested!

 



regards
Wolfgang

Re: Helical Curve Inacurate?

Phenom
Phenom

@hawcad thanks, that's exactly the problem, we were creating a helix <1 pitch long.

Re: Helical Curve Inacurate?

Experimenter
Experimenter

Hi @Alex_H,

 

I have just tested it in ST10 MP02 and it is still not fixed. When using Constant Pitch option the number of turns only operates to one decimal point in accuracy. So if you enter any value between 0.601 and 0.699 turns it calculates it to 0.7 turns.

 

If you want acurate curves then you need to use the variable pitch option and put the same value in the end pitch and pitch boxes. Both Veriable Pitch and Compound options will be acurate to three decimal places.

 

If you are creating a helical curve with turns of anything finner than one decimal place do not use the Constant Pitch option.

 

Regards,

 

Neil...