Equation Question

[TracyWillis]

Anyone know how to parametrically control the TO: range value in the Equation curve dashboard?
[cid:image001.png@01CE3CFF.6804B8B0]

I want to make an equation curve that will maintain the same helical pitch regardless of the part length.
The following equation will do what I need BUT - I have to manually edit the TO: field value of the curve and set it equal my PART_OAL_INCHES parameter.
Here is my equation....

r = .012
theta = t * 360 * EQ_PITCH_VAL
z = t

where EQ_PITCH_VAL = 9

Is it NOT possible to set that TO: field value equal to my length parameter?
*I've tried setting Z in the equation to Z = t * PART_OAL_INCHES parameter but that didn't work.
Is there something else wrong with my equation or a statement I can add that will maintain a constant pitch regardless of the length.

Any help will be greatly appreciated.
Thanks all - happy Friday

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[kimndave9]

It's a common misunderstanding - in parametric equations t varies from
zero to one.

To make z end up the total part length, use z=t * PART_OAL_INCHES

Dave S.

[TracyWillis]

Yes - tried that.... When I set that TO: field back to the default (1.000) and use z=t * PART_OAL_INCHES the curve does have same length as the OAL; but it has a tighter spiral on the shorter parts. How can I keep the pitch the same regardless of the OAL?
I tried adding the pitch variable into the equation to control that but I'm missing something....

[kimndave9]

Pitch is set by the rate of advance per the rate of turn - inches/degree.

By setting the end length to something other than one (the To value) the
pitch in your equation is changed.

To make it independent, make the theta a function of z. That is 16*z*360
would result in 16 turns per inch.

Dave S.

[TracyWillis]

I see now - Thanks Dave.
That did the trick; works great.

theta = LOOPS_PER_INCH * 360 * z
z = t * PART_OAL_INCHES

[ptc-4626282]

I think the equation should work fine if you are interpreting the "eq_pitch_val"

as a total number of pitch within total length.

[ptc-4626282]

Hi

Yo uprobably already got this but just want to mention

if you set "t" to range from 0 to1 for "z=t*part_oval_inches" to work.

J

[TracyWillis]

Let me clarify something... the modification to the equation works great except:
The part always says it hasn't been regenerated whenever I try to save the file.
Looking at the equation I tested below; I think I can see why that would happen...
Csys set to Cylindrical
r = .0625
theta = 12 * z * 360
z = t * 39.37
theta is calculated using "z" and then "z" is calculated using "t" ??
The part file will save but always prompts for regeneration first.
Is there some other way to do write equation so that that won't prompt for regen every time?

[dgschaefer]

Relations are evaluated in order, so I would think reversing the last two lines ought to do it.

--

[TracyWillis]

Yes - reordering the last 2 lines worked perfectly and eliminated the prompt requesting model regeneration.
Thanks to Dave and Doug for the solution.

You guys all have a good day