
Re: Setting Lines and Arcs to Equal Length
Kenneth Barrentine Sep 6, 2012 10:37 AM (in response to Josh Canner)no relation but equation will do it

Re: Setting Lines and Arcs to Equal Length
Troy Peterson Sep 6, 2012 10:42 AM (in response to Josh Canner)Add an equation to make the line = to the arc

Re: Setting Lines and Arcs to Equal Length
Alin Vargatu Sep 6, 2012 10:48 AM (in response to Josh Canner)Troy, he already linked the values. Adding an equation to make the line and arc equal will not improve matters. He wants the 5.500 dimension to drive, while the arc and line remaining the same.

Re: Setting Lines and Arcs to Equal Length
Glenn Schroeder Sep 6, 2012 10:50 AM (in response to Alin Vargatu)So he should be able to change the 5.500 dimension to driving and all will be good?

Re: Setting Lines and Arcs to Equal Length
Alin Vargatu Sep 6, 2012 10:51 AM (in response to Glenn Schroeder)nope, because that would overdefine the model

Re: Setting Lines and Arcs to Equal Length
Glenn Schroeder Sep 6, 2012 10:53 AM (in response to Alin Vargatu)If he changed the equal length arc and line dimensions to driven?

Re: Setting Lines and Arcs to Equal Length
Kelvin Lamport Sep 6, 2012 10:58 AM (in response to Glenn Schroeder)Glenn Schroeder wrote:
If he changed the equal length arc and line dimensions to driven?
When Linked, dimensions cannot be set to Driven.
When Driven, dimensions cannot be set to Linked.





Re: Setting Lines and Arcs to Equal Length
Alin Vargatu Sep 6, 2012 10:51 AM (in response to Josh Canner)Let's start by voting on this ER:
SPR 616783: Ability to create an equal length relation between a line and an edge, arc, or spline (curve).

Re: Setting Lines and Arcs to Equal Length
Alin Vargatu Sep 6, 2012 11:12 AM (in response to Josh Canner)Let's work on what Kenneth suggested which is building a more interesting equation.
So you know the 5.5 dimension and need to calculate the arc length. correct?
Let's consider this a problem of geometry. Who will solve it first? Take that as a challenge!
A few helpers:
Let's use the same annotations:
r = radius
d = diameter
c = chord length
a = arc lenght
t = angle value
k = 5.5
As far as I know:
c = d * sin(360*a/(pi*d))
t = 360 * a/(pi *d)
So I have to work backward. from the 5.5 to find c and that will generate the a.

Re: Setting Lines and Arcs to Equal Length
Alin Vargatu Sep 6, 2012 11:28 AM (in response to Alin Vargatu)Oops, just ignore what I wrote above. We need to use only a geometric construction to get an arc and a line to have the same length.
I might be able to do that if I am allowed to use 2 temporary sheet metal bodies.
... thinking outloud...

Re: Setting Lines and Arcs to Equal Length
Kenneth Barrentine Sep 6, 2012 11:53 AM (in response to Alin Vargatu)If an equation is going to work then;
.800 has to be driven
OR
Ø36.000 has to be driven
Can't have cake and eat it too.
We're talking about .0005"
Is this part that critical?


Re: Setting Lines and Arcs to Equal Length
Josh Canner Sep 6, 2012 12:33 PM (in response to Josh Canner)There really is no part here. I am simply using this to show a critical position of something within a concept. For a given diameter, line length and fixed spacing (in this case 36.000, 5.500, and 0.800 respectively), there should be exactly one position where the line segment and are segment are equal length. As far as I can tell, there are a lot of geometric and trigonometric relations that can be used to backward figure this into an equation....but it will take a long time.

Re: Setting Lines and Arcs to Equal Length
Josh Canner Sep 6, 2012 12:39 PM (in response to Josh Canner)I showed the original picture to a friend of mine (who is currently working on his Math PhD) and he began working on the equation. It is apparently more complicated than I thought, but he is confident that it can be solved using the constraints I have given. I will post when I receive more info.

Re: Setting Lines and Arcs to Equal Length
Kenneth Barrentine Sep 6, 2012 1:22 PM (in response to Josh Canner)Regardless of the equation, one of the dimensions (36.000, 5.500 or 0.800) will have to be set to driven.
Back to the question of using a relation.
If a relation existed then, it would lead you to the statement above, one of the dimensions (36.000, 5.500 or 0.800) will have to be set to driven.
Using the relation method (if it existed) one would have to conclude that the driven dimension (whatever is used) would not be rounded off perfectly with trailing zero's.

Re: Setting Lines and Arcs to Equal Length
Josh Canner Sep 6, 2012 2:15 PM (in response to Kenneth Barrentine)This would be true if I wanted to change the arc and line length, but I don't actually care what they are, just as long as they are equal. Once they are set to equal (relation or otherwise) their dimension then becomes driven by the 36.000, 5.500 and 0.800.

Re: Setting Lines and Arcs to Equal Length
Chris Michalski Sep 6, 2012 2:40 PM (in response to Josh Canner)Josh, you do realize that you've just guaranteed that my regular projects aren't going to make nearly as much progress today as before I found this thread....

Re: Setting Lines and Arcs to Equal Length
David Suelflow Sep 7, 2012 1:18 PM (in response to Chris Michalski)As my kids would say, I know, right. I’ve spent way too much time looking at a sketch knowing there is a geometric way to solve this…

Re: Setting Lines and Arcs to Equal Length
Chris Michalski Sep 7, 2012 1:25 PM (in response to David Suelflow)and the worst part is, that to look at it you'd say "it's just a couple of lousy triangles and one arc, how hard can it be to define the relationship......"



Re: Setting Lines and Arcs to Equal Length
Chris Michalski Sep 6, 2012 3:41 PM (in response to Josh Canner)1) Constrain the geometry based on radius, offset, horizontal line length, and taper length. This leaves the arc length temporarily undefined.
2) define the angle from horizontal to the end of arc.
3) create an equation that defines the horizontal line length as the length of the arc (using 2 pi R * angle / 360).
Then when you alter the taper length it will change the other 2 legs.
HOWEVER, you have to open and update the sketch several times as it only updates the angle, the next time it alters the line length, rinse, lather, repeat  SW doesn't iterate equations internally so you have to do that manually.
I'm sure there is a geometric relationship, but when you graph the taper length vs. the arc length you get a parabola.
I also put in an excel sheet tracking taper length vs arc length to try to fit a curve (that's where I found the parabola and abandonned an equation in favor of a relation).

equal line and arc.SLDPRT.zip 24.1 KB

equal line and arc.xlsx 26.2 KB

Re: Setting Lines and Arcs to Equal Length
Josh Canner Sep 6, 2012 4:32 PM (in response to Chris Michalski)Chris,
Thank you for the help. That would work perfectly if there was a quicker way to update the equations. For now it will have to do. It's faster than the way that I was doing it. I still feel like there should be a Relation that could be made within SolidWorks that would take some of the manual work out.

Re: Setting Lines and Arcs to Equal Length
Chris Michalski Sep 6, 2012 4:46 PM (in response to Josh Canner)I know there is a geometric relationship buried in there. Unfortunately after so many years of calculus in college (and the years in between then and now), the intricacies of geometry aren't as fresh as they once were.
Maybe I'll give it a try again tomorrow while I'm waiting on another 6 hour lab experiment. (although it might take more than 6 hours of head scratching)

Re: Setting Lines and Arcs to Equal Length
Alin Vargatu Sep 6, 2012 5:36 PM (in response to Chris Michalski)Please do that Chris. I am your biggest fan.


Re: Setting Lines and Arcs to Equal Length
Chris Michalski Sep 7, 2012 10:23 AM (in response to Josh Canner)Josh 
how accurate do you need to be? It's almost a parabola but not quite...
If you can live with a few % deviation between the true equal length and the calculated length you should be able to use the equation in the Excel chart as the driving dimension for both your straight length and your arc length with the taper as the input.
But if you change the radius or the offset distance you'd have to tweak the constants of the parabola again. I couldn't see a combination of the variables that was a perfect fit.
(Sorry to let you down Alin, my free time today got gobbled up when I got a flat tire last night that I have to run out and plug).

equal line and arc.xlsx 33.8 KB








Re: Setting Lines and Arcs to Equal Length
Joseph Weaver Sep 6, 2012 10:49 PM (in response to Josh Canner)
Re: Setting Lines and Arcs to Equal Length
Kevin Quigley Sep 7, 2012 9:52 AM (in response to Joseph Weaver)Without meaning to sound like an idiot here, what is wrong with simply applying a driving dimension to the line and the arc, and MANUALLY editing the dimension  I mean colour the text if you need to highlight it, but this works 100% of the time. Sometimes old school is the simplest

Re: Setting Lines and Arcs to Equal Length
Rick Remer Sep 7, 2012 12:32 PM (in response to Kevin Quigley)You can link the length dims of the arc and line in 2010. Does this not work in your version?

Re: Setting Lines and Arcs to Equal Length
Chris Michalski Sep 7, 2012 12:43 PM (in response to Rick Remer)But as Kelvin stated:
When Linked, dimensions cannot be set to Driven.
When Driven, dimensions cannot be set to Linked.
Josh wants to control the length of the angled line and make SW calculate the length of those 2 equal lines as driven dimensions. If you link them to be equal they are no longer allowed to be driven.




Re: Setting Lines and Arcs to Equal Length
Daen Hendrickson Sep 7, 2012 3:05 PM (in response to Josh Canner)Similar to what Chris found above, I had to perform a series of rebuilds to get things to converge.
I defined the 36" diameter and the 0.8 offset.
I created a dimension for the arc length.
I set the length of the horizontal line equal to the arc length with an equation.
I set the arc length dimension to driven.
Now I adjust the tapered line length.
In the dimension Modify box, I clicked the rebuild icon repeatedly. The number of rebuilds depends on the magnitude of the dimension change. Too large of a change and SW can't make the jump and the sketch fails. 1.2 inches of change seems to be the maximum delta SW could handle. But only in the negative direction. Changing the tapered line from 5 inches to 10 inches works. Reversing that does not. I have to step back down to 5 inches in smaller increments. A negative change of 1.2 inches takes 15 rebuilds on my machine. 0.5 inches change takes 14 rebuilds. 0.1 inches change takes 12. Going in the positive direction, a change from 5.5 to 10.5 inches for the tapered line takes 14 rebuilds.
I did not perform any checking when the 36" diameter was varied.
Daen

Re: Setting Lines and Arcs to Equal Length
Torsten Niemeier Nov 1, 2012 4:36 AM (in response to Josh Canner)Here are some solutions:
http://ww3.cad.de/foren/ubb/Forum2/HTML/024772.shtml
Check the posted videos and parts. The rest requires some german.
Torsten

Re: Setting Lines and Arcs to Equal Length
monika kodikara Nov 1, 2012 5:41 AM (in response to Josh Canner) 
Re: Setting Lines and Arcs to Equal Length
Chris Pratt Jul 2, 2018 7:46 PM (in response to Josh Canner)Lost souls searching google: as of SolidWorks (SW) 2016 there is a "equal curve length" relation in sketches. It can set equal the length of lines, splines, arcs, and circles but not ellipses (at least as of SW 2017). It appears after selecting the bodies of two of the previously mentioned sketch elements.