Unable to use "Offset Entities" on Splines and "Curve through free points" 1

[Congruity]

Dear Fellas
I seem unable to use the “Offset Entities”- tool (in sketch mode) on:

* Spline
* Curves created by importing a set of coordinates (in a .txt-file) via “Curve through free points…” (under “Curve” under “Insert”) and then using the “Convert Entities” to get them onto the actual sketch plane.

Using the offset tool on a “line”, a “rectangle” or a “circle” for example is no problem. I am using the 2003-version of SolidWorks. Is this the reason, that earlier versions have a limitation here? Surely it works for todays versions!? Now I solve it by simply extrude the part and “shell it” however I am quite crippled by this limitation.

 

[CorBlimeyLimey]

Offsetting a Spline works fine for me in SW13-SP2.

Can you post a sample sketch to test on other computers?

 

[TheTick]

Sometimes offset doesn't work on certain entities. One trick is to make an intermediate sketch and use Convert Entities to turn those into sketch entities. Then, in a following sketch, those converted entities can be offset.

 

[Congruity]

Thanks for the two responses. I made a sample sketch (attached here) as asked for by CorBlimeyLimey and when doing that I finally succeeded, by "MistakeEntities" but accidentily hit the "Offset entities"-button instead.

So… success came when making the spline (or curve through free points) on one plane (the second plane), creating a new parallell plane (the third plane), marking the curve on the second plane (while being in sketch mode on the third plane) and do “Offset Entities” right away without first doing “Converting entities”!

When I try doing “Convert Entities” first and then do “Offset Entities” “within the same plane (third plane)” so to speak, it does not work! My that’s what you, TheTick, meant that I should do!?

So sample sketch contain:

Right: Curve through free points

Plane 1: “Convert Entities” on “Curve through free points” from the right plane. And clockwise after this comes: “line”, “3 Pt Arc”, “line”, “line”, “Tangent Arc”, and finaly a “Spline”. You can see that it offsets all but the “Convert Entities” on “Curve through free points” in the beginning of the “clockwise spiral” and the “spline” at the end

Plane 2: Success with “offset Entities” from marked curve in “plane 1” (Was this what you meant, TheTick?)

Plane 3: Doing convert entities on the curve in plane 1 and then doing the “Offset entities” on this, no success, no different result then in Plane 1.

 

[Congruity]

Attached a jpeg of the sample file here as well.

 

[MartinShane]

I don't think Solidworks likes to offset splines with multiple inflection points. I can't say it isn't possible (I don't know) but it generally seems not to work for me.

I would guess that the same issue is involved in offsetting a non-sketch curve through points, and that solidworks sees those points similarly to inflection points on a spline. In your case it simplified into a spline with control points at the ends only, making it offset friendly.

I was able to get the double curvature spline to offset on Plane 2 by right-clicking the spline, and selecting "Split Entities" and breaking it into 3 distinct splines with endpoints at the inflection points.

I'll see if I can add a picture of my result.

 

[Congruity]

Thank you for your comment MartinShane, ok. you might be on to something, and your reasoning might be spot on however I am not sure if that is the full problem since I cant even offset the simplest possible spline, just three point making an arc and no inflection point (inflection point = where the second derivative changes it sign right).

Also the spline itself, the last (if going clockwise) part of the whole thing only had one inflectionpoint, If not counting the curve it was attached to.

I will attach the file and an image of this simples possible spline. Tell me if you can offset this one right away without any spacial treatment.

Did you say that you as well where unable to offset these curves before executing "split entities".

 

[Congruity]

The solidWorks file of the simple spline that I either cant offset (unless perhaps then offsetting it directly onto another plane)

 

[MartinShane]

Well, scratch my guess as to what is causing this.
I experimented some more and was able to create and offset a spline with an arbitrary number of inflection points.
Also, I could offset your new file with no modification. If you cannot offset that one then there is something else at play here.
For the record I tested it in SW2011 and SW2013 with positive results.


After playing around the only real constraint I could find seems to be in the the resulting angle or radius of curvature that the offset would cause, ie. if curvature becomes too tight the offset fails. You can see from the pic of the first trial (attached this time) that my "solution" pretty much eliminated the curvature and tangency between the segments which is not really a solution if you are trying to maintain a smooth curve.

I suppose when I had run into problems with offsetting curves in the past I was attempting offsets that were large relative to the radius of curvature of the spline or curve I was working from, and just assumed that the problem was more general than it really is.

 

[Congruity]

Thanks for your comment. Since you can offset and I cant I simply gonna assume there is a freak thing in, maybe not my version, but my installation of SW 2003. I will settle with that I know can offset if I do it by ofsetting on another plane.

Thanks again for your input!