Scissors handles: Does this approach look alright?

Working an a scissors handle now…
Thinking what would be good approach/workflow…

Here is what I did:

  1. I started to make a scissors handle from the inner ring, making a blendsrf between two reference surfaces.
  2. Split up the surfaces and did a sweep2 in outer surface and the surface created by the blendsrf a couple of times.
    (made a sweep2 surface in two parts since I wanted to add a cross section to shape up the surface)
    3)After that networksrf x2 to fill in the gap at the corner.

How is the approach overall?
->Should I change approach and use cross sections of the handle?
->Especially the part where I networksrfed… I also tried doing a loft at the corner then blending that to the top and bottom sweep2 and EdgeSrf, but that didn’t work too well… ended up with many smaller surface and a dent at the end…
->Also still trying to figure out a nice way to somehow get the left hand side patched up…

scissors_sample.3dm (470.9 KB)

Here is how I would fill in the missing pieces.

scissors_sampleX.3dm (319.3 KB)

1 Like

Thank you jim!
So that’s how you use blend curve. This data’s a keeper. :wink:
nice colors.

Just one question, for the trimmed blend surface, the original blend surface is from
the inner edge to the helper surface edge(and the helper surface is made from tangent line at the isocurve intersection of the Blendsrf edge)?

The method I used to create the red helper surface was as follows:

Split the pink blendsrf at the midline isocurve (hat you had already extracted). The command macro is:

split isocurve direction=U shrink=yes

or the less verbose version:

splitsrf U S

After you splitsrf the pink surface turn on their control points and you will see the 2 blue lines that i created from the control points.

After creating the 2 blue lines I copied them to the clipboard and undid the splitsrf. Then pasted the blue lines from the clipboard.
The Windows command macro for this operation is Ctrl + C + Z + V. ( Does that work om a Mac?)

Then you can make the red surface from the 2 blue lines by using Loft and Extendsrf to make it wider. Then you are ready to use the red surface as one side of the cyan blendsrf.

1 Like

Thank you for the details.

I missed the Loft between two lines. Now I got it clearly.
Thanks again!

yep same in mac.


If you have time…

I tried rebuilding from scratch, and got stuck again at the trimmed blendsrf.
Done up to blendsrf, but I couldn’t trim/split it using adjacent surfaces, or curves…
When doing blendsrf, is there something I should be careful of? or maybe the surface around in general…?
(blendsrf settings ?positional/tangency/curvature length of handles etc… length of the helper surface?..)

Also tried to use similar approach on the other side, but similar situation…
(This started from a blendsrf in the tip, and split at the isocurve.)
Not to mention surface transitions in other areas are also looking bumpy…

*if there’s good tutorial you know of doing this kind of surface, it’d help.

Scissors_2.3dm (989.4 KB)

I have found that you get the best results from blendsrf and Sweep2 if you arrange things so that the isocrvs of these surfaces are all gentle C-shaped curves. Any S-shaped isocrvs are something I try to avoid and that is why I extended the red helper surface outward in my previous example.

I think the S-shaped isocurves in the way you are doing the trimmed blendsrf is one reason you are having problems - maybe the only reason.

The enclosed file shows a couple ways I might approach that pointy feature on the end using sweep2 or blendsrf.

scissors_3.3dm (625.5 KB)

Thank you for taking the time jim.
You been a great coach.

I been looking around and T-Splines or the VSR plugin seems like the popular approach…
But as I’m using mac at the moment, eh, no luck there. & I still would like to learn with naked Rhino anyway.

Thank you for the tip with the Iso curve.
I’ll try out some more with a more relaxed isocurves.
Thanks again!


Question about Sweep2.
How are you getting the isocurve in the profile curve to match up with the sweep2 surface being made?

In below: Left is your surface, in the right, I tried to do a sweep2 and can’t get the
match of the iso curve in the cross-section curve. (I copied your helper srf and trimming curves [in red], but still not matching up.

Only way I managed is splitting the left and right surface at the isocurve, and sweep2 twice.

Scissors_2_ver2.3dm (1.7 MB)

This problem is due to the fact that those surfaces had been joined before and the joining created a more complex edge definition. You should just untrim those surfaces instead of splitting them. That restores the edge definition to its original isocurve form.

Another thing that will help improve surfaces made from blendsrf and sweep2 is to use RemoveMultiKnot. This will almost always improve the quality of the surface.

You might look into the plug-in called T-Splines. This would be MANY times faster and easier … after the initial learning curve, of course.

Here is a demo video of a pair of scissors by my favorite T-Splines guru, Kyle Houchens. Watch anything he does and you will learn and be entertained at the same time. Here is a link to some other demo videos.

I’m using mac at the moment and it seems plugin for T Splines are not available yet…
Thinking of moving to win rhino… also with all the rendering sw options…
I wish there was a ”upgrade” sort to speak to go from mac to win…
Thank you for the demo vids. I also watch Kyle’s video all the time. Learned much from it.

Thank you again.
I study more in making simpler surfaces.

Yeah, sorry I did not notice this was the Mac board! If you have the budget, I would definitely get the PC version of Rhino due to the many amazing plug-ins available right now.