Hi All,

I'm trying to make a truncated cone from 1mm sterling silver.
Attached is the 3dm model.

I would like to create a flat pattern which I can use to saw the sterling silver sheet
and then bend/solder it to create the cone.

Is there a way to do that?

Thank you in advance!
Gunter

Hi Gunter,

Your desired cone object has a thickness.
Back in 2017, unwrapping a cone, or frustum, was discussed, using the script UnwrapCone, or UnwrapCone2.
https://moi3d.com/forum/index.php?webtag=MOI&msg=8753.1

http://moi3d.com/forum/index.php?webtag=MOI&msg=6175.1

http://moi3d.com/forum/index.php?webtag=MOI&msg=6175.39

Your object has a "frustum_thickness" of ___ units.
The outer frustum can be unwrapped, to form "outer_planar" face.
The inner frustum can be unwrapped, to form "inner_planar" face", which is slightly smaller.
The slant seams of the inner and outer faces are parallel, so the top and bottom rings are at the same angle, and have the same "angleThickness".
If a normal to the outer face is drawn at the top, the top of the inner cone extends past the outer cone by "extendDistance", equal to the distance from where the normal intersects the inner cone, to the top of the inner cone.
At the bottom of the frustum, the outer core extends past the inner cone by the same amount, "extendDistance".
So align the "outer_planar" face with the "inner_planar" face, offset by "extendDistance", at the non-slantseam edges, at both the top and bottom edges.
Also, separate the two planar faces by the "frustum_thickness".
Connect pairs of the 8 outer corners with lines, and apply Planar. Join to solid thick planar object.

The above instructions should be checked out by doing the steps in MoI. An explanatory model should be done...


(I think that Flow could do some of the face conversions...?).

The influence of the ductility, or elasticity of the silver is ???
I am a little uncertain of the mechanics of physical conversion of a ribbon of silver, to a rolled surface. The planar cone model would work for spring steel, which has elasticity.
On the other hand, if a ribbon of steel is run through rollers, to make a curved ribbon, the outer surface stretches???
So maybe the silver should start out as an unwrapped cone, with rectangular edges, the same size as the inner unwrapped cone, and the outer unwrapped cone surface would stretch?
And the thickness would diminish?

- Brian

ps, how are conical cookies made?

Hi Brian,

Thank you very much the detailed explanation and script.
I downloaded it and have made some headway. Please bear in mind I'm not
a 'technical' guy so I'm struggling a bit with a few bits.

I think I managed to unwarp the inner and outer parts:




I'm afraid I don't follow this:

"If a normal to the outer face is drawn at the top, the top of the inner cone extends past the outer cone by "extendDistance", equal to the distance from where the normal intersects the inner cone, to the top of the inner cone.
At the bottom of the frustum, the outer core extends past the inner cone by the same amount, "extendDistance".
So align the "outer_planar" face with the "inner_planar" face, offset by "extendDistance", at the non-slantseam edges, at both the top and bottom edges.
Also, separate the two planar faces by the "frustum_thickness".
Connect pairs of the 8 outer corners with lines, and apply Planar. Join to solid thick planar object."

Would you mind clarifying please?

Apologies for not getting it :)
Gunter

Hi Gunter,

I don't think I can offer an explanation, but I wonder if you're not pretty close to a usable pattern with what you've done with Brian's help?

I don't know how precise your model and pattern need to be, but first I note that your model is made of sheet a bit thinner than 1mm. The edge thickness is 1mm, but since the edge is not perpendicular to the surface, the sheet is thinner, ~0.84mm

Will you form it over a cone mandrel of the same angle as your model? If so, wouldn't it just be a matter of unwrapping the inner surface and ignoring the outer surface? Use the resulting pattern to cut the silver and then form it over the mandrel?

--Larry

Hi Larry,

Thank you for your input.

I plan on cutting out the pattern and then bending it around with round nose pliers and half-round pliers. Once
aligned I'd solder it and then use a round punch on both ends to make sure it is properly round.

I think you're right about using one of the unwraps to create a template for cutting the silver sheet, I'm just not
sure if it should be the outer or inner? I feel if I use the inner unwarp, it might to too small?

Not sure though but I'll probably give it a go in brass first.

Many thanks Larry!
gunter

Hi Gunter,

I think I'd fix the model first, making sure that it is using a 1mm thick sheet.

If you're concerned about the size, maybe it would make most sense to make a cone through the mid-thickness of the model's sheet and then unwrap that? Similar to how you'd plan bends in other stock, use the middle line allowing for compression and shrinking of the inner and outer surfaces. Trial run in brass certainly makes sense to verify result before working with the silver! What is it that you're making?

_ConeUnwrap is a neat script Brian!!

--Larry

I spent an hour or so trying to do a random cone, with some frustration :-)
I should have used Gunter's model...

My attempt did not produce planar seam, but should have...

Probably best not to post my goofy attempt...

The "cone" apex of the outer frustrum is higher than the inner frustrum's apex.
The unwrap of the inner frustrum needs to be rotated a little, and moved a little...and offset by thickness...

Maybe cut the 3d solid frustrum, with a very tiny wedge, and Flow the solid to the outer frustrum unwrap???

- Brian

Edit, cut the solid frustrum in half with 90 degree cuts (?), and discard half, and Flow half to a flat, and then double it...???

Hi again Larry,

I will try that and see what happens. I'm trying to use moi3d rather than traditional methods
of creating a collet for a large round but shallow Peridot.

Lets see how it goes :)

Thanks again!
Gunter

Hi Brian,

Thank you for taking the time for my issue!

I'm going to attempt this in brass first and see where it leads me.

Much appreciated,
Gunter

Explanation in regards to "extendDistance" paragraph:

If a line is drawn perpendicular to the top point of the outer slant seam line, which is also perpendicular to the outer face of the 3D frustum, the intersection with the inner face will be offset from the end point of the inner slant seam line. And vice versa for the lower point of the slant seam line.

- Brian

Attempting Flow, no luck so far...

Success with Flow!!!

Using Half of the cone as a Solid, and another silver copy of the outer half face of the half solid as base surface, the solid will flow correctly to a planar unwrap outer surface.
However, rather than using Planar on the unwrap, which produces rectangular isolines, use sweep of one of the unwrapped slantseams, to sweep the arcs of the unwrap frustum.
This produces the proper isolines.

I do see some little artifacts on the smaller arc...?
And no confirmatory measurements were made.

- Brian

I'll have to try the full frustum solid...

Using the flatten surface command in RHINO.

Solid Frustum Unwrap using UnwrapCone2 script and Flow, and other routine MoI commands.
("Final" summary of procedure.)

Begin with a solid Frustum, which is a cone with a smaller cone located inside, with the same axis, with the tops cut off with a plane. Thickness is constant. (e.g. Sitting in Top or Bottom view) (Join may be used to create the solid.)

Use the script UnwrapCone2 to unwrap the outer cone surface, to produce 3 arcs and two lines. Trim off the apex portion of the unwrap, to leave the planar outline of the frustum. Trim away half of the planar arc.
Sweep the planar (half) frustum with one edge line, to make curvy isocurves, visible with Curve>Iso command. This planar arc surface is the Target for Flow. (Rectangular isocurves do not work here. The planar isocurves must correspond to the isocurves on the outer frustum surface.)

(e.g. in Front View) Create a plane passing through the slantseam, to divide the frustum into two portions. Return to Top view and Discard half of the frustum. The make the remaining half a solid, may need another trim utilizing the plane, and a join.)

Copy the remaining (half) outer face of the solid (half) 3D frustum, off to the side, and set it to a different color Style, to facilitate hiding and unhiding selection in Flow to come. This will be the Base surface for Flow.

Select the 3D (half) frustum solid, and select Flow. Follow the Flow directions.
Hide the solid using its color Style eye, and select the previously prepared Base surface, near a corner. Select the target planar arc near corresponding corner, and complete the Flow.
The result is thick, flat, unwrap of half of the solid frustum, with the arc sides beveled. This can easily be doubled.
(Minor face artifacts could be deleted and replaced with ending sweep???)


-Brian

Flow of Full frustum was not successful...
I imagine that a hole in the half frustum solid would also transfer with flow???

Hey Gunter,
“””””” I'm just not
sure if it should be the outer or inner? I feel if I use the inner unwarp, it might to too small?””””””

Taking the thickness into account is a bending thing as metal doesnt bend with exact dims. But for your cone unwrap, it will only affect the “seam” and it will have an “angle” instead of original flat ends.

When you coil your cone, the first part to touch will be the inner edge and you will be welding the seam shut on the outside.

For most accurate results, use the inner surface as your unwrap, then bead and fill the gap on the outside.

In theory, if you did both unwraps, you can determine the angle of the ends and the roll your cone to have no gap when it meets. Or determine your dims at centerline or something other than….

I am not a jeweler or silversmith, but this link was interesting.
Making a Band Ring:
https://www.instructables.com/A-simple-Sterling-Silver-Band-Ring/

- Brian

Fwiw, there is a software called Lamina out there that takes a 3dm (version 4) and creates flat sheet cutouts with all bells and whistles : www.laminadesign.com

It was quite expensive at its time, but the author lowered the price to a whooping $1.80 (one dollar, eighty cents) for commercial usage.

FreeCAD can unroll cone surfaces and much more.

Here is a video I did for a guy with another software, but the method is using the math needed which Michael gave me here!

So the thread regarding the math and needing the radians value is here in the MoI forum somewhere. Thanks again Michael!

If you want to just see the math, you can skip to 4.10 of the video. Then you don't have to sit through me explaining....

Nice suggestion, the best one.