[mattpatt]

Guys,

Here's my dilema.

Material is 0.7mm perforated (dia 2mm) sus304 sheet.

Using lofted bends in SW. Two sketches, and then a thickness of 0.7mm added, to create the part I want. The sketches are centrepoint arcs, not fully closed. Open just 0.1 degree so that I can unfold them.

Rolling a cylinder OD-50.8mm, L-390mm:

If I use a k-factor of 0.37 then this rolls up perfectly and is a nice push fit into ID-50.8mm part. Happy and have no problem with this.

Rolling a cone OD1-50.8mm, OD2-48.4mm, L-390mm:

I have to change the k-factor to 0.63 to get the two diameters to come out correctly sized.

Why is this? What's going on? Why wouldn't the k-factor be the same for the two models, or at least very similar?

Maybe I need to make the model a different way to start with and then convert to sheet metal.

I've already made the part so no big problem, just interested in why the k-factor results are so different.

Cheers in advance.

Matt.

[JerryFlyGuy]

Last I checked [last year] Solidworks did not apply the K value to lofted bends as it did w/ the other sheet metal features.

There actually was no real 'K' value applied to a lofted bend, instead the K value was assumed to be on the sketched geometry [or said another way, the sketch was at the K value location in the model/part]. In effect what one had to do was to calculate the actual location of the K plane [plane isn't the right 'word' but you get the idea.. maybe 'Median surface' is a better term?] of the material and draw your sketchs on that plane or in the case of a cone, AT that location .. it takes a bit of simple trig or a sketch on your model to figure out where the K value would be on the model. Doing these steps, makes it work out but then the displayed model is incorrect because the material in the model [as displayed] is offset one direction or the other from the sketch [inside or out]... to make it all work if you want something to 'look' correct, you'd have to create some configs where the displayed part is not the 'flat' part etc..

There is an SPR to get this fixed and make the K values actually work as K values, I've not seen that this has been implimented in 2012 or not.. I've not had to do a cone recently so.. never checked

To be clear this is only a concern w/ Lofted bends, all other sheet metal features work properly w/ K values..

Fwiw

JFG

[mattpatt]

Jerry,

Many thanks for your reply.

Not sure of the purpose of 'lofted bends' if it doesn't work properly!

I'll try a couple of other methods to get the same cone and report back.

Cheers,

Matt.

[mattpatt]

So I revolved a line the outside dimension of the cone by 359.9 degree and then thickened inward 0.7mm.
Sheet metal/Bends, selected an edge and errors!
I had to reduce the revolution from 359.9 down to 357 degrees to get it to flatten.
Not what I had in mind.
Tried the opposite, i.e. sraw inside of cone and thicken outwards....same problem.

What's wrong?:

Bends cannot be added to a conical part with such a small half angle

The geometry in the bend region is too complex.

I'll try something else....

Matt.

[mattpatt]

No........

Nothing seems to flatten properly unless I revolve leaving a huge gap.

Hmmmmmm

Back to the drawing board.

[SirDenisNayland]

I'm a bit of a sw noob, but why don't you just create the solid cone and then split it/cut extrude to center, rather than trying to loft incomplete circles?

[JerryFlyGuy]

To make a part from which to get a sheet metal flat pattern the lofted bend feature is the way to get the job done.

Matt, are your arc's having the same included angle? Here's one w/ a gap of 0.1 deg. I typically don't build [model] my cones this way, rather I make two parts for a complete cone [or more] but then usually they are heavy plate and are bump-broke to form.. breaking even 180deg of cone is more than tight on a typical press break. If your able to roll a complete cone it might be a different deal.. [read; able to do in 1 pc]

fwiw

[mattpatt]

Hi Jerry,

Thanks for the reply, but I'm unable to open your file. I have SW2010.

I make cones from a single piece and roll them by hand over an anvil.

Yes, the arc angles for the two sketches are the same.

I just tried the cone at 180 degree (using lofted bend) but I get the same result. i.e. the K factor for a cone (albeit only a 0.17 degree included angle) and a cylinder are very different.

But this cone k-factor definitely seems to change a little depending on the angles. But normally I'm making cones from about 2 degree up to 25 degree and the k-factor is around 0.4 ish.