how to determine shortest longitudinal length of cylinder

[Chipping]

I have a cylinder (Pipe Actually cut at different angles at each end) I want to rip it along it's shortest longitudinal length - to do so i need to place a point on the cylinder where the shortest length occurs.

Any tips on how to do this?

[JDMather]

It would be easiest to answer the question with an actual file.

Post a sample file the exhibits the same intent, if the actual file is proprietary.

[Chipping]

To minimise welding one wants to rip at shortest length. How to find and then place a workpoint on that shortest longitudinal length?

Example attached

[WHolzwarth]

That's been not quite easy.

For a first approximation, you could stop after Thicken2. But that's not the shortest distance.

Therefore, some refinement was needed.

Walter

[JDMather]

I assume that an "eyeball" shortest length would be close enough (absolute shortest length not needed), in which case the problem considerably easier.   In any case, Shell and Split is not the correct way to create a sheet metal part such as this. (the split cuts sides are not perpendicular to the flat in the flat pattern)

[Chipping]

I forgot to mention that I was after the shortest length that is paralell to the longitudal axis of the tube so after thicken 2 may suffice.

In saying that though the real shortest length is also of interest.

I thought to project an offest plane at each end of the cylinder that cuts though but misses the low point, then to project the geometry back to the plane obtain the mid point of a line between projected  geometry and then project or draw a sketch line back to the angle cut - thus giving the shortest path. I would asume that if pipe segments were sweept along a 3d line changing direction and angle, there would be relationship between the 3d line used as the path and the shortest length of all pipe sweep segments.

I will try my idea and see if it works - I asked the question though because I thought there may have been a coomand or function like minimum distance that would have found it. Turns out there is a bit of work to find the shortest length on such an example and that was what I was confronted with. 

[Chipping]

JD I understand what you are saying but if the sheet metal could be cut by 3d laser and in steel it can be so the edges not being perpendicular could be cut in steel giving a perfect butt fit after rolling. Unfortuanatly they can't bevel edge alluminium with laser due to reflection dangers.

In any case that perfect fit may not be desirable as most weld joints require a v to increase surface area. I am not sure if a V is desirable with say 3mm alluminium as the tig welder will fully fuse the weld through to the other side in any event.

When Inventor rolls out a flat pattern as per this cylinder it does indeed create the variable bevel. A 2d flat pattern even with bevels would then be the same  (NOT shape) but outer cut dimensions would be exactly as your methodology would it not? So then it just becomes an issue of how the model looks.

Also the thicken command in sheet metal behaves differently than that in 3d model and does not seem to enable the output of a new solid for assembly file purposes

[Chipping]

Eye ball shortest length is ok as long as they all line up with further tube segments created on the same path sweep.

[Chipping]

I wonder now if we take the cut that has the sharpest angle at it's shortest place and then a line paralell from that point will always give you the shortest paralell length to the central axis of the cylinder. Is it as simple as that??  The shortest length is not at 90 degree's

On the side - Surgeons use calculations like this to cut shortest length on rounded human parts!! like a fore arm.

I tried what I thought may work attached file but is no where near it. However the point from the cut end with the sharpest angle would enable a tangent work plane on the shortest paralell cut length but you only need a point for a rip so plane not required.

[Chipping]

Is it eaiser to determine in the flat pattern environment. I heard you can work with flat patterns in inventor - will try now. maybe i can rip it any where and then determine the shortest rip in the flat pattern environment. Mark the flat pattern then go to folded part and pick up that mark i made in the flat pattern. Would be nice maybe I'm dreaming

[Chipping]

wh I had a look at your work yep you found the shortest length alright!! I struggle to follow how you did it. One would think there would be an easy way. Partculaly if it has to be paralell to the cetre axis of the cylinder. 

[Chipping]

I get your boundary patches but can't figure where what or how you put that axis where you did???

[WHolzwarth]

Some remarks:

- Boundary patches 4 and 5 are planes at your cutting lines.

- Workplanes 11 and 12 are parallel planes to each. No exact distance is needed for them.

- Work axis 5 is the intersection line between WP11 and WP12. If you're looking right along it, you can see  both cuts placed rectangular to this view.

- In Sketch 15, a parallel tangent to this WA5 was placed at the outside of the tube, and a cut was placed at this position (Extrusion surface3)

Now this cut is near the shortest distance, but it's only near. For getting better, an unfold-refold operation was needed:

- Place a small flange at the gap (needed for unfold)

- Find a new shortest distance in unfolded sheet (Tangent circle and point-to-point line)

- Refold and delete the additional flange

- Wrap new shortest line back to tube and use it as path for a cutting sweep.

Well, I've been using a rectangle as cut sweep section. The new edges would need another both-sides intersection thickening for being rectangular. But that's a minor issue.

Walter

[Chipping]

Well I thought the browser listed part formation in order. The axis is listed in the browser before the 2 work planes. So I think the axis was created first hence why I could not figure out what geometry was used to create it.

So now I feel like I cant follow creation logic - I can't trust that the browser has creation in order because it doesn't - This is so confusing  for a new user like me.

Any way now I can proceed to follow your work

[Chipping]

Ok I get it sub directories so the sub items are used to create the first item on the tree like a sketch to create a split. ok ok I find autocad was easier to learn than inventor. Inventor is a whole new creation logic for me. 

[Chipping]

I have a few questions



Why is it necessary to put a flange extrusion on the cut edge to get a flat
pattern to unfold?



I thought once it was thickened and it had a cut or rip in it then it should
fold out or flat pattern - why the need for a small flange to get to unfold?



Also why does Inventor create two occurrences of thicken?



AND why did you use a sweep command to make the final unfold gap?

[WHolzwarth]

Why is it necessary to put a flange extrusion on the cut edge to get a flat
pattern to unfold?
Unfolding only works with a stationary reference = Flat face


I thought once it was thickened and it had a cut or rip in it then it should
fold out or flat pattern - why the need for a small flange to get to unfold?
See above


Also why does Inventor create two occurrences of thicken?

Not Inventor, but the user should do so. Sheet metal normally has rectangular edge faces. If you only do an angled split with a sheet metal tube, then this is not ok. Double intersection thickening (inside out and outside in) gets edges back to sheet metal shape.


AND why did you use a sweep command to make the final unfold gap?

Because Rip is not working in many cases, same here. Sweep did the job.

Walter

[Chipping]

Walter - I found something of interest. I not being a smarty here but your distance I think was not the shortest very close but not. Under "Inspect" then "Distance" if you select the edge of each end of the cylinder Distance will give us the shortest length between the the two ends. I did not realise this, where you aware of this?

Now the question I have is. Is there a way to easily mark a point at each end of that distance line?

[Chipping]

When I try to place a work point on the distance line upon clicking on work point the distance lines vanishes

[Chipping]

When executing the inspect distance command it gives the xyz cordinates i assume to the shortest point on the last edge there fore by writing this position down and then repeating the command this time selecting the other edge first it would seem I can get the xyz coords for each end of the shortest line. That may be one way if acheiving the task.