solid edge community edition woes

Now here's a question

premise

I believe that SE can accurately position a vertex of the intersection 2 arcs (or circles)

but circles are displayed default as 36 segments - can go to 96 under View options

When you zoom in you see the intersection of two segments but they dont form a vertex. You have to use the Trim tool which seems to provide the required accurate vertex AFAIK

2D we take this for granted drawing a radius to get an intersect

OK so far?

Now the interesting bit comes when you intersect 3 spheres to get an accurate radial point and line in space draw from the origin say.

Can SE do this?

You need this for example when you want to rotate faces or solids to an intersection

I havent got as far as making a sphere yet - not ready for a revolution

still sharpening my clutch pencil

For example try a simple tetrahedron

I don't understand 'intersect 3 spheres to get an accurate radial point and line in space draw from the origin say.' A drawing would help!

Don't know SE, but computer software typically separates the definition of graphical objects from display. What's shown on screen is only a loose representation of the definition. Behind the scenes the definition is as accurate as the machine's number base, i.e. near perfect, but the display is limited by the resolution of the media. This varies: screen, printer, plotter, or hologram - all different.

As CAD models can be made of thousands of graphical objects, programmers code for performance: they avoid the machine doing work whenever possible. SE probably represents screen circles as segments because that's the fastest way to draw them: rather than waste time calculating perfect circles, it whacks out a 'good enough' imitation, a series of lines at a fixed angle. However this is just for display and the software uses definitions, not what's shown on screen, to calculate intercepts and other geometry.

Manual 2D technical drawing often uses arcs drawn with a compass to fix mid-points and find intercepts etc. The draughtsman sets the radius, sharpens his pencils, and eyeballs the result. Mechanical methods aren't available to computers, so they use purely mathematical methods. This is one of the booby traps a 2D draughtsman converting to 3D might fall into: he's discombobulated because the computer absolutely doesn't work as he expects it too. Or wastes time setting drawings up manually from first principles, when the computer has a toolbar full of Wizards!

This tetrahedron is produced with a single click on a tool in FreeCAD's "Pyramids and Polyhedrons" Workbench.

Or I could have created a tetrahedron in the "Parts Design" workbench, which is best for most mechanical modelling, by sketching a triangle and lofting it to a point. Both methods, and there may be more, require the operator to learn the CAD tool. I know the loft method works in Fusion360, and would bet money SE supports it too, but I don't know if F360 and SE have a Tetrahedron button. It's not unlikely.

Dave

Dave,

those 2d draftsmen are the ones who also insist on placing features using coordinates instead of 'offset it 7microns from this bit'. Making things difficult for themselves in the process. That's before the part changes as part of the design.

One thing that puzzles me is that anyone who is used to 2d drawing using plans ought to be able to pick out profiles for 3d base features really easily, but actually seem to struggle.

F360 can do rectangular box, sphere, cylinder, torus, coil, and pipe. No tetrahedron.

I suspect the big problem for experienced 2D folk is that we carry the 3D object and 2D plan conversion process automatically in our heads. For me flattening an object from 3D space into 2D views or reconstructing 2D views into the 3D object happens so automatically that I'm not even aware of it. When working in orthogonal (or other angled views) you have to do it by co-ordinates or the process just won't happen.

Shift over a bit can be useful in the drawing process, I use the copy array feature of VectorWorks (ex miniCAD) a lot but the end result is always in co-ordinates. When dimensioning co-ordinate origin selection is very important to make machining easier. As I have a DRO on the Bridgeport and good edge finders much of the time I work ± off the part centre rather than reference edges. Which can make post machining checking harder.

Generally the driver for 3D is CNC.

From a manual perspective the major benefits appear to be verifying clearances and part fit. Its easy to loose track of fit criteria when you have a number of complex parts.

To make things manually 3D and solid views have to be have to flattened to co-ordinate or axis of rotation sets to make it. CNC can do arbitrary curves from arbitrary centres "anywhere" on the part given a clear tool access path. I can't do that. As far as CNC is concerned a flat part is simply the infinite radius end point of permissible curve radii data.

Clive

I think the disconnect between 2D and 3D is a mind-set problem, nothing to do with intelligence. Learning is a kind of habit, and - as we all know - habits are hard to break. I suspect converting from 3D design technique to 2D might cause the same cognitive problems in reverse. Future generations may be amazed by the complexity of our 'simple' Technical Drawing methods because their experience of computer applications make drawing board methods seem alien.

Similar conceptual collisions occur in other fields. In computing, fully competent functional programmers often have severe trouble grasping Object Oriented Programming. Like 2D/3D, OOP inverts the thought process. Our poor old brains struggle with inversions because learning normally builds straightforwardly on previous experience. We're in deep poo as soon as previous experience lets us down, which is why I and most other older folk all hate change.

Dave

The 4 separate lines mentioned above seems a long way to do things in Alibre I just choose the square/rectangle icon click and drag and that gives 4 4 sides at rightangles and opposites equal size. I can then constrain the size and position.

I don't get the 3 spheres bit either can you elaborate Brian, or do you mean striking arcs from known points to get the position of a third and another arc can be used to check. Used to use that for chain surveying at college and have used it a couple of times in the real world too.

Anyway your homework for this weekend is a semi transparent Tetrahedron with a spherical void in the middle. Oh and that is after you have cut those spur gears which have not been handed in for marking yet

I feel you may get on better with 3D if you think of it more like machining apart. Taking your cup for example, the method you describe of extruding a tube and then extruding a separate bottom could be likened to fabricating where the two parts are cut and then joined. My suggested way of drawing a cylinder and then cutting out is more like machining from solid where you face off a bar to length and then bore it out. the Revolve would be more like metal spinning or beating from sheet.

Indeed SOD I am dyed in the wool reactionary too

I still think in "thou" despite being fully metricated since we went over the the MKS SI

I cant relate to mu happily.

Well JB a lot of contributors are missing the point - perhaps the reference to balls clouded their vision

You see the derided 2D compass was the way to find an intersection in 2D

But take the tetrahedron , we have a base triangle and a point in space to draw 3 identical side lines to meet the others from their respective vertices.

obvious - have we lost them yet?

a compass will describe a sphere in 3D. So we are intersecting 3 spheres (which will give 2 points +/- Z)

BUT the CAD circle is approximated by a polygon (default 24,36 segments)

Without using built-in tools as may exist in some CAD apps, it is difficult to intersect 2 circles on the 2D plane - it wont give you an intersection point. In SE you have to use the Trim tool to remove the outer arcs leaving you with a lens

This lens will be given intersection points vertices you can use and its accurate (to 6dp)

Now there are glitzy tools in some CAD apps that will draw platonic solids ready made which skates over the fundamental issue here - your vertices must be 100% accurate (near enough is not good enough - which you can fudge in 2D). More than 3 must be coplanar or they wont make a face - plus the other manifold rules

to construct the tetrahedron with a given construction line drawn from centre up the Z axis, Can you draw a line from one of the vertices with the given side length so that it intersects with this Z line

If you can you cracked it.

I read that SE cant do 3D sketching whereas sketchworks can but yet I see a tab on the SE worksheet that says "3D sketch"

As Im still on the 2D plane I was afraid to open it but this has now confused me

Also a quickie?

When I open SE it defaults to Synchronous - should a noob be starting out with "Ordered" modeling ?

I hope these discussions will help other noobs because, as has been noted, the industry is utterly overpowered with confusing hype making the learning curve much more difficult than it needs to be - wading thru their rubbish - i remember Acad ws just as bad way back - telling you how wonderful it was and what you will learn without actually teaching you.

Ah, I see what you mean now. 3 spheres each with their ctr located at a corner of the base triangle will intersect at the top. I've left the top poking through a bit to make it more obvious.

hemispheres may be easier to see whats going on, view from below

And from above

Edited By JasonB on 11/09/2021 19:10:33

OBTW JB I have received some gear blanks which I will try out AWS

Yes its like ballet innit

is that intersection point accurate

can you draw 3 lines to intersect

are all the edges the same length to n dp

if so thats cooking on gas

Edited By brian jones 11 on 11/09/2021 20:06:30

you see i am doing my homework

I constructed my solid using lines not a glitzy extension.  SU2021 has addressed the intersection problem and it will now intersect in 3D space correctly, but I have yet to xlate this into an SE experience

FYI I booted up an old copy of Acad 2009 (last time I used it) which I still had on my trusty Acer aspire one notebook, still going strong after 15 years being toted around the world - its my repository of old XP sp3 progs that still have value

I note that this ver of Acad didnt handle circle intersects accurately.  it gave an approxinate point in 2D but if you zoomed in closely you would see that point did not coincide with the circle intersection.  I seemed to remember that I had to make a manual calc to get this accurate.

most of the time you worked in 2 or 3dp for eng purposes so it only affected the lsd and I only did construction stuff

such imprecision cant be tolerated in 3D geometry now

This may seem pedantic to 2D guys but 3D teaches you to be precise or suffer down the line

In those earlier days it was always said that customers were not willing to pay for the considerable extra time needed for 3D drafting.  The offshore industry had to take it seriously when designing modular packages to be craned onto platforms and had to fit together perfectly.  The interior space of these modules was highly constrained and had to accommodate fixtures from piping, electrical, instruments and vendor packages

You can imagine squeezing all those different discipline products into say a container box, plus room for human access and maintenance.  I guess an engine fitted into a modern car bay presents much the same challenge,  Before 3D Cad appeared we made plastic scale models in the DO. They were expensive in time and materials for scaled piping components, valves, fittings, gauges, cable trays etc - maybe 1000+ different pieces

Today 3D Cad is indispensable for many manufacturing and construction industries plus its interface with CAM and all the data produced for BOM, parts lists, assy, procurement schedules etc.

A far cry from the rather haphazard seat-of-the-pants way we ran construction projects back then (pre-windows btw)

I read recently that Tesla's model Y has a complete die cast aluminium chassis. This is huge and a remarkable achievement for which Tesla is leading the world

https://www.foundrymag.com/molds-cores/media-gallery/21932049/tesla-is-turning-to-diecasting-in-a-big-way

Now thats 3D designing

Edited By brian jones 11 on 12/09/2021 18:10:56