3D cad question

[GreenTwin]

I think we have. I'll stop now

Yes, but I have learned a lot, and so I presume others will learn a lot too.

Thanks for sharing the info.

Great stuff.

.

 

[Jasonb]

So Pat how do you know what size anything is on your 3Dmodels. lets take two simple parts one shaft and a block with a hole in it.

you select circle and click and drag a circle but what diameter is it. You then extrude it but have to enter a length or do you just drag it to some unknown length.

The other part how do you get the hole in it to fit the shaft if you don't dimension it or give it a size. And how do you position the hole in the block if you can't dimension it from an edge or ctr line.

I'm constantly using various constraints particularly concentric, parallel, symmetrical, tangent, colinear, right angle. Some come up automatically others I add as needed

 

[GreenTwin]

So Pat how do you know what size anything is on your 3Dmodels. lets take two simple parts one shaft and a block with a hole in it.

you select circle and click and drag a circle but what diameter is it. You then extrude it but have to enter a length or do you just drag it to some unknown length.

The other part how do you get the hole in it to fit the shaft if you don't dimension it or give it a size. And how do you position the hole in the block if you can't dimension it from an edge or ctr line.

I'm constantly using various constraints particularly concentric, parallel, symmetrical, tangent, colinear, right angle. Some come up automatically others I add as needed

I am going to split off a topic that was posted in another thread, since I think we drifted too far off of the original subject that was posted.

https://www.homemodelenginemachinis...-dimensions-in-3d-modeling.34573/#post-386723

 

[L98fiero]

OK Off to get the 30 day trial of Alibre. I watched to intro videos on the site and it looks pretty simple.

Joko Engineering has a lot of videos on Alibre Atom, the $100 CAD. He seems very experienced at CAD so sometimes it's hard to follow him because he's so fast but he does demonstrate how capable Atom is, here's a video of him doing a cylinder head. He also has a beginner tutorial and Alibre and a few others have beginner tutorials as well.

 

[ajoeiam]

Yes but the intolerance is a feature, not a limitation. It is protecting you from making bad geometry inadvertently. An open sketch cannot be extruded to a (at least mathematically correct) defined solid. This is equivalent to the Rhino type crash I was mentioning earlier. If the computational tolerance parameter is set coarser than the open gap, it kind of makes a 3D model, but its not 100% correct & can cause issues down the line.

Trimming is fine, but closing geometry as you click-click is just easy, faster & arguably less error prone. Look for the little yellow symbol as you approach the termination point. This same feedback theme also pertains to 'waking up' the centers of circles & arcs by hovering over them

Hmmmmmm - - - I find, in FreeCAD, that there is only ONE way to constrain one's model.
As I can tell you at least 3 ways of doing that I get frustrated - - - its also hard to understand what order they want things constrained in - - - if that order isn't correct - - - FreeCAD pukes!
Constraints is one reason I haven't spend more time even learning freecad - - - - I'm far faster using mathematics and describing point to point lines than with the goofy constraints system!

 

[ajoeiam]

I should mention that I don't just pick random values for dimensions, such as on the Galloway above.
I keep a chart of standard fastener, round/square bar stock, and drill/tap sizes next to my desk.
Any shaft or fastener dimension gets selected from the nearest standard size in the chart.

Bore and stroke are also rounded to the nearest reasonable numbers, often whole numbers.

Etc.

.

One of my frustrations is when one is forced to use internal tables of sizing for stock - - - -
and the list is truncated, inaccurate or loaded with errors.

There are so many forms of bolts, some different even in different industries, never mind
pipe and tubing which somehow are equated by the people developing FreeCAD - - - they
seem to be engineers but it is hugely relevant that they don't seem to have diddly amount of
personal experience - - - ie hands on.
Trying to get things added is incredibly difficult - - - all of this stuff is why I've gone back to 2D
drawing - - - it just takes less time and then make a paper/cardboard model and check for stuff.

 

[GreenTwin]

Constraints is one reason I haven't spend more time even learning freecad - - - - I'm far faster using mathematics and describing point to point lines than with the goofy constraints system!

No matter what people tell you about constraints, you don't need them for modeling work.
I came from the 2D CAD world (originally paper and pencil world), and I have never used constraints, and never had a problem, even with complex models.

I hear people talking about how you have to "lock down the model with dimensions".
I have never done that either, and again no problems.
The model does not change itself; you don't need to lock anything.

Perhaps constraints are useful if you are designing an oil refinery or something.

For model engine work, I find constraints to get in the way, so I don't use them at all.

.

 

[GreenTwin]

One of my frustrations is when one is forced to use internal tables of sizing for stock - - - -
and the list is truncated, inaccurate or loaded with errors.

There are so many forms of bolts, some different even in different industries, never mind
pipe and tubing which somehow are equated by the people developing FreeCAD - - - they
seem to be engineers but it is hugely relevant that they don't seem to have diddly amount of
personal experience - - - ie hands on.
Trying to get things added is incredibly difficult - - - all of this stuff is why I've gone back to 2D
drawing - - - it just takes less time and then make a paper/cardboard model and check for stuff.

One source of bolts is McMaster Carr.
You can download 3D models of their fasteners.

I generally draw my own bolts, without showing the threads on the shaft.
There is nothing to be gained by showing the threads on a bolt in a 3D model, unless you just want a very detailed look.

I show fasteners in an exploded view typically.

 

[awake]

Hmmmmmm - - - I find, in FreeCAD, that there is only ONE way to constrain one's model.
As I can tell you at least 3 ways of doing that I get frustrated - - - its also hard to understand what order they want things constrained in - - - if that order isn't correct - - - FreeCAD pukes!
Constraints is one reason I haven't spend more time even learning freecad - - - - I'm far faster using mathematics and describing point to point lines than with the goofy constraints system!

I have never found that there is only one way to constrain. I have found, sometimes on a very complicated sketch, that I get the constraints working against each other; this generally happens because I have been figuring it out as I go, and have made the constraints overly complicated. Generally at that point, I can re-draw and constrain the part very quickly, now that I know what I'm after. But even so, there are usually multiple ways to constrain that will work ...

On edit: Oops, I see that Pat has started a new thread on this topic - good idea, and I'll take any further comments there!

 

[Jasonb]

pat I replied in your other thread here, you are using constraints and dimensions but seems that you don't know it

https://www.homemodelenginemachinis...s-dimensions-in-3d-modeling.34573/post-386834

 

[timo_gross]

This is a typical 3D engine model for me, made with Solidworks.
Almost all the information taken from photos of my Dad's 7 hp Galloway.
No dimensions, no constraints.
No problems running it in simulation.

That looks very good, whish I could get something like this done with the 3d program , I still fiddle around with much simpler things. I do not get how you do it without any dimensions?
Does it mean all your dimensions are "free floating"? Cylinder bore, diameters etc. everything is more or less random numbers?

Someone might want to get some parts made by any of those robots (aka CNC, 3d printer, laser cutting, plasma cutting, milling etc. )
Usual approach today is to provide the computer file to the maker. E.g. for laser cutting they do not revise files they throw at the machine, what is in the file.
I learned the lesson the hard way.
Placed some holes in the wrong position, and they were in the wrong position in the finished part. The wrong position was the correct position in the "opinion" of the stupid robot.

Greetings Timo

 

[GreenTwin]

That looks very good, whish I could get something like this done with the 3d program , I still fiddle around with much simpler things. I do not get how you do it without any dimensions?
Does it mean all your dimensions are "free floating"? Cylinder bore, diameters etc. everything is more or less random numbers?

Someone might want to get some parts made by any of those robots (aka CNC, 3d printer, laser cutting, plasma cutting, milling etc. )
Usual approach today is to provide the computer file to the maker. E.g. for laser cutting they do not revise files they throw at the machine, what is in the file.
I learned the lesson the hard way.
Placed some holes in the wrong position, and they were in the wrong position in the finished part. The wrong position was the correct position in the "opinion" of the stupid robot.

Greetings Timo

There is a lot of confusion about 2D and 3D terminology, and I am still learning the 3D terms and what they mean exactly.

For me, adding "dimensions" to a sketch is a way to visually show how big something is.
Say you sketch a circle in Solidworks that has a 1" radius.
You will not know that the circle has a 1" radius by looking at the screen, because all you see is a circle, but it is indeed sketched to a 1" radius.
If you want visual verification that the circle has a 1" radius, you add a dimension to it, and then you can see the text 1" with its leader lines.

If you erase the visual dimension, the part still remains with a 1" radius.

So with or without the visual dimension, your part size is still the same, which is some distance that you determine (not ramdomly), such as a 2" bore.

.

 

[Jasonb]

But Pat how do you know that initial sketched circle is is 1" and not 2" . Are you using a grid and it is snapping to the 1" grid pattern or are you entering a radius as you draw the circle? Otherwise I can't see how the program knows you wanted a 1" circle.

What happens if you draw a random line near that circle and then make that line tangent to it? If you have not given that circle a position and size chances are the circle will move or enlarge to touch the line.

 

[timo_gross]

There is a lot of confusion about 2D and 3D terminology, and I am still learning the 3D terms and what they mean exactly.

For me, adding "dimensions" to a sketch is a way to visually show how big something is.
Say you sketch a circle in Solidworks that has a 1" radius.
You will not know that the circle has a 1" radius by looking at the screen, because all you see is a circle, but it is indeed sketched to a 1" radius.
If you want visual verification that the circle has a 1" radius, you add a dimension to it, and then you can see the text 1" with its leader lines.

If you erase the visual dimension, the part still remains with a 1" radius.

So with or without the visual dimension, your part size is still the same, which is some distance that you determine (not ramdomly), such as a 2" bore.

.

Ha, tha tclears up a lot of confusion. Chicken talking to the duck.....
If we talk about dimension in the 3d design is the fact that user "told" the computer in some way at some point in time something is 1" (25.4 mm) in diameter.
Something is concentric, something is parallel, perpendicular or tangential etc.
The computer has it saved and "knows" it. It is supposed to be 1" and not 1.0003" or 0.994" and the computer will keep this information unless it is instructed otherwise.
A visual indicator for a human reader is not necessary or usual, the computer takes care of it.

As soon as you type some number into the system, you have dimensioned it . It is possible to purely "paint" in those softwares without having anything fixed the computer will not keep dimensions, but rather tries to find a way to combine all given information and changes whatever the programming rules allow.
Computers are quite stupid, so the choosen changes can be quite pointless.

The pointless choices of the computer get worse, the more free choices the machine has, so a 90% defined and dimensioned sketch is already quite stable. A totally free floating sketch is asking for trouble

Greetings Timo

 

[GreenTwin]

But Pat how do you know that initial sketched circle is is 1" and not 2" . Are you using a grid and it is snapping to the 1" grid pattern or are you entering a radius as you draw the circle? Otherwise I can't see how the program knows you wanted a 1" circle.

What happens if you draw a random line near that circle and then make that line tangent to it? If you have not given that circle a position and size chances are the circle will move or enlarge to touch the line.

In Solidworks (not sure about other programs), you draw a random circle, starting with the center of the circle where you want it to be and preferrably snapped to some point, and then while the circle dialog box is open, you adjust the circle radius in the dialog box by typing in the desired number.

If I were going to draw a tangent line to a circle, in Solidworks you can hover over the circle, and at the tangent point SW will draw a dashed line from your cursor point down to the tangent point on the circle, so you know where to start drawing the line.
There is no need to draw the line and then move it, but if you do move a line with the move command, it will not move any other object, even if you snap to a node.

I have not used options like "make tangent to circle", and so I have never had anything move automatically on the screen.

.

 

[GreenTwin]

There is a lot of confusion about 2D and 3D terminology, and I am still learning the 3D terms and what they mean exactly.

For me, adding "dimensions" to a sketch is a way to visually show how big something is.
Say you sketch a circle in Solidworks that has a 1" radius.
You will not know that the circle has a 1" radius by looking at the screen, because all you see is a circle, but it is indeed sketched to a 1" radius.
If you want visual verification that the circle has a 1" radius, you add a dimension to it, and then you can see the text 1" with its leader lines.

If you erase the visual dimension, the part still remains with a 1" radius.

So with or without the visual dimension, your part size is still the same, which is some distance that you determine (not ramdomly), such as a 2" bore.

.

It should be noted that you can "drive" a sketch or shape such as a circle using the dimension, ie: you change the dimension and the circle gets bigger or smaller.
I don't ever drive shapes/sizes with dimensions, and I am not exactly sure how that works, but it can be done.

I feel like driving a shape with a dimension is asking for trouble.
Just let the shape be the size it is.
I am sure there is some good reason why some drive their dimensions/sizes.

For me, less is more; ie: the fewer feature configurations I have to remember, the better off I am.

.

 

[Jasonb]

To me and most others entering that initial 1" is dimensioning the circle and will lock it in to that size unless altered.

You also say preferably snap the ctr point of the circle, again you are constraining it to that snap be it an axis, ctr of another circle, etc

 

[GreenTwin]

To me and most others entering that initial 1" is dimensioning the circle and will lock it in to that size unless altered.

You also say preferably snap the ctr point of the circle, again you are constraining it to that snap be it an axis, ctr of another circle, etc

But the circle is still 1, and I don't need to lock it because I have never had anything move.

If its not broken, don't fix it.

Perhaps good practice, but entirely unnecessary as far as I can tell with all the engines I have modeled.

When you draw a circle, do you initially draw it at 1, or do you drive it to 1 using the dimension, or drive it to 1 with a dialog box?
Seems like you really only need to define it as 1 once, not twice.

Have you tried making sketches without dimensions?
Does making sketches without dimesions cause things to shift in Alibre?

.

 

[Jasonb]

But the circle is still 1, and I don't need to lock it because I have never had anything move.

Pat the reason it won't move is that you have snapped it to and axis and given the circle a 1" radius. The only way it will change is if you physically go back and change that 1" to say 2" or set a position for it's ctr that is not on that axis.

If I draw random circles and lines with no fixed (constrained) position or length/dia( dimension) then yes they can start to move about if I start dragging one with a mouse or constraining one to another. For example if I want a line tangent to one of those circles then depending on what I click first the hole may move or increase diameter to touch that line or the line may move to touch the circle. If that line is part of a larger sketch then it can drag the whole sketch all over the screen.

I When drawing a circle in Alibre you select the circle tool, click at the point you want the circle ctr and then drag the mouse, click again and you get a diameter where ever you click. So I could fiddle about trying to get my mouse at exactly 1" but its usually a few thou either way which is a waste of time. My usual way is to click and start the circle and the screen shows a box with the changing length as you move the mouse away from the ctr so rather than click again I just enter the diameter. Sounds like you do similar with SW So by doing that I have dimensioned that circle and it's diameter won't change again unless I enter a new value. Alibre will sense if you have a similar size circle and prompt that diameter so just hit enter if that is what you wnat.

This is why it is important to constrain and dimension things. You are doing it subconsiously in two ways - the computer is doing some for you and simply adding that initial 1" radius is you adding a dimension.

 

[GreenTwin]

Sounds like we are basically doing the same thing, perhaps in a slightly different way.

.