New user analyzing forum provided sketch (Solved)

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drmacro
Posts: 740
Joined: Sun Mar 02, 2014 4:35 pm

Re: New user analyzing forum provided sketch

Post by drmacro » Sun Mar 29, 2020 6:38 pm

Ask the questions. Sooner or later One of the explanations will create an "AHA!" moment. Until thenwe , well at least I, will attempt to rephrase or use different words to explain.
As a logic exercise take a sketch, #1 is in the X:Y plane, make another, #2 in the X:Z or Y:Z (your choice) - - - - merge them - - - - bingo - - - - your model is complete. What I don't know - - - - is how to program that intersection.
If there is a sketch on #1 and it is padded. And a sketch on #2 and it is padded to a length that it overlaps the first in 3d space, they are one solid.


Note, there are caveats. But this is the general case.
ajoeiam
Posts: 120
Joined: Sun Mar 03, 2019 9:36 pm

Re: New user analyzing forum provided sketch

Post by ajoeiam » Sun Mar 29, 2020 6:44 pm

Bance wrote:
Sun Mar 29, 2020 6:24 pm
Well done for posting this I'm sure it will benefit many others as well.
I'll try to address your points one by one.
ajoeiam wrote:
Sun Mar 29, 2020 1:56 pm
1. illogical numbering scheme - - - there are really 2 Sketch #1s
Sketch and in fact all Freecad objects as far as i know use programmers numbering which traditionally starts from zero.
ajoeiam wrote:
Sun Mar 29, 2020 1:56 pm
2. question as to why more than 1 pad needed
This is a plan of three bodies made from sketches containing circles that are concentric.
ThreeConcentricTop.jpeg
Then the profile.
ThreeConcentricSide.jpeg
Then an angled view.
ThreeConcentricTilt.jpeg
These are just a few of the possible outcomes of a pad operation, but how is the software supposed know which is the desired outcome?

HTH Steve
ajoeiam wrote:
Sun Mar 29, 2020 1:56 pm
1. both sketch001 and 002 are fully constrained yet I can't find a way to constrain sketch or any of its values - - why?
How were you trying to constrain Sketch? The lines were constrained to point on axis and vertical length, the only other way they could be constrained is horizontally.
ajoeiam wrote:
Sun Mar 29, 2020 1:56 pm
2. on the coincident circles was there a need to depict one sketch where a radius and a diameter are used and the
other uses 2 diameters - - - - is that necessary or ??????
I constrained them the way you specified in an earlier post, vis :- 1. Arbour (not specified, so out of habit used radius.) 2. ID of the carbide teeth. 3. OD of the blade.
ajoeiam wrote:
Sun Mar 29, 2020 1:56 pm
3. it is possible to edit the values in sketch but not in either sketch001 or sketch002 - - - why?
Sketch is as drmacro noted, a master sketch, it's purpose is to centralise parameters, other sketches are linked to master sketch so changing a parameter there is propagated. It is because these parameters are linked via expressions that they cannot be edited in situ.
ajoeiam wrote:
Sun Mar 29, 2020 1:56 pm
4. how are the values in sketch linked to those in sketch001 and sketch002?
They are linked using the expression engine. It is a very powerful mechanism that can utilise formulae and logic to manipulate values.
ajoeiam wrote:
Sun Mar 29, 2020 1:56 pm
5. why is sketch done as 'lines'?
I deliberately left them as lines to show that the sketch was abstract and not for using as a sketch in the modeling sense, I could quite as easily have sketched a section of the blade, which as has been pointed out could have been revolved to produce the model. I didn't feel that using a revolve would help in this case because you were focused on padding circles.

A good way of thinking about modeling in Part Design is, imagine you are using plastecine you can add to it or take from it but it is just one piece in your hand and for the most part you can only do ONE thing at time to it.
1. Ah, yes, the zeroth function. Except in mathematics its much much safer to use zero more as a place holder than as an active participant. I believe that most individuals don't start counting using zero.
2. OK, logical, might have been easier to understand if all values were one or the other though.
3. How are the parameters linked? (I can't see how or where this is done.)
4. Fascinating - - - expressions - - - - might make something like gear design a little easier - - - - except then you still have to toss in the metallurgy and also the materials science.
5. OK sorta makes sense. I was trying to figure out how to add the third dimension to the sketch.
Revolving a figure is in some ways simpler but that also would remove options like a wavy blade (used on farm equipment for at least one).
Sorry - - - - - I've been told a lot of times over many years to do things one at a time. Far more fascinating to figure out how to do two or three and each at a fairly high level. Sorta like standing in a room and listening to 4 or more conversations at once.

OK, this time the blade was modeled using the 'Pad' function.
Lofting (or revolving) is another option - - - - is there a 'good' tutorial on doing that somewhere?
Are there any other ways?

Thanks for the response - - - much of what you had done is clearer now.
drmacro
Posts: 740
Joined: Sun Mar 02, 2014 4:35 pm

Re: New user analyzing forum provided sketch

Post by drmacro » Sun Mar 29, 2020 6:55 pm

ajoeiam wrote:
Sun Mar 29, 2020 6:27 pm
Well a blade is actually comprised of multiple parts.
Oh yes - - - - a LOT of blades.
I think this may be the source of some confusion.
This would be an assembly of many parts (screws, carbide inserts, etc.) And, may be a sub-assembly of a milling machine.
ShellMill.png
ShellMill.png (25.15 KiB) Viewed 50 times
This is a saw blade. (yes, it has several carbide tips brazed on to form teeth. So, technically an assembly in and of itself.)
TableSawBlade.png
TableSawBlade.png (69.75 KiB) Viewed 50 times
What I've been envisioning from your descriptions is a shaft with many of these affixed in some manor.
openBrain
Posts: 3897
Joined: Fri Nov 09, 2018 5:38 pm

Re: New user analyzing forum provided sketch

Post by openBrain » Sun Mar 29, 2020 7:08 pm

ajoeiam wrote:
Sun Mar 29, 2020 6:25 pm
It would be wonderful to see a model like you describe in your first sentence.
Find attached. ;)
What I'm understanding very clearly is that I should not have asked this question at all.
Oh well - - - - lesson learnt!
Don't know which question you're talking about, and actually don't get the sense of this. :)
Attachments
saw_OB.FCStd
(10.66 KiB) Downloaded 3 times
Bance
Posts: 381
Joined: Wed Feb 11, 2015 3:00 pm
Location: London

Re: New user analyzing forum provided sketch

Post by Bance » Sun Mar 29, 2020 7:09 pm

ajoeiam wrote:
Sun Mar 29, 2020 6:44 pm
3. How are the parameters linked? (I can't see how or where this is done.)
Expressions can be used most places values are entered, Best read the wiki link, In this instance I simply gave the values a name and used that to create the link. Very sophisticated scenarios can be created with a little imagination (and Maths :twisted: )
There is a gears workbench but you have to install it, haven't had the need to use it, so cannot comment on usefulness.
ajoeiam wrote:
Sun Mar 29, 2020 6:44 pm
5. OK sorta makes sense. I was trying to figure out how to add the third dimension to the sketch.
Don't quite get this? All required dimensions are in the master sketch. (Including plate thickness and tooth thickness, which are the pad lengths.)
ajoeiam wrote:
Sun Mar 29, 2020 6:44 pm
Revolving a figure is in some ways simpler but that also would remove options like a wavy blade (used on farm equipment for at least one).
One can also loft, (pad from one shape to another) or pad along a path(think of an exhaust pipe) So maybe not so limited? :mrgreen:
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