Feature Request: Threads

Discussions about the development of the TechDraw workbench
maker
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Re: Feature Request: Threads

Postby maker » Wed Mar 20, 2019 9:31 pm

@NormandC
Again after a delay I would like to continue this topic and hopefully the discussion.
With reference to the post by ulrich1a you mentioned

https://forum.freecadweb.org/viewtopic. ... 10#p251462

After analyzing I cannot share the perspective ulrich1a has on the problem, because its too complicated to realise.

In other words I think the problem we are faced in displaying threads in Techdraw, is not a problem of "decorating a surface".
Lets focus the fact that in technical drawings it is not essential to build a real thread.

In contrast to this for a simple approach in Techdraw the main thing is
that threads in technical drawings according to e. g. ISO 6410-1 (Technical drawings; screw threads and threaded parts; simplified representation)
are described in simplified form.

My proposal for an easier way in Techdraw could be by means of the already existing functionality bore
in part design wb.
M4_bore_parameter_mask_01.jpg
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The needed functionality in Techdraw wb must follow the thread manufacturing steps and must be transferred to the programmed bore-parameter mask.

For example following the manufacturing steps for making an inner thread, e.g. M4 thread in a blind hole:

1. step: the core bore of the thread is drilled with classic drill tip angle 118°.
Example: M4 --> here the core diameter is 3,2 mm. The drill depth is e.g. 25 mm

2. step: cutting of thread M4 in core bore is carried out. Related to the existing core bore depth, the depth of thread is 18 mm. The tip is not relevant

So as always in thread manufacturing we receive 2 overlaid cylinders that are in a fixed relation.
[001317].jpg
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For e.g. metric iso threads the values are valid:
.
M4 Ø core 3,2 Ø thread 4,0
M5 Ø core 4,0 Ø thread 5,0
M6 Ø core 4,8 Ø thread 6,0
M8 Ø core 6,4 Ø thread 8,0
.
.

The structural main task is to combine the 2 cylinders in programming for the preparation of the technical drawing.

I would like to bring up again topics and opinions for discussions and hope that anyone could share this opinion?
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reox
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Re: Feature Request: Threads

Postby reox » Thu Mar 21, 2019 8:14 am

maker wrote:
Wed Mar 20, 2019 9:31 pm
In other words I think the problem we are faced in displaying threads in Techdraw, is not a problem of "decorating a surface".
IMO it is excatly that: The difference between information and representation. For a CAD package it should be enough to store the information that a certain feature is a hole with a given diameter and has a thread with a certain depth etc... Then the question is how to display this data in the 3D and in the 2D view. (Note that there are also many different types of threads, not just metric and UNC+UNF! Other CAD packages give a very extensive way of specifying threads).
One problem is, that the information about the features is lost in the process of translating from 3D to 2D, which is excatly what ulrich1a described.

So the current problem is, that we would need to get some information about the feature from the 3D object, in order to draw the correct representation in 2D. Just using some cylinders which match the sizes of the thread might be some workaround but does not solve the problem IMO.
If you use the Hole feature as you proposed, how should Techdraw decide that this is a thread and show the 3/4 circle for the thread? What if you just created a counterbore? Again, this needs some information flow from the Feature to TD - which is not possible right now.
maker wrote:
Wed Mar 20, 2019 9:31 pm
Lets focus the fact that in technical drawings it is not essential to build a real thread.
Have you seen the image I posted in the very first post? This is all the information we need and IMO it should be stored in the 3D Object and one should be able to translate it into the 2D Object. Displaying some helical structure might be fun but should not be the topic of this thread.
vocx
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Re: Feature Request: Threads

Postby vocx » Fri Mar 22, 2019 5:17 am

reox wrote:
Thu Mar 21, 2019 8:14 am
...
Have you seen the image I posted in the very first post? This is all the information we need and IMO it should be stored in the 3D Object and one should be able to translate it into the 2D Object. Displaying some helical structure might be fun but should not be the topic of this thread.
It seems to me that some users in this thread are getting confused and not understanding the issue. As you say, essentially the only thing that is needed is the 2D symbol that indicates that a hole is threaded. So, I think TechDraw just needs to read the information from the PartDesign Hole feature and display it accordingly. And I agree, displaying the helical thread is not really needed, as it may just make the processing of the page slower.
reox
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Re: Feature Request: Threads

Postby reox » Fri Mar 22, 2019 8:29 am

vocx wrote:
Fri Mar 22, 2019 5:17 am
So, I think TechDraw just needs to read the information from the PartDesign Hole feature and display it accordingly.

Yes - but this is not possible right now, as TechDraw does not know what line belongs to which feature in 3D :(
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wandererfan
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Re: Feature Request: Threads

Postby wandererfan » Fri Mar 22, 2019 1:11 pm

reox wrote:
Fri Mar 22, 2019 8:29 am
Yes - but this is not possible right now, as TechDraw does not know what line belongs to which feature in 3D :(
This is indeed the big stumbling block. The result from the projection algorithm is just a pile of edges, with no information about the Face or Feature of origin.

To do this in the current environment, we would go back to the Source object(s), inspect them for presence of a Hole feature, extract the Hole information, project it, then try to find the right spot on the drawing, then draw the appropriate symbology.

So, "doable" but probably not elegant or quick.
user1234
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Re: Feature Request: Threads

Postby user1234 » Fri Mar 22, 2019 3:23 pm

Hello!

Maybe a CompSolid helps? Just a thought .....

Greetings

user
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reox
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Re: Feature Request: Threads

Postby reox » Fri Mar 22, 2019 7:17 pm

wandererfan wrote:
Fri Mar 22, 2019 1:11 pm
So, "doable" but probably not elegant or quick.
Also, Outer threads are missing in PDN and as far as I observed the hole feature requires some care too...
So maybe the best solution would be to have a proper representation in PDN and then care about TD?
user1234 wrote:
Fri Mar 22, 2019 3:23 pm
Maybe a CompSolid helps? Just a thought .....
I guess that could work but still you would need to extract some information from the geometry to draw the correct line types etc...
I think this is also something worth implementing in PDN: A proper represenation of threads in the 3D view (like draw the actual thread vs lines etc)
chrisb
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Re: Feature Request: Threads

Postby chrisb » Fri Mar 22, 2019 8:08 pm

reox wrote:
Fri Mar 22, 2019 7:17 pm
Also, Outer threads are missing in PDN and as far as I observed the hole feature requires some care too...
So maybe the best solution would be to have a proper representation in PDN and then care about TD?
Good proposals.

The hole feature should have an additive counterpart with almost the same behaviour: based on sketched circles, diameter, length, ...
Only thing to be omitted: I don't see a counterpart for counterbore and countersink.
Jee-Bee
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Location: Netherlands

Re: Feature Request: Threads

Postby Jee-Bee » Fri Mar 22, 2019 8:15 pm

just revolve??

the only issue with counterpart of a treaded hole is just thread...
only difficulty on the word counter part is that thread isstill a function that removes material so it is still a cut operation.
user1234
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Re: Feature Request: Threads

Postby user1234 » Fri Mar 22, 2019 8:48 pm

Hello!
reox wrote:
Fri Mar 22, 2019 7:17 pm
A proper represenation of threads in the 3D view (like draw the actual thread vs lines etc)
This is what i mean. I do this also on my my projects and that work good. But the problems are the line information. This can only be solved when the toplolocical naming issue is solved.

Greetings
user
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