[Feature request?] TechDraw and Fillets/Chamfers

[aapo]

Hi everyone!

When using FreeCAD for technical drawings, I've found it to be a rather excellent piece of free software for all kinds of CAD work. Thanks!

However, I've met a practical problem with FreeCAD TechDraw and fillets in models, namely dimensioning filleted edges at angles. I made a simple model from a sketch that demonstrates the problem: There are two main dimensions: 50 mm width, and 40 mm height. I've subsequently padded the sketch, and filleted the edges with PartDesign. When I add dimensions in TechDraw, the projected width of the part is obviously not 50 mm any more, which causes the dimensions to be different from the sketch (see screenshots below).

I believe that the most standard way in technical drawings I've seen is to deal with the problem by extending the dimension to the position where the node would be without the fillet, so that the width dimension would be exactly 50.00 mm in the example. I think sometimes the edges are extended with dashed line, and sometimes not. However, I believe that this is currently impossible with TechDraw, and it would be somewhat difficult to implement, even if drawing on top of the projection will be implemented some day. So, I just wanted to make a note about the problem for future reference, in the hopes that someone would possibly be able to implement a solution for this fillet/chamfer dimensioning problem in the future. Thanks!

FreeCAD-filletmodel-sketch.png (18.41 KiB) Viewed 2864 times

FreeCAD-filletmodel-fillets.png (13.69 KiB) Viewed 2864 times

FreeCAD-filletmodel-TechDraw.png (63.97 KiB) Viewed 2864 times

OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.16616 (Git)
Build type: Release
Branch: master
Hash: f94cdfd798d0c493efe9c7d45084ad2c5dd18caf
Python version: 3.6.6
Qt version: 5.6.2
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedKingdom (en_GB)

[Syres]

It's a long while since I've been to Tech Drawing school but to achieve the correct final result both from a Sketcher and Techdraw point of view, please see screenshot. Note the arrowed 'helper' horizontal construction line in the Sketch and the way I've dimensioned the model in Techdraw. To be accurate, the 60 degree angle dimension and the horizontal 22.68 are an either or situation, so my tech drawing is over dimensioned IMHO.

[HarryGeier]

Well, it looks a bit like a missing feature of techdraw, but i would rather say, it´s mistaken use of fillet. One could not precisely manufacture this as the radius of the fillet never touches the extends of the original block.
You should construct this with ARCs then , afaik, you have the centerpoints which can used for reference of dimesion and obviously also for reference of a cnc machine.
I know, 3 Print is still possible with such, but 3d print is no precise mechanical operation, due to stl as the base allways sort of a close approximation only.

Edit : when using arcs, you must constrain the centerpoints and the radius . Still you will not be able to dimension the virtual matching point of the lines at the left side without some helper construction.

[aapo]

Well, it looks a bit like a missing feature of techdraw, but i would rather say, it´s mistaken use of fillet. One could not precisely manufacture this as the radius of the fillet never touches the extends of the original block.

I don't claim to know much about technical drawings, so I don't know if it's right or wrong, but I've noticed that professional engineers sometimes use the "continuations" of the fillet edges for dimensioning, and it's usually quite obvious what is meant by the design, even if it's impossible to measure the dimension with caliber. See the clipped example I took from a drawing made by a professional. I do agree that one should usually only define dimensions physically measurable with a caliber, so that the two surfaces under the measurement points would be parallel, but it seems that the pros break this rule for convenience every now and then. Possibly because parts are made with CNC, and the dimensions are just for reference..? Note on the quoted drawing, the center of the arcs are not at 21.2 mm from each other, due to the angled cone; so using center-of-arcs causes ugly values with infinite numbers after decimal point.

I'm struggling with a similar situation, but in the end decided to define the dimensions differently. In this case using FreeCAD forced me to find out a solution, where every dimension could be measured with a caliber or a protractor. Maybe that's a good thing.

FreeCAD-filletmodel-professional.png (14.91 KiB) Viewed 2839 times

[aapo]

It's a long while since I've been to Tech Drawing school but to achieve the correct final result both from a Sketcher and Techdraw point of view, please see screenshot. Note the arrowed 'helper' horizontal construction line in the Sketch and the way I've dimensioned the model in Techdraw. To be accurate, the 60 degree angle dimension and the horizontal 22.68 are an either or situation, so my tech drawing is over dimensioned IMHO.

In your example, it would be nice to get the whole width of the part (50 mm) visible, because it's directly measurable with a caliber. As you demonstrated, it's easily possible with sketcher, but not possible with TechDraw. Or; it's actually sometimes possible in TechDraw, too, but then you need to play with the isosamples option, and get lucky.

Your example is actually much much better demonstrating the problem than mine. Thanks! I hope someone will figure out how to do this properly in TechDraw.

FreeCAD-filletmodel-TechDraw-how.png (47.47 KiB) Viewed 2832 times

[HarryGeier]

aapo,

well you come to the same point as i do, the continuation and the point where both edge would cross. This point, even though i have no clue presently , how to expose it to techdraw ( maybe a datum point ) , needs to be constructed in sketcher.

Maybe someone takes it up and has the idea or wandererfan takes the idea of dimensioning line continuation up also ?

[chrisb]

Wilfried AKA freecad-heini-1 has discussed this some time ago. I think there even exists a ticket for it.

[wandererfan]

Wilfried AKA freecad-heini-1 has discussed this some time ago. I think there even exists a ticket for it.

issue #3004? It is about extrema dimensions, which looks like it would help, but not solve the problem completely. On the plus side dimensioning overall height/width doesn't look too hard.

Drawing additional lines (and points, I guess) that can be used for dimensions is on the TODO list. Some experimenting so far, but no timeline for delivery.

[chrisb]

The ticket seems to describe exactly what I was thinking about, yet I think there was another discussion.

ping

[freecad-heini-1]

The ticket seems to describe exactly what I was thinking about, yet I think there was another discussion.

ping

https://forum.freecadweb.org/viewtopic. ... 80#p280180
https://forum.freecadweb.org/viewtopic. ... 21#p280421

https://freecadweb.org/tracker/view.php?id=3780

It concerns the Sketcher-Workbench. But such a dimension tool would also be very helpful for Techdraw.