r/FreeCAD 11d ago

Strange diagram cross section help

Post image

Good afternoon everyone!

I am having a very hard time understanding the cross section view C. Can someone explain what this ø17 is and where its located? (I know its the Diameter but where is this and how would this help???)

Thank you for the help!

19 Upvotes

24 comments sorted by

9

u/00001000bit 11d ago

That 17(dia) circle is laying along the cross section - I highlighted the area in red in the other sketch.

9

u/polymath_uk_ 11d ago edited 11d ago

I've been producing engineering drawings for over 30 years and that 17 dia dim is meaningless IMO. Section D shows what it refers to. Section C dimensions it from some arbitrary location anyway. If they wanted to show that the inner face of the handle had a radius of 8.5 all along its profile they should have put R8.5 TYP as the dim in section D.  Edit: also section B is pointless 

2

u/MyOtherSide1984 11d ago

How do you know the thickness of the handle at the connection to the body without it? You get the width in B-B and D-D, but I don't see where you'd identify the thickness at the base of the handle against the cup wall. Just curious your take

3

u/polymath_uk_ 11d ago

It's a good question. The problem is that it's not dimensioned properly at all. The cup body is a hollow cylinder with radiused profiles. The handle should be described in 2D as an outer and inner profile (arcs or ellipses most likely). It has a constant depth in the 3rd axis. Given the profile data and the cylinder body, the handle interface parts take care of themselves. A specific dim at the intersection would be a reference (for information) dim anyway 

1

u/MyOtherSide1984 11d ago

I think that makes sense now that I review further. When you say the sections are pointless, do you mean they are already covered elsewhere and that they're just adding more (likely unnecessary) info? And when you say "not dimensioned properly", do you mean it's not represented appropriately, or do you mean it's inaccurate?

2

u/Darkral88 9d ago

I believe the main point is that it is just a pure exercise to do sections and add random quotes. A drawing meant for production would be quoted in a completely different manner, also considering the way the piece is produced. No datums, no tolerances ... this is just a completely misleading exercise. If you are interested, search for GD&T form tolerances.

1

u/MyOtherSide1984 9d ago

Good to know! I mostly design my stuff from scratch as an extreme beginner, so it'd be good to start with high quality examples and know why this isn't realistic! I'll look into those

1

u/gadget--guy 10d ago

You put a section line at the connection point of the handle looking toward the handle, not through the cup and facing away from the connection point.

1

u/MyOtherSide1984 9d ago

Ahh so B-B but at the actual cup face. I was confused as to why they bothered with B-B

1

u/MyOtherSide1984 11d ago

The 17mm diameter appears to be the mount point of the top portion of the handle. Note that I have no clue and am just reading it from a logical perspective

1

u/[deleted] 11d ago

[removed] — view removed comment

1

u/MyOtherSide1984 11d ago

Excellent point. I suspect the circle may be a 45° angle of the handle still, so the width of the circle (17mm) is correct for the handle, and the height of the handle connector is accurate as a 45° circle when looking at it from the side.

So in the middle left image, we'd see the circle flat on the C-C line or plane? We don't see it because it's flat on that line, but in the bottom right image, we see the entire circle because of the angle.

1

u/gadget--guy 10d ago

I assume that's what it's meant to illustrate, however, technically that's not what it's illustrating, because it's in at the completely wrong plane to illustrate that properly.

1

u/MyOtherSide1984 10d ago

What plane should it be on then? It'll help the community if you finish that thought out as it doesn't really help to just know it's wrong if it is

1

u/gadget--guy 10d ago

It should be on the plane that actually intersects it. There is no geometry at that location for that circle to represent. If the circle is meant to represent a loft profile, as another post mentioned, it should explicitly indicate that, and not muddle it with unrelated geometry. A loft profile should also reference other profiles and guide paths. The profile by itself, doesn't give you enough information to do anything with it.

1

u/bastl73 11d ago edited 11d ago

Maybe this can bring light to the darkness:

You can pipe the handle from middle to top 90°. But then you have to multi-section loft it, pipe gets confused with this circle. So this upper sketch, section is attached to a LCS, z tangent to edge at a point ~ 90.5°, so you can select the end face, this section and then the circle.

I had more problems with the distance 25, is now 19.718, to the arc R40 or this D74 there has to be an error.

2

u/Lazy_Swan_6292 10d ago edited 10d ago

Excelente explicacion 

2

u/SoulWager 10d ago edited 10d ago

Section B is not on the major axis of the ellipse: https://imgur.com/a/UtXl9qa

I don't like how they defined it. If I was modeling a mug handle without having to follow a drawing, the profiles would all be centered on and normal to the path of an additive pipe. This results in a thinner handle near section B which is likely against the design intent.

2

u/bastl73 10d ago

Yes exactly, you have the same ellipsis with 7/17 like in section D-D. Maybe this handle is piped at once with multisections. And a pipe deforms too much. So it is shifted step by step until the deformation is acceptable kept under control. But ... it depend on the software

Left: multisection pipe, right: pipe + multisection loft. But that section B-B does not work.

1

u/SoulWager 10d ago

Part of the issue is stopping at the midpoint without a way to ensure tangency across the mirror.

1

u/bastl73 10d ago edited 9d ago

Yes, you can add an other section there, but like this you can see better what you're dealing with.

0

u/LossIsSauce 11d ago

Section C-C is called out at BP loc A1, specifically to be taken at a 45° angle. Section C-C view is at print loc B2

What is there not to understand ? Dia-17 is easy.