Gap when joining onto a cylinder

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miker
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Joined: Thu Jun 30, 2022 8:57 pm

Gap when joining onto a cylinder

Post by miker »

Hi,

I am new to FreeCAD and I'm currently practising by building models from part drawings I find on image search, I am currently trying to build this part

Version: 0.19

Image

Everything was going well until I tried creating the joint between the two cylinders. I thought I could just expose some of the points from either cylinder and sketch the shape and pad it out like so:

Image

However this leaves me with these gaps, what would be a better way to do this please?

Image


Thanks for your help
GeneFC
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Re: Gap when joining onto a cylinder

Post by GeneFC »

This sort of problem has come up on the forum previously as a challenge. Without going into any detail, it is geometrically impossible to create a smooth join just using simple flat surfaces as shown in your image.

Lots of ways to create overlaps and other joining techniques.

You need to decide how you want to deviate from simple planar surfaces.

Gene
vm4dim
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Re: Gap when joining onto a cylinder

Post by vm4dim »

Just make it wider.
miker
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Re: Gap when joining onto a cylinder

Post by miker »

I added some small rectangles and padded those out, I don't think it is the most elegant solution but it seems to have worked.

Could anyone point me to some techniques for creating smooth joins and overlaps please?

Image
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Shalmeneser
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Re: Gap when joining onto a cylinder

Post by Shalmeneser »

:idea:
Attachments
JoinCylinder_SHALM.FCStd
(180.59 KiB) Downloaded 3 times
Capture d’écran 2022-07-01 101159.jpg
Capture d’écran 2022-07-01 101159.jpg (76.99 KiB) Viewed 213 times
miker
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[SOLVED] Re: Gap when joining onto a cylinder

Post by miker »

Thanks @Shalmeneser for the inspiration! :D

Image
chrisb
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Re: Gap when joining onto a cylinder

Post by chrisb »

SnipScreenshot-b60418.png
SnipScreenshot-b60418.png (19.01 KiB) Viewed 178 times
Here is a proposal with pretty much work in it, but you are rewarded with smooth transitions.
SnipScreenshot-2b80a3.png
SnipScreenshot-2b80a3.png (12.49 KiB) Viewed 178 times
I kept the middle part as proposed by Shalmeneser, to keep the plane face on top. The gap closing part can of course be made smaller.
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
chrisb
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Re: Gap when joining onto a cylinder

Post by chrisb »

For comparison purposes is here a model which uses just a loft in the middle. Looks nicer on first sight, because it has less seams, but the top is a complicated curved face.
SnipScreenshot-99310e.png
SnipScreenshot-99310e.png (24.07 KiB) Viewed 174 times
Attachments
JoinCylinderLoftOnly_cb.FCStd
(27.94 KiB) Not downloaded yet
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
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papyblaise
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Re: Gap when joining onto a cylinder

Post by papyblaise »

for fun, I'm redoing this exercise, but I stumbled on a bone: before (a long time ago) we could make the rays (marked red) ending in a point with the "filet" tool, we can't do it anymore today today, I had to use all my faculties to do this
and you :?:
Attachments
fillets.JPG
fillets.JPG (29.55 KiB) Viewed 152 times
fillets.FCStd
(366.18 KiB) Downloaded 2 times
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bambuko
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Re: Gap when joining onto a cylinder

Post by bambuko »

This is one of these cases where doing it with pencil is definitely easier
and permits quite a degree of "poetic licence" when drawing some edges :lol: :mrgreen:
3D CAD doesn't understand fuzzy logic and wants precision ;)
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