# How do I model a hexagonal grille enclosed in a hollow cylinder?

Hello everyone,

I’m relatively new to Shapr3D, and CAD modelling in general.
I’m trying to design a flow straightening section for a model wind tunnel I’m building as part of my final year Physics project for school. So I decided on placing a hexagonal grille in front of my airflow, and the cylinder will hold the grille.
I would be really grateful if someone here could point me in the right direction.

— Johann

Are you wanting the flow to go through the cylinder, with hex channels inside to reduce/ eliminate a vortex?

See if this helps get you there. Chamfer the front edges to reduce friction.

Aside: There is an interesting, ongoing, unofficial contest to design better 3d printed computer fan blades. https://www.youtube.com/watch?v=FIrjwzK3cdA

Thank you so much for taking the time to actually design the part! The issue I’m having is I don’t know how you got to that last step; what are the intermediate steps you took to get to the final screenshot? I would appreciate a screen recording or a video!

Yes, the flow goes through the cylinder, passes through the hexagonal grille and straightens itself out. The grille is the same length as the cylinder itself.

In the last step I selected all the hexagon faces using the area select (with tab key to select faces only), and then an extrusion arrow will appear. I simply dragged the extrusion arrow (faces) thru the cylinder and it extrudes hexagons until it reaches the cylinder and then cuts them into the cylinder if you keep going.

If you extrude a face thru a solid body it will cut the face out of the body as an extruded cut.

And that face I used to make the outer tube.

Something new has come up; I’m unable to chamfer/fillet the edges because Shapr3D says the operation would result in an invalid body. Is there some way to work around this?

Chamfering can be a challenge on small/ narrow surfaces. In the past I have had to play with decimals to get results. E.g. 1mm chamfer might not work on both sides of a 2mm surface but .95 might.

I also thought about making an array of hexagons that are extruded and then tapered by using the scale tool and then subtracting from the array from a cylinder to give very sharp surface at the leading edges, instead of chamfering the top surface.

Also you can double extrude the hexagons to get knife edges.

Oh, got it, I didn’t think about that. Thanks for pointing that out!

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My hexagons are a bit exaggerated, I suspect you realize this but I will still point it out that the draft angle of the hexagons would restrict flow I would think (I’m thinking venturi effect), without knowing how to prove it mathemagically. But straight hex shapes with no draft angle and with double extrusion knife edges might be optimal.

Sorry, often in trouble with my GF for over-explaining (Until I under-explain)

Can’t help it. It’s how I

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