Francis turbine | Spiral case | Weird loft along path

petr_bláha69

I am working on a Francis turbine school project that will be used for a fluid flow demonstration and for a real 3D printed model. But at the moment I'm stuck on modeling the spiral case.

https://cad.onshape.com/documents/03aa0b510e7bf1da4c64e519/w/c6e545882276973a5ed4feb1/e/6fa7e6f6599d3ae023813181?configuration=snaildiam=0.2+meter;snailsize=0.08+meter&renderMode=0&uiState=649160d46cbcaf67f6d2430e

I have the first sketch in the top plane as a snail trajectory for "Loft" along the path. Next to this path I have other planes with circles corresponding to the cross section of the spiral tube. When I loft from one cross section to the other, I get an object, but this shape is weakened in the middle and the resulting shape is distorted.

Is it possible to make the resulting shape in Onshape so that the Loft transitions evenly from larger to smaller?

Thanks for any idea :-)

David_YL_Nguyen

Hey @petr_bláha69,

Is it possible that you are using an education licence of Onshape? In that case you need to make the document public.
I tried to open your link but was not able to access.

Thanks,
David

petr_bláha69

Hi David, you are correct, I am using Edu version. Now document is public.
Thank you.

robert_scott_jr_

Welcome to Onshape. Please take a look at the document linked below. The approach used was to loft from the intended beginning of the loft to the intended end using the path you created and then split the loft using the existing planes. Perhaps the results are what you are after. - Scotty

https://cad.onshape.com/documents/9c62c824b84cfc33e43c8303/w/5be2cb6ff81a45e07aaea6b0/e/bf5f9a93bc18b6caac0df8b9

steve_shubin

@petr_bláha69  said:

Is it possible to make the resulting shape in Onshape so that the Loft transitions evenly from larger to smaller?

  https://cad.onshape.com/documents/58f0590e783b3bab7b7cbc6c/w/7a147a74c899c518d2178d51/e/9b7604138d7fef1c0f95e4cd

Take a look at the end conditions of the loft to see if you want to incorporate what is showing

petr_bláha69

Hi Scotty,

thanks for the advice, but there are still errors in this shape. Looking from the left view you can see that the final tube is smaller than the initial circle :-(

Petr

petr_bláha69

Hi Scotty,

thanks for the advice, but there are still errors in this shape. Looking from the left view you can see that the final tube is smaller than the initial circle :-(

Petr

steve_shubin

@petr_bláha69

I’ve added 2 Part Studios

With regards to the below definitions for the part studios — all three part studios are to be viewed from overhead looking downward, i.e. from TOP VIEW

Circular Inside —

The inside edge of the horn is circular

Circular Centerline —

The center of the horn is circular

Roughly Circular Inside —

The inside edge of the horn is roughly circular

petr_bláha69

steve_shubin said:

@petr_bláha69

I’ve added 2 Part Studios

With regards to the below definitions for the part studios — all three part studios are to be viewed from overhead looking downward, i.e. from TOP VIEW

Circular Inside —

The inside edge of the horn is circular

Circular Centerline —

The center of the horn is circular

Roughly Circular Inside —

The inside edge of the horn is roughly circular

Thanks Steve,

this is better, but still unacceptable, because the curve defining the spiral tube is not a circle, but a spiral.

robert_scott_jr_

I got curious about this and looked at the loft feature and played around with the Match Connections option. I discovered that the default connection (no vertexes selected) looked wonky. I modified sketches 2 and 3 to put vertexes in logical positions on the circles of the sketches. I used those vertexes in the Match Conditions option in the Circular Centerline Copy and the loft looks much better. Is this the result you are looking for?

https://cad.onshape.com/documents/425ed3d1a0dcf9147155b774/w/98c61cef74060eb0326cd299/e/df2341dce57792135bf518e4

-Scotty

steve_shubin

@petr_bláha69

Check my document above
There is now an inside spiral

steve_shubin

@petr_bláha69

I’ve added another part studio
This one follows a spiral that is at the center of the horn