Parametric Bahtinov mask is not increasing or decreasing in size correctly

[PJBenn1]

Hello, I’m trying to design a parametric Bahtinov mask, which is a diffraction mask that is used in astrophotography to asst in getting proper star focus.  The width of the slits and their spacing depends on the telescope’s focal length and the number of slits is dependent on the telescope’s aperture. The Bahtinov mask is going to be part of a larger project that will involve multiple different telescopes (I currently don’t even know what all the scopes will be). If I must, I can remake the mask for each telescope.  However, I would like to update the focal length and aperture in the parameters and have everything auto update.  However, I have run into a problem.  This is the top half of the mask designed for 86mm (Which matches a telescope I have for I can test the mask). 

When I update the design to a larger aperture 96mm I end up with 4 diffraction grids that are not attached to the rest of the model and are not cut to shape. As seen in the image below.

If I make the aperture smaller, it looks correct, but it does give a body reference is lost using cached geometry error.  Is there any way I can fix this problem and make the design parametric?  I will point out I am mostly self-taught with fusion 360 and this is my first time trying to use the forums. I have included (I think) the Fusion 360 file with this post. Thanks for your time.

Thank You

PJ

[davebYYPCU · Accepted solution]

Small change to the order of operations, will get you going.

What's happening?  The Extrude operations after the pattern do not see the changed pattern bodies when the count changes. 

More bodies - were not there when the Extrude was created.

Create the outside Ring first, make the first upright Extrude as Join. 

Pattern changed to select Feature (2nd Extrude)

Smaller fix, put the upright on origin, and pattern symmetric.

More bodies (fixed -) When your uprights are increased in number, all will be joined. 

New Extrude outside shape to trim off excess.

File changes for greater count, let you sort out the centre line upright if reducing count.

Your parameters are working as expected.

Might help....

[TheCADWhisperer]

@PJBenn1 

I think this can be further simplified with Thin Feature Extrude and Extrude-Intersect.  

I am busy today - but check back for simplified solution.

[PJBenn1]

Thanks for the reply I will check it out.

[PJBenn1]

Thanks for the reply I don't think I have ever used Thin Feature Extrude and Extrude-Intersect.  Probably one of the draw backs to being self taught.  I look forward to seeing your solution when you get a chance.

[PJBenn1]

A change in the order of orations and using a central extrude as join with a symmetric liner pattern worked.  The only thing I had to remember was to extrude the upright central grid  slightly thinner then the ring.  If it was not thinner I couldn't select it as a feature for the liner pattern.

Thanks for the Help