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Designing a fitting PCB

gauthier_östervallgauthier_östervall Member Posts: 99 ✭✭
edited October 2021 in Using Onshape
I have this design:

This is the underside of a plate that will be receiving switches. I would like to produce a flex PCB, that would join the switches appropriately, as well as accommodate for a few extra components. What I'm interested in is to get the flattened shape of the flex PCB from Onshape.

How would you do this?

I'm considering this for each switch:
1. create a plan a small offset below the surface
2. create a sketch in this plan, projecting the pin holes with "Use", and a square as big as needed to contain the pin hole projections
3. join the sketches with tangential lofts
4. use the sheet metal tools to flatten the result

As I'm sure you'll notice, I'm in deep waters.

For 2., I'm not sure how to make a surface out of a sketch. I've tried "Fill", but it doesn't let me have the holes (bottom left in the picture above).
For 4., I'm not sure if having a surface is the right approach.
In all, I'm not sure if this approach is viable at all.

I've tried doing the Sheet Model from a part, it did not go well ("only planar, cylindrical or extruded faces can be converted to sheet metal"):

Any insight?


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    gauthier_östervallgauthier_östervall Member Posts: 99 ✭✭
    edited October 2021
    I think I got it. The problem was that the joint (red in my question's last picture) was a normal loft. Changing it to a straight loft (not normal) let the Sheet Metal Model work. The shape itself is in a right side tab, and can be exported to DWG, which KiCAD accepts as layout import.

    Excluding faces is going to be cumbersome when I do the whole part, I'd rather select the ones to include. But it'll work.

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    lanalana Onshape Employees Posts: 696
    In order to get good precision in your flat pattern you might have to experiment with prototypes and figure out the best bend radius and k-factor to use with your material.  
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    S1monS1mon Member Posts: 2,365 PRO
    If you make an intermediate surface offset (of 0) you can select the faces you want, and then convert that to sheetmetal.
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    tim_hess427tim_hess427 Member Posts: 648 ✭✭✭✭
    Do you intend to make one single PCB for all of the switches, or several strips that are all 1 switch wide, like your example?

    If you are going to do it all in one, you'll probably run into issues because it looks like your shape might not be "developable" (it can't be flattened without adding creases, cuts, or stretching it).

    An alternative approach you might try is to extrude a single surface with curvature in one direction only, the best fits your model. Then project the holes onto that before flattening. If your PCB is flexible as you mention, this shape will probably be a closer representation of the how flexible PCB will deform (rather than straight segments connected with bends). Also, it'll be much easer to flatten a surface with a single curvature compared to something with many many more bends and straight segments. 
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    gauthier_östervallgauthier_östervall Member Posts: 99 ✭✭
    @tim_hess427 My intent is a single flex PCB for the whole thing. This is what I have so far, three columns:

    For info, flex PCB is this.
    Note here that I'm happy connecting the columns only at one of the switches. That way, I expect it would be developable.

    I don't understand "extrude a single surface with curvature in one direction only"?
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    gauthier_östervallgauthier_östervall Member Posts: 99 ✭✭
    @S1mon This is brilliant, thank you so much!
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    tim_hess427tim_hess427 Member Posts: 648 ✭✭✭✭
    @gauthier_östervall - Your approach seems to have worked out better than I expected - awesome!  

    My "extrude a single surface" comment was trying to suggest just drawing a 2d sketch of a curve starting from a side view to create a close approximation of your part's curvature, then extruding that along with width of the part. That way, you'd ensure that your surface is developable. 
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    bryan_lagrangebryan_lagrange Member, User Group Leader Posts: 796 ✭✭✭✭✭

    Bryan Lagrange
    Twitter: @BryanLAGdesign

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