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How to fillet this base so it is still planar?

Question asked by Josh Reed on Nov 7, 2017
Latest reply on Nov 8, 2017 by Josh Reed

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I have a part with base that is a planar edge, shown below in blue, parallel to the top plane. I'm trying to figure out how to fillet that edge so that the base is still flat (i.e., the bottom of the fillet is planar parallel to the top plane). A constant radius fillet results in an uneven base that is not flat. I also tried a full-round fillet as suggested in Possible to fillet this flat edge and keep it flat? , but the operation fails. It fails even when I tried segmenting the edge and adjacent faces. The edge forming the flat base that I'd like to fillet is in blue here:

Ideally, I'd like the fillet to continue all the way around to include the edges that aren't on the flat bottom as in:

I attached the SolidWorks 2015 part file.

Thanks for any suggestions!

Roland Schwarz Nov 7, 2017 7:13 PM

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The orange face is what you get when you cut just 0.1mm from the bottom. No way is that going to go with a full round.

My recommendation: restructure Loft5 so that you have a narrow planar face defining the bottom edge. Then use that as the middle face of the full round.

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simplified-base2.SLDPRT.zip759.6 KB

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Roland Schwarz Nov 7, 2017 7:13 PM
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The orange face is what you get when you cut just 0.1mm from the bottom. No way is that going to go with a full round.
My recommendation: restructure Loft5 so that you have a narrow planar face defining the bottom edge. Then use that as the middle face of the full round.
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- Josh Reed @ Roland Schwarz on Nov 8, 2017 12:26 PM
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  Hi Roland, Thanks for the suggestion. Adding the narrow flat surface on bottom worked great to achieve a flat fillet on the bottom. However, with that narrow surface, it creates a tricky transition point and now I'm unsure how to fillet that back corner and the edge continuing the rest of the way around the part - shown as the blue face here and the hard-to-see blue extending left from that blue face. Ideally I want to fillet the back corner like 2 or 3mm.
  Any suggestions? I attached the updated file.
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  - simplified-base3.SLDPRT.zip666.2 KB
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- Josh Reed @ Roland Schwarz on Nov 8, 2017 6:03 PM
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  Hi Roland, I ended up doing what you suggested and to round the back corner, I cut off the end and used a loft / boundary surface to fill it in:
  I attached the updated model file. There's a bunch more tedious steps but that's the idea that seems to work. I think.
  Btw, If, when you reply to a comment you click 'use advanced editor', you have the option to attach a file to a reply.
  Cheers.
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  - simplified-base3.SLDPRT.zip784.8 KB
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Kevin Chandler Nov 8, 2017 1:20 PM
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Hello,

I was able to fulfill your OP using Cut with Surface:
Create a line-point (or 3-point) plane to sketch on:

Create a tangent-tangent arc (sized accordingly) and add some stuff to create an exterior closed profile

Create a 3D sketch and convert entities on these (only one half at a time, you'll have to repeat all for the other half)

Create a Swept Surface with this path and profile
Then use Extend Surface and select the faces to extend all of both ends outboard of your part.
Select Cut With Surface (you need to toggle the direction if your part disappears to alter the resultant cut).
Nothing will look different because the cutting surface is still shown and the cut is blocked by this, so in the tree, go to Surface Bodies and hide the extended surface:

As I stated above, repeat for the other side.

Cheers,

Kevin C.
EDIT: I attached the part for others since it's a 2017 vintage.
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- simplified-base2.SLDPRT.zip861.0 KB
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- Josh Reed @ Kevin Chandler on Nov 8, 2017 2:09 PM
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  Hi Kevin, Thanks for the suggestion. My SW2015 can't open the file you attached so I can't check, but would cutting with a swept surface create a fillet that is tangent to the adjacent faces? In the pics, the profile to be swept specifies a tangency constraint, so the cut fillet will be tangent at the start of the sweep, but along the path of the sweep the angle of the faces changes so I imagine the cut fillet will only be tangent at the start?
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  - Kevin Chandler @ Josh Reed on Nov 8, 2017 3:07 PM
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    Hello,
    
    I did my reply with test/images for you because I'm on 2017.
    I only attached the part as an afterthought for others, if needed or curious.
    
    Yes, the arc of the cut is tangent to the side and to the bottom face, which are relations defined in the sketch.
    I looked at my image and I don't see the lower tangent, but regardless, it should be since that's a conditional requirement.
    
    One caveat I just thought of though, is that the tangent to the bottom face may not be valid when you transition to the other bottom face near the pointed end.
    If not, you will have to do this process four times, once for each bottom edge.
    Unfortunately, you'll have to create a new sketch plane for the second edge, but you may be able to reuse the first sketch as a derived sketch.
    
    Another thing to try for the far side is to mirror the surface used for the first cut so you won't have to recreate essentially the same surface for the far side cuts.
    
    Cheers,
    
    Kevin C.
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    - Josh Reed @ Kevin Chandler on Nov 8, 2017 6:05 PM
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      Hi Kevin, Thanks for digging into this. I think Roland's answer worked, once I snipped off the back corner and rounded it manually. I say "I think" because the round fillet looks kinda like it produced a non-smooth surface, but I'm hoping that's just a SW quirk.
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  - Kevin Chandler @ Josh Reed on Nov 8, 2017 3:15 PM
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    Hello again,
    
    I tried the mirroring of the first surface and was successful in cutting the far side, so that idea works.
    
    While there, I zoomed toward the front and there's a hard edge which indicates an incorrect cut somehow:
    I don't know if altering the swept cut parameters will correct this or if the whole concept is invalid.
    
    I'll have to dig in later when I have more time.
    
    Kevin C.
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    - Josh Reed @ Kevin Chandler on Nov 8, 2017 8:07 PM
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      The full round is producing some really bumping looking surfaces on screen, but the 'face curves' command seems to generate smoother ones. Do you know if this is to be expected?
      EDIT: I think this is a display issue - zebra stripes look good and export/import looks good as well.
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