Making a grommet to fit a curved surface

dave_woodward078

I'm trying to make a grommet to fit the attached setup. This represents a roll-bar passing through a car body panel (will actually extend beyond the surface it cuts through) which is just off perpendicular.

I want to create a grommet from the body panel which will accommodate the angular offset. Is there a way that I can use the cut face of the panel to create a new part?

Thanks

glen_dewsbury

Sketch your profile somewhere along the edge of the panel and sweep it.

https://cad.onshape.com/documents/ac0ecfe4f301c56899904542/w/f485e7914d309ca0473669c7/e/93fd0964fb082d8fbe4d3baa

dave_woodward078

Thanks for the quick response. I tried this but the challenge is that the inner face of the grommet follows the angle of curved surface rather then remaining true to the central column. The complexity is that the inner face of the grommet needs to marry with the face of the column whilst the outer face of the grommet needs to follow the contour of the panel (essentially some parts of the grommet cross section would have to resemble a parallelogram in shape depending on where you are in the sweep - inner face always remains vertical whilst outer face follows profile)

jelte_steur814

simplest is to add a replace face on the face that should stay true to the central column. (in this case with an offset):

dave_woodward078

I've managed to achieve the result I'm looking for but am sure there are better ways of doing this.

I duplicated the layer into three slices each with a depth equivalent to a vertical dimension in the grommet. I then used an extrude to cut the central hole vertically through all layers and then two wider intersects to slice each layer to its required diameter. Finally a fillet to create the rounded top surface. Very happy with the result.

dave_woodward078

Sorry Jelte, i didn't see your response. Will try that also. Looks a bit more straightforward ;)

MDesign

I took a stab at it with a series of move faces after splitting off the inner ring from the curved surface as a separate part. This resulted in inconsistent thicknesses of the grommet flange at the high side vs low side.

MDesign

Tried another method (made the grommet as a tube with replace face offset for top/bottom with the same result. It's less of an issue when the top and bottom land more on the horizontal'ish part of the surfaces.

dave_woodward078

https://forum.onshape.com/discussion/comment/111115#Comment_111115

I did find some very undesirable outcomes for the profile as it revolves, the issue being that its essentially rotating on a diagonal plane causing it to 'flare' as it rotates.

MichaelPascoe

@dave_woodward078 When sweeping, try selecting the Lock profile faces option. This will keep the sweep aligned with your reference face.

https://cad.onshape.com/documents/9a9947ce707903cce44c7daf/w/8ec2d7c71c784d4a406b42a9/e…

glen_dewsbury

I changed the sweep profile to look nicer. Then checked of 'lock profiles to faces' for the sweep with a much better result without all the layering.

Best select a fairly soft material that will compress around the stack if you're looking for a seal. If for abrasion resistance add some gap between stack and grommet from a harder material. Not so hard to stop it twisting the body. If there's a lot of these to make I'd think about a molded to shape of body and stack. Could also be done with just outside flange with nubs to snap into body and glued.

https://cad.onshape.com/documents/ac0ecfe4f301c56899904542/w/f485e7914d309ca0473669c7/e/93fd0964fb082d8fbe4d3baa

MDesign

https://forum.onshape.com/discussion/comment/111127#Comment_111127

I had to use Lock Profile direction vs faces. to get the desired result. Completely forgot about those options but a much quicker way to get the end result with those modifiers.

MichaelPascoe

@MDesign Heads up, if you lock the Profile Direction instead of to the face along the path, the cross section of the grommet will change depending on the direction of the path.