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Turbo Talk => Problems => Topic started by: Yuansheng on January 24, 2017, 03:56:35 AM

Title: "rail sweep" a circle alone with helix
Post by: Yuansheng on January 24, 2017, 03:56:35 AM
Dear All,
Please help to see if following can be done.
I want to create a "rail sweep" a circle alone with helix.
However, I need to make the "turn heigh" of the helix less than the diameter of the circle, and one turn required only. The result is similar to Torus, but in helix shape.
When try this, I get error of "The resultant object of ACIS Solid type is selfintersecting or invalid", and the object can't be created.
How can I create such subject?
Thanks in advance.

Best Regards
Simon
Title: Re: "rail sweep" a circle alone with helix
Post by: Andy H on January 24, 2017, 04:52:55 AM
Are you allowed to 'cheat' a bit.

When rail sweeping along helix (or anything like that) the ends are not horizontal/vertical, meaning the end of the rail sweep will bash into the start of it, causing self intersection.

A couple of ways (there will be more ways), click the helix with the edit tool, in the inspection bar change the turns to 0.999 (or 0.99), or use select tool and alter the turns in selection properties palette or properties dialog.

Rail sweep with 'rigid' not checked, this will leave a small get between start and finish, use the quick pull tool, or facet edit tool to move the end of the sweep filling in the gap.

Alternatively use the revolve tool with number of coils set to 0.9999, and which ever spiral pitch is required, obviously setting clockwise or anticlockwise as required 
Title: Re: "rail sweep" a circle alone with helix
Post by: Henry Hubich on January 24, 2017, 08:30:20 AM
In the Properties page for Rail Sweep, you can elect to create the object as a TC Surface before actually performing the operation. Selfintersection is allowed for a TC Surface.

Henry H
Title: Re: "rail sweep" a circle alone with helix
Post by: Yuansheng on January 25, 2017, 03:19:03 AM
Thank you, Andy and Henry.
Both works! and yes, I am allowed to cheat a little bit! :)

With Henry's solution, as I need to do the subtraction for these 3D objects, can I convert this TC Surface to Solid?
Thanks!

Best Regards
Simon
Title: Re: "rail sweep" a circle alone with helix
Post by: Andy H on January 25, 2017, 06:56:54 AM
With Henry's solution, as I need to do the subtraction for these 3D objects, can I convert this TC Surface to Solid?
Thanks!

Yes - But,  Trial and error,  I just gave it a go and changing back from sweep(TCsurface) to Solid and it gave self intersecting when trying to convert back (instead of converting it may have tried to re-sweep it),  a way round this is to explode from a sweep twice to get it to a say TC surface in the selection palette, it will then convert to solid (simply select the solid radio button in properties),  however there are drawbacks with converting TCSurfaces to solid, whilst still a sweep or extrude one can change the 'number of approximation lines' in the properties dialog which affects how smooth the surface will look,  you will probably want to crank it up a bit to make it smoother, there is a tick box for smooth which works well with Surfaces, but this is ignored when converted from TCsurface to ACIS so I wouldn't bother with it, the max lines is 90 but this will be slower to convert to solid.

Once selection palette says TCSurface, you cannot alter the number of lines so your stuck with a non-smooth finish unless you use undo,  either way,  in general, converting a curved TCSurface to ACIS may not be as smooth as leaving in its original form.
Title: Re: "rail sweep" a circle alone with helix
Post by: Henry Hubich on January 25, 2017, 07:50:49 AM
Perhaps a better approach is to use the "Revolve" tool, rather than sweeping along a helix. For some reason -- a programming oversight, perhaps? -- this tool does allow one to create a selfintersecting solid, by setting "Spiral Pitch" to a value smaller than the diameter of the circle.

Henry H
Title: Re: "rail sweep" a circle alone with helix
Post by: Yuansheng on January 26, 2017, 06:26:41 AM
Thanks, Andy and Henry.

Tried with Henry's approach. Works great!

:)

Thanks again.
Best Regards
Simon
Title: Re: "rail sweep" a circle alone with helix
Post by: Jeffin90620 on January 30, 2017, 01:57:32 AM
One other method is to re-position the Reference Point to the point on the circle that will be closest to the center of the Rail Sweep's path.  I'd use a Quadrant Snap to fix the position.


Jeff
Title: Re: "rail sweep" a circle alone with helix
Post by: Dean on January 30, 2017, 12:59:59 PM
Dear All,
Please help to see if following can be done.
I want to create a "rail sweep" a circle alone with helix.
However, I need to make the "turn heigh" of the helix less than the diameter of the circle, and one turn required only. The result is similar to Torus, but in helix shape.
When try this, I get error of "The resultant object of ACIS Solid type is selfintersecting or invalid", and the object can't be created.
How can I create such subject?
Thanks in advance.

Best Regards
Simon

Though you didn't post any numbers. ;D
I would explode the helix to a spline
Use the "Split"tool on the spline
Rail sweep as "Solid" the circle on both splines >compound profile on