SWEEPING A REAL THREAD ONTO A SHAPE

Proposals and Suggestions for new features in TopSolid.

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Top'Noob
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SWEEPING A REAL THREAD ONTO A SHAPE

Unread post by Top'Noob » Tue Sep 02, 2008 4:07 pm

Hello,

I find that the function SHAPE, MECHANICAL, THREAD is not adequate for my needs. I sometimes need to model actual threads for various reasons.

I have tried creating the thread profile and sweeping it along a helix but it fails to give me sufficient results. For example, sweep a 60° v-thread with sharp root & crest onto a cylinder. It can be done but you'll have to fight for it and the result does not "project" correctly in a draft document.

I would like an enhancement that allows the creation of truly accurate solid threads. I would especially appreciate if it was implemented in such a way that I wouldn't need to sweep the geometry... The best way would be to include this new feature under the existing SHAPE, MECHANICAL, THREAD function but with a new section for accurate threads and appropriate dialog fields which would allow us to specify all features of any thread... For example, Major Dia, pitch, flank angle, crest radius or crest flat, root radius or root flat, etc... It would also be very nice to use alternate thread forms such as ACME, Square, Buttress, Whitworth, Taper Pipe thread, etc...

All of these features would be nice but just to clarify the most important thing would be to improve the sweeping function to allow me to sweep thread type geometry along a helix without errors. It seems that currently there are parasolid errors where the swept geometry overlaps itself...

Looking at the first picture you'd think everything was perfect but the (zoomed-in) second picture shows that the geometry is a mess at the crest of the thread.

Image

Image

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jehronimo
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Unread post by jehronimo » Tue Sep 02, 2008 4:58 pm

Hi,

I think your section curve is not good and contains a "wrong intermediate" point in its path...Am I wrong?

Jehronimo

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Unread post by Top'Noob » Tue Sep 02, 2008 5:48 pm

Hello Jehronimo,

Thanks for looking at this problem.

Here is a file I made to assist this discussion (attached).

Note that my section curve for the thread form is .125 wide but if I try to change the pitch of my helical guide curve to .125 TS cannot sweep the geometry. As a result the threaded area of the shaft has a "rim" around it that is undesireable...

Maybe you can suggest how to do this correctly ?
Attachments
THREAD EXAMPLE2.zip
(257.77 KiB) Downloaded 592 times

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jehronimo
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Unread post by jehronimo » Wed Sep 03, 2008 10:12 am

Hi,

I think that what you are trying to design it is impossible, and you will always get a "small" edges or faces problems at the end of your fillet. Because you can not design the swept curve with the upper section that is tangent to the lower one (once you have make a first 360° turn). You will always get a Parasolid error.

The best solution, I guess, is to design the positive shape, then try to unite it to a main cylinder body.

Another tip : when your are trying to design a such swept shape, never use the ABS CSYS as the reference of your section curve. you must create a new CSYS on curve and point, select the curve, then its end point. Like this, your section will be always well oriented (the helix curev never finishes normal to the ABS CSYS....)

Let us know your feeling about this...

Jehronimo

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Unread post by Top'Noob » Wed Sep 03, 2008 1:32 pm

jehronimo wrote:Hi,

I think that what you are trying to design it is impossible, and you will always get a "small" edges or faces problems at the end of your fillet. Because you can not design the swept curve with the upper section that is tangent to the lower one (once you have make a first 360° turn). You will always get a Parasolid error.

The best solution, I guess, is to design the positive shape, then try to unite it to a main cylinder body.

Another tip : when your are trying to design a such swept shape, never use the ABS CSYS as the reference of your section curve. you must create a new CSYS on curve and point, select the curve, then its end point. Like this, your section will be always well oriented (the helix curev never finishes normal to the ABS CSYS....)

Let us know your feeling about this...

Jehronimo
Hi Jehronimo,

Thanks for the input. I understand that the parasolid system has it's limitations but I would very much like to see Missler find a way to model this feature easily. It is far too difficult now.

Come on, they don't want to be Bottom Solid or Middle Solid, right ? Lets make it work like Top Solid should ! :shock:

Anyway, I think I will try to model it differently next time as you suggested but I honestly expect the same parasolid error if I try to create the positive shape unless I compromise the geometry to leave a tiny flat. I wanted to create a thread with a perfectly sharp crest and root in this case and I don't like to have to 'cheat' to achieve something that is 'close-enough'... It is always much better to be able to design exactly what is intended.

I don't really understand the issue with the CSYS but I will follow your advice. 8)

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RICHARD LALONDE
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Unread post by RICHARD LALONDE » Wed Sep 03, 2008 2:38 pm

Instead to remove material have you think to add some. I mean instead to think as a machinist and substract a swept feature with some problem. I work on your file and I ADD some material to the minor diameter to obtain the result on the other end without problem
Image

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Unread post by Top'Noob » Wed Sep 03, 2008 4:09 pm

Thanks for the help Richard.

I maintain my opinion that it should be improved but it seems like you and Jehronimo have proposed the best solution currently available...

I have not had a chance to test this method yet but when I do I hope to see perfectly sharp root and crest...

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