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Unable to sweep object when attempting helical sweep for pipe thread


eKretz

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Hi all, new here, I am teaching myself to use ACAD 2013 and am working on a model for a former employer. (Long story, involving a bad back surgery and inability to work "for real" if you will). I have done quite a few searches relating to the problem and none really seem to answer what is wrong with mine.

 

I am attempting to model an internal 1/8"-27 NPT thread, both the through hole and the tapered part of the hole are modeled, but after I draw the helix and the polygon and orient the polygon to the helix correctly, (or even if I don't, I have tried it) it keeps saying unable to sweep object. I am using Sweep with Alignment with the No option. If I select the polygon first, then click sweep, it works, but rotates the polygon so that what I get ends up looking nothing like a thread profile.

 

I have tried reducing the polygon radius down to a ridiculously small value, thinking it might have been interference due to a possible trig miscalculation, but with no success, still have the same issue. FYI, I am using a .037" turn height for 27 TPI and a polygon radius of .0214", with a helix small end radius of .177" and large end radius of .189".

 

Thanks for any help...

Edited by eKretz
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I'm not sure what you mean? If you click the link you will get an instant download to your computer. I'm not sure how to attach a file here, do they give storage space?

 

Hmm, found that in the advanced reply, let's see if this works:

 

Drive Arm Model.dwg

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Welcome to CADTutor. :)

Try specifying the BASEPOINT on the polygon.

Is it a CLOSED polygon?

Seems counter intuitive, but try again using an OPEN polygon of the exact same shape.

Remember to specify the BASEPOINT.

You are aware that there are some internally threaded holes in your drawing already?

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I don't mean to be a smart-azz, but yes, I am aware that there are other threaded holes in the model. I'm not sure exactly how that is a relevant statement? I put them there. I didn't receive this model partially finished, I started it from scratch. I attempted to model the pipe thread using the same exact procedure as I used with the other holes other than using a tapered helix instead of a straight one at the pitch diameter. It won't work for the pipe thread for some reason I have yet to determine.

 

The polygon is closed; to make an open polygon do I just draw my own using the line command? Or not close the triangle? Hmm. I'm not familiar with basepoint yet, I will look into it.

 

Edit: If you are referring to setting the center of the polygon on the center of the endpoint of the helix, yes, I am already doing that. Also, if by an open polygon you are referring to a triangle formed with three separate lines instead of the polygon button in the ribbon, yes, I have also just tried that and it still will not sweep.

Edited by eKretz
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OK, update: I looked back through the command line history and I apparently missed an error message due to having too small of a command window. I am getting an error message that says unable to compute top curve. Any ideas why?

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I would suggest that you display a minimum of 3 lines at your commandline, so that you have 2 lines of history.

I was trying to model some rather peculiarly shaped suspension bridge pylons over the last couple of days,

and had a strange thing happen where my perfectly drawn closed polygon sections were not being accepted by the LOFT command as cross sections.

It took me a long time to figure out that by tracing over them with a new polyline, and leaving them complete, but not CLOSED,

I found that I was able to LOFT them through all 8 cross sections to the top of the pylons without any problem,

yielding a pretty cool 3D Solid, hollow all the way up with 2 foot thick walls.

I thought that might prove relevant in your case too.

Is there a reason that you chose to stop the thread before cutting through the face of the model?

 

You could also try creating the thread externally, then placing it through the model and subtracting it.

That is how I usually do internal threads, by using a positive to complete the negative.

 

Not 3 separate lines, but one continuous POLYLINE.

Don't use the CLOSE commandline option for the final leg of the triangle, just snap to the endpoint of the first side.

It may not help, but the 3 separate lines definitely won't sweep,, no surprise there.

 

Is your top curve too tight for what you are sweeping?

Does it become self intersecting?

You don't actually need to connect your triangle to the end of the helix, the software will do that for you, as long as you define all

of the parameters, like the base point of the item you wish to sweep.

Even if they are far apart, although I confess that I also usually align it myself.

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Hi all, new here, I am teaching myself to use ACAD 2013 ....

 

While it is interesting and good modeling experience and looks good -

usually threads are not modeled unless the part will be Rapid Prototyped.

I don't think you will be able to control the twist in AutoCAD.

 

Is there a reason you are not investing your time in leaning a modern CAD program like Autodesk Inventor?

You would have more control and more options .....and easier to boot.

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Actually, after reading another post I saw of yours regarding that exact subject I have switched. I was unaware that ACAD wasn't considered state-of-the-art anymore. It has been a while since I've worked with any CAD programs, so I wasn't familiar with the limitations of ACAD. I have started a new model in Inventor and it is much better, and definitely faster. A bit more involved as far as learning the different ways to do things, but once I figured them out, it's actually a bit more intuitive. After a little experience, I think you are right, it will be a lot faster.

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