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Helix & Subtracting solids - Need some help....


DaveS777

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Hi, still very new. Have a 1 turn spiral helix which I've arrayed 180 items onto the top surface of... .125" depth into the solid.

 

I can't seem to figure out how to subtract the 180 items; so that I'm left with the space or hole where they are... AutoCad keeps failing to perform the operation. Tried it various ways; as a surface, etc. but I can't figure out what I've done wrong.

 

In my limited experience with AutoCad; it seems it does not like Helixes. For example, if you wish to create a surface out of a 1 turn helix with a height of 4; you get some 'bs' error; about intersecting lines; and it won't do it... Have to make the surface have a height of 3.99 and then it will work... And then we can add thickness and get a solid, etc. Maybe totally the wrong way to do this...

 

But right now, I can't get it to subtract the solid array from the rest of the solid Helix. Looking forward to your thoughts and efforts...:)

 

Helix dwg 3.dwg

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One of the problems is that the 180 objects are currently not 180 individual solids, they're grouped together as single associative array, and you can't perform Solidedit commands on an array. XPLODE the array and you can likely perform the SUBTRACT. However, my experience is that AutoCAD helix's do not follow a true path about the axis... rather they "wobble" quite a bit. Also, I believe you'll have to make your takeout object a little larger because the way it's following the path, it wont remove enough material at the edges, (you'll see what I mean if you XPLODE the array and perform the SUBTRACT)

Edited by nestly
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Nestly, thanks for the info... Yes, EXPLODE does enable the process. Now, do I have to click on these individually, or is there a method to remove them all at once? And I do see what you mean about the material at the edges. Sometimes gone, sometimes not. Do you have a better way to make the helix? That would probably be hard for you to explain if you do; because of my 'immense' skill level at this program... Thanks much for your help.

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Nestly - (or anyone else) do you know if one could create two spiral helixes within AutoCad; and have both of the helixes be part of the same Array - to possibly significantly remove the 'wobble'?

 

I'll try it to see if possible; but I got a couple of heavy days of work; and won't be able to try it out for a bit... Just thought you might already know. Just wondering if in this case (for instance); and inner and an outer helix might be able to eliminate the wobble if both could be used to define an Inner an Outer edge single Array path...

 

PLUS, does anyone know how to tell AutoCad where to START the Helix?? I don't know how; I give it a cordinate location (for example rotate around 20,20,0); and it always seems to start the position of the Helix 'randomly'. I then get to magnify way up; and painstakingly 'rotate' the Helix to the correct starting point required to bring everything in sync with the rest of the drawing...

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Here's my technique for making helical objects that don't "wobble" around the axis. The procedure involves trimming/slicing a cylindrical object with a helical surface which extends beyond the base object.

 

In your case, the cylindrical object has an inner radius of 10 and an outer radius of 20, so I used two helix's (one with a radius of 9 and the other 21) to LOFT a surface to slice the solid cylinder/donut. There are still some variations along the perimeter in the Z-axis, but at least the radius/diameter are correct.

 

Demo -->

(increase the player size to at least 1024x768 for best visual effect)
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As for the 180 objects, I typically start with one object and copy/rotate it then elevate on of them by the proper increment... then copy/rotate those two objects and elevate them to by the correct increment... then copy/rotate those 4 objects and elevate... etc etc. Time consuming and tedious to be sure, but it's accurate, unlike using a helix as a path. Another tip is to make sure the subtracted object extends beyond the surface it needs to cut, ie make it 12 units long and .5 units high and then position it so it only cuts .25 deep into you solid before subtracting.

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Nestly - Fantastic. I haven't had the chance to actually try it and do the work; but I did watch the instructional video which you created. Is there a way for me to download that; and save it to my drive...? Thanks muchly for doing that btw.

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It should be downloadable now, but you might want to get it fast because someone has been eating up my bandwidth so my account has been hitting the monthly data transfer limit recently.

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Nestly - thanks again. Have it downloaded.

 

Seant - An extremely long thread, with not a lot of time early morning. General concept is impossible.

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. . . . General concept is impossible.

 

If you ever do find the time to read the thread you would see that we share that sentiment.

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