Author Topic: Drawing a screw (a lead screw to be specific)  (Read 1583 times)

roger_c130

  • Full Member
  • ***
  • Posts: 127
Drawing a screw (a lead screw to be specific)
« on: April 29, 2012, 09:25:47 AM »
I've used Sweep on a number of forms but I can't even get close to creating something that looks like a screw.  Any tutorials available?

herbertjackson

  • Full Member
  • ***
  • Posts: 198
Re: Drawing a screw (a lead screw to be specific)
« Reply #1 on: April 29, 2012, 06:55:31 PM »
which your E-mail I will send you a copy of a chapter from a book.  I will have to send you 8 zip files. they are to large to post here so I will send you 8 e_mails

I hope this helps you out. I got this from an old course I was took about 50 years ago.
Although all the drawings shown used a drawing board back then, they can easily be converted to cad.
The drawing shown are for machine screws, if you are drawing wood screws you can use the same idea’s as shown in this book, just add a point to the end of the shaft.

Dr PR

  • Hero Member
  • *****
  • Posts: 4479
Re: Drawing a screw (a lead screw to be specific)
« Reply #2 on: April 29, 2012, 08:49:50 PM »
roger,

The sweep command is tricky, but once you understand it you can make lead screws easily.

How the sweep command works:

http://forum.designcadcommunity.com/index.php?topic=3807.0

How to make a complex screw:

http://forum.designcadcommunity.com/index.php?topic=4260.0

If this doesn't answer your questions come back and tell us what it is that isn't working for you.

Phil
DesignCAD user since 1987

roger_c130

  • Full Member
  • ***
  • Posts: 127
Re: Drawing a screw (a lead screw to be specific)
« Reply #3 on: April 30, 2012, 09:07:05 AM »
Took a while but finally got it Phil.  Thanks.  The Number of Copies is still a mystery but if it isn't set to some acceptable number I could get any kind of spiral or a packed drawing without any spiral.  I ended up drawing a 4" screw but set the Number of Copies to 1000 before it worked for me.  That's OK though.  I can proceed with the rest ground shafting at each end.  Thanks again.

Rob S

  • Hero Member
  • *****
  • Posts: 3683
    • Construction Estimating Program for General Contractors
Re: Drawing a screw (a lead screw to be specific)
« Reply #4 on: April 30, 2012, 09:29:10 AM »
Hmm, do you really need that many?

Just curious what file size would result from a sweep like that, and how your rendering time would be?

I hope you don 't need to use very many of these screws in your finished product!!!
User since Pro-design

roger_c130

  • Full Member
  • ***
  • Posts: 127
Re: Drawing a screw (a lead screw to be specific)
« Reply #5 on: April 30, 2012, 12:30:37 PM »
Hi Rob.  I got tired of trying to really understand what Number of Copies was all about.  My original attempt at learning the sweep was for a 1" lead screw.  It took me awhile but I finally succeeding using 360 as number of copies.  Then I enlarged to a 2" screw and it also worked OK.  When I enlarged to the 4" and left the copy nr. at 360 weird stuff happened.  Because I didn't understand what the parameter did, and still don't, I got frustrated and entered the max nr.  The fact that it worked was OK to me.  Removing hidden lines and shading is almost as fast as a eye blink.  The only problem seems to be a few jagged outside edges that show up when shaded.  That's OK when viewed in other than a real close-up.  I'm going to try to put something together and send it to show what I experienced.  Thanks to all - again.

roger_c130

  • Full Member
  • ***
  • Posts: 127
Re: Drawing a screw (a lead screw to be specific)
« Reply #6 on: April 30, 2012, 12:50:53 PM »
To Phil and Rob.  I'm attaching a drawing containing two screws.  One of left with copies = 360 and one of right at 1000.  Diagram in middle is the set-up.

Rob S

  • Hero Member
  • *****
  • Posts: 3683
    • Construction Estimating Program for General Contractors
Re: Drawing a screw (a lead screw to be specific)
« Reply #7 on: April 30, 2012, 01:16:48 PM »
I see, you made a long piece!

On mine, it displays sectional on the left, and round on the right, so for it to render round with that many turns you do need that many!
User since Pro-design

roger_c130

  • Full Member
  • ***
  • Posts: 127
Re: Drawing a screw (a lead screw to be specific)
« Reply #8 on: April 30, 2012, 01:43:14 PM »
One of left and one of right.  You'd think by now I would know the difference between of and on.

Dr PR

  • Hero Member
  • *****
  • Posts: 4479
Re: Drawing a screw (a lead screw to be specific)
« Reply #9 on: April 30, 2012, 02:58:42 PM »
Roger,

The "Number of Copies" is the number of cross-sections of the original object that will be created through the entire length of the sweep.

For example, if you set the "Number of Copies" to 36 and sweep once around the axis (360 degrees) you will ge a cross section at every 360/36 = 10 degrees. In my experience this is just about the minimum angle between sections that will render smoothly at all zoom levels.

If you aren't going to zoom in too closely you can get by with 16 or 18 copies per sweep around the axis. At high zoom levels and some angles the surface will be rendered smoothly but the edges will be jagged.

This also applies to cylinders and other solid objects. I often use 12 sections for small details that will never be viewed closely, like small bolts. I use 8 sections for cables that won't be viewed closely. These always render as octagonal, and from a distance they look like multi-strand cables.

If you do three complete turns about the sweep axis the angle between sections will be 3x360/N where N =  the "Number of Copies." If N = 10 and you have three sweeps (1080 degrees) the angle between sections will be 108 degrees. This is so great that the shading algorithm treats the surfaces between sections as flat with sharp edges and the surface does not render smoothly. For three turns you need at least 3x36 = 108 sections to get a smoothly rendered surface.

The algorithm tries to figure out what it is you have created, and what it should look like. There is a maximum angle between sections for smooth surfaces. Beyond that the program decides that you have created something with flat surfaces and doesn't try to create smooth shadings. For example, it always renders surfaces at 90 degree angles to each other as flat surfaces that come together at a sharp edge.

The more copies you use the larger the file size, and the longer it takes to render. I once created a simple tubular hand railing up inclined steps using the default settings and it came out to be 13 Mbytes! I then redid it with 36 facet cylinders and 18 sections per 90 degree sweep and it was about 10 Kbytes. Both rendered to look exactly alike.

Phil
DesignCAD user since 1987

cavelamb

  • Full Member
  • ***
  • Posts: 185
    • The Cave Page
Re: Drawing a screw (a lead screw to be specific)
« Reply #10 on: April 30, 2012, 06:03:08 PM »
That was fun!
Ok, I didn't do it the way you guys do. (What's new there?)
And there were some small gotchas to watch out for.

But it sure makes a smaller drawing!  200k verses 800k?


Dr PR

  • Hero Member
  • *****
  • Posts: 4479
Re: Drawing a screw (a lead screw to be specific)
« Reply #11 on: April 30, 2012, 07:21:09 PM »
cavelamb,

I don't know what you used for the sweep object, but the resulting "thread" has far too many facets. In addition, it is a hollow grid and not a solid.

When creating solids, ALWAYS use planes, not lines. It will produce a true solid.

I redid your screw, sweeping a simple plane (blue), and file size is 80 Kbytes.

Phil
« Last Edit: April 30, 2012, 07:22:53 PM by Dr PR »
DesignCAD user since 1987

wisoak

  • Newbie
  • *
  • Posts: 32
Re: Drawing a screw (a lead screw to be specific)
« Reply #12 on: April 30, 2012, 07:56:17 PM »
Thats what I like about this forum. There's always a challenge to improve oneself lying within the next inquiry. Here's a bolt that took me about 6 minutes to draw using the sweep command. My first attempt gave me a left-hand thread, so all I had to do was mirror it for a RH bolt.
V21.1

Dr PR

  • Hero Member
  • *****
  • Posts: 4479
Re: Drawing a screw (a lead screw to be specific)
« Reply #13 on: April 30, 2012, 08:13:37 PM »
Nice work.

You can download DWGs of a lot of fasteners like this from sources on the Internet. I think McMaster-Carr has a library of fasteners.

Phil
DesignCAD user since 1987

Rob S

  • Hero Member
  • *****
  • Posts: 3683
    • Construction Estimating Program for General Contractors
Re: Drawing a screw (a lead screw to be specific)
« Reply #14 on: April 30, 2012, 08:56:15 PM »
Nice, indeed.

Anyone wondering if Designcad is a good choice, just check out these above here works of art & science!!!
User since Pro-design