Tapered screw

[peter737]

Hello everyone,

I need to design a screw(see attached diagram) where, from the left, one-third of the helix is of constant depth, the middle third is tapered, and the end is of constant depth. I drew a constant helix at the upper and lower ends first. And then a tapered helix at the middle. I have almost completed the solidworks model but the error is that i am unable to exactly join/merge the tapered part with the upper and bottom helix.

Any idea as to how to go about it?

Best Regards,
Peter

[Mike 1948]

Try making a composite curve out of the three different helixes to drive your sketch. If you already tried it then ????

Mike

[JerryFlyGuy]

If I was faced w/ the project, I'd do the helix part of the job first [just get the screw variations [I'm not sure if it was simply 'depth' from CL of the shaft or 'depth' as in pitch of the screw, either way]].

Following getting a helix sketch that shows the constant diameter helix I'd use it to create your helical geometry [solid or surface model] then I'd use a revolved sketch to trim the helix to the needed diameters at various stages along the length of the shaft.

Doing this, it would be possible to have a varieing pitch helix which has varieing diameters along it's length. CRAZY....

Fwiw

[JerryFlyGuy]

Aww.. what the heck.. here's a sample model of what I was trying to explain.. it's easier if you just have a look at this ... rather than trying to decipher my crazy writing..

[kriptonboy]

just draw 3 helixes on top of each other and aligned of course then convert the three to just one spline (3d sketch-> spline tools ->fit spline ) and use as path of a sweep feature...

hope that helps

[JerryFlyGuy]

Kripton, do you have something to illustrate? I'm not sure I can see it working? but then maybe I'm missing something??

[kriptonboy]

Hi Jerry, here is an example (sw2011), not sure if this is what you want, hope it helps

[JerryFlyGuy]

Ahh... stack the helix's makes sense, certainly a solution. I didn't mess w/ it too much but is it easy to change any dim and have it rebuild seamlessly? This is another option to get varying helix pitch as well.. pretty nice

[giz]

Assuming you are using SW2006 or later, just use the variable pitch helix feature...

[Raybies1]

Are you just trying to make a model of this screw or are you going to be machining it?

If it is machining as well as the model

Assuming that the root diameter of the screw is constant and that only the major diameters are changing it is an easy 2 step machining operation using a lathe and a cnc mill with a 4th axis.

I spent years making timing screws for the packaging industry.
I also have a nice little dos program to generate the code for screws using
4th axis milling which i would be happy to share with you.