Making thread over a cylindrical surface

I am trying from last few weeks
but i am unable to do threading over a cylindrical surface.
help me sorting out how to do this?
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The easiest way would be to buy a die and handle- put the cylinder into a vice and spin the die onto the end. The trick is to put a mild pressure on the die holding it tight to the end of the cylinder while the thread starts cutting. Voila- Done- !
Now there *ARE* other options for threading, like using a lathe, cnc milling, etc.. What exactly are you looking for?
Hey Dave, this sort of reply is kinda fun :)
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Do you mean you want your start surface to be a cylinder?
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John Wade
Nothing beats the thread mill! (In that spirit of fun)
Okay, okay, the guy's taken enough ribbing: So, sujit ojha, you wish to make a screw thread, correct? In Pro/e, do 'Insert>Helical Sweep'. If you've tried this, what is your problem? You first sketch the length of the cut by drawing a line as long as the cut (along the edge of the cylinder). Then, you sketch the profile of the cutting "tool", the tip of the single point lathe threading tool that Stu and John referred to (hint: it's an isoscelese triangle, 60-60-60), the base of the triangle at the surface of the cylinder, the point "inside" where metal will be cut. As the cylinder rotates, the lathe point also advances, at the rate of the "pitch", which is generally one triangle base per revolution. So, when it asks you for the pitch, you give it the base length or 1/base for US Customary Units, or TPI.) To review, there are three elements to a Pro/e thread: a length sketch showing, graphically, how far the thread goes, the pitch information (how far does the thread advance in one revolution of the screw) and the cutting tool profile (isoscelese triangle). Anything else we can do for you today!?! BTW, this description was based on the model of a subtractive thread (cylinder at major diameter, cut tip to minor diameter); another model that's commonly used is additive: cylinder at root or minor diameter, and the triangle adds thread material. This is all I know about threads. (Well, almost.)
David Janes
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David Janes

use in advance option helical sweep Or In cosmatic treds
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Then there are the threads that are used in plastic. If they're additive on the part, they're subtractive in the mold. What difference does this make? In an unscrewing mechanism, there must not be an undercut in the helix, so the end of the thread must terminate in the major diameter. Also, the thread can not go all the way to the starting surface because that would create either a diminishing thread (not possible in a ground thread) or a thread that continues out into the air (which would mean continues out into the steel, a thread grinder crash).
Then there are the threads that are molded "in draw", there is often an undercut created near the parting line. There are a few different ways of dealing with this, but your approach will dictate your modeling approach.
Sometimes I'll leave the major or minor diameter sharp to assist the tool guy by giving them an trajectory to follow, with the understanding the real profile will not be sharp.
The reason I bring this up is, I once designed a plastic assembly with threads like a machined thread, you know with a chamfer on the end etc. The parts wouldn't stay together due to insufficient thread engagement because where my last and first thread were chamfered, the thread in the plastic part didn't start until the thread profile became constant. I lost 1/2" a turn on both pieces, the result being they could be "popped loose".
Finally, the default helix starts and stops abruptly. To fix this you can create a helical surface, apply a vertex round, and have a good edge to use as a trajectory with a VSS. Trim it up neat with surfacing. This creates the nice clean end to your thread.
Also, creating threads on a helical surface is the best way I know to machine a pipe thread due to the taper. The thread mill function in Pro/NC doesn't do tapers.
Plastic threads are often not 60 deg. They're often 7 on one flank and 45 on the other. This creates either a push or a pull buttress thread. Stronger and a thinner root.
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Polymer Man

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