gun tube rifling

[tkocot]

Hello all,

I am trying to create internal rifling in a gun tube and could use some help.

1. I did this using a blend and created multiple cross sections down the axis of the gun tube. It works but is a brute force method and is not elegant. Meaning if you want to control the pitch of that blend, it become more difficult. You would have to figure out the distance between cross sections and their angle of rotation.

2. I tried swept blend and added a twist but that only goes form +/- 120 so if you want more than that it becomes more tricky.

3. I tried a sweep but i could not keep my cross seciton perpendicular to the diameter for the tube.

4. I tried a sweep with a trajpar function using a graph but could not get it to work.

Looking for some help. If someone know how to do this with sweep or trajpar that would be cool. If there is a better way then by all means.

Thank you.

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[TomD.inPDX]

Welcome to the forum, Timothy.

Helical sweep allows both normal to the trajectory and normal to the sweep. Subtle but important distinction. You will see which you are using from the section orientation.

[Patriot_1776]

Exactly. You'll need to know the cutting tool geometry to tell. For rifling, I'd say the section was normal to the centerline trajectory. Also, you don't need a graph to use trajpar, you can ues "t" to vary the degree value between zero and the total number of degrees.

[tkocot]

Thank you guys for the quick response. I tried the swept helix and give it a very large pitch. I only would the rifling to twist 1.5 times as it goes down the length of the tube. I also put it normal to the trajectory, but i still have problems. The cross section varies in shape as you move down the lentgh of the tube. The best method so far was the swept blend with the twist function but that can only twist so far. I would to do it with the swept helix if i could it would be nice and easy.

[TomD.inPDX]

I might suggest creating a sweep path by -Wrap'ing- a curve into the surface. You can control the feature's path very well this way if you can envision it along a "flattened" cylinder.

Have a look at this document: Closed and Ground Spring - Alternative to Helical Sweep

[TomD.inPDX]

...are you creating one flute and patterning it about it's axis or are you creating all the flutes with one sketch?

[Patriot_1776]

Good point Antonius. Also, you'll need to go to absolute accuracy of .0001 or smaller on a part that long with surfaces that small. Relative accurace does not work on long thin parts.

[TomD.inPDX]

Timothy Kocot wrote:

Thank you guys for the quick response. I tried the swept helix and give it a very large pitch. I only would the rifling to twist 1.5 times as it goes down the length of the tube. I also put it normal to the trajectory, but i still have problems. The cross section varies in shape as you move down the lentgh of the tube. The best method so far was the swept blend with the twist function but that can only twist so far. I would to do it with the swept helix if i could it would be nice and easy.

Curious... is this continually variable or does it have some exponential component to it?

Indeed, this calls for VSS and could benefit from the evalgraph function along the trajectory.

Making VSS functional is somewhat tricky but it works fine once you prove your sketch is robust enough to "twist" a full 360 degrees without distorting or becoming corrupt.

The pitch remains constant? If so, helical sweep should work just fine. As Frank stated, you can run into trouble with default accuracy settings.

[TomD.inPDX]

Helical sweep to create a guide curve and sweep to control the cut with variable fluting.

This method makes the cutter profile a little easier to define.

You still have the option of orienting the cutter tool

Creo 2.0 attached.

[tkocot]

This was very clever and very helpful.

[tkocot]

Hey Steven, Antonius, and Frank,

Thank you for all of the replies and all of your help. Steven you nailed. I uploaded the file and messed around with the section profile and the pitch and it worked out great. Frank, where do I go to change it to absolute accuracy. Antonius, I guess my thinking was to sweep it along a path that was the center axis of the gun. While it did this I would trajpar the section to rotate it, but the helical sweep worked. This forum is a great resource and I hope to be hearing from you guys in the future.

[Dale_Rosema]

Hey Timothy,

Don't forget to mark Steven's answer as correct for those that follow behind.

Again, welcome to the forum.

Dale

[tkocot]

will do.

[Patriot_1776]

Hey Tim. With a VSS you can vary twist, and the section. I did this lobed core with draft using a VSS.

As for absolute accuracy, you must first enable it in your config.pro: enable_absolute_accuracy yes Then you (at least in creo elements/pro 5.0) go to: file, properties, and under "Accuracy", change to "absolute" and give a value. Long thin parts with tiny surfaces need a very low accuracy.

One thing also about VSS's, and this I got from a senior-level PTC guy who was in charge of that type of geometry (ironically, it was on the above model that I talked to him), the internal centerlines can become unstable. If you're doing twists, always put in a construction line, and dimension your angle to that, not one of the existing centerlines.

[tkocot]

Hi Frank,

If possible could you send me that file for the VSS with a twist. I would like to be able to see how you did it. If not, no worries.