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Boltfluter

Plastic
Joined
Mar 30, 2018
Hey guys,

New to the forum. Need help programming a gain twist flute or groove. Thinking this would probably need to be in a macro. Twist rate would start at 360 degrees and go down incrementally to 270 degrees over 20". Thinking I would need to break the length down to about .002 increments to get a smooth twist. Any help would be greatly appreciated. :D

Paul
 
Boltfluter said:
Hey guys,

New to the forum. Need help programming a gain twist flute or groove. Thinking this would probably need to be in a macro. Twist rate would start at 360 degrees and go down incrementally to 270 degrees over 20". Thinking I would need to break the length down to about .002 increments to get a smooth twist. Any help would be greatly appreciated. :D

Paul
Click to expand...

Is any body out there?

Paul
 
I think he's talking about a specialized type of rifling in a gun barrel, where the spiral changes over the length of the barrel.



...but I could be wrong.
 
Ditto on more info. A macro could certainly do it. If you can describe what you want mathematically it should be a cinch with a macro. Can you post a print and let us know what you have to work with?
 
So after googling it, I see it is akin to a variable lead thread. One site described it as a parabolic curve. Obviously, you need to define a starting lead and an end lead. You're not going to see much change in only 90 degrees of rotation if the lead specs are quite long to begin with. Or did you mean 270 degrees of rotation? There's two ways you can go on a rotary axis, you've got to define it.
 
Aj,

Is right on th money. Sorry for the lack of info. I have a habit of thinking we are all on the same page. Basically I want to flute a rifle barrel on the outside with 6 flutes. Normally I do this as in 360 deg. of rotation over 20" as an example. Twist rate is spread out equally over the 20". With gain twist fluting like rifling the twist slows incrementally the farther down the barrel that you go. As an example the twist would start at 270 deg and at the end of the barrel it has slowed to 200 deg. of rotation. I would need to break down the length of the barrel in .005 lengths and let the controller do the math to slow the twist gradually to have a smooth transition over the full 20". Hope that makes sense. Thinking I need to do this in a macro to easily edit for different twists and barrels. Writing this long hand as I am one man shop. Here is a link to my site to show what I do if it helps to get us all on the same page. Home Thanks guys. Hoping someone can figure this out.
 
G32 would be the first thing I would try.

I have never done it, but theoretically I think you can use it for a changing pitch along the length.

If you can mill the shape with a bit of layout work in cam you can get it.
 
I think I'm getting what you want to do....

I've been doing some thinking about the formula you need for developing this. Rather than working with a .005" X increment and a varying A rotation, I think it's going to need to work with the .001 degree minimum increment on the A axis and adjusting the linear move per step of the macro.

A twist rate of 270 degrees per 20" of length results in .068 degrees per .005".
A twist rate of 200 degrees per 20" of length results in .050 degrees per .005".

So by reducing the twist rate by .018 (.068-.050) degrees over 4000 moves (20"/.005") results in in a reduction per move of less than the .001 degree rotary axis minimum increment.
 
I'd be tempted to play around with this problem graphically. I've got cadcam so I'd use it, because I am loath to handcode some huge program :D

A parabola is a cross section of a cone, but not on the axis of revolution of the cone, but parallel to the cone axis, IIRC. So using a solid modeller, I'd take a cross sectional slice through a 3d cone, and extract the edge. The profile can then be laid down on the XY coordinate work plane, and 4th axis wrap can be used to create a toolpath along one side of the parabola (which is symmetric so place it on the coordinate system so that is symmetric along the X axis).

Then I'd do a trial trace along a cylinder, using a marker pen held in the spindle while the path is executed on the 4th axis. Hopefully, I could then learn how to tailor the cone angle so that the cross section parabola can be modified to suit the job length.
 
If I am picturing this correctly in my mind :dunce: it shouldn't be that hard as you gradually increase the RPM of the Rotary. I of course, am thinking this is a C-Axis Lathe part.

The trick would need a Macro though, to make it "gradual" instead of Incremental. Or if you could somehow manipulate G96, by tricking the control to think it is changing diameters but not moving the Tool on the X Axis???

I think maybe I could do it on OSP control, by blocking the physical X Axis motion, but inputting a diameter change in the Program. Again thinking Lathe, so the same logic would be impossible with a Milling machine. But it would take a lot of doing and experimenting and "Markers".

R
 
If I read correctly your running a Haas TM with 4th axis.

Do you have G107 Cylindrical Mapping on that machine, think its standard with 4th axis or was?

When I need to do something like your asking I unwrap the cylinder dia with Pi, create my workspace in X and Y (example 3.5" dia x 14" becomes Y11.000" x X14.00") then plot my line, angle, curve or curves in simple XY moves. Or if doing a tapered part, plot in XYZ. Easy straight forward programming that can be tweaked on the fly.
Set your start point, lock the Y with G107 and let the control figure the rotary path. Once you have the single spiral the way you want its just a matter of dividing up the diameter to get spacing you want.
 
Sim,

Yes, I am using a Haas mill with a 4th axis and I have used cylindrical mapping for engraving. I will have to think on this but I think this may be the way to go. Thanks guys for all the help. Keep the ideas coming if anyone has any more. This is a head scratcher long hand.

Paul
 
Sim,

Will a G107 incrementally show down or increase the twist of the flute? I have limited experience with the G107.

Thanks, Paul
 
Vanbiker,

Sounds good to me. I am thinking if this statement was somehow written in a macro I could easily adapt it to different barrel lengths and twists. Do you have a formula for this as this is where I am stuck. Having no experience programming a macro.

thanks, Paul
 
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