device for turning polygon ends (hex, square, etc.)

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liveaboard
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device for turning polygon ends (hex, square, etc.)

Post by liveaboard »

I guess if one has a mill and a dividing head, this gizmo is redundant.
Still, I find the idea really appealing. Fairly simple to fabricate too.

https://www.youtube.com/watch?v=SffBNPlxHjo


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Bill Shields
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Re: device for turning polygon ends (hex, square, etc.)

Post by Bill Shields »

Standard function on a CNC lathe with milling tools.

Creative to jinn up without.
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Re: device for turning polygon ends (hex, square, etc.)

Post by rmac »

This is interesting indeed! I'm left wondering if the faces generated are truly flat, and also what happens when you try to make much larger or much smaller parts than the demo shows.

-- Russell Mac
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Re: device for turning polygon ends (hex, square, etc.)

Post by Bill Shields »

Faces are flat enough onto which you can put a wrench. Theoretically I'd the swing diameter of the tool is the same as the distance across flats, then the flats are just that...flat

Large diameter parts with few faces tends to be hard on the machine and/or slow going, but can be done

You can learn more with a search of polygon turning. Fanuc, mitsubishi and Siemens do it. Not sure about the clones of these controls.

It is just a matter of setting up an electronic gear ratio of the main spindle to the tool spindle...so if your machine will not to rigid tapping itvwill not do polygon turning since you require an encoder on the tool spindle.
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Re: device for turning polygon ends (hex, square, etc.)

Post by liveaboard »

But he does it mechanically on a manual lathe, driven from the lead screw.
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Re: device for turning polygon ends (hex, square, etc.)

Post by rmac »

Bill wrote: Faces are flat enough onto which you can put a wrench.
Yeah, the guy shows that in the video, and they sure LOOK flat in the pictures. But I'm puzzled about what's actually going on with a rotating cutter operating on a rotating workpiece to make that happen.
Bill wrote: Theoretically I'd the swing diameter of the tool is the same as the distance across flats, then the flats are just that...flat
I'm not following you here. For one thing, "distance across the flats" doesn't even make sense in the three-sided case. Maybe a picture would help?

I'm mostly wondering if the faces are 100% perfectly mathmatically theoretically flat, or if they're just so flat you can't tell they're not flat.

Think about Watt's famous parallel linkage. It provides motion that's "linear enough" for some practical purposes within a limited range, but when you actully analyze it you'll find that it's really a super gentle curve. I wonder if the same sort of thing is going on with this polygonal turning idea.

Maybe time to drag out the CAD program and try to figure this out.

-- Russell Mac
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Re: device for turning polygon ends (hex, square, etc.)

Post by Bill Shields »

How about " circumscribed circle diameter"?
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Re: device for turning polygon ends (hex, square, etc.)

Post by Bill Shields »

The mathematical result of the ratio of head rpm to tool rpm is what is important..along with a specific index point
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Re: device for turning polygon ends (hex, square, etc.)

Post by rmac »

rmac wrote: Maybe time to drag out the CAD program and try to figure this out.
I did exactly that this afternoon and convinced myself that the flats are not perfectly flat. I didn't try to see "by how much" because I think that depends on a bunch of different things. I also found a related YouTube video. It's mostly about how to program a particular CNC machine to do polygon turning, but near the end they showed a chart that confirmed what I suspected about the flats not being flat.

-- Russell Mac

ss.png
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Re: device for turning polygon ends (hex, square, etc.)

Post by rmac »

I'm probably beating a dead horse here, but I thought it would be interesting to plot the path taken by the cutter relative to the workpiece. (In other words, imagine that the workpiece is held stationary and that the rotating cutter and the lathe and everything else rotates around it.) Here's the result for the three-sided "very suitable, little concave" entry in the chart in the previous post.

cutter_path.png

Sure enough, the sides of the little triangle formed in the middle are slightly concave, as the chart predicts. You could make them straighter and straighter by increasing the diameter of the cutter holder relative to the size of the thing you were trying to turn.

The horse is dead for sure now.

-- Russell Mac
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Re: device for turning polygon ends (hex, square, etc.)

Post by Bill Shields »

Nothing I have not experience the past 20+ years.

I you have a small, non ferrous part and need a quick polygon cut and do not have a Y axis available...take a run at it
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Re: device for turning polygon ends (hex, square, etc.)

Post by liveaboard »

That's a cool graphic, it gives a true impression of how the idea works.
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