Extruding a curved tube of pasta dough

[Tom.G]

I haven't used the pasta machine yet and was surprised to see a video of it where the round noodles came out curved. There is no apparent curvature or asymmetry to the die. It's a round (serrated) hole with a round center piece. Maybe my eyes are missing something.

View attachment 348809

The curve is outward from this die whereas all of the commercial ones I saw recently on the internet curved inward. Maybe it has something to do with how the dough is fed?

In arbitrary units, measurements from the core to the closest point on the fluted edge:
7 o'clock position: 0.237
8 o'clock position: 0.242
11 o'clock position: 0.272

Measurements taken with PhotoShop from an enlarged screen capture.
Inner edge of the metal part of the die measured 3.346 inches -- so scale the gap measurements proportionally.

Holding a ruler to the screen shows the diameter as 7 inches. The spacing difference is just visibly discernable at that scale -- if you look for it.

Cheers,
Tom

 

[JT Smith]

Are you sure you aren't simply measuring an artifact of how the photo was taken (hand held smartphone)?

 

[Tom.G]

Are you sure you aren't simply measuring an artifact of how the photo was taken (hand held smartphone)?

Only moderately.

I was aware of that possibility, so I did a visual inspection and also checked how closely a circle in PhotoShop matched the circular die outline. Although I deemed it a worthwhile project, it could still be wrong!

Cheers,
Tom

 

[JT Smith]

I wonder how good that circle test is? Seems like a good geometry problem.

If what you are proposing is true then the pasta will have slightly uneven thickness. More confusing is that the direction of curvature of the pasta is at about 3:30 in that photo but that doesn't correspond to the apparent thinnest area.

I took another photo of the same die rotated to approximately the same orientation. I wish I had a better camera but it's just my old phone again. I tried to center everything as best I could. The letters are an attempt to get the phone to focus on the surface. I think the pattern of apparent spacing is different now.

 

[JT Smith]

I built a simple die out of half inch plywood and a u-bolt (to hold the inner piece). The outer diameter is one inch and the inner is 5/8 inch. It's hand made by an amateur so it isn't perfectly centered, but pretty close. The hole is offset so that it is very close to the wall. The eccentricity ratio, as defined by that paper posted above, is about 0.08. That is, the one inch hole is about 1/4" away from one wall and 2 3/4" from the opposite wall. The extruder shaft is four inches square. It's a North Star extruder for pottery clay.

Anyway, the result was nil. There was no apparent curvature upon exiting the die. None.

After extruding some of the clay I manually bent it into a curve. That of course distorted the cross section, flattening it.

Close but not quite what I was going for so maybe I'll try something else. Not sure exactly what.