Extruding a curved tube of pasta dough

[sophiecentaur]

a pressure gradient is established, that forms the curve.

Yes. In that machine, it looks liked the pressure is high - or it may be that the total force (Pressure X area) is high - much higher than a home machine. I bet the mix is pretty critical to get the shape right. The offset hole is just visible at 39s.
Glorious old piece of film though.

I've made pasta with the roller type machines before. It's a lot of work. Nowadays locally made fresh pasta is readily available in markets. It's a little bit pricey compared to dried pasta but not bad when you figure in the labor costs of doing it yourself. Frankly I don't think fresh pasta is better; it's just different. I buy it once in a while just for the change. There IS a difference in the quality between dried pastas though. I find it's worth it spend extra as even the more expensive pastas are still pretty cheap.

BTW, I tried the machine today. It was easy to operate and produced nice little noodles but the dough collected in every nook and cranny. Cleaning looked to be quite the chore. Then I discovered that the central pathway wouldn't come out of the housing which would make cleaning a lot harder. I tried to get it free, even succumbing to using WD-40 on where I assumed it had fused with the shaft. No luck. Maybe it will come loose with some soaking time. I'm not going to be making pasta with this thing anyway. Probably it will be in next week's trash.

Thanks for that response. You'd have to be pretty strongly motivated to DIY regularly. It seems much harder work than making bread at home, which I do all the time. It's our sole source of bread except for the occasional sourdough loaf. Sourdough making is more a way of life than just a recipe.

 

[JT Smith]

Thanks for that response. You'd have to be pretty strongly motivated to DIY regularly. It seems much harder work than making bread at home, which I do all the time. It's our sole source of bread except for the occasional sourdough loaf. Sourdough making is more a way of life than just a recipe.

Probably you get more efficient if you do it regularly. I went through a phase of making sourdough bread twice a week for about a year. I had just come back from an extended period of time in Europe to what felt like a bread desert and I was keen to attempt to reproduce some of the great breads that were ubiquitous there. While I was in the groove it was an easy routine. Now I can't find the time to make one loaf. I went through similar phases making beer, kimchi, yogurt, buttermilk, etc. In each case I ultimately found that once the novelty of DIY wore off I realized could more easily purchase what I liked -- except in the case of bread. The U.S. has not changed very much in that regard unfortunately.

I made some clay extrusions yesterday and I think I'm now more interested in exploring that than pasta. The dies are bigger and so easier to make myself. And the raw material can be recycled repeatedly.

But I still can't quite figure out what a die that produces a curved hollow shape should look like.

 

[Lnewqban]

... But I still can't quite figure out what a die that produces a curved hollow shape should look like.

This may help:
https://www.mdpi.com/1996-1944/14/7/1603

 

[some bloke]

The symmetrical die produces curved pasta bacause the dough being pushed out at the edges of the barrel is moving slower than the dough in the centre. The dough is pushed out via the middle, which drages the next "ring" of dough, which drags the next, all the way to the outside edge where the "ring" of dough drags the outer walls, which do not move. The friction here slows down the outer "ring", which slows the next, all the way back to the centre, by less and less each time.

Essentially, the dough moved through like a big paste-like watersnake toy, so the middle moves the fastest and the edges, which are being rolled along the outside of the extrusion tube, don't move at all. The natural result is that the length of the tube closest to the centre is longer than that produced by the outer edge, over the course of the same time, and this causes a curved tube to be made.

Edit - to answer the OP's original question, move the whole die such that one edge of the die is at the edge of the extrusion tube, and the other edge is closer to the centre of the extrusion tube, and the edge closest to the middle will naturally form a longer extrusion of the same thickness, making a curve.

 

[JT Smith]

Thank you. I had already figured that was likely the reason from the paper that Lnewqban linked where there is discussion of what they call the "eccentricity ratio" -- essentially how offset from the center the die is. I am actually about to build a pair of dies to test this out. I was going to post about it here once I'd finished testing them later this week.

In the commercial machines I found photos of online the pasta curved inward. Perhaps the explanation is essentially the same but it's not clear. As that paper pointed out there is more than one way to achieve a curve.

 

[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.