Extruding a curved tube of pasta dough

[JT Smith]

TL;DR Summary

What features of an extruder die would result in a curved tube of pasta dough?

I have a pasta extruder that has a die for a straight tube form. It's simple: just a circular hole with a smaller solid circle suspended in the center. I was wondering what sort of die would produce a curved tube. Would offsetting the inner solid circle have that effect? Or is it more complicated than simply choosing a different die. Any ideas?

 

[Baluncore]

TL;DR Summary: What features of an extruder die would result in a curved tube of pasta dough?

Or is it more complicated than simply choosing a different die. Any ideas?

Yes, it is more complicated. The pasta needs constant thickness so it cooks evenly, so do not offset the centre.
The rate of extrusion is determined by the back pressure of the material extruded earlier. Guide the extruded material away in an arc, so one side grows faster than the other. You can achieve that by extending and curving the central part of the die. You will have to make a short or a long pasta helix, by cutting it regularly as it is extruded.

 

[JT Smith]

Thanks. That makes sense. Something to play around with. I also received one suggestion to load two parallel columns of dough, one firm and the other soft. But I suspect that would be more of a short-lived effect, if it worked at all.

 

[Baluncore]

"The curved shape is created by different speeds of extrusion on opposite sides of the pasta tube as it comes out of the machine".
https://en.wikipedia.org/wiki/Macaroni

There is a video that shows the manufacture of macaroni elbows.

At 39 seconds, this shows the input side of the die used to extrude the curved tubes. The output side is flat, so the knife can cut the elbows. It looks to me like the extrusion path is bent with the "hole" starting on one side, inside the plate where it obstructs flow, and then moves to the centre at the exit. By initially feeding the dough across the entry to the die, a pressure gradient is established, that forms the curve.

 

[sophiecentaur]

TL;DR Summary: What features of an extruder die would result in a curved tube of pasta dough?

I have a pasta extruder that has a die for a straight tube form. It's simple: just a circular hole with a smaller solid circle suspended in the center. I was wondering what sort of die would produce a curved tube. Would offsetting the inner solid circle have that effect? Or is it more complicated than simply choosing a different die. Any ideas?

How accurately can you measure the internal and external diameters and the spacing all the way round? Also, is there any alignment problems? You would need a cheap digital calliper (less than £20 and useful for many other things)

 

[Baluncore]

Here is a picture of the inlet side of a Macaroni Elbow extruder plate. The outlet side is a symmetrical annulus. The core rod enters on the inside of the elbow, where the flow rate is being restricted to curve the elbow.

 

[JT Smith]

Very interesting.

I found photos of the inside faces of two other elbow macaroni dies.

And here is the one from that old video along with the latest one you posted:

They're all different!

 

[JT Smith]

How accurately can you measure the internal and external diameters and the spacing all the way round? Also, is there any alignment problems? You would need a cheap digital calliper (less than £20 and useful for many other things)

I can measure accurately enough and the alignment is not an issue. Why do you ask?

 

[Baluncore]

They're all different!

We cannot see light through the holes. I suspect that some of the extrusion plates are made from two or more plates, to achieve the bend, and the variable flow.

There is a nontraditional technique for making precision curved holes, it is called "die sinking". It employs spark erosion between a graphite plug and the extrusion plate as the work piece. Sinking is carried out in a bath, under an electrolyte such as kerosene, that is continuously circulated and filtered.
https://en.wikipedia.org/wiki/Electrical_discharge_machining#Die-sink_EDM

 

[JT Smith]

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.

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?

 

[sophiecentaur]

I can measure accurately enough and the alignment is not an issue. Why do you ask?

An off - centre middle die would surely be expected to introduce a curl because of the different feed rates. What are the OD and ID and what is the offset? Obs the pasta is not a linear medium but the curve in the result could maybe be calculated for an ideal case due to different speeds if the speed is (perhaps) proportional to the spacing on different sides.

 

[Baluncore]

An off - centre middle die would surely be expected to introduce a curl because of the different feed rates.

The exit from the extrusion plate is symmetrical, as are the pasta wall thicknesses. The key to good pasta design, is keeping all the wall thicknesses the same, so they cook at the same rate.

It is the entry to the extrusion plate and the attachment of the centre rod that is asymmetric, which results in the differential velocity.
The pasta will also curl slightly, if it is wiped across the plate entry, rather than being pushed directly onto the surface.

 

[sophiecentaur]

The exit from the extrusion plate is symmetrical,

I was just enquiring what the actual measurements are. How 'straight' is pasta made in this simple way? If we were extruding high quality steel tube then no one would ignore the die dimensions. The nature of the medium could possibly exaggerate the effect.

 

[Baluncore]

How 'straight' is pasta made in this simple way?

Macaroni elbows are not straight. They can be from 45° to just short of 180°, which has a radius tighter than 10 mm.

 

[JT Smith]

The die in my photo above has a center piece that is 10.4mm in diameter and the outer diameter (from widest point of the serrations) is 13.9mm. The gap is roughly 1.8mm and appears to be the same all the way around. But I can't get consistent readings because it's too tight a space to insert the caliper jaws very far and the edges are rounded.

EDIT: I made a kind of feeler gauge and there is no discernible difference in the gap around the die.

From that video of my machine when using this die:

 

[Baluncore]

From that video of my machine when using this die:

Are four cartridges used, and are those symmetrical?
How is the dough pushed into the cartridge?

To measure or compare narrow gaps, use a taper or a matchstick split into a long wedge. Mark the depth it can be inserted into a gap, then measure the wedge at that point.

 

[JT Smith]

Yes, this module has four outlets. The dough is forced through via an auger, a screw. It's a manual crank machine with some gearing. It's a "Regina Atlas".

 

[Baluncore]

The dough is forced through via an auger, a screw.

Look at the end of the auger, where it is close to the extrusion plate.
Work out which way the dough is being moved at that feed point.

 

[JT Smith]

Here is the auger:

Here is the end that feeds the die:

When in operation it rotates clockwise from this perspective.

 

[sophiecentaur]

EDIT: I made a kind of feeler gauge and there is no discernible difference in the gap around the die.

Cheers. That's what I wanted to know. The curl must be due to the flow towards the upstream side of the dies then. From your image of the emerging pasta tube, the tubes curve outwards. It looks as if there is a velocity gradient in the flow; faster at the centre and slower at the outside and that could be explained by the drag at the outside and the outward curve of the pasta tubes. Your result seems not to be perfectly 'straight' though, so the die doesn't seem to do what it claims.
As a (relevant) aside, do you find that home made pasta is worth the effort? I tried making some once and ended up with the kitchen draped with yards of strips drying on towels. But that was with a simple rolling pin and the thickness 'varied' (to put it kindly).

Macaroni elbows are not straight.

Agreed; that's what the stuff (elbows) in my jar looks like. The OP mentions "straight' for his die (not elbows) and it seems to measure as symmetrical. That confirms what I was thinking. Asymmetry can easily produce a curve. If you really wanted sphagetti-like straightness, you'd probably need to follow the tube die with a long section of straight tube to allow it to settle down into straight (or a collimating length on the way into the die).. `Extruded' metal is probably produced with some tension downstream to avoid too much curve - and the process must be more expensive too.

But you only die once.

 

[Baluncore]

If you really wanted sphagetti-like straightness, you'd probably need to follow the tube die with a long section of straight tube to allow it to settle down into straight (or a collimating length on the way into the die).

Spaghetti is extruded in bulk, vertically, downwards.

 

[JT Smith]

The OP mentions "straight' for his die (not elbows) and it seems to measure as symmetrical.

The puzzle to me is why this symmetric die produces curved pasta. I suspect it has to do with how the auger pushes the dough but I can't wrap my brain around how that plastic screw might do that.

 

[sophiecentaur]

Spaghetti is extruded in bulk, vertically, downwards.

Ahh. The pull of gravity. Macaroni also, I guess. What sort of length would support itself, I wonder. Old glass stretched like that during production of windows, as it cooled down.

 

[JT Smith]

Ahh. The pull of gravity. Macaroni also, I guess.

Gravity might be a factor but it's clearly not the only one.

 

[sophiecentaur]

Gravity might be a factor but it's clearly not the only one.

Yes. Radius, length and mixture.
All this talk of pasta making and I feel like doing some myself. But that could involve the pain of making a suitable 'mangle' myself. Don;t hold your breath.

 

[JT Smith]

As a (relevant) aside, do you find that home made pasta is worth the effort? I tried making some once and ended up with the kitchen draped with yards of strips drying on towels. But that was with a simple rolling pin and the thickness 'varied' (to put it kindly).

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.

 

[Baluncore]

Ahh. The pull of gravity.

Take a look at the short video in post #4.
It starts showing spaghetti being extruded downwards, then being folded to dry.

 

[JT Smith]

I forgot to mention, I also tried out a clay extruder. There was a die that made 1.5" diameter hollow round tubes and I found that I could bend them simply by guiding them out in an arc. Once out they were still bendable with care up to a point but it was dead easy to do as they emerged. Probably could do that with pasta too but it would take a week to make a plate of food that way.

 

[Baluncore]

I could bend them simply by guiding them out in an arc.

The pasta extrusion plate has a flat surface, so the rotating knife can regularly cut the extruded pasta. If the pasta is guided beyond the extrusion face, there will need to be some other way to cut the pasta.

There is also a problem with wall thickness. Where you bend the profile after extrusion, you will vary the wall thickness, and so the cooking time.

 

[JT Smith]

There is also a problem with wall thickness. Where you bend the profile after extrusion, you will vary the wall thickness, and so the cooking time.

I thought that this was what you were suggesting in post #2:

The rate of extrusion is determined by the back pressure of the material extruded earlier. Guide the extruded material away in an arc, so one side grows faster than the other. You can achieve that by extending and curving the central part of the die.

Or do you think that my hand holding the extruding clay would not actually provide any back pressure?

I'll have to try it again and see how much the wall thickness is affected.

 

[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.