Extruding a curved tube of pasta dough

[JT Smith]

TL;DR

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.