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Rifling Design - Machining Limitations

Rifling Design - Machining Limitations

Rifling Design - Machining Limitations

Hi there,
I am looking at adding a rifling design through a fluid cavity to "swirl" the flow as it passes through. Does anyone know what is the size limitations to manufacture this feature? Diameter, Length, Clearances, etc....

Thank you in advance for your help!

RE: Rifling Design - Machining Limitations

Tangential entry to a prechamber would probably be much cheaper.
See 'Francis turbine' and 'volute'.

That said, rifling can be produced with broaches. See 'broach' .

A certain Arsenal near my hometown used to make cannons.
BIG cannons.
The barrels were rifled by pulling broaches through them with a cable.
There were a series of, I think, 31 broaches, to be pulled through in sequence, in order to produce some pretty deep rifling in a pretty big bore.

I've been told that the engineers couldn't figure out why the last, final, broach lasted half as long as the rest.

I've also been told that everyone in the facility, except the engineers, knew that the production crew only used half the broaches on each barrel; i.e. barrel N got broaches 1,3,5,7, etc.,
and barrel N+1 got broaches 2,4,6,8, etc.,
but every barrel got the last, finish broach, which duh, wore out faster than the rest.

Mike Halloran
Pembroke Pines, FL, USA

RE: Rifling Design - Machining Limitations

After reading this several times, I think the OP meant to say "riffling" instead of rifling. As in baffling or windage tray ???

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Rifling Design - Machining Limitations

OP wrote RIFLING twice. Still, could be something else.

Assuming he meant rifling, it may not work to induce much swirl in the bulk fluid, unless the rifled bore is also lined with a plug, so that _all_ the fluid gets some rotation.

Depending on the fluid, given a bore with a central plug, it is also possible to produce a rifled annulus by inserting helically twisted vanes between the plug and the outer wall. That may be cheaper than rifling a thick tube, though producing the correct blanks, e.g. laser cut arcuate flats, and twisting them correctly, could be interesting. Perhaps the blanks could be equipped with ~1T wide tabs inserted in radially drilled holes in the plug, secured by tack welds, maybe with the whole core assembly having its OD trimmed in a lathe to fit the big tube, and retained by welding or some other means.

Or just have a radial volute fed with a tangential inlet, and a simple central axial exit into a simple tube, sort of like one element of a Lee Visco-Jet(r), which would be much simpler to fabricate. That's a good example of tangential entry to a prechamber.

Uh, Paul, are we understanding your wishes correctly?

Mike Halloran
Pembroke Pines, FL, USA

RE: Rifling Design - Machining Limitations

I believe just about anything is possible.. components manufactured with 'rifling' of various types range from small and short to huge and long.

But- all of these parts are made using very specific tooling, custom made for each application; they are mostly either small and made in giant quantities (think handgun barrels) or very large and made in small quantities for a customer who isn't cost sensitive (think artillery piece or tank cannon barrel).

So the real question is- what do you have to spend and how many parts are you making?

If you're making 1 of this widget, this will be prohibitively expensive. If you're making 100 million, it won't be.

RE: Rifling Design - Machining Limitations

I've known guys who could rifle a hole that small, but for a liquid, with an open bore and no plug, you won't get any rotational flow to speak of, because the rifling will only be twisting part of the laminar sublayer next to the wall, and the rest of the flow will be strongly laminar unless there is an extreme pressure difference along the hole.

Look at the illustration captioned 'Mixing Action' on this page:

Just use half of one Lee Viscojet pair; only the entry swirl generator, in roughly the proportions shown.

It still may not do what you want; at low Reynolds number, the flow in the swirl generator will just go radially from the tangential entry right to and through the central hole.

At least it's relatively easy to machine, for someone who does small holes for a living.

Mike Halloran
Pembroke Pines, FL, USA

RE: Rifling Design - Machining Limitations

You were right, Mike!

Wow, that's a small bore. Helical broaching would be very difficult. Maybe EDM?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Rifling Design - Machining Limitations

I'd bet my friend Siggy Tunger could do it. He'd probably try a mechanical helix generator and a single point broach and a lot of patience. ... but he died a while ago.

I'm sure he's skiing on God's mountain now.

Mike Halloran
Pembroke Pines, FL, USA

RE: Rifling Design - Machining Limitations

One could pull a broach straight through it and then twist the tube.

RE: Rifling Design - Machining Limitations

It's a very short tube to grip, let alone twist.

Mike Halloran
Pembroke Pines, FL, USA

RE: Rifling Design - Machining Limitations

Start with a longer tube and cut to length?

RE: Rifling Design - Machining Limitations

Length is a little over 1.0 mm.
Deburr the cut, and the part is gone.

Mike Halloran
Pembroke Pines, FL, USA

RE: Rifling Design - Machining Limitations

In that case the part cannot be produced?

RE: Rifling Design - Machining Limitations

I was enjoying a little hyperbole.

The part as envisioned by the OP can be produced at considerable expense, but will not do what the OP wants it to do.

Luckily for the OP, rotation is mostly conserved in flow, so it's possible to get the bulk flow rotating in a larger lumen, and it will continue spinning (faster, I think) as it transits a lumen of the desired size.

Mike Halloran
Pembroke Pines, FL, USA

RE: Rifling Design - Machining Limitations

Thank you everyone.

This is used for injection pressure (which is why the hole is so small), I am looking for an additional swirl for the individual holes (4X) which will create a swirl on its own. This should improve droplet breakup.

The pressures are around 4-6 bar (approx. 58-87 psi) for this application.

I would even conceder an insert for ease of manufacturing, which could be pressed into my assembly.

RE: Rifling Design - Machining Limitations

Have you read the posts?

Now that you've explained what you're trying to accomplish, it seems clear that what you want to happen will not be the result of the machining operation you have in mind.

Your best option is to add tangential velocity to the fluid stream BEFORE it hits this orifice.

RE: Rifling Design - Machining Limitations

Rifling is a very bad idea and will not work for you. Also, 1.0 mm = 0.040" not 0.004" (roughly). Mike's suggestions are spot-on. Create a swirl with tangential entry as shown in Mike's link. The orifice itself should be as short as possible to avoid damping the swirl before it exits the orifice. 0.004" is good, 0.040" is bad. Two approaches to such orifice design are to make a straight hole through a thin sheet metal disc, which is supported on back, or a tapered hole through thicker material, with a knife edge exit.

I suggest that you spend a couple dollars at the hardware store and buy a trigger-pump spray bottle and examine how it works. You can turn the nozzle cap to go from a solid stream to a cone spray.

My favorite nozzle on my back pack sprayer from Harbor Freight has four holes, and can be adjusted from four solid streams to a single cone pattern. In this design there is no swirl. the fluid enters through a single center hole and passes radially through an adjustable gap and approaches each of the four orifices from the side. Each hole creates a fan spray, which adds-up to a single cone. Having four cone spray orifices next to each other is not a good idea, as droplets will coalesce as they hit each other. After a spray nozzle all droplets should move away from each other to avoid this.

RE: Rifling Design - Machining Limitations

I have seen this tried on many levels at different sizes of bore been involved in experimenting and testing of trying to create a swirling flow of fluid with rifled grooves or splines what ever you want to call them the results were always the same. The influence of the outer layer of fluid did not transfer to the major mass of the fluid and any achieved rotation was canceled out immediately upon exiting the rifled section. Been there done that does not achieve the desired result at least in the cases I have seen.

RE: Rifling Design - Machining Limitations

But his diameter is so small.
1. Is there really any actual "straight" flow through the "center" of the laminar flow liquid around the ID of the tiny through hole?

Which brings up the elephant in the room (er, tiny weeny little bitty through hole). What rate of flow, what viscosity of liquid/plastic/die filling fluid/resin/metal being injected, what temperature of the die and the fluid and the final injection receiver?

2. For that small a through diameter, what "height" of rifling does the OP think he needs to spiral the injected liquid? What is the thickness of laminar flow liquid does the OP believe he will get in a "typical" flow velocity of a larger hole? One say 0.100 inch (nominal 3 mm) or 0.250 inch (6 mm)?

RE: Rifling Design - Machining Limitations


This should improve droplet breakup. The pressures are around 4-6 bar (approx. 58-87 psi) for this application.

So. A fuel injector? Did I guess right? Can you just buy one?

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