How it's Made? Sheet Metal Helix 2

[DistressedNerd]

Hello - I am stumped on how they make the sheet metal spiral for something like this (see image below). I can see how they would make a sheet metal helix without the room for a rod through the center - but can not wrap my head around the manufacturing process for a sheet metal helix with room down it's center to be welded on a rod. The process in the linked video is what could be used to make a helix of sheet metal - how would the flat piece of sheet metal be altered to have room for rod down it's center?
Link

 

[KENAT]

Does it really 'have a hole' or is the ribbon of sheet metal wrapped around the shaft?

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[GregLocock]

Neither. They are discs of metal with a hole in them, slit, and then bludgeoned into shape. Then weld the discs together. Or at least, that is the agricultural method.

Cheers

Greg Locock


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[GregLocock]

Comme ca

Cheers

Greg Locock


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[KENAT]

et voila, cheers Greg

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[dhengr]

DistressedNerd:
I believe something like you show can be made by taking a long sheet metal strip and put it in a long set of rollers at a skew angle. Then, you may roll it several times, tighten the rollers, and/or changing the skew angle. If you wanted to roll a short circular band (a short piece of duct/pipe) you would put the sht. metal strip in the rolls, exactly perpendicular to the axis of the rolls, and by tightening the rolls you would roll a smaller dia. circular band. In both cases the resulting piece ends up rolled about the long axis of the rolls. Also, look up the layout of a spiral chute in a sheet metal or light steel layout and detailing textbook.

 

[JohnRBaker]

Actually it's fairly easy. Just take a strip of metal and roll it up like a roll of tape and then, while holding one end, pull the other end out of the middle of the roll. Anyone who's old enough to remember opening a one of those 3-lb cans of coffee and then taking the 'key' and pulling it out to form a twisted helix.

We used to save them and hang them on our Christmas because they looked sort of like shiny 'icicles'. The results would look something like this:

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[BUGGAR]

Somewhere in my files are the equations to layout a helix on a flat sheet. But a crafty engineer could figure out the formulas. I saw a metal shrinker that could make a continuous "potato peel" but the inside radius was relatively large.

 

[btrueblood]

Continuous helix former...

https://www.youtube.com/watch?v=6vsuUYr6EHo

https://www.youtube.com/watch?v=2beBQns4FUw

Though it's not as common as the welded method Greg describes.

The strip in the o.p.'s post appears to be brazed or soldered to the center shaft, not welded, but it's tough to tell from the photo.

 

[JNieman]

Actually it's fairly easy. Just take a strip of metal and roll it up like a roll of tape and then, while holding one end, pull the other end out of the middle of the roll. Anyone who's old enough to remember opening a one of those 3-lb cans of coffee and then taking the 'key' and pulling it out to form a twisted helix.

Unfortunately, I don't think that will result in the shape you think it will. I suggest you try that with paper and see what you end up with.

Note that the outside of the spiral has a -much- longer circumferential length than the inside... you don't get that by rolling up parallel-edge strips.

What GregLocock posted is the only practical solution.

 

[KENAT]

Well thanks Btrue, now I'm thinking I'm not so stupid as that's what I was envisioning (maybe not in so much detail) when I mentioned rapping a 'ribbon' around the shaft.

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[DistressedNerd]

btrueblood - I think we're on to something - the spiral blade cold rolling mill looks to form the desired shape, but I could not find one that would make a small enough spiral helix to be skewered by a 3/16" inch diameter rod. The smallest one I could find does down to a inner diameter of 20mm Link

 

[3DDave]

https://www.youtube.com/watch?v=-_oqBEJBOmE

But with a bigger crank handle.

Maybe start with trapezoidal wire, wind into a spiral of mean radius, and then run between flattening rollers to finished thickness. The trapezoid preform provides the material to retain the spiral.

 

[JStephen]

You can form cones and cylinders from a flat surface just by bending. Forming a dished shape, or a helix, requires stretching/compressing the plate in its plane, not just bending it. Consequently, a layout to form that surface on a flat plate is going to be approximate to some degree.

John, your "Jeweled Icicle" shape can be formed by putting the piece in a lathe while one end is held stationary.

 

[btrueblood]

DN, google spring winding machines; this is just like that, except you have to have a guide to hold the strip and force it to bend the "hard way". I'd think you could 'gin up a bender using a lathe or similar spindle, and be able to clunk these out fairly quickly.

 

[btrueblood]

A discussion from days of old (1903) on the development of rollers for helical conveyor bending/winding machines:

https://books.google.com/books?id=G...q=think metal helix strip -bimetallic&f=false

 

[MintJulep]

Bludgeoning machine to make them from disks.

https://www.youtube.com/watch?v=1egmm_4Y3Rk

 

[Compositepro]

This is how a skilled craftsman does it:

https://www.youtube.com/watch?v=JAD0hu-pwSA

 

[Don56]

Compositepro,
Definitely a skilled craftsman. Where can I get some of those OSHA safety shoes? I burned mine up welding at home?

 

[JohnRBaker]

I liked his use of 'fixtures' and 'gauges'. While you can't see it, I suspect that there was another 'tab' welded to the back-side of that vertical pipe that he used to gauge the proper pitch of each segment I would guess that the final results were pretty damn good, particularly since the original 'blanks' looked very consistent, as if they were punched and sheared using a more modern technique, i.e. a large hydraulic(?) punch press.

In my many visits to India I've personally witnessed several situations where the use of 'hand labor' was done where we in the West we would have used machinery. The classic example was when I visited a client of ours and I noted upon entering the facility that about a dozen men or so were digging, with picks and shovels, what I assumed was some sort of trench between two buildings for either water/sewage or some other kind of service lines. Across the street, inside the fence of another company, there was another trench being dug but this time using a conventional back-hoe and only a couple of laborers helping. When I asked our host about this and mentioned what I saw across the street, he said that yes, he could have hired someone with a back-hoe but he decided to go the route that he did because tonight there would be 12 families with food on the table instead of only three.

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