# Helical slot in stainless steel tube - anyone have the equipment for this?



## HightonRidley (29 Nov 2022)

I've made 3 progressively larger prototypes for a solar tracker. The heart of the mechanism (my own idea / design) is a 'sleeve' tube with a helical slot. A guide pin fits through the slot into a tube that fits inside the sleeve. As a motor lifts the inner tube, it's forced by the guide pin to rotate.
In the latest two prototypes, I've used an aluminium tube for the sleeve becasue I can just about make the slot myself by drilling and filing.
In the final version, I want the sleeve tube to be stainless steel but making the slot in that material is beyond the tools (and skill) I have.
Here's a web page wot I wrote showing the second prototype build and a speeded up video of it in action tracking the sun:
second protoype build
Does anyone here (living in the UK) have the ability to cut a helical slot in stainless steel? The tube dimensions are 25mm outer diameter, 19mm inner diameter. The slot needs to be 5mm wide and reach around the tube by approx 220°, rising as it does by 80mm
I'm happy to pay a reasonable fee


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## Inspector (30 Nov 2022)

If the tube can be made from flat sheet it could have a straight angled slot cut and then rolled into a tube with the seam welded. The machining is then the easy part (relatively speeking) but making a tube out of it presents its own problems. Best of luck with your project.

Pete


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## deema (30 Nov 2022)

You need a tube laser cutting company.


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## HightonRidley (30 Nov 2022)

Inspector said:


> If the tube can be made from flat sheet it could have a straight angled slot cut and then rolled into a tube with the seam welded. The machining is then the easy part (relatively speeking) but making a tube out of it presents its own problems. Best of luck with your project.
> 
> Pete


That's a great thought, thanks for suggesting it @Inspector


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## HightonRidley (30 Nov 2022)

deema said:


> You need a tube laser cutting company.


I didn't know that such a thing existed. I've done some searching and it looks like a one-off would be prohibitively expensive.
Thanks for the info, @deema - learning, learning, every day a school day


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## Linus (30 Nov 2022)

Could it not be cut using an angle grinder and cutting disc?


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## Lorenzl (30 Nov 2022)

Have you thought about having a gear on the shaft instead of the slot and it is driven by a gear on the motor/gearbox? You could have two microswitches at each end of the travel to reset with some hard stops.

I would think this would be more efficient than the slot.


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## Spectric (30 Nov 2022)

What about a die grinder or even a Dremel !


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## Spectric (30 Nov 2022)

A lot of missing information, the motor raises the inner sleeve which is forced to rotate by the helical slot but how heavy is the load being raised because this mass is supported by the pin in the slot so could be a potential weak link. If I was doing something like this I would mount everything on a platter which has it's own means for rotation and then the sleeve / tube arrangement without the slot for the raising part.


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## Homeless Squirrel (30 Nov 2022)

HightonRidley said:


> I didn't know that such a thing existed. I've done some searching and it looks like a one-off would be prohibitively expensive.
> Thanks for the info, @deema - learning, learning, every day a school day


Plasma cutter or even water jet,


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## Yojevol (30 Nov 2022)

Beg, steal or borrow a routerlathe and fit an end mill into the router. You may have to play around with the r/l feed rate or redesign the mechanism to suit the standard r/l helix angle. 
Brian


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## Homeless Squirrel (30 Nov 2022)

Far better is to have tube with collar inside running on a threaded drive bar(Lathe gear/vice/clamps etc type shaft)pitch/thread would need to be relatively shallow for micro pitch and ease of driving load as step threads equals higher drive load and less fine tuning.
Run if off a reduction gear either cogs/chain or bevel and can reasonably easily find suitable candidates to "Recycle" ooops someones nicked me windscreen wiper motor!


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## niall Y (30 Nov 2022)

Could this not be done on a milling machine? By attaching the previously made aluminium version , firmly to the end of a stainless steel tube, and improvising a cradle to hold the assembly down, then by the use of a fixed pin located in the original. rotating the tube will make ,it follow a fixed a cutting path. Just a suggestion.


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## HightonRidley (30 Nov 2022)

Linus said:


> Could it not be cut using an angle grinder and cutting disc?


This is my absolute last resort (I've only got a Dremel) and it would consume a lot of the cutting discs. But the main issue is getting a smooth curve on the helical slot after the cutting. I'm not saying it's impossible but....
Thanks anyway, @Linus


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## HightonRidley (30 Nov 2022)

Lorenzl said:


> Have you thought about having a gear on the shaft instead of the slot and it is driven by a gear on the motor/gearbox? You could have two microswitches at each end of the travel to reset with some hard stops.
> 
> I would think this would be more efficient than the slot.


Good thoughts there, @Lorenzl but the advantages of the slot approach outweigh other options. For example, the weight of the load (the solar panels) allows the inner tube to drop-and-twist the panels to their dawn start position as the motor completes one revolution. No need for anything more complicated.


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## HightonRidley (30 Nov 2022)

Spectric said:


> A lot of missing information, the motor raises the inner sleeve which is forced to rotate by the helical slot but how heavy is the load being raised because this mass is supported by the pin in the slot so could be a potential weak link. If I was doing something like this I would mount everything on a platter which has it's own means for rotation and then the sleeve / tube arrangement without the slot for the raising part.


Good points, @Spectric. The load is supported / lifted by a mechanism on which the bottom of the inner tube rests so the guide pin doesn't have much force on it. As the mechanism lifts the inner tube, the guide pin against the slot causes the rotation. The rise angle (is that the right term?) of the slot means little force gets applied to the guide pin.
In this youtube proof-of-concept video you can see that the eyelets allow the lifting cords to lift the thing (technical term!) that the inner tube rests on: proof of concept video
The issue with using a platter (if I understand you right) is returning the solar panels to the dawn start position at the end of the day. Using the helical slot approach makes it the simplest it can be: the lifting motor always turns in the same direction; no end stops are needed. The only reason for the raising part is to make the helical slot do its job of twisting the attached solar panels to follow the sun - with a platter there'd be no need for lifting.

(The 'thing' is a short piece of stainless steel bar with a recess milled in the top that holds some small ball bearings. The inner tube has a closed end at the bottom and this rests on the ball bearings. The eyelets screw into tapped threads on either side of the short piece of bar and the sleeve has slots to allow the eyelets to freely move up and down)


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## HightonRidley (30 Nov 2022)

Homeless Squirrel said:


> Far better is to have tube with collar inside running on a threaded drive bar(Lathe gear/vice/clamps etc type shaft)pitch/thread would need to be relatively shallow for micro pitch and ease of driving load as step threads equals higher drive load and less fine tuning.
> Run if off a reduction gear either cogs/chain or bevel and can reasonably easily find suitable candidates to "Recycle" ooops someones nicked me windscreen wiper motor!


Thanks for those ideas, @Homeless Squirrel. What you're describing sounds like a linear actuator but with rotation thrown in. If it is, I did consider using one but the complication is in reversing the motor to bring everything back to the starting point and then re-reversing it to get it going up again on the next day.

All things considered, the simplicity of the helical slot approach wins hands down - except cutting it in the first place!!!


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## HightonRidley (30 Nov 2022)

niall Y said:


> Could this not be done on a milling machine? By attaching the previously made aluminium version , firmly to the end of a stainless steel tube, and improvising a cradle to hold the assembly down, then by the use of a fixed pin located in the original. rotating the tube will make ,it follow a fixed a cutting path. Just a suggestion.


I like the way you're thinking, @niall Y. I don't have access to a milling machine


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## sawtooth-9 (30 Nov 2022)

Homeless Squirrel said:


> Plasma cutter or even water jet,


I suspect plasma cut will be too rough.
Water jet would work, but my experience is that the width of the cut may not be accurate enough and the finish will be slightly serrated .
I had a similar exercise with cutting a scroll into 5 mm thick stainless steel. Water jet was OK for this job, but milling would have produced a better quality cut.
If you want a smooth, accurate spiral you may have to find someone with a CNC mill or have it spark or wire cut.


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## Jameshow (30 Nov 2022)

HightonRidley said:


> That's a great thought, thanks for suggesting it @Inspector


That won't work as when you roll it the routed section will bend much more easily, unless heated till red hot?


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## Ttrees (30 Nov 2022)

Linus said:


> Could it not be cut using an angle grinder and cutting disc?


If it's the case of buying a whole length to obtain the required length,
then I can't see why not, as a small angle grinder is near a necessity.
One could make a jig to hold the tool, as it's got regular thread on both sides on all.

Some tape with trial and error, edit _a drill bit looks like its perfect for alignment somehow?_

would get the alignment sorted, using thin 1mm discs.
The possible trick to it would not be cutting past the material as that would remove unwanted material.

I've seen a new disc on youtube, which looks rather indestructible,
but I'm thinking smaller diameter would be more precice,
wondering if they make'em ?
Hopefully you have a vice, I have identical ones which has proven to be an asset for bodge engineering using the angle grinder.

One could make steadies if one does not have such luxuries,

I've done similar in the past, not suggesting you do below, having a bit more room for error on this operation, I would have no bother making a more rigid thing for something needing more precision.
Not suggesting rigging a grinder upto a drill, it turned out to be easier to do this kinda thing on the bench.










What better excuse to buy a grinder?
Get some files too, as it sounds like you're ones are either dull or too fine.
Perhaps a half round for the ends, and something not too wide for any cleaning of the long cuts, perhaps a triangular or square file for the job.


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## ChaiLatte (30 Nov 2022)

Jameshow said:


> That won't work as when you roll it the routed section will bend much more easily, unless heated till red hot?



You would not necessarily have a rectangle of material with a diagonal slash in it.

You could have a parallelogram, such that each sloping side is one edge of the slot, with a projections top and bottom to close the slot and to form the solid 360 - 220 = 140 degree parts of the tube.

Look inside an empty toilet roll and see how the cardboard tube is made - if it was fabric, we would say it was cut on the bias.

The method is sound, it is just the combination of thickness (3mm) and small diameter (25mm) that makes it very difficult in practice. If it were much bigger diameter or the material much thinner, it would be easier.


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## sploo (30 Nov 2022)

Putting the tube on a lathe, and a die grinder or router mounted to the lathe toolpost might be a solution - but only if the lathe could form a screw thread of the required pitch. I suspect the pitch wouldn't be within the range of most lathes though.

I have a CNC machine with a DIY 4th axis, but it's not capable of cutting steel, so that's no good.


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## ChaiLatte (30 Nov 2022)

sawtooth-9 said:


> If you want a smooth, accurate spiral you may have to find someone with a CNC mill or have it spark or wire cut.



Please, do you have experience with wire EDM? I do not but would think a one-sided slot in a tube might not be possible with a wire machine. What path does the wire follow? Thanks.


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## ChaiLatte (30 Nov 2022)

sploo said:


> ...but only if the lathe could form a screw thread of the required pitch.



You can work out the pitch as 360/220 * 80 = 131mm pitch, so somewhat tricky on a lathe with let us say a 6mm pitch leadscrew. It would be possible by reversing the drive path and using the leadscrew to turn the spindle, but the change gears 131/6 approx 22:1 ratio would be difficult (normal maximum ratio is something like 0.5mm pitch on a 6mm leadscrew or 12:1 ratio, so it would need nearly twice that much).


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## TFrench (30 Nov 2022)

Sounds to me like you need either a tube laser company as someone suggested or (and I think this is probably easier) someone with a CNC mill with a 4th axis. It's the sort of thing that would have been done years ago with a driven dividing head, lots of calculation and half a day or so of setup on a manual machine, but can be done now in 5 minutes on the right machine.


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## Ttrees (30 Nov 2022)

TFrench said:


> Sounds to me like you need either a tube laser company as someone suggested or (and I think this is probably easier) someone with a CNC mill with a 4th axis. It's the sort of thing that would have been done years ago with a driven dividing head, lots of calculation and half a day or so of setup on a manual machine, but can be done now in 5 minutes on the right machine.


 I would'a thought they might have used an equally sized drill and use some follower tool on the mill?


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## frogesque (30 Nov 2022)

I'm puzzled. The usual approach for a solar tracker is to have an axis pointed to the Pole Star and rotate round the axis once per Sidereal day. Depends somewhat on the magnification you are using but the drive is usually via tooth wheel and a worm drive on a stepping motor. For very high magnification you may get some 'cogging' (a bigger problem for clockwork drives) with long exposures but it can be reduced with the addition of a flywheel. 

Look up equitorial drives, loads of both commercial and DIY jobs. 

The other solution is to have two independent dives, one for azimuth, the other for elevationThese are more suitable for tracking planets, the moon, comets and other bodies that appear to move against the stellar background. Think most GTo telescopes use this system.


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## frogesque (30 Nov 2022)

Another thought if yo wish to use your original design. 

Obtain, beg, borrow, steal or last resort buy a length of stainless steel keyway bar and with a bit of heat and pesuation put a twist on it. Fairly basic blacksmith job although precision might be a challenge.


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## TFrench (30 Nov 2022)

Ttrees said:


> I would'a thought they might have used an equally sized drill and use some follower tool on the mill?


"follower" tools in mills are pretty rare. Deckel made some pretty monster size pantograph die sinkers but they're rare, and judging by how many are left, probably weren't all that good. I think the driven dividing head is the way it would have been done with any precision - the head is linked to the travel of the table, so as the table traverses the dividing head rotates a corresponding amount. 4th axis on a CNC works the same way, just without the calculating of gears and massive setup time.


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## Homeless Squirrel (30 Nov 2022)

HightonRidley said:


> Thanks for those ideas, @Homeless Squirrel. What you're describing sounds like a linear actuator but with rotation thrown in. If it is, I did consider using one but the complication is in reversing the motor to bring everything back to the starting point and then re-reversing it to get it going up again on the next day.
> 
> All things considered, the simplicity of the helical slot approach wins hands down - except cutting it in the first place!!!


Tripole switching used in so many electrical circuits Electric car windows is one they go down and have to go back up.


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## Homeless Squirrel (30 Nov 2022)

sawtooth-9 said:


> I suspect plasma cut will be too rough.
> Water jet would work, but my experience is that the width of the cut may not be accurate enough and the finish will be slightly serrated .
> I had a similar exercise with cutting a scroll into 5 mm thick stainless steel. Water jet was OK for this job, but milling would have produced a better quality cut.
> If you want a smooth, accurate spiral you may have to find someone with a CNC mill or have it spark or wire cut.


Plasma cutting is smooth those metal stencils you see of printed signs are laser cut


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## sawtooth-9 (30 Nov 2022)

ChaiLatte said:


> Please, do you have experience with wire EDM? I do not but would think a one-sided slot in a tube might not be possible with a wire machine. What path does the wire follow? Thanks.


 I have not done wire cutting myself, but worked with a fellow who I am sure would be able to do this.
You program the wire path to cut the shape and depth. I guess you would need to have a means of rotating the tube as it is cut, as I think these machines are 3D
Just suggesting a possible alternative, buy probably cost prohibitive


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## imageel (1 Dec 2022)

I'd have thought a better solution to what you have designed is to use a lead screw/nut similar to those used on metalwork lathes to allow the saddle holding the toolpost to traverse the length of the beds. There are lots of companies who sell these quite cheaply since depending on the accuracy you require they are commonly used in modelmakers 3D 'CNC' printers. One of them a suitable length and a NEMA stepper motor and a couple of limit switches and job-done! ...well maybe a few lines of code and an Arduino would sort it


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## Fergie 307 (1 Dec 2022)

Two ideas. You could do this easily on a milling machine using an index st up to turn the tube as you adbance it. Essentially cut a series of overlapping holes along the slot, then tidy up with a file. Secondly Crosman made a semi auto pistol where they used a square section bar with a follower consisting of a plate with a square hole which ran on the bar. The bar was simply twisted so that as the follower went to and fro it followed the twist and so turned through an arc to operate the action. Have a look at articles online about Crosman 600 pistol to see the idea. Might be a simpler way of achieving the same thing.


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## Fergie 307 (1 Dec 2022)

Following on from above, if you want to stick with the slot idea find a decent gunsmith. Loads of firearms use this sort of idea, and slots for bolt action etc. They should be very familiar sith how to do it, and have the tools. Always makes me grin when people immediately suggest " you need a laser CNC flux capacitor to do this" You can see similar things that were hand made hundreds of years ago on clocks, guns and so forth by someone with some skill and basic tools.


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## Fergie 307 (1 Dec 2022)

TFrench said:


> Sounds to me like you need either a tube laser company as someone suggested or (and I think this is probably easier) someone with a CNC mill with a 4th axis. It's the sort of thing that would have been done years ago with a driven dividing head, lots of calculation and half a day or so of setup on a manual machine, but can be done now in 5 minutes on the right machine.


I would agree entirely for production, but likely to be prohibitively expensive for a one off prototype, unless you can find a keen diy type who has such a machine and would do it for you just for the fun of it, which I doubt.


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## Fergie 307 (1 Dec 2022)

The other thing I would say is why stainless? I can see your reasoning for a finished product, but you are just making life harder for yourself with a prototype. Much easier to make it in CDS tube and then get it plated if you want a degree of corrosion resistance, or maybe even brass or, if strong enough, plastic. All much easier to work with if you are trying to make it yourself, and are just looking to prove the concept works.


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## Fergie 307 (1 Dec 2022)

Jameshow said:


> That won't work as when you roll it the routed section will bend much more easily, unless heated till red hot?


Not if you are using a proper rollimg machime. This is exactly how the barrel shrouds for the Browning machine gun were made during the war. Flat sheet with holes punched into it then cold rolled into a tube and welded along the seam. The little Clark etc folding machines have a tube rolling function which will do this sort of thing.


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## Jonm (1 Dec 2022)

Would a metal cutting chop saw do it with a series of cuts. Bit of care needed to line it up when the tube is rotated. Obviously two cuts would be required. Drill a holes at the ends before cutting the slots.


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## evildrome (1 Dec 2022)

Hang on.... if I'm seeing this correctly the 'lift' component is just a function of the way you've decided to deal with the rotation.
If all thats *actually* required is the rotation (about 270 degrees?) then why not just mount the shaft in a bearing and rotate it with a small servo? Either geared or direct drive.


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## Fergie 307 (1 Dec 2022)

evildrome said:


> Hang on.... if I'm seeing this correctly the 'lift' component is just a function of the way you've decided to deal with the rotation.
> If all thats *actually* required is the rotation (about 270 degrees?) then why not just mount the shaft in a bearing and rotate it with a small servo? Either geared or direct drive.


Does seem a case of engineering overkill, not sure exactly why this design has been chosen. But hey the original question was how to cut a helical slot in a tube, and some interesting ideas have come out of it.


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## ChaiLatte (1 Dec 2022)

TFrench said:


> It's the sort of thing that would have been done years ago with a driven dividing head, lots of calculation and half a day or so of setup on a manual machine...



Minimal calculation. Assume 5tpi leadscrew and 40:1 dividing head. 38:59 gearing between leadscrew and dividing head input is near enough. Setup is quick as unlike a helical gear, you do not need to angle the table.

Working out below:

He wants 80mm over 220 degrees, so 131mm or 5.154" lead (7200/1397 exactly). A 1:1 ratio between screw and DH will give 8" lead. We thus need to gear down 5.154/8 (0.6442 or 900/1397 exactly). Using a continued fractions calculator, 38/59 (0.6441) is close enough.


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## Fergie 307 (1 Dec 2022)

Have to say having looked at your videos and read the description i feel i must be missing something. Surely this could be accomplished at a fraction of the cost and complication by just using a suitably geared turntable?


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## Jonm (1 Dec 2022)

Jonm said:


> Would a metal cutting chop saw do it with a series of cuts. Bit of care needed to line it up when the tube is rotated. Obviously two cuts would be required. Drill a holes at the ends before cutting the slots.


I was thinking of something like this 









Titan TTB599BNS 2100W 355mm Electric Chop Saw 220-240V


Order online at Screwfix.com. Powerful and portable saw for the cutting of steel, steel pipe, angle iron and box section. Features quick-release vice adjustment and easy blade replacement. Large spark guard for improved safety prevents backward scattering of sparks. Cutting head can be locked in...



www.screwfix.com





Set it to the angle of the helix, clamp tube in place, cut making sure disc does not cut other side of tube. Rotate tube, move it a bit and cut again. Seems fairly simple. Am I missing something?


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