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

[HightonRidley]

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

 

[Inspector]

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

 

[deema]

You need a tube laser cutting company.

 

[HightonRidley]

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

 

[HightonRidley]

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

 

[Linus]

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

 

[Lorenzl]

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.

 

[Spectric]

What about a die grinder or even a Dremel !

 

[Spectric]

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.

 

[Homeless Squirrel]

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,

 

[Yojevol]

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

 

[Homeless Squirrel]

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!

 

[niall Y]

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.

 

[HightonRidley]

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

 

[HightonRidley]

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.

 

[HightonRidley]

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)

 

[HightonRidley]

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!!!

 

[HightonRidley]

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

 

[sawtooth-9]

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.

 

[Jameshow]

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?