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

[Ttrees]

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.

 

[ChaiLatte]

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.

 

[sploo]

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.

 

[ChaiLatte]

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.

 

[ChaiLatte]

...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).

 

[TFrench]

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.

 

[Ttrees]

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?

 

[frogesque]

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.

 

[frogesque]

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.

 

[TFrench]

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.

 

[Homeless Squirrel]

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.

 

[Homeless Squirrel]

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

 

[sawtooth-9]

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

 

[imageel]

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

 

[Fergie 307]

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.

 

[Fergie 307]

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.

 

[Fergie 307]

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.

 

[Fergie 307]

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.

 

[Fergie 307]

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.

 

[Jonm]

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.