Going around ever decreasing spirals until disappearing up.........

[MorrisWoodman12]

Thank you for all of your answers chaps (and chapesses if you are there). I really only posted the picture as an example of A spiral, I don't need to have the trapped ball feature just a spiral that can be felt. So a spiral cut into the surface with a 6mm ball cutter will suffice like the result from Matthias Wandel's spirograph as linked in by @Sachakins. However I don't want to make a spirograph as well even though it maybe useful on occasion.
I like the basis of your idea @Sideways though I think I will need say two or three overlapping templates. Overlapping so that the ends can hold the ends of the walls of the arcs are held together as one piece.
I also like the thinking behind the post and string method but even with a palm router one cannot get near enough to the centre before the router body clags on the post.
Thank you @Essex Barn Workshop I may take you up on your offer: I'll keep it in mind. And thanks @Ian down london way though I find I can create SVG files using LibreCad.
I'm sorry if this all sounds a bit negative from my end. I guess I'll have to make a couple of templates. I am truly grateful for all of your suggestions and offers: if it was easy I wouldn't have to have asked - probably.
Regards
Martin

 

[slimshady]

What about two/three thin slats of timber Steamed around themselves.

Alex,

 

[Sachakins]

Thank you for all of your answers chaps (and chapesses if you are there). I really only posted the picture as an example of A spiral, I don't need to have the trapped ball feature just a spiral that can be felt. So a spiral cut into the surface with a 6mm ball cutter will suffice like the result from Matthias Wandel's spirograph as linked in by @Sachakins. However I don't want to make a spirograph as well even though it maybe useful on occasion.
I like the basis of your idea @Sideways though I think I will need say two or three overlapping templates. Overlapping so that the ends can hold the ends of the walls of the arcs are held together as one piece.
I also like the thinking behind the post and string method but even with a palm router one cannot get near enough to the centre before the router body clags on the post.
Thank you @Essex Barn Workshop I may take you up on your offer: I'll keep it in mind. And thanks @Ian down london way though I find I can create SVG files using LibreCad.
I'm sorry if this all sounds a bit negative from my end. I guess I'll have to make a couple of templates. I am truly grateful for all of your suggestions and offers: if it was easy I wouldn't have to have asked - probably.
Regards
Martin

The spirograph (pantograph) is far more versitile, have a quick look here 3-D router pantograph

 

[Stanleymonkey]

Haven't read all the replies thoroughly. Apologies if this is repeated.

Can you not cut a template in 6mm MDF on a bandsaw or scrollsaw and then use a flush trim bit on a router to copy the shape onto thicker pieces of MDF?

If it's more complex than that - surely there must be a jig like a circle cutting but on rope / chain and the rope winds up around a central pillar getting shorter as you move it around the circle and spiralling the router in.

Good luck and I hope you get this done for the kids to use and benefit from.

 

[Stanleymonkey]

Also - if a large and heavy ball is used - could you simplify it by have a spiral of dowels with spacing smaller than the ball. Lay it out and drill out the majority on your drill press and if your drill press won't reach - freehand drill the last few.