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

[MorrisWoodman12]

I've been asked to help at our local children's respite centre by making some sensory boards. One particular version has my mind going around in circles - well ever decreasing spirals really. How do I cut the spiral like that in the picture below? Draw the spiral onto a board and try and trace it with my router? I don't have a CNC or any of Matthias Wandel's complicated geared machines ( or the inclination to build one). I'm not sure of my free hand router technique so can anyone offer me some advice in order to cut a clean/smooth curve?
Thanks
Martin

 

[Luke Barnard]

I think that's a big cut to do with a freehand router and I'm not confident I'd get good results. If I were to have a go at this, I think I'd be inclined to try bandsawing it first.

 

[Yojevol]

I would be inclined to produce CAD drawing and from that make a 6mm MDF router pattern by bandsawing and hand sanding to finish. A bit laborious but easier than trying to cut and finish the final workpiece in one go.
If I can help with a drawing get in touch.
Brian

 

[Spectric]

I think the template is going to be essential and it will require multiple passes with a decent router bit but I would also look at removing some of the excess material first. Maybe a jigsaw or a series of drilled holes.

 

[CaptainBudget]

I would be inclined to produce CAD drawing and from that make a 6mm MDF router pattern by bandsawing and hand sanding to finish. A bit laborious but easier than trying to cut and finish the final workpiece in one go.
If I can help with a drawing get in touch.
Brian

I'd seriously debate going one stage further and giving the CAD file to a laser cutters. They can then cut it out of plywood/MDF/plastic/Alu ~6mm thick and you can use that with a router. The cost of the laser cut part would likely more than offset the time required to do this by hand and would probably produce smoother curves.

I'd also second tracing the template on the material and rough cutting the bulk of the waste out with a bandsaw before finishing with a decent router bit guided by the template.

EDIT: If it's about 1ft/300mm DIA and 6mm thick I'd expect to get some change out of £25.00 +VAT for that in 6mm M/steel or aluminium as a very rough guess if that helps...

 

[Phil Pascoe]

Presumably the ball is trapped, so the undercut is difficult to do with a router.

 

[sploo]

Looks like it's trapped with a sheet of clear perpex on the front, so it could be done with a straight plunge.

 

[Essex Barn Workshop]

I'd seriously debate going one stage further and giving the CAD file to a laser cutters. They can then cut it out of plywood/MDF/plastic/Alu ~6mm thick and you can use that with a router. The cost of the laser cut part would likely more than offset the time required to do this by hand and would probably produce smoother curves.

I'd also second tracing the template on the material and rough cutting the bulk of the waste out with a bandsaw before finishing with a decent router bit guided by the template.

EDIT: If it's about 1ft/300mm DIA and 6mm thick I'd expect to get some change out of £25.00 +VAT for that in 6mm M/steel or aluminium as a very rough guess if that helps...

Depending on overall size, I can do that for you at about 4mm thick mdf or ply. as it is such a worthy cause, Materials and post only. The bed of my laser is a bit over A4 to give an idea.
All i need is the pattern sent to me as an SVG file.

 

[Phil Pascoe]

Looks like it's trapped with a sheet of clear perpex on the front, so it could be done with a straight plunge.

Yes. Of course.

 

[Droogs]

Use a thick centre post with a cord that is securely attachted with the pin at one end and a small palm router at the other. As you keep the cord tight and rout a circle the cord will wrap around the post and shorten giving you a fibonachi spiral cut as it gets shorter

 

[Sideways]

I'd make two templates - half and half so that the curves are well supported arcs, not spirals.
I'm make them of 6 or 10mm MDF to use with a guide bush.
I'd be happy to freehand rout these (templates) with a 1/4" router to a drawn line. The templates then stop you messing up the finished piece.
I'd probably touch up the edges of finished piece freehand after using the templates to guide me through the repeated passes to cut out the bulk.
With a good 1/4" router you can freehand very successfully as long as you take light cuts.

 

[MikeJhn]

Droogs posted exactly my thoughts as I was reading the thread, but do have a look on U-Tube for cutting a staircase handrail Volute which is a fibonachi spiral.

 

[Adam W.]

I'd carve it and finish it with a lovely faceted texture, then burnish it so that it is soft and silky.

 

[Cooper]

I'd carve it and finish it with a lovely faceted texture, then burnish it so that it is soft and silky.

No gold leaf then Adam?

Droogs is spot on.
It reminds me of my days teaching Geometric and Engineering Drawing.

 

[Sachakins]

 

[Ian down london way]

Depending on overall size, I can do that for you at about 4mm thick mdf or ply. as it is such a worthy cause, Materials and post only. The bed of my laser is a bit over A4 to give an idea.
All i need is the pattern sent to me as an SVG file.

Inkscape is a great free software package for creating SVG files. A bit of a steep learning curve, so I'd be happy to create a file if you like. I'd need some size information, in particular, what width of channel (or diameter of the marble) and the overall size

 

[Sachakins]

To be honest you don't need the pantograph arm. Just a thick post at centre, string from post to router, keep taught and guide router round. You get the exact same Fibonacci curve.

 

[Sgian Dubh]

To be honest you don't need the pantograph arm. Just a thick post at centre, string from post to router, keep taught and guide router round. You get the exact same Fibonacci curve.

I think a pantograph rig would be required to work with a router to create something very close to the form and dimension that's shown in the original photograph. Without the pantograph the router would rotate around a central post to which the string is attached, as well as being attached to the router, and would stop cutting when the router base bumps into the post. This would mean the finished item would have to have a much larger diameter than the original along with much larger central lump of material.

This larger scale might be acceptable to both the respite centre and to the users, although I suspect only the OP can find that out, and it certainly eliminates the need to make a pantograph, which simplifies the task, and fits in with the OP's stated disinclination to build some sort of complicated geared machine. I suspect the easiest option would be to get it (them?) knocked out on a CNC machine, but no doubt there'd be a cost, which may also be unacceptable. Slainte.

 

[Tris]

I might have missed something but couldn't you use a printed template, scrollsaw it out, thin ply backing and a perspex cover. A simple bobbin sander rigged up on a drill press to smooth it out?

 

[Sachakins]

If its a one off, then scroll saw and lots of sanding.
Second easiest option is 4mm MDF, scroll saw groove big enough for a bushing in router. Attach this to wood and do a few shallow passes.
Third easiest way, combine both above. Rough cut spiral with scroll or coping saw. Make template as above but to finished groove size, attach to wood and use a flush trim bit and bearing to finish to size.

There are easy ways, if you got cnc, pantograph router etc, but the all involve money to do.