Grasshopper Skeleton clock scape wheel cutters

[Ernienoatrainz]

Does anyone know how this shape can be ground for the escape wheel cutters for the Grasshopper clock by Smith? Book title “How to Make A Grasshopper Skeleton Clock”

 

[gradient]

From the sketches it looks like it might have been done freehand on a grinding wheel. Might also make use of a rotary table to get the large curve. You could also grind about half of the thickness of the rod off, blue it, then use a paper template to scratch the curve in and finish by hand grinding.
Good luck

 

[ttabbal]

I'll take a stab at it... Start with 1/4" HSS round, or tool steel and harden/temper.

Make a jig to hold the tool and grind the radius. It could be a simple jig that holds the tool at 5/8" or 1.25" and pivots.

Grind the flat, with some back rake. It looks like 15 degrees is called out? That should work well for most material.

Grind the side rake/relief. Looks like 5 degrees back, 15 degrees under, but I doubt it's critical. Don't go too nuts, you just want it not to rub. When looking tip-on, you want to see the tool fall away from the edges.

Hone, putting the radius on the tip.

While I was typing, @gradient mentioned grinding the flat and laying out the radius on the flat. That might be easier.

 

[francist]

My first thought was to mount the blank on a small sacrificial holder of wood, say, with a pivot set for the radius and gradually advance it in to the wheel. But the more I thought about that the more work it sounded like, and in the end I’m thinking along the lines of @gradient and just free-handing it using a sheet metal template as a reference. The curve and the opposing face are really the only tricky ones, any others are just relief.

-frank

 

[Ernienoatrainz]

I have lucked out as a builder of this clock as offered me his cutter to use. Thanks all to the ideas here. Ernie

 

[pontiac428]

I could grind the whole part on my Deckel clone grinder, including the radii. The small escape wheel cutter radius would be pushing the limits for radius, one might need to fab a quick 90 degee adapter to hold the work for that sweep, but still doable.

 

[JRaut]

If you’d rather buy rather than making your own, I believe PP Thornton makes a form-relieved cutter for that sort of escape wheel. Worth perusing their website.

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Cutter Sharpening Service Our quality PP Thornton cutters are very durable and cost-effective to sharpen so that you continue to get the best results. £35.00 exc VAT Products Testimonial It may not seem like it to you, but you have a talent that is exceptionally rare in this world. Josh Huether...

ppthornton.com

 

[markba633csi]

Unless I'm missing something, the exact shape of the cutter is not critical. Many variations are possible, if it creates the desired gear tooth profile
If the cutter radius forms the back of the gear tooth then yes, it needs to conform to the shape
-Mark