Pantograph spring balance
This is why I have a spring balance on the pantorouter to help lift up the router.
I arrived at this shape a long time ago, and in the past always made it using paper templates, but having built this one so far without printing anything, I drew the spring cam from dimensions as well. I approximated the main lobe of the cam as a circular arc.
I compared it to the cam on my old pantorouter and was satisfied that these were sufficiently similar.
The cam is attached to the long pantorouter link with a wooden offset or spacer, which I'm drilling the holes in here. I had to slightly angle the screw holes to be able to drill them with my drill press. I guess I could have just drilled them from the other side too.
The cam has a string attached to it, which goes through a hole with a knot on the other side to hold it in place. The spring attaches to the edge of the sliding base, but it attaches right where the template holder goes.
So I took the template holder off, drilled a hole and finished the cuts with a bandsaw. I knew I needed to put the spring there all along, but I was too keen on trying it out to bother cutting that slot earlier.
Another cam attaches directly to the short link. Rather than drawing that shape again, I used the cam I already made to trace the shape onto the new part, which I'm making from a scrap piece from cutting out the pantograph.
With both springs attached, the pantograph compensates for most, but not all of the weight of the router. It makes it much more comfortable to operate. It's also nice when the pantograph comes to rest with the router in the bottom position, whereas, on the metal pantorouter the springs are strong enough that the router comes up when you let go of the handle.
That said, if the springs were to over-compensate for the weight of the router, you would always have to push down on the operator handle a little, and that would be more comfortable than pulling it up, even if you have to pull very little.
The cam part is on its own shorter piece of shaft. I used a separate piece of shaft to make it easier to put the whole thing together.
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