[muleskinner]

Knickknack - if you think about it, as the work piece swings through the arc it stays a constant distance from the pivot point and thus constant in relation to the router bit, hence a perpendicular dado. At least that's what my morning fogged brain is telling me. After a couple more cups of coffee I may have to rethink it.

 

[KnickKnack]

In fact, upon more research, I think this pivoting thing is what's described in this patent - Patent number: 5988242

Which leaves me, of course, wondering what kinda line my idea would cut.

 

[oldnovice]

The set ups he showed worked because the router bit is located at the exact center between the pivot point and the set up point. Basically working in a similar fashion to the old center finders and the mortising router base Rockler sells.

The center pin (sharp point) is the router bit, one end pin is the pivot point, and the other is the set up point. The greater the distance between the two pins the less error will be introduced into the set up. Obviously, the router bit must be dead center.


In light of the Rockler tool and existing center finders I am surprised that this patent was not considered prior art!

This does not answer the cross cut!

 

[muleskinner]

Yeah, Hans, it almost seems like he's patenting geometry.

 

[wormil]

KnickKnack, I've never been good with gears so I can't tell what your setup would do but I think you are on the right track. After looking through the patent, I believe the fence is moving along a logarithmic arc.

 

[oldnovice]

Contrary to what the video shows, the changeover from cutting along the fence to cross cutting is not that simple as the video would have the viewers believe.

I read over the patent discovered the following:

1. The set up for cutting along the fence is pretty straight forward if the pivot points, and the router collet are aligned to some degree of accuracy.
2. Change over to cross cutting requires the left pivot point to be replaced by a slot and a follower pin placed in the fence to follow an arc cut in the router table top and is defined by the formulas shown in sections 5 and 6 (I could not recreate the formulas without the superscript and subscript symbols in this post).
3. If there are errors in the table slot the cross cut will not be normal to the workpiece edge!

At this point I stopped as I don't want a long arc cut into my Benchdog cast iron TS extension wing!

 

[wormil]

Good detective work. I meant to sit down this weekend and go through the math but my wife wanted her new bathroom finished instead, can't blame her.