Help with a jig

[James Hart]

I hope i can desribe this well.

I'm putting oak treads on a neighbors spiral staircase. Not a full 360 or anything, just a gentle turn.

Each tread has a gentle concave curve on the left side and convex on the right.

I'm planning a template jig out of MDF. Will have a template for each end that I'll scribe to the curve. A lip on the front to register to the front edge of the stair. I plan to trim the template to fit, then use it with a pattern bit on the router to finish trim the tread.

Question; I want a stretcher of some kind between the two end templates that will allow me to push the two end templates flush, then lock the stretcher to capture the right width of the tread. What I can't figure out is how to lock the stretcher and still be able to lay the template flat on the router table.

I'm using a pattern bit rather than flush trim because I also have to shape the lip of the tread, which is 5/4, the tread is 4/4. The tread/template won't lay flat on the table if the template is on top.

Thanks,

Jim

[Rob Will]

James,
My daughter just made 20 tapered fan blades for her school project.

The part being cut is sandwiched between a 3/4" ply base and the pattern on top. The pattern is mounted on hinges with enough space in between for the thickness of the part. Everything is held together with toggle clamps.

The way it worked was to run one straight side, then flip it over in the jig. That gave us a straight line to register against the back edge of the jig. Then, we ran the ends and the opposite straight side. We got a finished part with no holes and using no sticky tape.

Maybe you can modify something like this to make the stairs. A rabbet inside of the jig would accept the 5/4 lip and solve the problem of not laying flat on the router table. Your part would be in the middle.

Rob

[James Hart]

Rob,

Fantastic response, thanks. I can't say I've completely solved in my mind the challenge of getting the length of the stair and the right curves on each end, but your thoughts solve the problem of having the piece have to lay template-face-down on the table.

I think I'm close.

thanks again,

jim

[Rob Will]

James,
Maybe you could add "adjustable" end templates on top(?).
I added two more pics to the original post.

Thanks,
Rob