45Views2Replies

Author Options:

Parabola Jig? Answered

I want to make a parabolic dish out of wood.

Given a glued-up stack of plywood (each layer being a ring cut to approximate shape) I want to use a router to cut a parabola out of its center.

Does anybody know of a jig or mechanism where a person could accurately do this?

If you can excuse my MS Paint graphics, above is a side-view.

Discussions

0
Josehf Murchison
Josehf Murchison

10 days ago

Parabolic dishes have a focal point in front of the dish.
All you need is a tether from the focal point to the router.
A simple tripod and rope.

0
Downunder35m
Downunder35m

20 days ago

You already got the picture ;)
A 3D CNC router will do this with ease.
On a hobby level not so much, but you can cheat ;)

You know the focus point of the finished dish . or its center point.
Means you build a rig to hold your hobby level router with a ball type router bit.
The mount point is the same as the center of the sphere your dish would form.
A ball swivel and rod give you the "axle" you need.
Have the rod with a matching outer or inner one that is threaded that holds your router steady to the axle with the router bit in its center.
Imagine your grey ball being the router bit, the yellow box is your router - you add a "pendulum" to the center of your sphere ;)
Adjust the length of the rod to first only reach outer edges of the plates, then slightly increase the length one you can't take any material off any more.
The key is to stop once your router bit creates a nice even surface of the desired curvature.
If you need precision you need to include something to keep track of the real distance from the mount point to the tip of the routing bit.