My Astromonical Miscellany

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An Improved Circle Maker

    Poorly designed circle cutter jigs for routers forced me to come up with a better circle maker.  My biggest criticisms about circle cutting jigs are 1) the router sits on the piece you are cutting, (2) they are flimsy and 3) it is difficult to make fine adjustments.
    Let me elaborate on each criticism:
1) When the router sits on top of the piece you are cutting, how do you hold the piece down and cut it?  Screw or nail to an other board?  Clamp it down? Can't it be easier?
2)  The commercially made jig I brought for my router was not strong to hold the router square with the piece.  The bit putted a small angle on the edge.  I want it square!
3)  Ok, I want to take a 1/32 of an inch on the radius.  How do I do that? That little bolt thing.  Yeah right!

    My first thoughts were along the idea of a Router Table.  I like the fact how the piece slides along a fence.  The router is firmly attach to the underneath of the table in an inverted position.  My only dislike is that router bit is in the open.  A possible safety hazard.  So I decide that I wanted the router right side up.  Next, the piece should rotate and router sit still.  Last thing, I want fine motion control.  Heck with taking off a 1/32th, how about 1/64th?
 
   So I came up with a =circle cutter with the following advantages.  1) The router is upright.  2) The bit is safety tuck away.  3) The piece rotates on a pin. And 4) The pin position's is finely control.

   A drawing is worth a thousand words.


On the left, the router sits on a board that I named the Router Base Board.  The Router Base Board in supported by four bolts that comes up from the Router Table board.  The height between these two boards can be adjusted by adding or removing nuts or washers to the four bolts.  In the middle of the drawing is the Center Pin Carriage and Center Pin.  The Carriage rides on two plastic pipes. 
Inside the carriage is a threaded wood insert sometimes called a brass insert.  It is a threaded nut with a screw threads on the outside of it.  The position of the carriage can be adjusted by a turning the threaded rod which is attached to the handle on the right.


This view is from the handle end.  You can see the Center Pin Carriage that rides on the plastic pipes.  You can also see the threaded rod that run into the center of the carriage containing the threaded wood insert.


A circle that been just made.


The Router and the Router Base Board have been removed.  The threaded rod is held in placed by two locking nuts.  One on each side of a 2 by 4.  The threaded rod is only allowed to rotate.


A view from above.  You can see the locking nuts holding the threaded rod in place.


The Center Pin Carriage.  It rides on the plastic pipes and on top of the side rails.

The handle that controls the position of the Center Pin Carriage.  The threaded rod is 3/8-16.  One rotation of the handle moves the carriage 1/16 of an inch.  A quarter of a turn moves it a 1/64 of an inch.

The back of the Circle Cutter.  The plastic pipes are threaded into the floor flanges.


An Altitude Sector ready to be cut.


The radius have been set!  The router bit is ready to be lower and start cutting.



A finish Altitude Sector for one of my small Dobsonians.

Downloadable PDF DrawingsSide View    Top View

Watch it in Action!  The Video

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This page was last updated on Oct 22, 2009.

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