How does this work? - Ellipse Jig

Sean Wright

Member
Messages
902
Location
WNY, Buffalo Area
I just recently made a circle cutting jig for my router. I was looking through Rockler's site and I saw that theirs says it will cut an Ellipse along with a circle. I read the instructions that they posted for making an ellipse, but it doesn't make any sense to me.

Their Instructions: http://images.rockler.com/tech/RTD10000285AA.pdf

If anyone can explain how this works, it would be appreciated.

It would be great if I could use the jig that I made to cut both circles and ellipses. :thumb:
http://familywoodworking.org/forums/showthread.php?t=3560


Here is the product that I am refering to:
http://www.rockler.com/product.cfm?Offerings_ID=17282
Designed for use with just about any plunge router, the Rockler Ellipse/Circle Router Jig lets you cut circles and ellipse shapes over a wide range of dimensions and proportions. Set up takes only a couple of minutes and is virtually math-free. Using the jig is just as easy. As you move the router through the cut, the jig's sliding dovetail mechanism keeps the router precisely on the cut line.
Maximum length for major axis is 52".
Maximum difference between minor and major axes is 8".
Includes jig arm, jig base, two dovetail keys, and two locking pivots.
Single pivot can be locked to make circles up to 52" diameter.
Pre-drilled for Porter-Cable 690/890 routers or routers with 6" base footprints.
Made from 1/4" thick phenolic for durability.
 

Norman Hitt

Member
Messages
1,813
Location
Odessa, Tx
Sean, there have been some plans in some of the WW mags in the past to build a jig for cutting elipses, and I have seen at least one on the web, but can't seem to remember which site it was on. Your circle cutting jig could be used as "Part" of the jig to cut elipses, but you would have to make the shuttle block that is the black square in the LV picture with the blue slides in it, and you would also have to make a spacer block to go under your router to raise the trammel up at that end to match the thickness of the elipse shuttle block. You connect the trammel in two places, (at each of the blue slides in the shuttle block). When you rotate the trammel around, one shuttle block cannot move but the other one will until it is at the end of it's travel, then the other one will move in it's slot, (due to the angle of the tramel at that point). These movements vary the radius as the trammel moves around in a circle, forming the elipse.

It's kind of like a puzzle with a crank on it. As you turn the crank, one slide moves in it's slot in one direction, (during the first 90* of crank travel), and then the other moves in it's slot, (for the next 90* of crank travel, then the first one moves back the opposite direction, (for the next 90* of crank travel), and then the other moves back in the opposite direction as you complete the 360* turn of the crank.

(probably not a very good description, but hopefully you will get the idea). :dunno:
 
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Sean, there have been some plans in some of the WW mags in the past to build a jig for cutting elipses, and I have seen at least one on the web, but can't seem to remember which site it was on.
IIRC, it was somewhere on Popular Woodworking web site. I do have a printed hardcopy at home somewhere.
 

Sean Wright

Member
Messages
902
Location
WNY, Buffalo Area
Norman,

Thanks for the explanation! :thumb: :thumb:


Or, as seen here ... a crank (meaning me :wave:) with a puzzle on it!



Toy made from scraps circa 2000. Picture taken 10 minutes ago.
Kerry,

Thanks for the picture. :thumb: I think I understand how it works now.

-The router would be where the handle is (with a block under the trammel the same height as the center block)
-If I undestand correctly, you would use 2 holes in the circle jig and put pins in them so that they rotate, one in each of the dovetail blocks.
-As the router (handle) is turned one dovetail block is held in place and the other slides from one end of the track to the other. When it gets to the end of the track it will be held in place and the other block will be pulled in the track perpendicular to the first track... creating an elisple where the router is cutting.

If I undertand this correctly you never have to move the blocks by hand once it is set up. Moving the router (handle) takes care of moving the blocks for you.

Let me know if i got this right..... Thanks !
 
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Sean Wright

Member
Messages
902
Location
WNY, Buffalo Area
I know that the idea of the circle jig is for it to rotate around a center pin, but based on this design of the elispse cutter it looks like the center block should stay fixed.

Ok, now that I get the concept.... How do you keep the center block attached to the work piece for the cut?

--double stick carpet tape ?
--hot glue ?

This is assuming that you want to keep the inner piece. If you wanted to keep the outer piece you could just screw the center block to the inner piece.
 

Kerry Burton

Member
Messages
1,129
Location
Orem, Utah
Ok, now that I get the concept.... How do you keep the center block attached to the work piece for the cut?

--double stick carpet tape ?
--hot glue ?
Sure - whatever works best for the piece. The first time you do this will make one time more than I have done it, so a word from someone with actual experience would be good. But I think you're on the right track.

[Later ...] I should have reviewed the Popular Woodworking page again.

Jim Stuard for Popular Woodworking said:
Add rubber feet on the bottom of the jig to keep it from moving while in use.
Of course, their particular jig is just intended for DRAWING an ellipse with a pencil. If it were me, hooking up a router instead of a pencil, I'd probably go the double-stick tape route.
 
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