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Old 24th March 2009, 04:33 PM   #1
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Default oval cutouts

So I'm staring at my circle jig and an oval driver and thinking hmnn....
Any good methods for routing oval cutouts?

Help appreciated.

-MrKramer
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Old 24th March 2009, 04:43 PM   #2
soongsc is offline soongsc  Taiwan
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The distance from any point on an oval to the two focal points will add up a constant value.
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Old 24th March 2009, 05:19 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

Or in other words if you put a loop around two spaced nails and
then go in a circular motion with a pencil you will get an oval.

/sreten.
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Old 24th March 2009, 05:25 PM   #4
indymwt is offline indymwt  United States
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Default oval cutouts

rockler sells an ellipse jig and there are serveral diy on the web.

in between clients or i would post some links search ellipse router jig and you should find several

Mark
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Old 24th March 2009, 07:57 PM   #5
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Default Re: oval cutouts

Quote:
Originally posted by mrkramer
So I'm staring at my circle jig and an oval driver and thinking hmnn....
Any good methods for routing oval cutouts?

Help appreciated.

-MrKramer
If you don't have a router table make one. A moderate sized piece of your favorite sheet good drilled out for your router mounting pattern and to clear the bit will do; do what you need to to affix it to saw horses, a workmate, garbage can, etc. Less than 2x2' would do for small pieces.

Trace the driver outline on a piece of scrap 3/4" MDF. Cut the outside over-sized by no more than 1/8" with your jigsaw. Cut out the center to clear the driver surround. Affix the wood to the driver with double-sided carpet tape. Cover the driver with cardboard or something if it has an exposed magnetic gap as on a dome tweeter. Trim with a flush-trim bit in your router table to make a male pattern. Feed the work into the cutting edge.

Affix the male pattern to a larger piece of scrap that will be big enough to support the router base to make a female pattern using a guide bushing. You may need additional pieces of scrap to support the router.

You'll need to either attach both the waste piece of the female pattern and outside to a sacrificial work surface, or don't cut all the way through. You can leave a thin scrap connecting the pieces and cut it with a jig saw and then use your router + bearing guided bit (top or bottom) to remove the excess.

Make progressively deeper passes and plunge while moving if you're not using a spiral bit.

Use a guide big enough to provide clearance; for instance 7/16" with a 1/4" bit. The resulting female template will be over-sized by the bit diameter plus the difference in radiuses between bit and guide OD.

When using the female template you need to undo the offset from the bit and move inward two bit diameters, so add that to the original bushing size. Starting with a 1/4" bit and 7/16" OD bushing you'd move to a 15/16" OD bushing. Lee Valley sells a 7/16" ID, 15/16" OD brass bushing for this purpose which will let you use the same setup for female template + product and guarantee the errors due to router bushing + bit concentricity errors cancel out when you maintain the same router orientation for cutting your production parts and female template. You want to move the router clockwise around the pattern so it pulls itself into the edge.

The limits here are that the smallest radius on your recess can't be less than that of the guide bushing you use to cut the final product.

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Old 24th March 2009, 08:41 PM   #6
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An oval and an ellipse are not the same (at least in my mind). An ellipse is how people describe it here, the distance to the two focal points is always constant. I always thing about an oval as two semicircles with straight lines between them. If it in fact is an oval you want to make it should be straightforward to route out two circles with a certain distance between them and then set up a simple guide to do the straight cuts.
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Old 24th March 2009, 08:56 PM   #7
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Oval is a pretty broad term. Remember it came from ovum or "egg shaped".

Yes an ellipse is a type of oval. What you are describing is not an oval but for the life of me, I can't remember the name for it. I thought it was epitrochoidal but that's not it. It's the shape of a running track. I'll see if I can dig it up.
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Old 24th March 2009, 09:01 PM   #8
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Old 24th March 2009, 09:02 PM   #9
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I stand corrected on the definition of an oval I think my definition came from how we used the term in Norway, when I lived there. Maybe the OP could specify what kind of shape we are dealing with here?
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Old 24th March 2009, 09:04 PM   #10
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If the driver is round, it's likely to be truncated or pincushion.
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