# Elliptical Cove Calculation?



## MAFoElffen (Jun 8, 2012)

Figured this is where to ask this question--

The standard calculation for cutting a cove on a Table or Radial Arm Saw is attached. That calculation tells a person which angle to set a fence to be able to run a piece of work obliquely across that blade to create a certain symetric cove cut.

Does anyone know of a calculation or of an online calculator to create asymetric cove cuts?

That involves depth of cut, width of cove, width of blade kerf, diameter of blade << to get >> oblique angle across blade and tilt angle of blade...

Someone said it can be figured out with a CAD program (which I don't have), by creating 2 10" blades, 1/8 inch apart from each other, then create a table 2 1/2 inches above it... (there is more, but)


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## routerworks (Feb 20, 2012)

Well I have been using this site for uite a while and have built some of the machines. Try this for a cove calculator
Fred
Cove cutting table calculator


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## MAFoElffen (Jun 8, 2012)

Fred- 
That is for symmetric coves (Using the same formula above) and not for asymmetric. The big difference between the two- Symmetric coves have the apex centered. Asymmetric coves have the apex to one side. This affects the shape of the ellipse, causing a sharper radius on one side than the other. 

For a blades cutting it- In a symmetric cove, the only angle is the angle of the work going across the blade. (The tilt remains at 0 degrees for all symmetric coves.) A asymmetric cove has a angled fence to guide work over the blade just like when you are cutting a symmetric cove, but additionally introduces tilt/bevel of the blade coming out of other than 0 degrees...

Then that changes if you use a step fence to lift one side of the work... which slightly changes the look of the ellipse.

//
I don't think there is such an animal... as a guide. I looked all yesterday afternoon/last night. I know there is a way to figure it out in mathematics and engineering. But I am not an engineer or mathematition.

There 's supposed to be a way to do it in CAD. I drew it up in Google Sketchup - a blade (it's 2 surfaces, 1/8" apart) with the surface of the table... But I don't know enough about CAD modeling to be able to group the surfaces of the blade together and make it raise and tilt like it would in a table saw. 

I guess that leaves me with what I do for creating router profiles... Just start cutting on scrap and record the settings of each cut- depth, width, angle & tilt... Until I recreate it. Then reference wise, I'll have something to go back to.


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## MAFoElffen (Jun 8, 2012)

What I ended up needing was 35 degrees across the blade, 45 degrees bevel and a 2 degree lift on the loose end.

Done.


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## Chris Curl (Feb 13, 2012)

you guys are way over my head ...

for the education of those of us in the dark (i hope i'm not the only one inthat category!), can you describe what an elliptical cove is, and when or how it is used?

thanks


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## Cherryville Chuck (Sep 28, 2010)

Mike, you might be able to find something like you want by searching for CMT's Lonnie Bird molding set. It comes with a saw blade that has radiused 1" wide tips for cutting the main cove on crown moldings. I saw a chart somewhere that gave the various coves it would make by changing the angle on the fence and blade tilt and it seems to me that some of the curves were asymetric. I have a set on order and I watched a video on You tube about it quite a while back. I can't remember if that is where I saw the chart.


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## MAFoElffen (Jun 8, 2012)

Chris Curl said:


> you guys are way over my head ...
> 
> for the education of those of us in the dark (i hope i'm not the only one inthat category!), can you describe what an elliptical cove is, and when or how it is used?
> 
> thanks


Chris-

Any profile that has a semicircular convex cut in it is a cove cut. All coves are elliptical except if it is approached at 90 degrees. Symmetric cove means the apex or deepest part of the cut is in the center, with mirrored curves on each side of it. An asymmetric cove means the apex or deepest part of the cut is off centered. The curves on he sides of that do not mirror each other, with the curve sharper on the short side (see attached pic's).

















Restoration carpentry- When you have to recreate a profile that exists somewhere in the architecture... Whether that is recreating moulding that doesn't exist anymore to trim out a new room like the rest of the house is already... a profile on a cabinet header or raised door, so a that the new cabinet matches other cabinets that are already there...

When you come down to it, there is many ways to create the same profile, with many different tools. 

I could create that same profile if they bought a $80 bit and manipulated it. Shaper cutter would be more expensive. I can't afford either right now. I could create that profile with 3 bits, using 4 setups and using a jig... I can create it with 2 bits and 2 saw dado setups. All those would involve some sanding to blend it in. Or I can create it in 1 setup with a table or radial arm saw doing a cove cut. I do have to recreate it 16 times. Easy decision.

The attached should answer what you're asking about


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## Chris Curl (Feb 13, 2012)

thanks mike, i understand what you are talking about now!


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## routerworks (Feb 20, 2012)

Your right Mike I sent you the incorrect link. Try this for asymmetric coves.Asymmetric cove cutting.
Fred


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