# Cutting a cove in a curve



## Chris Sterricker (Jul 21, 2017)

Hello all, looking for some help. I am new to the forums and a basic, at best, woodworker. I would like to make a wooden life ring like the one pictured. My plan is to use clear maple or birch for the white sections and purple heart for the red sections. Here's the catch, I would like each section to be a separate piece (each white piece and each red piece) and both coved and cut in half length-wise. My reasoning for this is to be able to 1) keep the overall weight down for wall hanging and 2) I would like to pass the rope inside the halves (after drilling holes) and tie knots to keep it from pulling through once the halves are glued together. Problem: I have no idea how to cut a cove in a curved piece of wood. Keeping in mind I'm very new at this any suggestions? Or do you think coving is even necessary?


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## woodnthings (Jan 24, 2009)

*your choice of terms ???*

Can we understand you want to make a "donut" shape with 8 separate pieces THEN slice it in half like a Bagel to spread the cream cheese on?

I don't understand the cove you want, what it would do or where it would go or it's relationship to the rope...? Can you clarify this?

In order to create this donut shape you would most likely make it on a lathe on a support surface, one half and round over the inside and outside surfaces. I can't imagine making it in separate pieces without some elaborate jigs and maybe a shaper based on the typical size of a life preserver. You could use a router, but it would take many passes to achieve the rounded surface in that size radius and then some considerable hand work sanding it smooth.


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## allpurpose (Mar 24, 2016)

I'm not understanding the cove part of the equation either unless you plan to hollow out the back. 
I would think that increasing sizes of roundover bits might round over the corners of the donut shape, but what do I know? 
If you're new to woodworking in general just cutting the appropriate miters accurately will be your first big challenge, getting the overall shape round next and rounding the edges next..
Personally if it were me and it was a new project you've never done before I'd use an inexpensive wood to make a prototype (pine probably) and if all goes well then spring for the more expensive wood after you're confident it's going to work at all. Otherwise you may just spend a lot for a project that ain't gonna turn out so hot.. Just my opinion.


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## Chris Sterricker (Jul 21, 2017)

I guess Woodnthings said it best, bagel cut in half with the inside of each halve hollowed out. The purpose of the cove is to both save weight for hanging on the wall and to pass the rope into. Instead of securing the rope to the outside of the ring like on an actual life ring I would like to have four sections of rope. The ends of the rope would pass into the coved out area and be tied in knots to prevent them from pulling out. Then the halves of each section glued together, then each section glued together. Make sense?


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## woodnthings (Jan 24, 2009)

*To put it simply ...*

I think you are describing about a hollowed out 1/2 donut, the hollow (cove) being in the inside, or hidden?

This is most like a molded plastic part rather than a turned wood part. Once you start rounding all the surfaces it becomes next to impossible to get a grip on the shape to hold it for further machining/turning. Not saying it can't be done, just that it's dang sophisticated and then throw in 8 different sections....:surprise2: Almost certain it's a project for a wood turner. Maybe someone will offer their expertise?


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## FrankC (Aug 24, 2012)

Are you asking how to just hollow out the inside or how to shape the half donuts as well?


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## 4DThinker (Mar 13, 2013)

I get challenged with such projects on a nearly daily basis. As I understand it you want a donut shape with a coved out inside made of 4 white and 4 red individual sections. 

You've got 2 major challenges. Even if the sections were split in half to be cut on a CNC, holding them in place once one side is done will be difficult. Not impossible, but a challenge. Next you want to join the ends of each section together to make the donut. Although just butting them together with glue in between might hold for awhile, it would be hellish to try and clamp while the glue dries. The different woods used will likely expand and contract differently than each other as the humidity changes, and it could be VERY bad depending on the orientation of wood in each piece. If the "skin" is left fairly thick you have opportunity to use dowels between them. With some complex CNC work you might be able to make each section socket into a recess in the adjacent half. Attached is an example I did using Aspire from vectric and several different tool paths. You would need a slightly different top half, and two different short halves for the red sections. Lots of cut time. Expensive.

4D


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## GeorgeC (Jul 30, 2008)

That being difficult to make is an understatement. I can see a carver being able to do it given time and wood that was not too hard.

Otherwise a large shop with CNC machines.

George


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