# Double-roundover on arc



## shawnnelson (Sep 6, 2010)

Hey everyone,

So I'm working on a project around the house and I've run into a bit of a problem. Sparing the boring details, I am making molding for a window that has a slight arc at the top. Now, the routing for the straight pieces was easy, simple roundover bit run along top and bottom of the wood to give a double roundover. Now, the arc is where I run into trouble; The arc is supposed to look as if one were to get one of the straight pieces, and bent it to the shape of the arc. Normally this would be just what I'd do except the wood in this case is 3/4" thick, so I figured I'd just cut an arc from a plank and router it. Problem is, using a standard roundover bit, the router needs to travel on the top of the arc (easily done) AND the bottom of the arc...which can't be done since it's an arc and the router base is flat. I considered a double-roundover bit, but due to the difference in length of the top of the arc and the bottom, I'm not sure I'd get the desired affect. Only other thing I could think of is a bit that is effectively a roundover bit only with it's axis of rotation shifted 90 degrees...but I'm not sure if such a bit even exists. Anyone happen to know what I could use to do this? 

If needed, I can provide illustrations to help clarify what I am attempting.

Thanks!


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## 01stairguy (Apr 18, 2010)

your first thought was right, make sure before you cut the arch to lenght, you do the round over, so that way you dont run in to the ends that are allready cut. if this is a light arch you can make it out a 1x12 pc depending on the lenght, and if you dont know what the radius is just center the board in front of the wall or window, center that pc, then trace the inside radius, just make sure that board is wide enough, then cut the inside radius, make sure that cut is nice and clean, then with your combo square you can go, let say depending on the withd of the casing 3 1/2 you can set it up for 3 1/2 and start marking that out side radius, going of your inside radius, thats the reason why that inside radius has to be almos perfect, i hope you get the whole idea, i can tell you are on the right path. good luck


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## bobj3 (Jan 17, 2006)

Hi

"If needed, I can provide illustrations to help clarify what I am attempting."

Pls. do 

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shawnnelson said:


> Hey everyone,
> 
> So I'm working on a project around the house and I've run into a bit of a problem. Sparing the boring details, I am making molding for a window that has a slight arc at the top. Now, the routing for the straight pieces was easy, simple roundover bit run along top and bottom of the wood to give a double roundover. Now, the arc is where I run into trouble; The arc is supposed to look as if one were to get one of the straight pieces, and bent it to the shape of the arc. Normally this would be just what I'd do except the wood in this case is 3/4" thick, so I figured I'd just cut an arc from a plank and router it. Problem is, using a standard roundover bit, the router needs to travel on the top of the arc (easily done) AND the bottom of the arc...which can't be done since it's an arc and the router base is flat. I considered a double-roundover bit, but due to the difference in length of the top of the arc and the bottom, I'm not sure I'd get the desired affect. Only other thing I could think of is a bit that is effectively a roundover bit only with it's axis of rotation shifted 90 degrees...but I'm not sure if such a bit even exists.  Anyone happen to know what I could use to do this?
> 
> ...


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## shawnnelson (Sep 6, 2010)

I'll post pretty pictures tonight.


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## shawnnelson (Sep 6, 2010)

Ok, so here is a picture illustrating what I am doing (it's in paint, didn't have enough time to do it in AutoCAD).










So you can see, running the roundover bit on the top of the arc is ok, but running it on the bottom doesn't work. Does this help?


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## shawnnelson (Sep 6, 2010)

So you can see, running the roundover bit on the top is the arc is no problem it's running it on the bottom that doesn't work (square peg, round hole)

Any ideas?


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## shawnnelson (Sep 6, 2010)

sorry for double post :-/


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## gregW (Mar 14, 2007)

shawnnelson said:


> So you can see, running the roundover bit on the top is the arc is no problem it's running it on the bottom that doesn't work (square peg, round hole)
> 
> Any ideas?


I think I understand what you are trying to do..a beading bit usually allows a reveal to be cut on each side of the radius so a setup like this might work.


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## bobj3 (Jan 17, 2006)

Hi 

Try the bits below one of them should do the job,do the job in one pass of the bit..

1 PC 1/2" SH Double Corner Round Assembly Router Bit - eBay (item 130427187143 end time Sep-08-10 11:43:12 PDT)

http://cgi.ebay.com/3pc-1-2-SH-1-2-...419952253?pt=Routers_Bits&hash=item1e5da28a7d

=========


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## shawnnelson (Sep 6, 2010)

gregW said:


> I think I understand what you are trying to do..a beading bit usually allows a reveal to be cut on each side of the radius so a setup like this might work.


ah ha! yes that looks like it would do nicely! I'll give that a shot, thanks guys!


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## Phil P (Jul 25, 2010)

I'd think slightly differently. If you make-up a full-size template and attach this to the underside of the workpiece then the bull-nose could be machined using a bull-nose bit with a guide bearing such as these by Amana


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## bobj3 (Jan 17, 2006)

Hi

How about buying one bit that will do it all 

1 PC 1/2" SH Double Corner Round Assembly Router Bit - eBay (item 140454198050 end time Sep-22-10 15:51:41 PDT)

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Phil P said:


> I'd think slightly differently. If you make-up a full-size template and attach this to the underside of the workpiece then the bull-nose could be machined using a bull-nose bit with a guide bearing such as these by Amana


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## gregW (Mar 14, 2007)

[/QUOTE=bobj3;203859]Hi

How about buying one bit that will do it all 

1 PC 1/2" SH Double Corner Round Assembly Router Bit - eBay (item 140454198050 end time Sep-22-10 15:51:41 PDT)

==========[/QUOTE]

Hi Bj,

that looks like a neat cutter at a good price but how could you route the profile on the face of the curved molding using that bit?


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## bobj3 (Jan 17, 2006)

Hi Greg

It's all done with the trim router on it's side and with the trim router attachment fixed to the router,it will follow the curve easy.

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gregW said:


> [/QUOTE=bobj3;203859]Hi
> 
> How about buying one bit that will do it all
> 
> ...


Hi Bj,

that looks like a neat cutter at a good price but how could you route the profile on the face of the curved molding using that bit?[/quote]


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## allthunbs (Jun 22, 2008)

shawnnelson said:


> So you can see, running the roundover bit on the top is the arc is no problem it's running it on the bottom that doesn't work (square peg, round hole)
> Any ideas?


Hi Shawn:

Mount your round over bit in a a router table. It doesn't have to be fancy, just a piece of MDF or plywood big enough to support your arc fully and hold and position your router. Using a bearing and a safety pin (see Router Workshop videos on The Woodworking Channel ) run your arc, inside and out, past the bit. Flip it and redo. I would suggest several passes on each side. 

I highly recommend that you fashion really big push blocks to keep your fingers well clear. You'll be concentrating too much on the bit to keep an eye on your fingers. Put some sand paper on your push blocks to "grip" the workpiece and it might be handy to add some slipperiness to the table top.

Now, I really want to see how this is mounted when you're finished. Lots of pictures please. Are you going to paint or stain this? What wood?

Neat idea.


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