# Cutting a 90 degree arc on a router table



## TanOak (May 31, 2010)

Hello All:
I have a project that requires that I round corners into quarter circles with a radius of about 2". In the past I have just drawn the arc and cut them with a jig saw then followed up with a sander. But this is a production run where I want a really precise arc. Plus, I'm using plywood so I don't want to use a jig saw which might tear out the veneer. 
So I want to use a circle cutting jig on my router table. The trick is that I'll have to locate things precisely so that the tangents flow nicely into the two sides. My thought is to use a 1/16" pin in the table positioned the correct radius from the bit. If I don't position the piece properly the tangent could actually dig into the edge rather than flow into it. 
I guess the conservative approach would be to position the piece slightly further away from the cutter. This way the arc would not be 90 degrees but it would avoid a really ugly outcome. 
So.... what do you guys use for a positioning pin for a circle cutter? Do you have any tips for position?
Thanks,
Jim


----------



## Cherryville Chuck (Sep 28, 2010)

There are several ways to do it. Jigsaw or bandsaw and sanding work. Using a sanding drum the right diameter also works. In both cases I like to clamp left and right sides together so that the curves are exactly the same. If you are going to make a few I would make a template and use a bearing guided bit or a template guide which can be done on a table or freehand. Quite often the curves don't need to be perfect, they just all need to be the same.


----------



## TangoDown3727 (Oct 13, 2013)

If it is a production run, what about making a template (or pattern) of the corner radius, then you could cut all the corners close with a jig or band saw and then clean it up with the template and router with a flush trim or upcut spiral pattern bit with a bearing? Just a thought. Good luck to you!


----------



## MAFoElffen (Jun 8, 2012)

TangoDown3727 said:


> If it is a production run, what about making a template (or pattern) of the corner radius, then you could cut all the corners close with a jig or band saw and then clean it up with the template and router with a flush trim or upcut spiral pattern bit with a bearing? Just a thought. Good luck to you!


+1 on this... Depends on how finished looking you want it.

*** Reasoning for using a pattern using a pattern trim bit, while trimming down close with a jigsaw or band saw? Trimming down close with a saw is going to cut your router tooling time down drastically. Using a pattern with a trim bit is going to get your production piece finish cut quick and consistent. If you trim to around an 1/8" with a saw, the router'ed pattern cut should be just a quick single pass.

But the other big reason that was not mentioned is that using a pattern with the veneered ply you said you where going to use is going to sandwich the veneer between the pattern and the rest of the ply and you should get no or little tearout. The quality should be a good "finish" cut doing it that way.

If you are still worried about tearout on your saw trim cut, when cutting veneered' ply with a saw, I cover the veneer over the cut with painters tape and score it where the cut will be (go along the edge of the template with a knife). The tape helps keep the veneer from lifting and tearing out. The scoring, if it down lift, the scored cut should limit the tearout. If saw trimming with a pattern attached, you can use a regular toothed saw blade and the attached pattern will help support the veneer. 

If trimming down without an attached pattern, you could use a downcut blade on a jigsaw which will have less tearout or use a fine toothed bandsaw blade with a zero clearance insert. That all assumes that you cut with the Visual finish veneer side up...

Preference would be to use a template with a flush cut or pattern bit... Not a template with a spiral cut bit. A template would not support the veneer and a spiral would tearout the veneer. (one side or other depending on double sided veneers and up-cut or down-cut spirals.


----------



## rjunique (Jul 21, 2012)

You could use a spiral compression pattern bit to give crisp edges on both sides.


----------



## GulfcoastGuy (Feb 27, 2012)

you could buy something like this:









Amazon.com: General Purpose Drafting and Design Templates radius guide: Arts, Crafts & Sewing

... and use it to make something like this:









Router Radii By Peachtree Woodworking PW2897 - Amazon.com

... or just buy it outright.


----------



## TangoDown3727 (Oct 13, 2013)

MAFoElffen said:


> But the other big reason that was not mentioned is that using a pattern with the veneered ply you said you where going to use is going to sandwich the veneer between the pattern and the rest of the ply and you should get no or little tearout. The quality should be a good "finish" cut doing it that way.
> 
> If you are still worried about tearout on your saw trim cut, when cutting veneered' ply with a saw, I cover the veneer over the cut with painters tape and score it where the cut will be (go along the edge of the template with a knife). The tape helps keep the veneer from lifting and tearing out. The scoring, if it down lift, the scored cut should limit the tearout. If saw trimming with a pattern attached, you can use a regular toothed saw blade and the attached pattern will help support the veneer.
> 
> ...


Good points indeed! If at all possible, I would choose a bandsaw for cutting close to your finish line, instead of a jigsaw, they are usually just too hard to control tearout of veneers. You can get better control on the bandsaw because the piece is supported on the table. You certainly want to take off as much material as you can (leaving no more than 1/8" from your finish line is good), this will make the routing job go much easier. If you then attach the pattern/template to the piece and finish the cut on the router table, you should get a perfectly clean finish cut. Just make sure you have a clean, sharp bit in your router and you'll be golden!


----------



## TangoDown3727 (Oct 13, 2013)

GulfcoastGuy said:


> you could buy something like this:
> 
> 
> 
> ...


That clear lexan template looks really cool but those metal indexing pins look awful close to the edge, you'd have to be super careful not to hit one with the bit. Worth looking into though!


----------



## smart alex (Nov 20, 2011)

*Have a look at this from Woodpeckers*

Try looking up Woodpeckers Corner Radius Quick-jig on YouTubes - A simply and very easy solution.

In the infinite wisdom of those who run this routerfourum I was not allowed to post a URL to a YouTube video that demonstrated their product until I had made 10 posts. Buggered if I know why??????? Give me one good reason why.

I am not impressed.

D


----------



## jw2170 (Jan 24, 2008)

*...a good reason....*



smart alex said:


> Try looking up Woodpeckers Corner Radius Quick-jig on YouTubes - A simply and very easy solution.
> 
> In the infinite wisdom of those who run this routerfourum I was not allowed to post a URL to a YouTube video that demonstrated their product until I had made 10 posts. Buggered if I know why??????? Give me one good reason why.
> 
> ...


Hi "D".

Sorry that the forum policy has upset you. 

But this policy is a VERY effective way to reduce the number of hackers and spammers that attack every forum.

I see that you have been a member for some time. If you pick the next few new members introductions and say welcome, you will make your 10 posts in no time flat.


----------



## jw2170 (Jan 24, 2008)

For "D".

Woodpeckers Corner Radius Quick-jig - YouTube


----------



## jw2170 (Jan 24, 2008)

Personally, I would use a circle jig to make a template for the required radius.

Also, if you can get a copy from your local library, check pages 6-7 of Router Magic by Bill Hylton.


----------



## TomE (Dec 17, 2010)

jw2170 said:


> For "D".
> 
> Woodpeckers Corner Radius Quick-jig - YouTube


Nice little jig but it looks like a  one time run and production was 'retired' 7/18/11
Might be able to find some residual kits out there.


----------



## jw2170 (Jan 24, 2008)

TomE said:


> Nice little jig but it looks like a  one time run and production was 'retired' 7/18/11
> Might be able to find some residual kits out there.


Hi Tom that was just a suggestion from some I found on the web.

In any case, the items on sale only seem to go up to 1 1/8". The OP wanted a 2" radius.

I would make the jig as per Bill Hylton's book with a 2" radius.


----------

