# corner radius



## bluebonnetcabins (Aug 17, 2010)

I know I need a 6 1/2" corner radius. How do I use my compass to determine the 6 1/2"?:wacko:


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## bobj3 (Jan 17, 2006)

Hi

From each side ,but a mark at 3 1/4" out from the corner , take your sq. and draw a line to the center of the board on both marks, where the lines cross put your compass point on the X mark and draw your radius, from each edge of the board..

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bluebonnetcabins said:


> I know I need a 6 1/2" corner radius. How do I use my compass to determine the 6 1/2"?:wacko:


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## xvimbi (Sep 29, 2009)

Bob, I think it should be 6-1/2", not 3-1/4", unless I don't quite understand correctly.

In other words, put marks 6-1/2" out from the corner on both edges. Take your square and draw lines from the marks perpendicular to the respective edge into the board. Where the lines intersect, put your compass, set it to 6-1/2" and draw the radius. 

In yet other words: draw a 6-1/2" square at the corner in question. The corner of the square that's farthest away from the corner of the board is the one you put your compass at.

MM


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## Demiurgous (Aug 11, 2010)

xvimbi said:


> Bob, I think it should be 6-1/2", not 3-1/4", unless I don't quite understand correctly.
> 
> In other words, put marks 6-1/2" out from the corner on both edges. Take your square and draw lines from the marks perpendicular to the respective edge into the board. Where the lines intersect, put your compass, set it to 6-1/2" and draw the radius.
> 
> ...


Don't know anything about it...but I'll chime in anyway. Using Bob's method, you get a circle with a 3-1/4" _radius_ and a 6-1/2" _diameter_, which I totally don't understand. To me, I think your answer is correct as far as _radius_.

You can also use a little math and trig to figure out where to set your compass, but the above would be easier, me thinks.


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## RJM (Apr 11, 2010)

If the edges are already cut, then drawing the square would be the best solution. If the edges are not cut but the outline of the shape is drawn, then all that's needed is the compass set at 6-1/2". This si really very fast and easier than drawing 2 more lines to make a small square.


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## xvimbi (Sep 29, 2009)

RJM60 said:


> If the edges are already cut, then drawing the square would be the best solution. If the edges are not cut but the outline of the shape is drawn, then all that's needed is the compass set at 6-1/2". This si really very fast and easier than drawing 2 more lines to make a small square.


Yes, indeed. The drawback, and the reason I have not suggested this method is that small errors in initially setting the compass add up to potentially become a significant error. I think, first measuring the distances with a ruler and a square might give a smaller error, but I haven't calculated the error propagation as I don't know the errors in the rulers, squares and compass involved.:dirol:

There are quite a few methods. Either one of the mentioned two will work.

MM


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## RJM (Apr 11, 2010)

xvimbi said:


> Yes, indeed. The drawback, and the reason I have not suggested this method is that small errors in initially setting the compass add up to potentially become a significant error. I think, first measuring the distances with a ruler and a square might give a smaller error, but I haven't calculated the error propagation as I don't know the errors in the rulers, squares and compass involved.:dirol:
> 
> There are quite a few methods. Either one of the mentioned two will work.
> 
> MM


Using a compass will introduce some error in that the initial setting of the compass might be off but if this is not changed, the result will be that the final radius is off by the same amount. This is usually okay. The only other errors would be placement of the compass point at the exact intersection of the arc. The width of the pencil lines can be controlled to minimize some of this error but the wood grain may cause the point to shift slightly when placing the compass; however, all this is tiny compared to actually making the cut.

Another method would be to make a pattern of the radius and use a router to cut them.


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## Dr.Zook (Sep 10, 2004)

Welcome to the RouterForums Bluebonnetcabins. Thanks for becoming a member of our community.


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## bobj3 (Jan 17, 2006)

Hi Guys

I'm not a big fan of using the router and a templates on the corners, you will always have a upgrain on the corners that the router bit will lift up and rip out , I think by using a good jig/band/scroll saw it will cut the stock without ripping the stock out, but by using a template to mark the stock they will all be the same radius..

Most jig saws come with a edge guide that can be drill out with a 1/8" hole for a pivot pin and can be use just like a cir.jig  you can buy blades for the jig saws that will cut as smooth as a router bit, once set the radius will be all the same. (Bosch blades)


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RJM60 said:


> Using a compass will introduce some error in that the initial setting of the compass might be off but if this is not changed, the result will be that the final radius is off by the same amount. This is usually okay. The only other errors would be placement of the compass point at the exact intersection of the arc. The width of the pencil lines can be controlled to minimize some of this error but the wood grain may cause the point to shift slightly when placing the compass; however, all this is tiny compared to actually making the cut.
> 
> Another method would be to make a pattern of the radius and use a router to cut them.


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## BobandRick (Aug 4, 2004)

Just to verify cutting corners with the bandsaw or jig saw is not the best way to cut corners...the router does the best job and you can make all corners exactly the same and you don't need to cut up-grain ever see my how to video here


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## harrysin (Jan 15, 2007)

Then there is a simple jig like this, made to whatever radius is required, for this one I used a jig saw followed by sanding to the line drawn around a suitable size tin can! Once made, every corner routed will be identical.


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## bobj3 (Jan 17, 2006)

Hi Harry

That way works great on a small radius but on a 6 1/2" corner radius on real wood the part needs to be precut with the jig saw why not just use one tool to get the job done.. (good jig saw with cir.guide)

http://www.amazon.com/Milescraft-14...1_fkmr0_2?ie=UTF8&qid=1282239648&sr=1-2-fkmr0
http://www.amazon.com/Festool-49011...1_fkmr1_2?ie=UTF8&qid=1282239648&sr=1-2-fkmr1
http://www.amazon.com/Bosch-1591EVS..._1_2?ie=UTF8&s=hi&qid=1282240298&sr=1-2-spell
http://www.amazon.com/Bosch-T5002-1..._1_3?ie=UTF8&s=hi&qid=1282240298&sr=1-3-spell

I will say on the small type radius corner , I use the big round over router bit (1 1/2") in the router table, can beat the router bit to make them the same all the time..plus no precut cut needed..

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harrysin said:


> Then there is a simple jig like this, made to whatever radius is required, for this one I used a jig saw followed by sanding to the line drawn around a suitable size tin can! Once made, every corner routed will be identical.


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## BobandRick (Aug 4, 2004)

This is a router forum, right? And putting a radius on a corner is exactly what the router has been designed to cut. It cuts exactly what your pattern has been made for or use a piece of 1/4" plywood, small nail as a circle jig for the larger diameters...2" - 10" radius etc...this is nothing high tech...

But if we are talking about using alternative tools why not use the hand coping saw or the scroll saw, etc...you will get a much finer cut. Let's remember the finish of the cut with these tools needs sanding, the router does the job and doesn't need sanding. 

As always after cutting with the many cutting tools you can then move the bumps around with the disk, drum or hand sander making an uniquely shaped corner. If you have more than one corner you can make them all different and have a variety of shapes on your project...

Come on BobJ3 a jig saw? 

In conclusion, if you want the job done right then I am with Harry the router is the tool.


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## BobandRick (Aug 4, 2004)

Using 1/4" plywood a small nail and a guide as the circle jig for the router. With this you can creating a specific radius on the corner of the project piece. Cost maybe $1.50. The pictures are of a 1" hole cut into the 1/4" plywood then use the 1" guide to connect the router to the plywood. Don't have a 1" guide then use the base screws and mount the plywood to the router directly. 

Now you have the perfect tool used to cut the exact radius and guess what no sanding...


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## allthunbs (Jun 22, 2008)

BobandRick said:


> Using 1/4" plywood a small nail and a guide as the circle jig for the router. With this you can creating a specific radius on the corner of the project piece. Cost maybe $1.50. The pictures are of a 1" hole cut into the 1/4" plywood then use the 1" guide to connect the router to the plywood. Don't have a 1" guide then use the base screws and mount the plywood to the router directly.
> 
> Now you have the perfect tool used to cut the exact radius and guess what no sanding...


Ok, Rob: (not Bob3J) I'm going to take this to the next step. Say I've got a piece of maple. Beautiful artsy grain that goes all over the place. I use your compasses but where the grain varies, I get slight tear out. How to solve that puzzle? Or, I have a piece of redwood with really pronounced grain and everytime I cut across the grain I get tearout. Suggestions?

Ron

(P.S. I use a cabinet scraper)


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## bobj3 (Jan 17, 2006)

Hi Rick

You know I love the router but it's not always the best tool for the job at hand..
I think once the radius is put in place most will go back and use the router bit to put on a profile..no need to have a real fine cut b/4 the profile cut, little bit of sanding it's set to take on the router bit.. 

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BobandRick said:


> This is a router forum, right? And putting a radius on a corner is exactly what the router has been designed to cut. It cuts exactly what your pattern has been made for or use a piece of 1/4" plywood, small nail as a circle jig for the larger diameters...2" - 10" radius etc...this is nothing high tech...
> 
> But if we are talking about using alternative tools why not use the hand coping saw or the scroll saw, etc...you will get a much finer cut. Let's remember the finish of the cut with these tools needs sanding, the router does the job and doesn't need sanding.
> 
> ...


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## bobj3 (Jan 17, 2006)

This is not Bob3J 

" (P.S. I use a cabinet scraper) " how about using a power tool like a router, it would be quicker I think than the cabinet scraper  LOL 

=



allthunbs said:


> Ok, Rob: (not Bob3J) I'm going to take this to the next step. Say I've got a piece of maple. Beautiful artsy grain that goes all over the place. I use your compasses but where the grain varies, I get slight tear out. How to solve that puzzle? Or, I have a piece of redwood with really pronounced grain and everytime I cut across the grain I get tearout. Suggestions?
> 
> Ron
> 
> (P.S. I use a cabinet scraper)


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## harrysin (Jan 15, 2007)

bobj3 said:


> Hi Harry
> 
> That way works great on a small radius but on a 6 1/2" corner radius on real wood the part needs to be precut with the jig saw why not just use one tool to get the job done.. (good jig saw with cir.guide)
> 
> ...


Young Bob, the second shot that I showed was a quick set-up in answer to a member's question quite some time ago. In actual fact, irrespective of the radius, I zap the corners off on the radial arm saw before routing. On "real" wood, because the router is being held firmly in both hands, and remembering that I use a "tank of a router" (your words) I've never had a problem routing in both directions to prevent breakout. Whilst the router is my main tool, like you Bob, I wouldn't use it if I considered that there was a more suitable tool for a particular job.


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## paduke (Mar 28, 2010)

Regarding accuracy in determing the radius center point. Every measurement has a built in error. Pencil line thickness matters. With striking arcs from the corner you use a distance greater than the radius needed. Then stike arcs from squared edges and a very accurate center point is defined. With the compass point and a mechanically fixed distance operator error is greatly diminished


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## harrysin (Jan 15, 2007)

With woodworking, I've never found a reason for super accuracy, let us face it, wood moves with the weather, hence the fact that in the jig shown, I didn't even bother to use a compass, finding a suitable tin can in the shed and positioning it in the corner to draw around was accurate enough for any project that I can think of.


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## bobj3 (Jan 17, 2006)

Hi Harry

I'm glad to see I'm not the only one that use the tin can way to draw the radius.


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harrysin said:


> With woodworking, I've never found a reason for super accuracy, let us face it, wood moves with the weather, hence the fact that in the jig shown, I didn't even bother to use a compass, finding a suitable tin can in the shed and positioning it in the corner to draw around was accurate enough for any project that I can think of.


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## harrysin (Jan 15, 2007)

Bob, I hadn't been a forum member very long when I first realised that you and I have a great deal in common, including the fact that we are first and foremost practical men, if there is a simple way to achieve a particular result without resorting to maths or deep theory, then that's the way we go, right?


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## bobj3 (Jan 17, 2006)

Hi Harry

Right on ,,,,,so many go off the deep end a make it a job it's a fun hobbie not math or theory games 


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harrysin said:


> Bob, I hadn't been a forum member very long when I first realised that you and I have a great deal in common, including the fact that we are first and foremost practical men, if there is a simple way to achieve a particular result without resorting to maths or deep theory, then that's the way we go, right?


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## Titus A Duxass (Jan 6, 2010)

Hey you two "old" guys are my role models (if you can have role models at 49!):lol:


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## bobj3 (Jan 17, 2006)

HEY hahahahahahaha

Harry is the OLD Guy, he's got me by 15 years or so ,,,hahahahahahaha LOL
I still have a full head of hair hahahahaha LOL, a bit gray but still in place..just like it was when I was 20 years old  and still cut the same way LOL 


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Titus A Duxass said:


> Hey you two "old" guys are my role models (if you can have role models at 49!):lol:


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## RJM (Apr 11, 2010)

paduke said:


> Regarding accuracy in determing the radius center point. Every measurement has a built in error. Pencil line thickness matters. With striking arcs from the corner you use a distance greater than the radius needed. Then stike arcs from squared edges and a very accurate center point is defined. With the compass point and a mechanically fixed distance operator error is greatly diminished


I don't understand this. Could you explain more? maybe with a picture?


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## RJM (Apr 11, 2010)

harrysin said:


> Bob, I hadn't been a forum member very long when I first realised that you and I have a great deal in common, including the fact that we are first and foremost practical men, if there is a simple way to achieve a particular result without resorting to maths or deep theory, then that's the way we go, right?


 


bobj3 said:


> Hi Harry
> 
> I'm glad to see I'm not the only one that use the tin can way to draw the radius.
> 
> ...


 
*I agree with both of you. If I wanted a 6-1/2" diameter corner radius and happened to have a 13" diameter can, I would use it to draw the radius.*

Here's the original question: "I know I need a 6 1/2" corner radius. How do I use my compass to determine the 6 1/2"?

Notice the original poster makes no mention of how this is going to be cut out.

I run in to the "Why would you want to do that?" and the "You don't want to do it that way." syndromes all the time. Sometimes, these are valid but here, on this forum, if someone asks how to do something, or explains how they are going to do something, or shows us how they did something and all they get back is "You should do/have done it this way, they may never come back.


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## BigJimAK (Mar 13, 2009)

My post is a response strictly to the "compounding of errors" solution and is offered up as a method of reality-checking your error if you use the "drawing 2 lines 6.5 inches offset" method. After drawing both lines, measure from the corner of the wood diagonally to the intersection of the lines. After consulting with Pythagorus I learned the line should be 9-3/16 in length (to way beyond woodworking tolerances). 

If you're very far off this you've either miss-measured or your two sides aren't an accurate right-angle. If it's too far off for your sense of accuracy it's time for the tin-can method or plan on fiddling with the template you like it.


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## harrysin (Jan 15, 2007)

bobj3 said:


> HEY hahahahahahaha
> 
> Harry is the OLD Guy, he's got me by 15 years or so ,,,hahahahahahaha LOL
> I still have a full head of hair hahahahaha LOL, a bit gray but still in place..just like it was when I was 20 years old  and still cut the same way LOL
> ...


Titus, Bob is alluding to the fact that my hair is thinning slightly on top!


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## Titus A Duxass (Jan 6, 2010)

harrysin said:


> Titus, Bob is alluding to the fact that my hair is thinning slightly on top!


A case of more beach than waves.


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## harrysin (Jan 15, 2007)

You've got it in one my friend. I'm sure that Bj will have something less subtle to say!


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## jw2170 (Jan 24, 2008)

harrysin said:


> You've got it in one my friend. I'm sure that Bj will have something less subtle to say!



BJ "less subtle".......I doubt it.........


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## bobj3 (Jan 17, 2006)

Hi Harry

Always  but this time I will pass  Mate 

Subtle | Define Subtle at Dictionary.com

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harrysin said:


> You've got it in one my friend. I'm sure that Bj will have something less subtle to say!


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## harrysin (Jan 15, 2007)

Thanks Bob because I felt sure that you would find a photograph somewhere in your files showing that my description might not have been perfectly accurate!


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