Calculating Chamfer Radius

[custard]

I know this has been covered many times before, but searches aren't turning anything up.

I need to make a couple of templates to mark a curved chamfer on both the edge and the face of a board. One chamfer is 200mm long and has a maximum "depth" of 8mm, and the second chamfer is 300mm long with the same maximum "depth" of 8mm.

Can someone remind me of the formula to calculate the radius required for these two chamfers?

Thanks!

 

[Myfordman]

I can't visualise what you are trying to do. Can you give diagram please?

 

[ColeyS1]

I cant write the formula on my phone...

Half the span squared + rise square

Divided by 2 times the rise.

Think thats what you might be after :?

 

[custard]

Thanks for your assistance. I seem to recall it's related to the formula for chords.

Imagine a horizontal line 300mm long with a point at each end. There is a third point, 8mm directly above the middle of the line. The question is, what radius circle connects these three points and what is the formula for calculating this radius?

 

[bugbear]

Thanks for your assistance. I seem to recall it's related to the formula for chords.

Imagine a horizontal line 300mm long with a point at each end. There is a third point, 8mm directly above the middle of the line. The question is, what radius circle connects these three points and what is the formula for calculating this radius?

Ah - you mean CAMBER, not CHAMFER.

http://www.mathopenref.com/arcradius.html

BugBear

 

[xy mosian]

Hi, I just drew it out in Sketchup. The reported radius is 1410mm.
xy

 

[oakfield]

Hi, I just drew it out in Sketchup. The reported radius is 1410mm.
xy

I just did the same - I find Sketchup very useful for working out angles and measurements that would otherwise take a lot of maths!

I got 1410mm for the 300mm line and 629mm for the 200mm line.

 

[custard]

Thanks for your assistance. I seem to recall it's related to the formula for chords.

Imagine a horizontal line 300mm long with a point at each end. There is a third point, 8mm directly above the middle of the line. The question is, what radius circle connects these three points and what is the formula for calculating this radius?

Ah - you mean CAMBER, not CHAMFER.

http://www.mathopenref.com/arcradius.html

BugBear

I do mean chamfer not camber (think negative space), but that is exactly the formula I was looking for. Thanks!

 

[Jacob]

Easy peasy (I think)
diameter = D
then 8/150 = 150/(D-8)
so (D-8) = 150 x 150 / 8 = 2812.5
so D = 2820.5
so radius = 1410.25

 

[xy mosian]

Nice one Jacob. I had to scratch my head a little to follow it through, good exercise.
xy