Replies

1. 
   MStehelin | May 27, 2002 07:44pm | #1

   There is a softeware program "out there" that does all of that. Sorry I can't rememer its name. Read about it as a new product in a more commercial style wood working magazine. I'll see if I can find it.

   I used to do a lot of coveing and found that it was difficult to make the exact piece if I removed the set up, and then came back a couple of days later. If you are finding that your pieces are too eliptical try tilting your blade a bit.

   Mitt

1. 
   SCFrankland | May 28, 2002 05:11am | #2

   If you know how wide and how deep you want to make the cove then all you have to do is raise the blade to the height that is equal to the depth of the cove. Second is to make a simple jig that has two strips that are parallel to each other and are the same distance apart as the cove is wide. By placing this over the blade and twisting it so the back of the blade just touches one stick and the front of the blade just touches the other stick, this will determine the fence angle. With the angle found set the fence so its is were you need to cut the cove lower the blade and start making your cuts.Scott C. Frankland

   Newfoundland Wood Worker

2. 
   robertcarli | May 28, 2002 05:11am | #3

   Do you have access to any graphics programs like Visio????  There is a way to graphically represent the cove using a diameter of the saw blade and then overlaying an elipse of the same major length and then using the cord length of your profile to calculate the minor length and then to determine the approach angle of the wood that you want to cove cut.  I was making a jig / fixture to hold PVC piping and wanted an exact cove to match the pipe.  In some sort of brief burst of reckoning I was able to determine quite exactly for purposes of repeatability the approach angle and height of blade.  I would only be able to send you my example with graphics and text as I laid it out several years ago, if you're interested.  It still sounds complicated, but by keeping the arc of the saw blade in mind, and at the right height you're basically looking for the approach angle to accomplish the correct radius of removal.

   Bob

3. 
   roninfante | May 28, 2002 01:43pm | #4

   There was a detailed article about cutting coves on a table saw published in Fine Woodworking a few years ago. The author was Frank Klausz III and if I remember correctly it was derived from a senior thesis at Harvard.

4. 
   kcg99999 | May 28, 2002 03:57pm | #5

   Hi Mjaec,

   Angling your fence off 90° to the blade changes the cut from a part of a circle to a part of a parabola. The more the fence is angled the narrower the parabola becomes. If you angle the blade the parabola seems to pillow. The height of the blade, of course, is your third variable. You combine the three to get the curve you want. You should be able to site down the fence and see the general outline of the curve (made by the outline of the blade) that you’re going to get without having to cut stock. This will get you close. Then knowing how the system works will tell you which variable to change. This should speed up your trial and error process.

   Hope this helps.

   Best,

   Kim Carleton Graves
   Carleton Woodworking

1. 
   BarryO | May 31, 2002 03:40am | #10

   "Angling your fence off 90° to the blade changes the cut from a part of a circle to a part of a parabola"

   Actually, I believe it become part of an ellipse.

   What you're basically doing is taking an oblique slice through a cylinder.  You can't generate a parabola that way.

1. 
   kcg99999 | May 31, 2002 04:42pm | #11

   Hi Barry,

   You know, I thought it was an ellipse too. But then Masha said it looked more like a parabola. And since she’s usually right about such things, I deferred to her without thinking about it. But, you're right, it’s an ellipse - I think. ;-)

   Regards,

   Kim Carleton GravesCarleton Woodworking

5. 
   EBrandt | May 29, 2002 12:08am | #6

   I've never used it, but I saw a program at Badger Pond available for download that claimed to do it. Go here:

   http://www.wwforum.com/faqs_articles/

   and look at the rightmost column, it's called  'Cove Cutter 1.0' and it claims to do all that you are asking.

   Hope that helps,

   Eric.

1. 
   mjaec | May 29, 2002 12:34am | #7

   Thank you for your help on this issue of tablesaw cove molding. mjaec

6. 
   StanleyNiemiec | May 29, 2002 10:56pm | #8

   The approximate formula I worked out previously for this is based on some trigonometry.

   I say approximate because I am not certain considering the thickness of the teeth (kerf) as a factor in determining the true length of the cove width (more below).  

   If you are feeding wood at an angle, the in-feed side of the blade will have that blade-side's teeth cutting on the upcut (from the table saw surface to a line perpendicular to the table saw top at approximately the arbor center) while the out-feed side of the blade will have the teeth down-cutting from approximately that perpendicular line centered on the arbor to where the blade "sets" below the table top surface.

   I have determined the formula given below with the understanding that you will have already determined the depth of the cut (depth of the cove) and are seeking to determine the angle of feed to obtain the appropriate width.    You will need to know:

   1.    The depth of the cove you desire to cut.

   2.    The true diameter (radius) of the blade you are using.

   Therein you can use the following formula to determine the chord of the blade actually in the cut:

   Chord c = 2 ( 2br - b² ) ^1/2

   read as 2 times the square root of the quantity 2br minus b squared.

   Where:

   b = the depth of cut, or rise of the chord (the distance between the table top surface to a line of tangency from the highest tooth).

   r = blade radius

   To determine the width of the cove, you need to be able to calculate the feed angle (assuming that the center of the board being fed is directly over the center of the blade).

   This angle will be determined from a 0 degree angle (ripping a board) to 90 degrees (feeding perpendicular to the rotating blade plate).

   Angle A = INV Sin (desired cove width/actual chord width).

   Thus if the desired cove width is 2" and the chord width is 4", two divided by 4 equals 0.5.  The INV Sin of 0.5 is 30 degrees.

   I suppose that if you want to be absolutely correct in your calculations, the actual  chord of cutting can be determined by some function of the Pythagorean theorem.  The actual cutting width will be based the legs of the width of the kerf and the length of the blade chord.  I am trying to visualize whether the hypotenuse is the actual dimension desired or whether it has to be somehow adjusted dependent on the angle of feed.

   I hope this is right and it helps!

7. 
   DKowlasky | May 30, 2002 12:56pm | #9

   Or..........instead of all that math.. you could check this out.. on my web site I have a how-to on cove cutting.. with a link to a chart in the text.. and some photos..  http://davewoodshop.homestead.com/TScove.html    

   Dave²   http://www.homestead.com/DaveWoodshop/     

8. 
   JosephJohn32 | May 31, 2002 09:36pm | #12

   MJAEC,

   Sorry, no discript answers here, but I've done what your doing several times, and seem to experience just as much trial and "error" as you have.  Which ever method you decide to employ, please BE SAFE AND SLOW!  That blade has a tendancy to suprise you and reveal itself rather unexpectantly at the end piece of your stock.  Saw makes unsettling noises as well.  Be prepared to do a reasonable amount of sanding the inside of the cove. 

   Regards,

   Joe

   "Hide not your talents, they were for use made.  What's a sun-dial in the shade?"                

   - Benjamin Franklin