Hello!
I’ve a conundrum. But, before I ask the question here is the background.
Needing to make a cove cut on a maple wood block using a
contractor tablesaw (Dewalt DWS7491RS, 10″ blade, .125″ kerf).
1. Block height is 1.6875″;
2. Block width is 2.5000″;
3. Block length: 11.6875″.
4. The bottom of the cove is to be .250″ from the bottom of the block.
5. The cove itself should be cut until .125″ peaks on the edges or 1″ deep, whichever comes first.
6. Miter gauge midpoint can either be zero or 90 degrees depending on which one I use.
In looking for the appropriate primary fence angle, after destroying 3 butternut blocks, I find that
1. The Fine Woodworking calculator shows 67 degrees for zero; 23 degrees for 90.
2. The Woodpecker calculator shows 67 degrees.
3. The DKnudson calculator shows 18.27 degrees.
4. The Shop Notes calculator shows 76 degrees.
5. Harry Foster’s cove cut APP shows 14.528 degrees.
I have no spare scrap wood the size needed. I have only one chance to get this right.
Microsoft’s COPILOT AI can’t access the Fine Woodworking Calculator for some odd reason. It tells me this (edited taking out the repetition).
Copilot
Hello, Charley! 🌟
Trust the Consensus: While there are variations, the consensus between Fine Woodworking and Woodpecker (both suggesting 67 degrees) provides a strong basis. These sources are reputable and widely used by woodworkers.
Test on Scrap Wood: Since you have only one chance, consider using a piece of scrap wood (even if it’s not the exact size) to test the calculated fence angle. Make a trial cut to verify the fit of the cove. Adjust as needed before committing to your maple wood block.
Fine-Tune as You Go: Remember that woodworking often involves fine-tuning. If you’re close to the desired result but not quite there, you can make minor adjustments during the actual cut.
In summary, I recommend leaning toward the 67-degree fence angle based on Fine Woodworking and Woodpecker. However, always trust your own judgment and adjust as necessary during the process. May your cove cut be precise and successful! 🪚🌳
The question: whose report should I believe? Also, looking at YouTube videos, should my primary fence have the top pointing left on the right side of the saw blade or pointing right on the left side of the saw blade? I lean to the left side of the saw blade.
Thanks!
{charley}
[email protected]
Replies
Last time I did this I used:
https://woodgears.ca/cove/calculate.html
The right or left depends on your comfort and what's best for clamping a fence to your saw. Feeding from either side will work.
With such a short workpiece add a second "capture fence" and build a nice full-size push block. Oh, and take little bites.
Thanks for the reply. I do have woodgears but didn't list it.
Trial and error is the best way to go. Go to almost any construction site where they are doing wood framing and ask for some scraps. They will likely be happy to get rid of some.
I don't understand your finished dimension requirements. A sketch would be helpful.
Thanks for the reply! I see that it is my fault you didn't understand my question. I didn't state the question clearly.
The question is which of the five fence angles listed in my original message is correct?
I don't have a readily available sketch, but a similar picture is in the latest WOODCRAFT MAGAZINE starting on page 27. Title: Coved Jewelry Box bu Geoff Noden. Mine will be close but not exact.
Thanks again.
{charley}
.0001 thou???? You need to take it to a machine shop. ha ha ha
I don't understand your question. Is it a 2 1/2" wide piece with a 1/4" cove or is it a 1 " cove? 1" deep on a 2 1/2" piece would be a very accute angle, 1/4" not so much. As someone said, trial and error is your best bet. You can clamp a fence or you can make or probably even buy a 2 sided jig. With a clamped fence your going to be taping it back and forth until you find the sweet spot. Each pass, and I would only go 1/8" at a clip, will be wider each cut ..if you want equal reveal on the sides or even something else given run out and minor error ,even pencil width, no matter how careful you are it's likely that you will be a hair off. Why? Because the gods of woodworking get really pissed if it's too good! Test on scrap wood will solve that or start with a piece wider than your finished width and correct the reveal after you create the cove. That's a very short piece your talking about...watch your fingers!5
I would like to add I have done this from time to time and more once -- like 40 /50 years ago. It's not my favorite way to do this- routers and shapers are preferred. When I read your post my first thought was --" They have calculators for this?!!!" In short there is your finished depth of your cove and there is a finished width of your cove. With the blade extended when those two factors align-- that's your angle.
The last time I did it I needed 20 feet of a simple maple crown. I drew a full size pattern until I was happy with it then traced it to some 3/4 plywood and cut it out. Then set it on the saw table and raised the blade to full depth of the cove and began to adjust the fence and blade height until it filled the arc. Worked perfect but it is always nice to have some scrap to experiment with....glue up some 2 by or whatever to play with. This is my plywood pattern that I made.
Thanks to all who took time to reply! Wow! Although I didn't reply individually I have taken the comments to heart and am taking another look at my project.
For PANTALONES868: " They have calculators for this?!!!" My thought in reply? "Perhaps that's my problem...heheheh..."
Thanks again to all!
{charley1}
Hello all!
I've decided to cease-and-desist for the time being in trying to make a decent cove cut.
What I did today was cut grooves from one end to the other at 1/8th increments with the table saw to open up the width to where I need it. It is looking good.
Within the next few days my sharp chisels will remove the remaining waste and I'll be ready to sand, then complete the project.
You guys encouraged me to use my brain and that's appreciated.
Thanks again to all!
{charley1}
I think part of the problem is that you don't have a single definition.
There are only two things you can change here - the height of the blade and the angle at which you pass the block over the blade.
You have two conflicting heights - 1" deep or 0.25" from the bottom of the block - this would be 1.4375" so for a start, which is it?
I assume 1" as that is a pretty chonky cove in it's own right. That makes the chord length of the blade 6" - this is the length of blade at the level of the table top. https://planetcalc.com/1421/ gives the calculation - radius - 5". Of course if your blade is not 10" then that will alter the equation, and many nominally 10" blades are a little more or less.
The angle is that angle which will allow the 6" chord to fit across
the width you desire.
With a 2.5" block and wanting to leave 1/8" on both sides, you need a 2.25" wide cut.
Cos-1 (2.25/6) gives the angle that will allow a 6" hypotenuse across the block - 68 degrees. (well, 67.957 if you want precision)
Measuring from the line of the blade, your holding jig will need to be positioned at 22 degrees relative to that line. Either side matters not.
The best way to do this is to make a 'sled' with 6mm MDF as the base. Give it runners for stability. Slide over the blade to mark the centre. Just like a crosscut sled, it needs to hold together. Mark your 22 degree line and fix on a fence along that line. Put your piece against the fence and attach another fence the other side to ensure movement is possible only in the desired direction. Mark the centre of your workpiece on the end grain and use this to make a mark on your sled exactly on the saw kerf line.
push your sled into place and raise the blade until one tooth just protrudes. Line this up with your centre mark and fix the sled securely in place. Check again and you are ready to cut. Take many small bites.
Remember that non-through cuts are high risk for injury - be safe and ensure you keep fingers well away.
Thank you! I have made a print copy of this for future use. I really appreciate the time you took to write this for me.
Thank you again.
{charley1}
"There are only two things you can change here - the height of the blade and the angle at which you pass the block over the blade."
There are actually more possible adjustments:
- Hieght of blade
- Angle the workpiece crosses the blade
- Blade tilt angle
- Blade diameter
https://www.finewoodworking.com/project-guides/shop-machines/how-to-cut-coves-on-the-tablesaw-2
Tilting the blade can result some very interesting shapes.
Absolutely, if you REALLY want to screw with your head!
For completeness I'll use a 45 degree tilt as this is the most that most saws can do, so it shows the extreme case.
The height of the blade and thus the depth of the cut can be calculated by:
Blade Protrusion at 90 degrees * Sin Blade angle relative to the saw top.
If you wish to obtain the same depth of cut, you must extend the blade further - in this case, at 45 degrees, you would need to extend the blade to 1.41"
This gives a chord length of 6.96"
cos-1(2.25/6.96) =71.1
You would need an angle of 19 degrees relative to the blade to give the same cut as before.
From a practical perspective, this may somewhat increase risk from the method as more of the blade will be exposed. The top will also protrude first.
It does, however, offer a way to broaden the cove base if the original jig is imperfect - if you have reached target depth before target width, a bit of angle on the blade may suffice to fix it - you can effectively 'subtract' or 'steepen'/make more acute up to 3 degrees in this case.
I can't see how you could 'add' to an incorrectly fixed angle though, if you had a very slightly smaller diameter blade then that might be finagled to allow a slightly higher cut.
As I said, not every 10" blade is 10" - some are a little more or less.
I suppose the upshot of this thought model is - use your biggest blade of a given nominal diameter if you have more than one so that you can increase depth if you hit width before depth by reducing the blade diameter, and use the blade-tilt if you hit depth before width.
It may even pay to very slightly under-set the angle, perhaps 21.5 or even 21 degrees in the initial assessment as you can always get that back with the blade tilt.
Lost me at four decimal places. That's ten-thousandths of an inch.
Ain't this "FINE" Woodworking? heheh...