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A few days ago I started making a desk for my younger granddaughter. Last year I made the same desk for her older sister. I cut most of the wood for the second desk at the same time as I made the first desk.

I am cutting the tenons using a dado setup in my table saw. A sacrificial wood fence is attached to the regular fence. The fence is set so that I get a tenon with face approximately 3/8" from tip of board to shoulder. I use my miter gauge and keep the tip of the board against the wood fence.

I cut the waste off one side and flip the board and cut the other side. The problem is that the two sides are not cut the same. One side is longer than the other. Or maybe one side is shorter than the other. It varies between 1/32" and 1/64" in difference.

As I type this I realize I should have noted if it is consistently the same cut (first or second) that is short (or long). I have shut down for tonight so will not be able to pay attention to this until I do some more experimentation tomorrow afternoon or Wednesday . (Tomorrow morning is scheduled for golf.)

If the dado was wobbling the same thing would happen to both sides. The fence is not moving. I am keeping the tip of the board against the fence. The face of the board is square. (I just checked my combo square to be sure it was accurate.)

As I said, I am puzzled.

George
 

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boards are 4" wide or so?

I always use the miter guage for tenons against the sacrificial fence. There is no safety issue since the cut is open on the end over the blade. It does assure the workpiece stays 90 degrees to the blade/fence. I would look at the fence to see if it is attached securely to the main fence. I know you have a new Biesemeyer fence so, maybe you are using a "U" shaped sacrifial fence that caps over the Biesemeyer. How snug is that fit? A strip of tape will make it a snug fit.

Is there any lateral play in the arbor? Can you move the dado set in or out when the power is unplugged. That should even itself out under power at any case.... just looking for possibilities.

It the arbor nut securely fastened?

Is there a paper washer or other compressable piece in the dado stack?

I'd get several scraps and make some test pieces to recreate the condition. Keep the same face down for a test and flip it around.
Then turn it over and make the opposite side cut...any difference?
 

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are you positive that your miter gauge is 90 degrees to the blade? If not....when you flip it your tennons would off. 89.5 degrees might be enough to screw it up....
 

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Discussion Starter #4
I always use the miter guage for tenons against the sacrificial fence. There is no safety issue since the cut is open on the end over the blade. It does assure the workpiece stays 90 degrees to the blade/fence. I would look at the fence to see if it is attached securely to the main fence. I know you have a new Biesemeyer fence so, maybe you are using a "U" shaped sacrifial fence that caps over the Biesemeyer. How snug is that fit? A strip of tape will make it a snug fit.

This is exactly what I do. NO bES FENCE.
SACRIFICIAL FENCE IS SECURILY CLAmPED.


Is there any lateral play in the arbor? Can you move the dado set in or out when the power is unplugged. That should even itself out under power at any case.... just looking for possibilities.

nO PLAY OF ANY TYPE.

It the arbor nut securely fastened?

Checjed and double checked.

Is there a paper washer or other compressable piece in the dado
stack?

NO.

I'd get several scraps and make some test pieces to recreate the condition. Keep the same face down for a test and flip it around.
Then turn it over and make the opposite side cut...any difference?

Been there done that. Will run more tets in net couple of days.

George
 

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Whats the runout on your fence from one end of the blade to the other end....

If your fence is set .001 toed out.....this could cause it.
 

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Sounds like your blade is not perfectly parallel with the miter way slot. This takes a special adjustment to your saw. You shouldn't use the rip fence with the miter gauge. Attach a wood fence to the miter gauge that is longer than your parts and extends past the dado blades a few inches. With a small C-clamp you can attach a stop block to this wood fence. Glue some sandpaper to the wood fence so the parts can't slip. Don't back up after the cut.
 

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Discussion Starter #8
Sounds like your blade is not perfectly parallel with the miter way slot. This takes a special adjustment to your saw. You shouldn't use the rip fence with the miter gauge. Attach a wood fence to the miter gauge that is longer than your parts and extends past the dado blades a few inches. With a small C-clamp you can attach a stop block to this wood fence. Glue some sandpaper to the wood fence so the parts can't slip. Don't back up after the cut.
A parallel issue would effect both sides the same.

I also do not normally use the fence and miter gauge at the same time. However, with a dado operation there is no problem of a small part becoming trapped and flying back.

George
 

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not if as you cut, the blade is moving deeper into your piece (away from the fence)......then when you flip the piece for the other side it cuts exactly opposite. I had almost the same issue on my saw until I squared up my fence to a tighter tolerance. Then the problem was solved.
 

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Discussion Starter #11
not if as you cut, the blade is moving deeper into your piece (away from the fence)......then when you flip the piece for the other side it cuts exactly opposite. I had almost the same issue on my saw until I squared up my fence to a tighter tolerance. Then the problem was solved.
Remember, is there is a wobble it is happening at thousands of times a minute. How can it be different in a different time period?

'not if as you cut, the blade is moving deeper into your piece (away from the fence).' The blade never mover "away from the fence." It (they in the case of this stacked dado) is always rotating parallel to the fence.

George
 

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It is not rotating parallel to the fence If the fence is not perfectly parallel to the blade.....which was my question....is the fence perfectly parallel to the blade?
 

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My guess from a thousand miles away is the end of your stock is not square, or your reference surface your butting up to is not square,Your square your using is no longer accurate!
Try this reference on a smaller spot on the end of the stock same place each time.Right in the middle.
 

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I am cutting the tenons using a dado setup in my table saw. A sacrificial wood fence is attached to the regular fence. The fence is set so that I get a tenon with face approximately 3/8" from tip of board to shoulder. I use my miter gauge and keep the tip of the board against the wood fence.
The difference could be just from how hard you are forcing the piece into the fence. You might try positioning the sacrificial fence to stop just where the blade starts to cut.




.

 

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Also, a dull blade can sometimes push the stock ever so slightly one way or the other depending on grain and density variations. This is more likely when crosscutting and holding the piece against the miter fence by hand.

Kevin H.
 
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