Table saw dado cut question

[Shane Sura]

Hi all,
I installed my brand new Freud SD208 tonight (mini gloat sorry no pics) on my Jet Deluxe Xacta saw. After picking up the dado insert and cutting the hole in it I went to make some test cuts. I followed the instructions for the 23/32nds cut and stacked the dado together. I made a total of three test cuts. In each cut I used a different run through speed. Each time it appeared that the back of the cut (the last section of the board through the blade) was slightly smaller in dado width than the start of the cut. At first I thought it was my run through speed and as such I really slowed down. I noticed that when I went slower the difference in width remained the same and all I got for my troubles was burning on the cut.

I checked with my calipers (non-digital) and it appears to be about a 64th out of wack. It is just enough to cause the plywood to not fit on the end.

As far as set up I was using my mitre guage to push the cut through. I was using a wide piece of scrap baltic birch plywood for the cut. As I said before I had it set to 23/32nd and I also had it set to a 1/4 inch deep cut. To test the fit I was using cabinet grade oak plywood.

Any ideas? This is the first I have ever run a cut through a dado stack so I am unsure if there are special techniques you all employee or tricks of the trade I am not aware of. What about speed do you all go extremly slowly or at a normal feed rate? Suggestions, hints, opinions welcome.


Shane

[Cliff Rohrabacher]

That's spooky.
The width changes.
Weird. Not a thing I've encountered.

Are the sides of the cut even and square to the side of the stock that was against the fence?

Or stated another way :
Is one side of the dado cut square and the other not?

Is the saw arbor wobbly?

Does the miter fence slide in a nice snug fit with the track.

Do you use an extension (straight chunk of wood extending the miter fence) on your miter or do you use it naked?

What about if you use a sled that tracks in both miter slots?

Have you enough slop in the miter fence to put a bit of scotch tape on one side of the rail?

My focus on the miter fence and track is really my thinking that there seems something sloppy about the track / rail assembly that allows it to rattle around early on in the pass and then it tightens up as you engage the rail further in the track.

Other than that, I'm stumped.

[Charles Wiggins]

Shane,

My first thought is that it wasn't your dado slot, but that your test stock wasn't a consistent thickness, but you seem to have accounted for that?

Are you saying you measured the width of the dado slot with the calipers and one end was 1/64" narrower? If you did, and one end is actually tighter than the other, I would be looking at any factor that would have allowed your stock to shift side to side while moving over the dado blade.

Or possibly (just guessing here), if the arbor nut wasn't completely tight, you might have begun your cut with a bit of play in the dado stack and the resistance of your stock might have allowed things to "tighten up" as you progressed.

[Dave Falkenstein]

I suspect it might be your miter gauge. If the miter gauge is not snug in the table slot, and if you move the miter gauge in the slot as you make the cut, that could cause the problem you described. You might be starting the cut pushing the miter gauge against one side of the slot, and finishing the cut pushing the miter gauge against the other side of the slot.

[Rick Gooden]

Sounds supernatural to me. How does the width of the blades shrink or expand?

[Bruce Wrenn]

My first choice would be that you have the outer cutters on the wrong side. When you look at teeth, the points should be on the outside of the stack. Outer blades should be labeled "This side out". Also, check and see that you don't have a chipper in backwards. I can tell you from EXPERIENCE that this doesn't help matters. I have a Forrest Dado King, but my SD-208 is the workhorse in my shop.

[jerry nazard]

My guess is the stock is shifting laterally against the miter gauge. Stick a strip of sandpaper onto the face of the miter gauge to keep the stock stationary, or clamp it to the gauge.

[Tom Veatch]

There are only two things I can think of that would cause the width of a stacked dado cut to vary along the length of the cut. One has already been mentioned - allowing the work to slide to the side slightly as the cut progressed. However, I would expect that to cause the end of the cut to be wider than the beginning of the cut. That's not what is being reported.

The other cause is allowing the miter angle to vary from "non-square" to "square" as the cut progresses. That would cause the start of the cut to be wider than the end of the cut and is what I think is happening here.

Assuming the dado is about 8" in diameter and is set for a 1/4" deep cut, that means 1/4" of the blade is exposed above the table and about 2 7/8" of the blade is exposed along the table in the direction of the cut. With those parameters, a variation in miter angle of only about 0.3 degrees would be sufficient to cause the width of the dado to vary by about 1/64".

The OP didn't say how wide the work was, other that it was a "wide piece of scrap". I know with my Jet Exacta using a miter gauge with any work piece wider than about 9-10 inches is very loose and imprecise at the beginning of the cut.

My guess is that at the beginning of the cut, the miter gauge isn't fully engaged in the miter slot and allows the angle to "wobble" by the aforementioned 0.3 degrees causing the dado kerf to become wider. Then as the cut progresses, the miter gauge becomes more fully engaged reducing the "wobble factor" as well as the slop in the dado width.

[Charles Lent]

I agree with those who think your problem is play in your miter gauge. On a wide board with very little of the miter gauge's bar in the T-slot you can get quite a bit of side play. Try making another cut, but this time use your miter gauge backwards - put the head of the miter gauge in the slot first so your board follows the gauge rather than leads it. This makes holding the board against the miter gauge a bit more difficult, but the miter gauge's bar will be further into the T slot when the blade is making the cut. I do this sometimes, but usually prefer using a home built cutting jig whenever I need to make straight cross cuts on wide boards, as the miter gauge just isn't a very accurate way to cross cut or dado cut wide boards on a table saw.

Charley

[Shane Sura]

Thanks for all the highly detailed responses. The more I think about it you are probably right about the mitre guage. I do know I put in the blades right as I checked the directions three times! It was also late last night when I was doing my test cuts so I am going to do some more tonight and let you know my findings.

Shane

[Rusty Elam]

Why dont you do some test cuts with your fence?

If its the same width end to end it has to be your miter gauge or slot.

[Michael Panis]

Hi,

I'll bet my 50 cents on the mitre gauge, especially if you didn't finish you cut by pushing the wood all the way across the blade. If your mitre gauge is misaligned and you stopped once half the blade cut through your workpiece, then the rear of the blade would have cut through the front of the piece, but not the back, explaining why the side that enters the blade first is wider than the side closest to you.

---Mike