Tablesaw techniques

[Kevin Manuele]

Probably not new info for the pros here, but:

My son bought a new SawStop. After setting it up he was doing some test cuts, and said he was seeing about 0.003" difference at the ends of a 24" long ripped piece (narrower at the leading edge). Normally, 0.003" would not be a problem, but we did some sleuthing to find the source. This is what was happening.

He was not using a featherboard, which was a clue. With the saw off, and the blade clamped onto the riving knife, we found that the blade will deflect to the left when a test piece was pushed against the blade, and the piece would lift away from the fence at the leading edge. The greater the offset between push point and blade line the greater the deflection, which makes sense.

Adding a featherboard eliminated almost all deflection, though some could still be seen if pushing harder than normal (or advised) adjacent to the fence.

Test cuts using feather board and pushing closer to the blade line resulted in 0.0005" differences. The miter slot location limits the use of a featherboard to narrower pieces, so wider pieces would benefit from pushing nearer the blade line rather than at the fence.

All this is probably somewhere in table saw operating guides, but we thought we would share.

Kevin

[Jim Dwight]

.003? .0005? You'd better have really good technique on the micrometer you are using to even suggest you measured this kind of difference on wood. But that sort of difference is of zero practical significance when making something out of wood. I still think in fractions and .003 is about 1/256. For most things, 1/64 accuracy will work out fine. Half that essentially always.

You didn't mention which sawstop but my PCS arbor is very beefy. If you got defection of the blade, it would be the blade itself deflecting IMHO. That is a LOT of pressure. I also wonder if your fence is not towed out too much causing you to want to push really hard on the wood to keep it in contact.

I agree that featherboards are a good idea, especially if your technique may not be great (yet).

[Robert Hazelwood]

Some people here get really touchy when you talk about small numbers.

Ignore it, and thanks for sharing. And yes, AFAIK its accepted standard technique to push closer to the blade rather than the fence, because in the former case the rotational force keeps the workpiece tight against the fence.

You may also want to look at the fence straightness and alignment, if you haven't already. And magnetic featherboards are nice for not being limited to the miter slot.

[Andy D Jones]

1/256" is ~0.0039", much closer to 4 thousandths than 3.

The relative lack of hardness (and therefore also stiffness) in wood, compared to most metals, makes such small errors meaningless. The wood (and glue) will easily conform to such errors in joinery.

Such errors in surface finish may be a different matter...

Andy - Arlington TX

[glenn bradley]

Thanks for sharing this. The phenomenon you were experiencing is the reason many of us use push blocks instead of push sticks. This applies a greater surface contact and control area while feeding the stock. That being said feather boards are always used in my shop when I’m after a high degree of accuracy right off the tablesaw. Very few parts that I use in my pieces are used directly off of a machine however.

If you are using thin kerf blades, use a stiffener. Control your feed rate so that the saw is not under stress . . . oops, before I start rattling off a lot of advice, maybe we should know which Saw Stop model and what blade(s) you are using. Advice for a 5HP saw with a .146" kerf blade will differ from a 1HP contractor format saw with a TK blade.

[David Buchhauser]

After setting it up he was doing some test cuts, and said he was seeing about 0.003" difference at the ends of a 24" long ripped piece (narrower at the leading edge). Normally, 0.003" would not be a problem, but we did some sleuthing to find the source. Kevin

Hi Kevin,
I'm just curious - what kind of wood was it, how wide was the ripped piece and what were you using to make your measurements (micrometer, digital calipers, etc.)?
Thanks,
David

[Mike Cutler]

Kevin

Thank you for the information. While some may believe it meaningless, or non-essential, finding the cause of an error is never a meaningless exercise.
For those pointing out the "statistically unimportant" .003", cut 10 of them and glue them up and now you have .030", which is not statistically unimportant, or cut longer pieces and compound the error over the length.
I would also put forth that if you have a quality vernier micrometer, or dial caliper, a reading of .003" is very easy to quantify with repeatability, even with wood.
The wood will be a different dimension in a hour, or a day, but at that moment, it is the value.

[Brian Holcombe]

The error is worth removing. Parallel is parallel, .003” is a taper. It continues to allude me as to why chasing out small errors is a point of contention at all.

Accurate woodwork is done to very tight tolerances but woodworkers remain unaware of this as we generally do not measure for those tolerances. Instead we typically trim to fit.

As example, I make art frames. The frames I make have a removable back frame that is fitted into the exterior frame. This fit when done properly allows the frames to be screwed tight without distorting one another. However spending hours on it is not possible, instead the cutout must be done accurately.

The finished frame is accurate to within a few thousandths or less in order to accomplish all of these things. If I started with stock that had a .003” taper on all sides this process would require hand fitting which is time consuming. In a batch of 10 frames that would be hours of work.

So, drive toward accuracy, it will not be a detriment to your work.

[Patrick Walsh]

Try A blade stiffener and a feather board.

No promises but it may help, then make sure your fence is goes in and out properly and make sure it’s absolutely flat. Often they are not.

But start with a blade stiffener and see what you get?

[johnny means]

I keep reading the original post and all I seem to get is that if you don't hold the wood against the fence, it won't stay against the fence. Am I missing something?

[Mike Cutler]

I keep reading the original post and all I seem to get is that if you don't hold the wood against the fence, it won't stay against the fence. Am I missing something?

Johnny
I think the post illustrates the beneficial use of featherboards for consistent, repeatable, results.
Odd as it may sound, I never really used featherboards much on a table saw. I used them religiously on the shaper, but was not the tablesaw.
Basically, yeah, the wood has to be held tight against the fence as you pointed out.

[lowell holmes]

I replaced the blade insert with a wooden insert with a vertical wooden riving knife.
I never get kick back.

[Doug Garson]

I replaced the blade insert with a wooden insert with a vertical wooden riving knife.
I never get kick back.
I have the same setup on my saw but just to clarify what you have is a splitter not a riving knife. A riving knife is set at or just below the top of the blade and moves up and down when you raise or lower the blade. Yes this greatly reduces the chance of kickback but that is not what this thread is about. It is about consistent repeatable cuts which a splitter has little impact on.

[lowell holmes]

I agree mine is a splitter. I also use a push stick after cutting my thumb one time.
I also sometimes wear safety glasses.

[Derek Arita]

I keep rereading the OP's post, but can't quite grasp what he's trying to say. So many questions. Was the board jointed and all sides made parallel? Is it flat, with no twist. Is he feeding the board using his hand to keep it tight against the fence? Is the splitter exactly in line with the blade?

[kent wardecke]

I've noticed boards walking away from the fence. And way more than .003". It's even more noticeable on my uncle's 5hp Oliver with a 14" blade. It stands to reason, there's a lot of shear force being asymmetricly applied to the board

[lowell holmes]

I have a Dewalt thickness planer that will take twist and small bow out of lumber.
If you start with 1 1/2" material, there is plenty of stock to work with.

[Billy Merrill]

What are your results from the 5 side cut test?

[Doug Garson]

What are your results from the 5 side cut test?

I'm familiar with the 5 cut test from William Ing's video to square up the fence on a table saw sled. Not sure how you apply the 5 cut method to boards ripped along the fence.

[Andy D Jones]

I have a Dewalt thickness planer that will take twist and small bow out of lumber.
If you start with 1 1/2" material, there is plenty of stock to work with.

With a sled?

Andy - Arlington TX