Main Table Alignment

[JPG]

Your prescribed method for checking flatness is?

No check other than to determine if it 'wobbles' and then pick a 'high' spot.

Same as 'Nick', but mark the disk.

Frankly I have found the tool kit in the miter gauge stop rod holes to be quite adequate. But then I do not measure the workpiece with vernier calipers.

[keakap]

Suppose that you removed the saw blade and mounted a router under the table. The spinning router bit has no preferred direction of cut.

Now feed a workpiece into the router bit, guiding it with your miter gauge. You will make a straight cut that is exactly parallel to the miter slot. No other surface is relevant.

Cutting with the saw blade is, in principal, the same. Except that to cut properly on through cuts, it must be aligned parallel to the miter slot, within a very small range.

I bought a ticket on the same train.
One could say band saw as well as router bit. And that leads to looking at a circular saw having but one effective contact point like those others. (what I used to get myself thru the process of a cutting operation without tools, i.e. in my head).

In a proper setup a cut is made in a workpiece at the blade tooth. Period.
Then the piece is advanced until another tooth makes contact and another cut is made. This continues through the piece. The cutting operation is complete (note "cutting") when the last fiber has cleared the passing teeth of the blade. As long as nothing is pushed laterally into the blade there will be no more contact/cutting.

Since the only cut is at the (front) tooth, the distance from the cut to the fence will not change, thus a series of cuts (the "kerf") will be parallel to the surface at the fence.

What a waste of materials! There's (what) an 1/16 of an inch or so of forward/back space involved in the actual cutting- where the tooth meets the work- while all the rest of that stuff is merely support!

Hm, had a thought (ouch!)- what if someone came out with a table saw blade that had only cutting teeth on one side? No Kick-Back!
(within reason...)

[dusty]

I bought a ticket on the same train.
One could say band saw as well as router bit. And that leads to looking at a circular saw having but one effective contact point like those others. (what I used to get myself thru the process of a cutting operation without tools, i.e. in my head).

In a proper setup a cut is made in a workpiece at the blade tooth. Period.
Then the piece is advanced until another tooth makes contact and another cut is made. This continues through the piece. The cutting operation is complete (note "cutting") when the last fiber has cleared the passing teeth of the blade. As long as nothing is pushed laterally into the blade there will be no more contact/cutting.

Since the only cut is at the (front) tooth, the distance from the cut to the fence will not change, thus a series of cuts (the "kerf") will be parallel to the surface at the fence.

What a waste of materials! There's (what) an 1/16 of an inch or so of forward/back space involved in the actual cutting- where the tooth meets the work- while all the rest of that stuff is merely support!

Hm, had a thought (ouch!)- what if someone came out with a table saw blade that had only cutting teeth on one side? No Kick-Back!
(within reason...)

If only we could have these discussions face-to-face with a Shopsmith handy to help make our points.

Yes, saw blade cutting occurs only at the front edge of the blade.

If the fence moves away from the blade, there will be NO BINDING and there will be NO KICKBACK unless the work piece is allowed to moved laterally toward the blade. Kickback occurs when the work piece contacts the blade on the back side as it comes up out of the table and toward the operator.

It is when the work piece is forced laterally (or allowed to move laterally) toward the blade that kickback occurs.

This is why the riving knife is aligned so that the right side of the blade (the teeth not the body) are in line with the right side of the riving knife. To work properly a riving knife need not be as wide as the kerf being cut so long as they are properly aligned.

One of the differences between a riving knife and a splitter.

Having said all of this, I still attempt to align my fence to be parallel with the blade to within .005" (front and back of blade at table height).

[BuckeyeDennis]

If only we could have these discussions face-to-face with a Shopsmith handy to help make our points.

Yes, saw blade cutting occurs only at the front edge of the blade.

If the fence moves away from the blade, there will be NO BINDING and there will be NO KICKBACK unless the work piece is allowed to moved laterally toward the blade. Kickback occurs when the work piece contacts the blade on the back side as it comes up out of the table and toward the operator.

It is when the work piece is forced laterally (or allowed to move laterally) toward the blade that kickback occurs.

This is why the riving knife is aligned so that the right side of the blade (the teeth not the body) are in line with the right side of the riving knife. To work properly a riving knife need not be as wide as the kerf being cut so long as they are properly aligned.

One of the differences between a riving knife and a splitter.

Having said all of this, I still attempt to align my fence to be parallel with the blade to within .005" (front and back of blade at table height).

Very interesting. I have always tried to align my riving knife to be centered on the saw blade. I'll have to think about that one.

I think I now see where we have been talking past one another. I agree wholeheartedly that, in an ideal world, cutting would only take place at the leading edge of the saw blade. But assuming that the wood doesn't pinch (or "flare"), that leaves exactly zero clearance on both sides of the kerf for the backside saw teeth to pass through on the upstroke. And it seems to me that since perfection is unobtainable, then some slight amount of cutting on the backside of the blade is inevitable. I believe that's what algale was referring to back in post #14, when he said that "only the kerf width will vary".

If your goal is to align your fence to within .005" of true parallel to the blade, that implies to me that shaving an extra 0.005" off the workpiece with the backside of the blade must be acceptable. But obviously, if the alignment gets too bad, the backside cut gets too large, and requires too much force, leading to kickback. And if the width of backside cut gets larger than the tooth overhang (or the tooth set, on a steel-toothed blade), you will have a problem in a big hurry.

[dusty]

Very interesting. I have always tried to align my riving knife to be centered on the saw blade. I'll have to think about that one.

I think I now see where we have been talking past one another. I agree wholeheartedly that, in an ideal world, cutting would only take place at the leading edge of the saw blade. But assuming that the wood doesn't pinch (or "flare"), that leaves exactly zero clearance on both sides of the kerf for the backside saw teeth to pass through on the upstroke. And it seems to me that since perfection is unobtainable, then some slight amount of cutting on the backside of the blade is inevitable. I believe that's what algale was referring to back in post #14, when he said that "only the kerf width will vary".

If your goal is to align your fence to within .005" of true parallel to the blade, that implies to me that shaving an extra 0.005" off the workpiece with the backside of the blade must be acceptable. But obviously, if the alignment gets too bad, the backside cut gets too large, and requires too much force, leading to kickback. And if the width of backside cut gets larger than the tooth overhang (or the tooth set, on a steel-toothed blade), you will have a problem in a big hurry.

We must be cautious here. There are no absolutes is this hobby. Variables like twist in the wood, runout of the arbor and flatness of the blade, etc all come into play.

The reason why you measure the same tooth on both the front side and the back side of the blade rotation is to compensate for some of that (arbor run out and blade flatness).

I just reallocated a combination blade to "plywood" because I could not hold tight alignment to the table.

I have been toying with a different method of measuring for parallelism. Using the one tooth in two locations (front and back rotation) is using two points of measurement along the cut line that are at most 10" apart.

If you make that same measurement at the front edge and rear edge of the table, you are using two points of reference along the cut line that are 22" apart.

[ATTACH]26192[/ATTACH]

With this setup, I measure mine blade right now at 3 36/64" and 3 37/64". See the attached image. If you want to be declared radical you could measure this with a micrometer rather than a ruler.

That is a reliable straight edge (a Starrett) positioned so that it just touches the tips to two teeth (front and rear) on the blade. I measured from the edge of the straight edge to the edge of the miter slot. The edge of the miter slot could (should) be better defined by having a runner in the slot that rises above the table top. My tables have been used extensively and they show the wear and tear. The edges are no longer clean and sharp.

I was pleased when I made these measurements today. It has been a couple months of regular, daily use since I did a table alignment check.