Table Alignment (Squareness) Done on the Work Bench

[reible]

In theory the difference between the thickness of the body of the blade and the kerf divided by two gives you the clearance. Now take into account the angle through the blade caused by the off set from perfect alignment and you have a reasonable acceptable error.

Since blades are different those numbers are different but just as an example say I have a blade with a width of cut of .094. The body is say .084 then the difference is .010 so we half that and the number is .005. Now I don't have real numbers here but I could or you could but that is how one can come up with a base number.

When you do that with a real blade you would want to pick the worst case you have, ie the one with the least difference between kerf width and body thickness. I'm guess that those number are not a constant between manufactures and maybe even styles of blade.

Interesting enough a cheap blade might make things better as it might have a wobble dado effect??

Ed

[dusty]

OKAY, that's good information.

Here are some real world numbers to bounce against that theory.

The blade (plate) is .085" thick. The kerf created by that blade measures .136" or .137".

Therefore, the pass/fail criteria is (.137 - .085) = .051" / 2 = .026" and not the .005" that many of us have been using.

Some calculations using measurements depicting the span from the left side of the left miter to the left face of the blade. In each example, the 4.xxx" numbers are the front and back measurements on a given tooth.

(4.298" - 4. 276") = .022 / 2 = .011"

(4.284" - 4.254") = .030 / 2 = .015"

(4.136" - 4.086") = .051" / 2 = .026"

(4.285" - 4.273") = .012" / 2 = .006"

[reible]

Wow that is a thick kerf blade!!!!!!!!

Most of the blades I have are either .125 or .097 ish kerf but I don't have their base measurement. If one can assume the body at .085 then the numbers are in the .0065 range on the thin kerf. Again about the .005 number that we use.

I'll try and get out and do some measurements later today.

Where did you get a blade that has such a wide cut?

Ed

[dynabase]

"Some calculations using measurements depicting the span from the left side of the left miter to the left face of the blade. "

For clarification is it the left side of the left miter or the right side of the left miter?

[dynabase]

Shopsmith list several part numbers for rubber bumpers (517135, 517113, 516667). Does anyone have the part number for the 1 3/8 bumper. If I can get one of those I think my blade will finally center. I have the 1 7/16 bumper now and I'm still a little off of center. (Of course many people that know me will attest that I have always been a little off center.)

Michael

[dusty]

"Some calculations using measurements depicting the span from the left side of the left miter to the left face of the blade. "

For clarification is it the left side of the left miter or the right side of the left miter?

as stated: the left side of the left miter to the left face of the blade

[dusty]

OKAY. I rechecked the kerf width using a grouping of feeler gauges. Previously, I used a digital caliper to measure the kerf. This time I get .135
". This is the sum of all feelers from .020" to .025". It is not a blade that I use frequently but it has been in my inventory for a long time. I can not tell who the manufacturers is. It has been sharpened twice as indicated by an engraving on the plate by the sharpener.

[BuckeyeDennis]

OKAY. I rechecked the kerf width using a grouping of feeler gauges. Previously, I used a digital caliper to measure the kerf. This time I get .135
". This is the sum of all feelers from .020" to .025". It is not a blade that I use frequently but it has been in my inventory for a long time. I can not tell who the manufacturers is. It has been sharpened twice as indicated by an engraving on the plate by the sharpener.

Dusty, it sounds like you are measuring the kerf of an actual cut, rather than the width of the saw teeth. If so, the calculation of acceptable blade misalignment is "circular".

Unless the blade is perfectly aligned (with the miter slot if cross-cutting, or the fence if ripping), the teeth will cut both at the front (on the downcut), and also at the rear (on the upcut). Thus a mis-aligned blade makes a wider kerf in the workpiece.

This is theoretically true even if the misalignment is less than the clearance from the side of the tooth to the blade plate, although I suppose that for very small misalignments, the upcut may just rub/burnish without actually cutting.

[dusty]

OKAY. I rechecked the kerf width using a grouping of feeler gauges. Previously, I used a digital caliper to measure the kerf. This time I get .135
". This is the sum of all feelers from .020" to .025". It is not a blade that I use frequently but it has been in my inventory for a long time. I can not tell who the manufacturers is. It has been sharpened twice as indicated by an engraving on the plate by the sharpener.

Dusty, it sounds like you are measuring the kerf of an actual cut, rather than the width of the saw teeth. If so, the calculation of acceptable blade misalignment is "circular".

Unless the blade is perfectly aligned (with the miter slot if cross-cutting, or the fence if ripping), the teeth will cut both at the front (on the downcut), and also at the rear (on the upcut). Thus a mis-aligned blade makes a wider kerf in the workpiece.

This is theoretically true even if the misalignment is less than the clearance from the side of the tooth to the blade plate, although I suppose that for very small misalignments, the upcut may just rub/burnish without actually cutting.

Yes, that is what I measured using feeler gauges to get the width. The first time, I used a digital caliper to measured the width of the saw teeth.

http://www.esabna.com/us/en/education/b ... g-kerf.cfm

Look at the numbers though. The mis-alignment is minimal. I feel no risk in using the Mark V the way it is.

If I am wrong, I certainly hope some one tells me so and why.

[reible]

So looking at several blades in my collection the thin kerf ones are all advertised as .097". They do not speck the base portion of the blades but using a micrometer they vary from a very thin .075 to a .088. Again using worst case measurements the .097 - .088 = .009 thus a .0045 number. In the case of the thinnest blade the .097 - .075 = .022 or .011. The combo blade that I use most often is the one with the smallest room for error.

Again I don't know where one gets in trouble but at some point you will end up being off enough that the cut will be less smooth followed by a lot of back side teeth marks followed by potential kick back situations.

If it is off one way when ripping the wood will simply pull away from the fence and your rips will be narrow or in the worst case the the wood will be forced into the fence resulting in a jam and or kickback. This is where the danger is.

From information I have gathered .005 is a reasonable number and it is quite easy to do. If you can't get that alignment then you have either have a procedural issue or bad equipment. A lot of "experts" look for .003 which is also doable on a shopsmith. If I do an alignment and it checks at .005 I'll let it go but if I'm anything over that I tweak it. A lot of the times I'm better then .005 in fact I'd say 85% of the time I'm there on my first try.

Ed