Tablesaw alignment puzzle

Cherryville Chuck said:

It's a problem that doesn't make sense David. I would check and make sure your square is accurate first. I just bought a $70 stainless steel one and it came with directions for truing it up if it wasn't perfectly square. Every time you make a measurement flip the square over 180* and make the same measurement from the other side. The only other thing I can think of is that there may be a slight deflection in the blade and arbor when you apply pressure to them but this should show in the saw groove in the sled. It would be noticeably wider than the blade. Is the back of the blade dragging and leaving saw marks when you cut on one side but not on the other?

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+1 with Charles.

Logically ==== How you can check the true of a cut it to cut something in half <> take one side and flip it over and line the kerf back together. If the kerf is perpendicular to you and the resulting near edge is not straight across the kerf, the fence is not lined up perpendicular to the blade. Doing what I described will show the off error and multiply it by two. That is how you can check is without a square.

If you bisect something into 2 pieces across it's width, you have 2 resulting angles that add up back into to 180 degrees. If one side is off, the other side is off the same opposite amount. That is just physics and math. (unless you have arbor bearing problems, but even that is rare.

Here is a quick 3 cut check to line up a sled or crosscut fence. This is a simple way I check my 4'-6' crosscut fences on my panel saw.

Take a 6" square piece material (ply, mdf, etc) and cut an edge and mark that edge as "A". Spin clockwise so the cut is against your fence and cut another edge of the stock. Mark that edge as "B". Turn the piece over (spin), so that edge "A" is still against the fence, "B" is furthest away from the blade and you will be cutting the side opposite from "B"... After trimming, mark that side as "C". Measure at the corners across from edge "B" and "C". That is twice what your fence is off by. Set to that measurement at twice that distance out from the blade (about 1 foot) on your sled fence.

I put a feeler gauge against the fence of that measurement, clamp a block to the table against the feeler gauge, remove the feelr gauge... then move the fence to that block, clamp the fence there, as I reset it.

On my 6 foot fences, I go out as far as I have support (about 4'), multiply the off distance by that off amount per/ft and reset my fence. On a sled, I leave one screw in tp pivot the fence and use "new screw holes" for the rest to fix it into place. Do not try to use the same old holes!!! The old screws holes will pull the fence back "off" towards the original holes.

Ray Y said:

Nick may be on to something. The arbor could draw to one side or the other if there is lateral play in the bearing. The blade may remain tight to one side on the right hand cut, but move from one side to the other on the left hand cut causing it to appear that the tracking is not parallel to the grooves.

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That is a rare defect and reaching. If that were true, you would notice any of that by the kerf in the bottom of the sled. As you cut from one side it would be tight against the kerf on one side and have room on the other side of the kerf, between the blade and the kerf. Remember that a blade cut the original kerf and should still be a zero clearance kind of affair... That kind of wear will want to pull the work "to" the blade, towards where the most force is applied... Aloose bearing also has the tendency to wander to the limits of it's looseness and follow the grain, resulting in an un-straight cut.

But if an arbor bearing is loose, they are not like wheel bearings. They are not tapered bearings. They are in fixed races(, most of them are sealed bearings) and not adjustable. There is no adjustable preset. If they are off, they are off and should be replaced. If they have lateral movement because of race wear, they will also have wear enough to pivot slightly on it's axis. And that kind of wear, you can "feel" by trying to move the blade by hand while it is attached... (unplugged for safety)

Hwdavid2 said:

Thank you Nick and Charles for your suggestions. Charles I favor your suggestion of slight deflection in blade and arbor. I do see a slightly wider groove at the head of the groove on the side that isn't square.
Nick, I have been careful to keep the pressure straight forward. Also, I get the same behavior with all three of my blade types. I wiil look for a lifting on one side. On my recent project I was crosscutting a half inch thick piece of maple which is 4 inches wide. The maximum deviation from square is about 1/32 over the 4 inches.
David

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Let me explain a different way so you can visualize something... Think of a loose bearing, bent blade or blade deflection in a different perspective... Say you have a bent blade. It would act like a wobble dado. Assuming your fence was true (as you implied), the cut would be true with a kerf wider than the blade. If the arbor bearings are loose, the arbor will deflect with pressure "each" side-- be a wider kerf and have burning one the side of the most force. The toe of the blade gets pushed away, as the heel of the blade gets pushed back against the work. That is the side the heel of the blade will be deflected and scuff against the work. If the bearings have play, it will have both burning, wide kerf and have rough saw marks. If you change sides to cut, those characteristics will change and move accordingly. You see blade deflection more often in high angle bevels and miter cuts... not usually straight up and across a crosscut or rip (unless. of course, it is really really dense hardwood).

Blade deflection "cut's" will not result in a straight up cut nor a consistently "straight" cut across through wood... Meaning, if a blade is going to deflect, it does not deflect consistently across the whole cut... nor does it delfect just on one side of the blade more than the other (changing directions or sides) rather you see a flutter in the cut and it is not consistent saw marks. Wood is just not consistently dense and you are not using a power feeder. You are not going to get a controlled, "consistent rate of deflection" outside a CNC Saw. I see blade deflections... but if a blade deflects on one side, it deflects as much on the other (normally). Unless... as someone mentioned on one side being dull... but those have a wandering kerf that pulls on the work... and you see that in the cut... More common or possible would be that the fence is off by a small amount.

0.03125" out at 4 inches... 0.09375" out per foot... 0.5625" out at 6 feet. That's would be like my 6 foot crosscut fence being off over a half inch out at 6 feet. It adds up.