checking TS fence parallel - does it matter?

Hookay - this one question worries me. The right half of the brain is convinced it'sa stoopid question, the left half thinks it's worth asking. Today's Lefties day, so here goes.
Been wondering about ways to check to see if the fence is parallel to the blade. Already checked the mitre slot to the blade, already checked blade for 90 degrees. Don't have any fancy dial indicators or TS-Aligner style tools.
So, my brilliant 5:30am, coffee induced idea was to rip a long strip of something. And measure consistency of width at the front and the back. I ripped about 5 feet of MDF, 3" wide and checked it with a caliper. 3.064" inches at the start of the cut and 3.058" at the end of the cut. Close 'enuff for me.
Then the Right half of the brain starts in with "you really didn't measure anything. Simply the distance between the cutting point of the teeth and the corresponding point on the fence." The Left half, denied the assertion for a few minutes and then tried the ad-hominem attack.
The Right side responded with - "all I can know (surmise) is that the fence does not deviate towards the plane of the blade - since I haven't had any kickback incidents. It could still be out of parallel, but deviate away from the blade plane. Or it might be parallel. My experiment was inappropriate!"
A few hours later, after the electroshock induced migraines left, I started wondering: does it matter, do I even care? My rip test indicates that I get a consistent width when using the fence and that's all that matters, right!?!
Ignoring *kickback issues*, would I care whether the fence is parallel with the plane of the blade?
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1) To check if the fence is parallel either slide it up against the blade, use the same sort of measuring that you used to check that the miter slot is parallel or simply check to see that it is parallel to the miter slot by sliding it over to it. The last has the highest potential error since it requires twice the number of measurements.
2) You will get tooth marks if you feed the wood through the blade at an angle. Sure it will cut, but it cuts best when the blade is parallel to the direction that the wood is moving.
3) Your test proves nothing. The piece of wood that is left will be no wider than the smallest distance between the fence and the blade. You could have a curved fence and have the same result. The quality of the cut would suck and the chances for kickback would be tremendous, but it would still work. It won't tell you anything about whether the fence is parallel to the blade.
-Jack
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mttt wrote:

If your miter slot is parallel to the blade, just check to see how parallel the fence is with the miter slot. You can clamp a piece of wood to your miter gauge and slide it over so the end of the wood touches the fence at the infeed side of the saw. Push the miter gauge towards the outfeed side of the saw (blade will have to be retracted) and use whatever (feeler gauge) to measure the size of the gap between the end of the wood and your fence. If the wood binds up as you push the miter gauge, your fence is closer to the miter slot at the front and you'll need to adjust the wood in the miter gauge at the back of the fence and pull forwards.
Since you have calipers, you can also use the depth measuring feature and check from the edge of the miter slot to the fence at both ends.
-Bruce
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: Then the Right half of the brain starts in with "you really didn't measure : anything. Simply the distance between the cutting point of the teeth and the : corresponding point on the fence." The Left half, denied the assertion for : a few minutes and then tried the ad-hominem attack.
Right hemisphere wins.
: The Right side responded with - "all I can know (surmise) is that the fence : does not deviate towards the plane of the blade - since I haven't had any : kickback incidents. It could still be out of parallel, but deviate away from : the blade plane. Or it might be parallel. My experiment was inappropriate!"
Yup.
: A few hours later, after the electroshock induced migraines left, I started : wondering: does it matter, do I even care? My rip test indicates that I get : a consistent width when using the fence and that's all that matters, : right!?! : Ignoring *kickback issues*, would I care whether the fence is parallel with : the plane of the blade?
Well, you don't really want to ignore kickback issues to begin with, and proper alignment of the fence is important to avoid that.
But otherwise, if your fence is out of parallel with blade, then the wood (during a rip cut) is going to get cut more roughly than if it were travelling parallel to the blade. And secondly, you aren't going to be able to get consistent width of the rip.
Ed Bennett (maker of the TS Aligner Jr) recommends less than .005" deviation front to back. I'm not sure how a deviation from parallel affects width of the ripped stock, but your piece of MDF has a .008 difference in width, and you can get better than that, I imagine.
The TS aligner is a really nifty tool. I spent some time on Monday aligning my new cabinet saw, and was able to get the blade parallel to the miter slot by .002", and the fence parallel to the miter slot by .001". They weren't out much to begin with, but it was nice to get it fine-tuned.
    -- Andy Barss
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NO...! ;~) Your fence can be way out and the width of your cut will still be consistant.
You want as close to perfect as possible to eleminate rough cuts and to avoid having to clean up the cut after sawing.
First of all you want to be "certain" that the blade is dead on as possible to parallel to your miter slot. If you have no dial indicator you can get very close with this method. You can attach a board to your miter gauge and put a screw into the end of the piece of wood. You want the wood to be attached such that the screw will reach and "JUST" touch a front tooth on the blade. MARK THAT TOOTH with a magic marker and rotate the blade until the tooth is at the back side. Move the miter gauge to the back side of the blade and see if the screw touched that same tooth. If it does not, adjust the table or trunion until the screw "JUST" comes in contact with the tooth in both positions. Be sure the miter gauge bar is not moving around in the slot if the bar does not fit snugly in the slot. Idealy you want to be with in .0 and .003" of being parallel.
After you have got the slot aligned to the blade you can drop a straight uniform thickness 3/4" thick board edge wise into the slot and push the fence up and against the board. Adjust the fence to lock in that position. Ideally you want the fence dead parallel to the blade also.
Test your adjustments. My saw is set up such that I am getting rips that seldom show any tooth markes on either the waste or keeper side of the board.

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Close is good, as long as you aren't pinching at the rear of the blade. Some people deliberately leave themselves a touch more clearance to minimize kickback by aligning the fence up to 1/16 out front to rear.
As to smoothness of cuts being affected - horseshit. If you can measure the deviation between the _only_ thing that affects the smoothness of the cut, the front to back of the tooth/work area, your fence is waaaay out of line.
Are you willing to bet the factory edge you ripped to is any straighter than the difference you measured?

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