How to Check Parallelism of a Table Saw
George VondriskaDescription
Raise your hand if you have not thoroughly checked the table saw to make sure the blade is perfectly parallel to the miter gauge slot in the fence. Now be honest, you can't shortcut this. You've got to make sure that they're right. If you don't take the time to do this, you can run into all sorts of problems. Kind of the least bad problem is that you're not gonna get the cut quality out of the blade in the table saw that you should be able to expect.
In the category of more bad problems, you can have safety issues, because it's possible, if the blade is not parallel to the slot in the fence, that you get binding issues that can cause kickback. And that's very, very bad. So what we want to do is make sure they're right. And what I want to do is show you a way that's very very low-tech and easy, and I hope that means then that you're gonna do it. So first thing, saw is unplugged.
Next thing, I'm gonna remove the guard. And I'm gonna raise the blade as high as it'll go. Now what's cool about this is that our tools are really, really low-tech. All we're gonna do is use a framing square and a metal ruler in conjunction with the table saw's miter gauge in order to do this check. Way it works is that the long leg of the framing square is gonna go up against the side of the saw blade.
Now, when I do this, one of the things I'm watching for at the leading edge and at the trailing edge is that I'm not on a carbide tooth. I'm on the plate of the saw blade because what'll happen is, let's say I'm on carbide on the back and I'm not on the front. Then there's a gap there alongside the blade. And because I'm offset by the thickness of the tooth. So dial that back down and right there, now I'm on the plate.
Now, very simple check. What I'm gonna do is make contact with the metal ruler against the framing square here, hold it in place on the miter gauge, and move it all the way to the back. And we can hear it. It's dragging along the edge of the framing square. If it loses contact, that tells me that the blade is goin' this way and my ruler is goin' this way.
Now to be double sure, what we want to do is also then check it from the back. So I slide it over, kiss it to the edge of the framing square, hold it with my fingers against the miter gauge, drag it back, and again, we can hear it making contact all the way down the framing square. If this is way out, if they're angled in like this, what's gonna happen as we move in that direction, is that this is gonna start to bind up. My metal ruler is gonna start to bind up against the framing square because of the angle. So it's one of three things is gonna happen.
It's gonna go perfectly like it did on this saw. Or as you move from one end to the other, it's gonna start to have a gap between the metal ruler and the framing square, or it's gonna start to bind up between the metal rule and the framing square. Those two actions, the binding or the gap, are gonna tell you what direction you need to move the blade in. At that point, check the owner's manual for your saw, make the correction, test it again, take the time to make sure that you get it just right. Again, low tech, simple way.
Framing square and a metal ruler is a great way to make sure your table saw is doing everything for you that it should be doing.
When I set up my Sears table saw years ago (first thing I did before using it) I check/set parallelism using my combination square, the head rode in the miter slot and I adjusted the steal ruler to touch the blade. as I slid the square along the blade I could see if there was a gap, there was so I tweak the mounts per the manual. Every so often I check it to ensure it is still parallel, its been solid over the years. I like the straight edge idea though, I will try it the next time I check the saw.
The article says to check the parallelism of the saw, the blade and fence but you don't complete the job. This only checks the blade and the miter slot relationship, a good start but then you need to also check the fence.
Yes, but... In woodworking, there is no such thing as "exact." There has to be some play in the miter gauge slot or couldn't move it. The face of the miter gauge is not exactly 90° to the slot. If the vertical plain of the blade isn't parallel to the miter slot, how can you even adjust that since it is factory-set? When you then tilt the blade for an angled cut, all bets are off. What about flexing of the blade? Lastly and just as importantly is a parallel and vertically perpendicular fence. Is it parallel to the blade along its entire path? Dirt, dust, rust and wear will affect its tracking. A test dial can only be used over short distances and has to placed exactly perpendicular to the table at each position, which is technically impractical and really impossible for the usual hobbyist woodworker.
But most important- isolate the power before doing any adjustments.
I have a used model 70 powermatic with no manual. my 12" blade to miter slot is out about 14 thou. How do i adjust it