Adjusting the miter fence

[buddyroo]

I have spent about three hours attempting to adjust the miter fence on my BT3100.

The directions on page 39 of the manual leave a lot to be desired. "Push left rear of miter table snugly against miter base as shown by arrow S in figure 56 and secure." Just exactly how does a person "secure" it? Tighten the hex nut? Tighten the screw? Tighten them both? Hold it with your hand while simultaneously holding the square against the blade and the fence with your second hand, leaving your third and fourth hands free to adjust the other screw while keeping the hex nut from moving?

I read the "three steps article" but was unable to figure it out. Got lost when it said that if your measurements were the same that the saw was aligned, leaving the left front screw loose.

The Kirby article about aligning the saw assumes a piece of MDF that I do not have, nor do I understand how to make one.

Any suggestions would be appreciated.

[gmack5]

Some thoughts......

Buddy, your right! I think you're confused.

The first thing you need to do is get the SMT adjusted to run parallel to the Saw Blade (forget the Miter Fence for now).

Once you have the SMT adjusted to run parallel, THEN you can adjust the Miter Fence to be perpendicular to the Saw Blade.

Keep in mind that if you attempt to reverse the proceedures, it will not work as you think it will.

You MUST get the SMT adjusted to run parallel to the Saw Blade before you attempt to adjust the Miter Fence. There are several different ways this can be done..Do a search on "SMT" and "Adjustment".

[buddyroo]

I already adjusted the SMT to run parallel to the blade before I moved on to adjusting the miter fence. Sorry, should have mentioned that.

[JR]

I already adjusted the SMT to run parallel to the blade before I moved on to adjusting the miter fence. Sorry, should have mentioned that.

So there's really not much left to do!

• Loosen the knob on top of the miter fence
• Apply a carpenter's square to the side of the blade, making sure it doesn't rest on any teeth
• Align the miter fence with the second leg of the square
• Tighten the knob on the miter fence
• Cut wood at 90 degrees

JR

[buddyroo]

Doing exactly that, my estimate of the amount of the error is 1/16" in one foot. In other words, if one side of the square is held firmly to the uncut part of the wood that was held against the miter fence, and the square is touching the corner of the cut side, the square will be around 1/16" away from the cut side of the wood at a distance of 12" from the corner. What amount of error is to be expected?

[LarryG]

What amount of error is to be expected?

None, basically. Wood being wood, absolute, machine-shop-like precision is difficult, but over 12" you wouldn't want to accept variations of more than a few thousandths.

Is your square truly square? Some framing squares are, many are not. They are tools intended mainly for rough carpentry (house framing and the like), for which 1/16" in 12" would be plenty close enough. For woodworking, not. Do you know how to test your square, and "tune" it? Better yet, do you have a drafting triangle you can use instead? (These too are subject to manufacturing errors, and thus should be tested for squareness themselves, but they are usually much more accurate than framing squares.)

[buddyroo]

The square is a Stanley carpenters rafter square. No idea how to test or tune a square.

[LarryG]

Testing: Hold the long leg against a known straight surface, like the edge of a sheet of plywood. Draw a line (with a VERY sharp pencil) along the outside of the short leg. Flip the square over and place the long leg back against the straight surface and align the short leg with the pencil line. If there's any deviation, i.e. if the short leg doesn't follow the pencil line exactly, the square isn't true. The amount of error will be equal to one-half the observed deviation. (If your square is indeed off by roughly 1/16" over 12", this means you could see a discrepancy of more than 1/8".)

Tuning: To make the ends of the two legs move away from each other, i.e. open up the angle they form, strike the square with a hammer at the INSIDE of corner where the two legs join. To make the ends of the two legs move TOWARD each other, i.e. close up the angle they form, strike at the OUTSIDE of the corner where the two legs join.

The tuning operation is a little delicate, and takes some practice to get right. Strike the square only two or three times, check it for squareness, repeat as needed.

Which is why itis better to start with a drafting triangle and check its accuracy using the same method described above.

[buddyroo]

I have a new sheet of plywood in the garage. Checked the square and it is fine, but thanks for the tip on checking and tuning it. I printed it and put it in my misc. woodworking file.

[JR]

Checked the square and it is fine

Ok, so the square is good, but the cuts are not.

IMO, you gotta go back and check your SMT alignment. If the fence is square to the blade, but the cuts are not, then your SMT is not moving parallel to the blade. You want the SMT to move within a few thousands " of parallelism.

Then, (sorry for repeating myself, but it's an important point) you have to cafefully place the square against the blade so it's flush up against it. Raise the blade to maximum height to assure you've got plenty of blade to work with. Don't put so much pressure on that the blade deflects. With the miter fence loose, carefully move the SMT so the fence butts up against the square. Tighten the fence down and take note of the square and fence relationship. If they're not tight against one another, do it over again.

JR

JR

[rcp612]

Testing: Hold the long leg against a known straight surface, like the edge of a sheet of plywood. Draw a line (with a VERY sharp pencil) along the outside of the short leg. Flip the square over and place the long leg back against the straight surface and align the short leg with the pencil line. If there's any deviation, i.e. if the short leg doesn't follow the pencil line exactly, the square isn't true. The amount of error will be equal to one-half the observed deviation. (If your square is indeed off by roughly 1/16" over 12", this means you could see a discrepancy of more than 1/8".)

How about using the 3-4-5 rule? I've tested my square this way more than once and it seems to work OK. Call me paranoid but I don't trust plywood edges, or any other lumber edges to be "straight".

[buddyroo]

Got it done.

I believe that the problem was that both the SMT base was out of square AND the miter fence was not exactly square to the blade. First, I made note of which direction I had adjusted the miter base and when that adjustment improved the cut I continued adjusting in that direction. I also discontinued the use of the quickstop, which I think needs readjusting, and set the miter guage much more carefully.

Thanks to all of you who contributed their time and ideas toward helping me.

I greatly appreciate your assistance, as well as the efforts of all those who share their expertise in these forums.

[JR]

I also discontinued the use of the quickstop

You know, in all the years I've owned my BT I've never once used that thing.

Glad to hear you got 'er going!

JR

[cgallery]

Some day if you are at Harbor Freight, I'd pickup an inexpensive indicator and use my instructions to dial your saw in. My SMT base and fence are parallel to the blade by better than .001". And they are parallel to each other by approx. .002" front to back.

http://www.cgallery.com/jpthien/3k.htm

[LarryG]

You know, in all the years I've owned my BT I've never once used that thing.

No kiddin'? I use the BT's quick-stop all the time. In fact I virtually never use the SMT fence without also using the quick-stop, since I use the BT's SMT for wider, 90d crosscuts and make almost all mitered cuts on my CMS.

Funny how different owners view the value of different features of a given tool (or whatever). Part of what makes the world go round, I guess.