Miter slots NOT parallel - problem?

[keith ouellette]

Good work then.

[Bob Wingard]

O.K. one last time, and I'm giving up .. ..

Those of you who have dial indicators and doubt my logic, try this.

Mount your indicator to a stud chucked up in a drill press, making sure the stem is as perpendicular as possible to the table ..

Set the quill to stop somewhere near mid-travel of the indicator stem ..

Lightly bring the quill down to the stop, and read the dial ..

Now, tilt the indicator such that the stem is at a 45 deg angle ..

Bring the quill to the stop, and read the dial ..



Test #1 .. the stem perpendicular to the surface will read a greater number .. and that is the way any machinest or tool & die maker will tell you how to setup an indicator.


<<<__ Bøb __>>>

[Kevin Downs]

I have to say that I'm now confused. Any chance you can snap some pictures to show/prove what you are saying? Please

[Tom Veatch]

...Those of you who have dial indicators and doubt my logic, try this.

Challenge accepted:
Here are the pictures for the 90° case:

First piicture is the setup. Note the quill stops are set to limit the travel to about 0.10 inches. Second picture is the dial indicator with the quill at the upper stop and the scale zeroed. Note the small pointer is at the "5" mark. Third picture is with the quill at the lower stop. Note the small pointer is at the "6" mark. Total quill travel is about 0.10 inches. See the next post for the 45° case.

[Tom Veatch]

Here are the pictures for the 45° case:

Quill stops have not been changed, dial indicator has been rotated so that the plunger is at an angle to the direction of quill travel. Angle was not measured, but is shown in the first picture.

The second picture is of poor quality, but I think you can make out the pointer positions. The quill is at the upper stop and the dial has been zeroed to the large pointer position. Note the small pointer is approximately on the "3".

The third picture is with the quill at the lower stop, a quill travel of 0.10 inches as measured in the prior 90° case. Note the readings. The small pointer is past the "4" and the large pointer is at approximate "44". A total plunger travel of approximately 0.144 inches.

These are exactly (within experimental error) the results predicted in my previous post, #26 in this thread.

[Chip Lindley]

Bob, I assume you are speaking of *plunge-type* dial indicators most common to woodworking machine setup?? Any measurement taken with a plunge indicator NOT at a right angle to the work will give a skewed and proportional measurement instead of a *true* reading!

But what about Dial Test Indicators?? The indicator point can be affixed at many angles relative to the head! ....Ya know what? Never mind!

For our woodworking purposes, would you not agree, that as long as that same angle is *somewhat* maintained, *proportional* readings will still be sufficient to indicate any runout or out-of-parallel condition?

Woodworkers are not machinists. A fraction of a Thou makes little difference in our work!

[george wilson]

Bob is correct.I am also a machinist. To prove,or understand what he is saying,draw a right angle triangle on a piece of paper,with the longest side parallel to the bottom of the sheet of paper. Make it aproximate a standard 30-60-90 degree drafting triangle. The exact angles aren't important,just approximate it. Next,some distance from the top corner of the triangle,draw a horizontal line across the vertical side,and extend it across the hypotenuse(sp?),or angled side.

Measure the length of the straight side from the top corner down to where you drew the horizontal line. then,measure the length of the slanted side from the top of the triangle down to where the horizontal line crosses it. You will easily see that the slanted length is longer than the vertical side's length. Apply that to what he has been trying to explain.

[Tom Veatch]

...
Test #1 .. the stem perpendicular to the surface will read a greater number ...

...You will easily see that the slanted length is longer than the vertical side's length....

George, I fully agree with you. And that cannot be reconciled with the above quote. As you said, the slanted length is longer and an indicator stem lying along that hypotenuse will read that greater length as a greater deflection than one that is lying along the vertical side, perpendicular to the surface. My previous post showing the experimental results should conclusively prove that.

[David Keller NC]

"My 'problem' was with the slots to each other and a double runner table saw sled. I wanted to know if having my slots spread away from each other (going front to back) would BIND the sled. This problem had nothing to do with cutting and everything to do with a double runner sled."

I think this will depend on the sled and how you make it (or how it's designed if you buy it). Generally speaking, you will not want to use a sled with wooden runners without at least 10-15 thousandths "slop", because humidity changes will likely lock it in place on the saw - you may need to use a hammer to remove it.

Similarly, I rather doubt you can make a sled with aluminum runners and place the screws so accurately that you can use aluminum extrusions that fit in the miter slot within a couple of thousandths. This, by the way, is something I learned the hard way, and had to take off significant portions of the side of the aluminum runners to get it to slide smoothly on the saw table.

[Wade Lippman]

Drop Grizzly an email and tell them your slots are out of parallel by 0.001" and post their reply.

[Phil Thien]

Bob is correct.I am also a machinist.

Boy, you guys almost convinced me.

But then I remembered that when I was 20 (almost 25 years ago) I was designing control systems for final dimensioning/polishing of control rods for nuclear reactors. So I can't be wrong, otherwise we'd all be dead.

[Duncan Horner]

You will easily see that the slanted length is longer than the vertical side's length. Apply that to what he has been trying to explain.

That's also precisely what I'm trying to explain.

The slanted line is longer, and this makes the measurement more sensitive to deviations. I'm not talking about absolute measurements, only that measuring at an angle will make any deviation more obvious, due to the greater travel of the gauge.

[Duncan Horner]

From yesterday

The angled indicator will read LESS than the actual amount.

The angled plunger will actually make the indicator read a lesser number

From today.

At about 90 degrees.

Total quill travel is about 0.10 inches.

At about 45 degrees

A total plunger travel of approximately 0.144 inches

Didn't this experimental result posted by Tom (thanks for the correction Tom) directly contradict what you earlier said?

[george wilson]

Usually the metal lathe's cross slide,which is graduated in thousanths, is used at its "straight in" angle of 90 degrees to the work,to reduce the diameter of work being turned. If you want to remove a very small amount,like .0001",ten times smaller than the .001" graduations,you set the swiveling compound ,which is on top of the carriage,to 8 degrees from the work,or nearly parallel to the work,8 degrees from being parallel. Then,when you move the dial on the compound .001",the cutter moves mostly sideways,only advancing .0001" into the work.

I'm not explaining this very well,sorry.

[Duncan Horner]

I'm not explaining this very well,sorry.

You explained it perfectly, and I understand completely. Thank you.