What affects getting a square crosscut with the miter gauge

[JPG]

Assumptions are necessary so as to exclude them from affecting the discussion(i.e. the assumed things can affect the results, but are not relevant to the discussion at hand).

1) The table is aligned to the blade so the miter gauge slots are perpendicular to the axis of rotation.

2) The table top surface is parallel to the axis of rotation.

Those two assumptions remove any non-squareness not caused by the miter gauge angle relative to the miter gauge bar that rides in the miter gauge slot.

That leaves us with two variables.

a) The angle of the miter gauge face to the miter gauge bar about a vertical axis when in the normally used position(bar in the slot).

b) The angle the face of the miter gauge makes to the table top that deviates from vertical.

Now the issue is, does the face angle cause the cross cut angle to be altered or indeed does it create a compound cut.


An angled face could cause the workpiece to rotate if held tight against the face(which causes the workpiece to lift off the table at either the leading or the trailing edge depending upon the direction of the face angle deviation from perpendicular to the table top.

That will not cause an unsquare cross cut nor a compound cut. The workpiece does rotate, but about an axis that is parallel to the saw blade axis of rotation.

If the workpiece is held tight to the table then the workpiece will have a single line/corner contact with the mitergauge face. That will also not cause an unsquare crosscut nor a compound cut.

If you want to verify this, place a round dowel under a workpiece with the dowel and the workpiece held tight to the miter gauge face. That simulates an extreme deviation from vertical of the miter gauge face. The resulting cut will be square. You must use your perfectly aligned miter gauge and check using your perfect square against the edge of the workpiece that contacted the miter gauge face.

Oh and that edge must be straight and flat.

[everettdavis]

I am unsure where you wanted to take this question but my thoughts are:

Beyond a blade that runs true, mounted securely on an arbor and on a true shaft (quill) presuming on a Shopsmith within the cut tolerances of the machine itself;

1) The relationship of the miter slots to the blade being equal throughout the cut (Parallel to each other)

2) The table surface being at 90 degrees to the vertical blade

3) The miter gauge on the table being 90 degrees to the blade and straight

4) The edge of the stock against the miter gauge being straight (cleaned up on the joiner)

5) Securing the stock through the cut

Am I answering in a way you are asking the question?

Everett

[benush26]

Okay,
However, thinking of this as multi contact rather than singular straight line contact (as in the case of the dowel) if the miter gauge face is not perpendicular, top to bottom for the entire width of contact, to the surface of the table , still given that all your other parameters are constant and consistent,, how could it not be a compound cut? If the work piece has four points of contact to the miter face yet the contact is skewed vertically, wouldn't that yield a compound cut?
Just spit ballin' here!

Be well,
Ben

[Hobbyman2]

[JPG]

Okay,
However, thinking of this as multi contact rather than singular straight line contact (as in the case of the dowel) if the miter gauge face is not perpendicular, top to bottom for the entire width of contact, to the surface of the table , still given that all your other parameters are constant and consistent,, how could it not be a compound cut? If the work piece has four points of contact to the miter face yet the contact is skewed vertically, wouldn't that yield a compound cut?
Just spit ballin' here!

Be well,
Ben

The difference is in what plane the workpiece is 'tilted'. Normally to create a compound cut either the blade is tilted or with a SS the table is tilted. That causes a the end on the workpiece to be cut a different distance from the blade at the top and bottom surface of the workpiece(i.e. a bevel). A compound cut will result if the miter gauge angle is also positioned non perpendicular to the slot/blade.

With a non-vertical face on the miter gauge the workpiece will tilt perpendicular to the axis of rotation of the blade if it is pulled tight against the non-vertical face of the miter gauge. Nothing has changed relative to the cutting action of the blade(cut line). A compound cut will not result if the miter gauge is positioned non perpendicular to the slot/blade.

[dusty]

I think the salient point is that perfection can not be achieved without performing a proper alignment. The entire system must be aligned not just those that are being used at the moment. Alignment is much more than just table to blade.

Example: We have not discussed here the alignment of the drill chuck (axis of rotation for some) to the table when in the drill press mode.

[Dansmith]

Excellent thread. I guess that what can be stated as a general premise is that one has a perfectly square square from which to guage (and good eyesight) . I learned plenty from my recent thread on square cross cuts.

[everettdavis]

I attempted to relate in quantifiable standards, verifiable conditions in terms of parallel, parallel through the range, 90°, straight, or flat.

Obviously if one's square isn't 90°, it is no longer a square.

Depending on the quality (and current condition) of the square, the quality in the blade, the uniformity of the stock cut, perfectly square is always measured to a standard defined by the precision of the measurement tools used to verify the cut.

"Yes, that's a square cut may mean one thing in woodworking, yet to a machinist, it could still be .0001 off.

If one's square is truly not, and the machine itself is adjusted using it, then it may be hard to determine if the stock cut is truly square, using that tool.

It will be off to the same degree as it was in establishing the reference for machine set-up based on how you position it.

If measurement uses the errant tool along the same plane of reference it may seem almost square, if juxtaposed, it could appear to be off by twice as much as exists.

What were we trying to quantify in the question, and have we answered it yet?

Everett

[JPG]

The intent of the initial post was to explain that the perpendicularity of the miter gauge face relative to the table top will not cause a 'compound' angle cut.

We are beating a dead horse, but some still are not convinced(do not yet understand) re several things mentioned in two previous threads.

Those who are not convinced would do well to understand all that Everett has posted here.

[Sherlock]

And make sure knob tightened down. Just learned that a few minutes ago. Hand tight may not be enough. Hence the holes in the knob. Just right to add a little oomph with the Allen wrench. Usually use miter saw or radial overhead but tied up at the moment and thought what the heck. Piece a little long and created enough drag no longer at 90 at end of cut. Learn by doing? Jeff