compound slide

nightowl499

nightowl499

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ok guys i need a rule of thumb or a kentucky windage here, on my lathe compound set at 30 degrees
what is the depth of cut versus what the dial on the compound says ? please dont make my head explode with trig functions

thanks

Gary
 
nightowl499 said:
ok guys i need a rule of thumb or a kentucky windage here, on my lathe compound set at 30 degrees
what is the depth of cut versus what the dial on the compound says ? please dont make my head explode with trig functions

thanks

Gary
Click to expand...
Either half if 30 deg from parallel to Gluck axis, or 0.866 timers compound if 39 deg off square ( perpendicular) to chuck centerline axis. This is actual indeed towards axis for each movement along compound.
Basis of answer is either the sine or cosine of 30 deg in machinist handbook or on a calculator.
 
Big Bob said:
Either half if 30 deg from parallel to Gluck axis, or 0.866 timers compound if 39 deg off square ( perpendicular) to chuck centerline axis. This is actual indeed towards axis for each movement along compound.
Basis of answer is either the sine or cosine of 30 deg in machinist handbook or on a calculator.
Click to expand...
Excuse typos. Gluck was meant to be 'chuck'. Also '30' deg off square.
 
Another way to word it:
Amount compound wheel turned * sin(angle compound set at) = DOC (depth of cut)

If you turned the compound wheel .001 and the angle was set at 30 deg it would look like:
.001 * sin(30) = .0005

If you turned the compound wheel .007 and the angle was set at 15 deg it would look like:
.007 * sin(15) = .0018

Big Bob said:
Excuse typos...
Click to expand...
Just a heads up, there is an Edit button if you wanted to use it...
Bottom right corner of any post you make, just to the left of the 'Reply With Quote' link/button.
 
Last edited:
Big Bob said:
Either half if 30 deg from parallel to Gluck (chuck) axis, or ...

...Basis of answer is either the sine or cosine of 30 deg...
Click to expand...

iMisspell said:
Another way to word it:
Amount compound wheel turned * sin(angle compound set at) = DOC (depth of cut)

If you turned the compound wheel .001 and the angle was set at 30 deg it would look like:
.001 * sin(30) = .0005
...
Click to expand...

But neither of those answers is correct. To get rise & run, you need neither sine nor cosine - you need tangent, which yields 0.5773" of radial movement per 1.000" of compound movement if the 30 degrees is parallel to the lathe's axis. To get the compound dial to ALMOST EXACTLY correspond to diameter instead of radius, you need to set the compound to 26.5 degrees. You probably can't set it any more precisely than that, but if you could, you'd set it to about 26.564 degrees.
 
TDHofstetter said:
But neither of those answers is correct. To get rise & run, you need neither sine nor cosine - you need tangent, which yields 0.5773" of radial movement per 1.000" of compound movement if the 30 degrees is parallel to the lathe's axis. To get the compound dial to ALMOST EXACTLY correspond to diameter instead of radius, you need to set the compound to 26.5 degrees. You probably can't set it any more precisely than that, but if you could, you'd set it to about 26.564 degrees.
Click to expand...

Sorry TD but your trig is wrong. With the compound set 30* to the lathe c/l the compound is moving along the hypotinuse of the angle. We are trying to determine the tool travel perpendicular to the lathe center line. That is the side opposite the 30* angle. Therefore the tool travel is =(compound movement) * sin(30). Previous posters are correct.
 
Beans. Everybody get a good look at this - ya won't see it often... me being sheepish. Yer right, I was wrong - I was thinking a little different direction, and I can't even blame old age for it yet.

Tan(angle) would get you the "north" travel per unit traveled WEST, not per unit northwest. Sin(angle) gets you north per unit northwest.
 
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