Miter slots NOT parallel - problem?

[Bob Wingard]

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.

Thank you, George .. GREAT analogy .. I wish I had thought of that several posts back !!

I knew if these folks would just ask a Machinest or Tool Maker, they'd get an explanation that would satisfy them.

I knew I was correct, just couldn't explain it as simply as you just did.



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[Duncan Horner]

Thank you, George .. GREAT analogy .. I wish I had thought of that several posts back !!

I knew if these folks would just ask a Machinest or Tool Maker, they'd get an explanation that would satisfy them.

I knew I was correct, just couldn't explain it as simply as you just did.



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So working at an angle makes the machining scale more sensitive, but makes the measurement of deviation less sensitive?

Your experiment showed my point. Measuring at the 45 made the same deviation show up as a larger number on the plunger. The absolute measurement isn't accurate, but it does allow you to see a smaller deviation. More angle = more (qualitative) sensitivity, less (quantitative) accuracy. When you're looking for relative differences, an amplified scale increases the visibility of such differences.

[Bob Wingard]

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!

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?

I THINK this is what I started out saying .. .. for the purpose of comparing one end of a slot to another, in an attempt to align same, the actual number is meaningless .. you are trying to get both extremes to the same spot. All I started out saying was that in a skewed position, the "NUMBERS" are not true. I've used a screw in a piece of wood and a set of feeler gauges to determine alignment, and didn't care WHAT the number was .. only that it was the same at both ends !!


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[Tom Veatch]

...Your experiment showed my point. Measuring at the 45 made the same deviation show up as a larger number on the plunger. The absolute measurement isn't accurate, but it does allow you to see a smaller deviation. More angle = more (qualitative) sensitivity, less (quantitative) accuracy. When you're looking for relative differences, an amplified scale increases the visibility of such differences.

You've got it, Duncan! (but, for the record, it was my experiment, made in response to Bob's challenge, that was posted.)

[Bob Wingard]

So working at an angle makes the machining scale more sensitive, but makes the measurement of deviation less sensitive?

Working the cross slide at an angle allows you to take very fine cuts because each 0.001" movement of the cross slide yields something less than 0.001" of travel. You can take extremely fine cuts, but the accuracy of the dial on the lathe is gone .. unless you are an experienced Machinest and you know what the travel indicated on the dial equates to in the advance of the bit. As I stated in the drill press challenge, it takes more travel at an angle to accomplish the same forward advancement of the tool.

That probably didn't help, but I'm running out of ways to get my point across .. .. maybe George can help again ??


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[Duncan Horner]

You've got it, Duncan! (but, for the record, it was my experiment, made in response to Bob's challenge, that was posted.)

I knew I'd mess up the quotes somewhere, and I did, sorry, and thank you I'll go fix 'em

You can take extremely fine cuts, but the accuracy of the dial on the lathe is gone

Exactly what I've been saying. I think we've come to an arrangement. I was never interested in the number of the measurement, although it can be calculated rather easily given the angle. I'm simply interested in using the angle the measurement is taken at being used to amplify the magnitude of the dial travel.

[Phil Thien]

I knew I was correct, just couldn't explain it as simply as you just did.
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If it makes you feel better, go on believing that ..

[Bob Wingard]

If it makes you feel better, go on believing that ..

It does .. .. I will .. ..

thank you .. ..



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