Re: Direct Reading cross feed dial.
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"I find numerous problems with the scheme of moving both handwheels like that for the purpose of making a 29.5 degree vector."
I could be wrong, but I didn't read it as him DOING it that?way or suggesting that we do it that way.? Rather, he was using vector analysis to CALCULATE how far the tool? move directly into the work when you advance it a certain amount on the diagonal and to work out a table of those values.
Mike Taglieri?
On Sat, Jan 27, 2024, 18:14 Charles Kinzer < ckinzer@...> wrote:
I find numerous problems with the scheme of moving both handwheels like that for the purpose of making a 29.5 degree vector.? That's all that is happening.? Two vectors at right angles combining to produce a vector at an angle.
First, the standard way doesn't require any trig at all.? You simply view the compound dial as direct reading.? Of course, this is an approximation because the sine of 30 degrees is 0.5 which would relate to exactly a direct reading.? the sine of 29.5 degrees is0.4924 so, technically, there will be an error.? But it is so small that it is typically ignored.? For example, if you had a 0.100 thread depth (pretty big thread in the mini lathe world at least) you get 0.0985" thread depth or a 1.5 thousandths error which is going to be within pretty much anybody's spec for a thread like that.? For typical smaller threads the error is in tenths because the error is about 1.5%.? How much absolute error is that for a 10-32?
Second, the primary purpose of the 29.5 degree compound is to have most of the cutting done on one edge and the other just as a skim cut.? By using the cross slide as part of creating the vector, that goal is substantially degraded as there will be too much cutting on the right edge (for typical right to left threading).? Since the scheme violates the primary goal, anyway, why not just go straight in and be done with it.
Third, you have to accurately set NEW positions on two handwheels.? That certainly increases the exposure for an error and a spoiled part.? Machinists typically don't want to do things a hard way when there is an easier one.
Charles E. "Chuck" Kinzer
On Saturday, January 27, 2024 at 11:17:39 AM PST, davesmith1800 < davesmith1@...> wrote:
Take a sharpie and cross out the numbers on your dial, then double them and write the new numbers in.
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Brian?
Sharpie may last 30 seconds. I like the look of manufacture type dial. My second lathe had most of marks worn off and I used a center punch to fix it look tacky Dave?? Dave?
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