Harold Hall

Workshop Processes


The calculation has to be carried out at each position that the infeed is changed and from the same baseline, see Sk. 4


Initially, I chose to make the changes in diameter at 1/8" increments, being one turn of my lathe's leadscrew. This resulted in quite large steps at the smaller end and I finally opted for 1/16" increments, half a turn of the leadscrew, resulting in 26 increments. A benefit of this choice was that as precision was not required it was unnecessary to read the micrometer dials just observe the position of the handle on the hand wheel, typically up and down.


Viewers will no doubt be interested in my method for avoiding the lengthy process of manually calculating the twenty-six tool infeed values. Actually, purely out of interest, I tried two methods.   First, using my CAD system,         see Sk. 5, I drew actual size the distance between the two extremities X and Z and positioned point Y (B). Using these three points I asked the system to draw a circle based on these (C) and from this called up the resulting radius. It was satisfying to find that even when calling up the value to 8 decimal places the result was identical to the calculated value.


I then drew a vertical line tangent to the peak of the curve, being the zero point for the tool in its starting position and drew horizontal lines at each of the 26 infeed positions, (D). These lines were then trimmed to the vertical straight and curved lines (E). With that done I chose a typical position and requested the length of the line, manually calculating this value also. Again, I found both values identical even at 8 decimal places. I have though exaggerated the curve and reduced the number of points on the sketch to make the drawing more easily read.


My CAD system has a database facility but I have never found the need to conquer it and this was also not the time to attempt this. As a result, I would have to select each line individually and write down the values as a list. Because of this, I resorted to my favourite method where repeated calculations have to be made, that is using a spread sheet.


It would not be appropriate to discuss spread sheets in detail for this process item but their major advantage is, over say a programmable calculator, or a CAD program, the ability to obtain a print out that can be used away from the computer, typically, in the workshop. Also, where only a limited number of values require imputing (HV, IVD and VD in this case) these can be changed and other sets of values obtained almost instantaneously, more about that to finish with.