Gallery, Projects and General > How do I??

How do I measure approx 60" ACCURATELY ?

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russ57:
What is the longest you can accurately measure? Assume 6". Make yourself 2 accurate 'guage blocks' and leap-frog them down the length of the table, measuring the last gap with whatever you have.
Or make 10 and line them up end to end.

Not as good as a 60" vernier but they are not common i understand..

-russ

WeldingRod:
I would expect a rational number.
Thus, I suggest setting an easy gaugable angle based on the assumed length and do a sine bar check on what you actually got.

Sent from my SM-G892A using Tapatalk

efrench:
Interestingly enough,  that angle (7.125 degrees) makes measuring the leg lengths easy.

awemawson:
Now that must be why they chose that odd angle, the ease of setting it up !

This is the angle of the  spindle nose taper of the A1 / A2 series of lathe noses. In my case I’m grinding test gauges for A2-5 and A2-6 chuck recesses.

That’s obviously more than just a mathematical co-incidence. I’d cottoned on to it being 7.125 degrees but not WHY it was chosen in the first place.

awemawson:
To set the swivelling upper table to 'zero swivel' the only accurate way seems to be grind something and do iterative adjustments until it is parallel, so at this point in time the headstock centre and tailstock centre are dead in line and on zero. Now sliding the tail stock to another position inevitably slightly alters this setting. Even tightening the table clamps makes slight movement of the swivel angle.

So my action plan is to grind a bar parallel (the one you see currently in the machine), and this bar is the same length as the arbor the gauge I want to finally grind to that odd angle is mounted on. So the bar can be removed and the arbor fitted (sprung loaded tailstock)  WITHOUT moving the tailstock.

Then using the calculated swivel displacement the upper bed can be swung over and the taper ground (hopefully!) accurately.

The tailstock obviously obstructs the bed ways when it comes to measurements of length.

In the past I've made up a long fat parallel test bar hoping to set it between centres and use a dti to set zero - it just doesn't work. In fact I can remember John Stevenson telling me to forget the idea (he used to run one of these grinders at one stage of his career) saying that you just have to keep making tiny adjustments and re-measure. In fact googling the question of setting a cylindrical grinder parallel I came across his answer to my question back in 2004 !!!!)


OK as promised, some pictures:

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