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Making-A-Taper-Gauge

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awemawson:
So having totally failed to be able to accurately measure the J&S cylindrical Grinder table swing radius I thought I'd 'just go for it' using the table angle calibrations and check progress with micrometer blue and adjust accordingly. Now I have removed the chuck I have it's female taper as a 'standard'.

Setting the table to 14.25 degrees the graduations are rather coarse, however the first tentative 'bluing up' showed reasonable (but not perfect) contact (Don't be confused by the layout blue that the parallel section of the gauge is covered in - this is just so that I can see the grinding as it happens) I've never set the table over so far all the time I've had this machine!

One iteration of angle tweaking later and the contact was pretty good so I went on to remove 25 thou of diameter in stages bluing for contact and checking engagement depth at each increment. By recording progress hopefully I can accurately predict an endpoint when the taper is the right length and the smaller face has just come into contact with the inner face of the chuck recess.

Had to stop at this stage due to other commitments but will resume play later !

awemawson:
I finally got back to finish grinding the taper gauge after many distractions and interruptions.

Continuing to plot progress in a crude chart gave me a bit of confidence that I wouldn't overshoot, and in the end I left a calculated 90 microns between the two faces that squash the O rings, while still giving full taper engagement. As a check I used progressively thinner shims to prove engagement depth, a surprisingly delicate test - you can adjust things so the taper just 'floats' on the shim with no trace of looseness.

I just need to put it on the surface grinder and put a flat on the upper edge as a tell tale for full engagement for the final part.

awemawson:
And finally - I finished grinding the 'tell tale step' at correct insertion depth this afternoon so hopefully that's the gauge finished.

The grinding set up was more stable than it looks, but I wanted to leave the expanding mandrel in place just in case I need to give it another lick on the taper face. Although the expanding mandrel will re-locate pretty accurately in the bore we are talking fractions of a gnats tender bits so it's asking a bit much to get it back bang on.

Hopefully the next step is to actually use it in earnest !

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