I am going to make a plate that is a close fit on the neck of the compound as well as being a close fit up under the compound base. The measurement of the diameter of the neck and the distance between the degree ring and the underside of the compound base are both critical measurements. The other dimensions for the plate are not critical. There was some differences in the gap that I'm measuring in the picture above so I am opting to make the plate to the biggest dimension then hand scrape the underside of the compound to effect a very close fit. The underside of the base is a bit concave near the neck but this won't worry anything, I am not measuring close to the neck, only out near the periphery of the degree ring.
Here is a close up showing the step on the degree ring, there will end up being a clearance recess in the plate to accomodate this step. The recess in the plate will also have a clearance recess for the larger diameter of the degree ring to fit in. If you look very close you may be able to see the slight concave area on the underside of the compound in close to the neck.
Here is the first side, top side, finished. The bore that fits the neck is finished and is a very close fit on the neck. The neck can be offered up to check fit. By measurement and test I got it nearly to fit then I polished the bore to remove the last poofteenth with a linishing stick. When holding it in the 4 jaw I made sure that there was enough room at the back to get a hook nosed tool in there to do a small "set-up" cut on the back face.
Here is a close up shot, the small "set-up" cut can be seen to the right of the jaw.
Job removed from chuck showing the back side and the "set-up" cut.
I am holding the plate using Aluminium "soft jaws". I will use both the set up cut area and the faced section of the first side to set up this side of the job. It is actually a job as it's not mine, it's a paying job, be a bit of pocket money for more nick-nacks. I had the owner send me the bottom bits of his compound so I could make the plate to custom fit.
Here the job is finished being set up. The bore is true and the faces are true. I got the faces so the needles on the indicators were only deviating more or less within the width of the line and needle. Certainly well less than .01mm that both indicators are marked. .01mm is about .0004inch. It will pay to have the top contact face of the plate as parallel as possible to the recess face that the degree ring contacts.
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