Now is the time to complete the vernier assembly and all its associated parts. We are aiming to produce the assembly shown below:-
There are five parts to this not already made (all of which are brass except the central shaft, which is silver steel):-
The first is Item 39, the Micrometer Dial.
The central hole should be reamed 4mm.
Item 40, Micrometer Shaft
Silver Steel. Remember that this could be made from 4mm brass to eliminate the greatest source of potential navigation errors from changes in temperature.
Item 44, Micrometer Thread
This part can be threaded using either a single point tool on the lathe or by using an M20 x 1.5 fine die. The former choice takes longer, but will be better in this application as you have more control over the thread form. Added to which, if you haven't got a die, it'll be an expensive purchase to do just one job. The central hole should be reamed 4mm.
Now the locking screws to keep everything on the shaft:-
Obviously, these items can be bought, but for completeness, I've drawn them. Also, having had to buy material to make other 3mm threads, I wasn't going to spend extra money on buying locking screws.
Now, the assembly
Item 77 is Loctite 222 thread lock. If you are certain that you've done nothing wrong, you can solder Item 44 to the shaft - this will enable you to stop worrying about stripping the tiny thread on Item 45.
Note: 0.025mm (half a thou') axial float of item 39 relative to item 44 can lead to a 1 minute of arc (1 nautical mile) error. This is VERY important to set up with negligible float. If you can get an automotive feeler gauge in to the gap, it's too big!
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