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How do I disassemble Vickers dual metric/imperial dial?

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Oily Rag09/10/2020 13:03:08
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550 forum posts
190 photos

Russ,

Taking Michael G's suggestion (thanks Michael!) of scanning the gear I have measured the tooth form of the dual dial driver gear as 21 deg 28 min included angle between the straight flanks, 0.034" depth of tooth, and with 0.0145 flat crest on tip and a 0.010 flat in the root. I can knock one of these up for you if you need me to but would prefer to make in brass (I hate machining nylon!)

PM me if you want to discuss 'offline'.

vickers dual dial 001.jpg

Regards,

Martin

Russ B10/10/2020 10:15:33
635 forum posts
34 photos

Well, I got there in the end!

After all the trouble I had with the crossfeed dial I decided to strip and clean the compound, which turned into a full strip and clean of the compound slide.

Interestingly when I stripped the much smaller vickers dial, it was actually exactly the same internally, the graduated dials were just machined down to around 3/8th larger than the press fit hub as per martin’s photo above actually, you can see comparing his dials to mine, mine have much more meat on the dials!

After some comparison between the two, I reached the same conclusion but for a different reason which is kind of important just in order to understand what went wrong. Basically the press fit steel hubs internal spigot had been machined or rubbed down, presumably damaged OR a replacement part intended for what looks like the later design that Martin has NOS of? So when the knurled wheel was tightened, rather than locking the steel hub/graduated dial to the shoulder on the shaft it was pushing it into the steel mid plate. After machining the mid plate down there was then a small interference with the gear carrying backplate that retains the driven wheel and mid plate, only very minor, a quick hone and everything was as good as new, almost. The locating peg that holds the driven half of the assembly in place is a bit damaged, and slotted more than it should be! The whole assembly has obviously seen some abuse.

So all functional now, albeit without the imperial readout as I had to remove the damaged pinion gear.

Edited By Russ B on 10/10/2020 10:17:16

Oily Rag10/10/2020 10:55:56
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550 forum posts
190 photos

Glad to hear you have sorted it. The offer is there if you want me to make you are new pinion gear - I can borrow a suitable cutter from my 'instrument man'. If you want a replacement - just check that the details of yours are similar to mine.

Might as well have it functioning as intended!

Martin

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