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Vintage GEM with babitted bearings - Lubricate..?

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#1 metricpoodle

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Posted 21 May 2009 - 09:54 AM

As posted in the Classic scope sub-forum, I am new, proud owner of a 1950's Newtonian built after the Thompson book, all the way down to the poured babitted bearings for the GEM mount over wooden tripod.

The whole has not been cared for in a very long time, and I wonder if I should lubricate these, and what to use.

Any suggestions?

#2 Rusty

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Posted 21 May 2009 - 10:02 PM

Babbitt alloy isn't a standard; it can consist of tin, copper, lead, and/or antimony. It should be treated as a soft material (although the alloy matrix consists of hard and soft crystalline structures). It should NOT be exposed to unlubricated operation.

Most likely, yours isn't motor-driven, so its demands for lubrication are quite modest. You didn't mention if grease fittings are installed; if they are, a cheap grease gun and any lithium soap-based grease will do. If you have to disassemble to lubricate, investing in Super Lube General Purpose Grease will do well.

#3 metricpoodle

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Posted 22 May 2009 - 07:58 AM

The mount was made per the Allyn Thompson book, which called for "pure lead" -insisting on spending a few more dollars for the real thing(!).

Does a pure lead bearing surface have any special requirements..?

#4 Rusty

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Posted 22 May 2009 - 10:54 PM

I would doubt that it's "pure lead", as that's generally unsuitable for bearings (although it can work in continuous-lubed high-speed low-load applications, but that would be archaic, and rare). Most likely it's one of the high lead-containing Babbitt alloys (Something like 80% PB, 10% Cu, 10% Sn).

Same recommendations regardless of the alloy proportions, even it was made unwisely of pure lead.

#5 Bart

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Posted 23 May 2009 - 08:35 AM

How about some pics of the scope in question?

#6 metricpoodle

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Posted 24 May 2009 - 07:32 PM

Yes, pics of course...!

I keep the scope in a week-end place where skies are decent.
I will follow up with pics as early as possible.
The scope builder was a mechanical engineer, so he may have strayed from the Thompson book instructions a bit.
For example, I noticed that the mirror cell and mount look very much like the unit offered by Criterion Mfg Co. , Conn. in ads of the day. Criterion was a couple of towns over from my builder's home town.

#7 John Carruthers

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Posted 25 May 2009 - 02:42 AM

The mount was made per the Allyn Thompson book, which called for "pure lead" -insisting on spending a few more dollars for the real thing(!).

Does a pure lead bearing surface have any special requirements..?


I've used graphite powder to good effect on plain bearings.






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