Saturday, September 2, 2017

Big Bertha 3.0 and Vibration

Big Bertha (arrival and assembly pictures here) has been a bit frustrating because of vibration when moving it in altitude.  At first I thought the problem was the truss tubes were not stiff enough.  DobStuff who did the rebuild has since switched to an 8 Serrurier truss tube design instead of 6.  They offered to rebuild it for the cost of materials, a very generous offer.  The prospect of disassembling and sending it back was too traumatic, so I toyed with replacing the aluminum 1.25" OD truss tubes with 1.375" OD steel.  Yes, that will be stiff enough!  (I looked into carbon fiber tubes, but the cost was just too high.)

Before I got fully started on this rebuild, I found myself wondering if the real issue might be that resistance on the altitude bearing was the real issue causing the assembly to fight attempts to move it, leading to vibration.  At DobStuff's suggestion I applied Lemon Pledge furniture polish to the altitude bearing.  (I have never lubricated it in the three years since it was delivered.)  Last night it was better, but still fighting me.

Pledge helped, but still a bit much resistance causing vibration, so I  applied olive oil cooking spray to the altitude bearing.  It is now so smooth that the weight of the mirror cover will slowly put the scope upright.  With mirror cover removed, it is completely stable and smooth.  I had thought of using BreakFree CLP, but I think it has some penetrating power into some materials..

1 comment:

Fidel said...

I'd be concerned that the olive oil will both get gummy with age; and become much more viscous with cold temps (ever put any in the refrigerator?). And depending on your bearings, cleaning it could be difficult.

I'd consider some synthetic motor oil. It won't get gummy and should remain fluid at any temp you're likely to need it at. I use Mobil-1 for most things, and Mobil-1 Jet Oil 254 for weapons lube. A quart is about $15, (cf the latest miracle gun oil prices) and lasts years and years.