The context in this case is a KI256 which is a vacuum driven horizon, so the bearings see a ton of sh*it blown in; everything below a certain size according to the filter spec. I have never seen the inside of a KI256 but I bet it is pretty dirty.
Electric gyros should last a lot longer but rumour has it that – in some cases at least – they don’t. They have a DC input and use an inverter driving a 3 phase motor so the frequency could be anything at all…
OK; yes. The other “legal” aspect is that lubrication (and presumably the use of loctite) is banned per the MM, so the only option is to replace any affected parts. But since this type of servicing would be done, ahem, in the field, none of that is relevant.
I reckon this thread is going to be extremely helpful to a lot of people, especially as HBK move all repair work to themselves in the USA which will render repairs of all this stuff uneconomical to do legally, yet most owners of older hardware will not be able to rip it out and fit “glass” for 20k upwards.
Peter wrote:
In the last KI256 the repairer reported a “worn shaft” which I don’t quite get since surely the only wear should be in the bearings?
We now know from the part number that the radial play is to be in the range of 0.0002" to 0.0004". The bearing will need to be a light press fit into the housing and probably onto the shaft as well. It would only take a tiny amount of wear on the shaft to make the fit slightly sloppy – where “slightly sloppy” is more than the specified play in the bearing.
I reckon you must have found it, Alan. Brilliant work. I ought to buy some and see what they actually look like. It’s hilarious that they get charged out at something like $500.
No such thing as an unhealthy interest in anything to do with engineering… just don’t put it in your Tinder profile
The other thing that is peculiar about the bearing, and which I hadn’t appreciated when I made my initial comments is that it is of odd proportions – that is a large OD given the size of the ID. The technical term is that it is a “modified dimension” bearing (really!) The alternative part number I quoted does appear now to be good:
SSRI-6632ZA0205MCRA7P24LB15P
The basic bearing is SSRI-6632ZA0205, which you will find here:
The decode for the rest of the part number MCRA7P24LB15P you will find here
In case you are wondering why I have this apparently unhealthy interest in bearings, I did a big project early in my consulting career in the 80s around ultra high precision encoders.
Brilliant work vic!
Now… how does one select a bearing for this application?
That’s a good page LeSving but I can’t see any which meet the requirements. These two are ok but not on the diameter, so as per Vic’s suggestion one would have to make a sleeve
90k rpm is surely enough?
For avoidance of doubt my shelf-spare KI256 has been overhauled by a 145 facility… this thread is just for fun, and of course to help others should the overhaul options go the way HBK want them to go i.e. evaporate
I know only one ball bearing manufacturer, and that’s SKF. http://www.skf.com/group/products/bearings-units-housings/ball-bearings/deep-groove-ball-bearings/deep-groove-ball-bearings/index.html
or here, see the PDF:
mini ball bearings
and the hole is 4.73-4.75 (I don’t have an accurate way to measure it).