Angular Contact Bearing Advice – Fobco 7-Eight

[VannParticipant @vann]

Hi everyone, my first post here and looking to tap into the wisdom of the internet.

I'm a retired electrical engineer with an interest in oldish wood and metalworking machinery.

I'm in the process of renovating a Fobco 7-Eight pillar drill which was bought as a non runner, partially dismantled and I've reached the point where I need advice about angular contact spindle bearings. Context below, question at the end.

I checked runout of the spindle early on using a new but unproven test bar and 1-2MT adapter. It clocked approx 0.1mm 4 inches out from the end of the spindle so I've decided to replace the spindle bearings and have removed the spindle..

Spindle nose bearings are a pair of open angular contact bearings. Type unknown but measuring 72mm OD / 30mm ID / 16mm thick. They do appear to be metric although the machine is otherwise imperial.

There is a single SKF deep groove bearing at the top end of the quill to keep the spindle striaght.

I believe that the drill has had a fairly easy life but I don't know if the bearings are original. What is interesting is that the two races at the spindle nose are installed in tandem not F-F or B-B which I believe to be more common for machine spindles. Excellent for handling the load of heavy drilling but maybe the reason for the poor runout I measured as I did not think to place the spindle under axial load while measuring the runout.

Some simple estimates make me think that the 7-Eight should be designed to cope with axial drilling loads of maybe 400Kg force.

Does anyone know how the bearings are SUPPOSED to be mounted in the 7 and 10 Eights, and whether a new pair of bearings installed face to face for better precision would tolerate axial loads of this magnitude ?

Thanks in advance

[VannParticipant @vann]

[Brian HParticipant @brianh50089]

Hello Vann, I'm afraid that I cannot be much help on angular contact bearings but my understanding is that they should be fitted back to back.

Before you discard the old bearings it may be worth cleaning them and checking for wear as they should be a matched pair according to this site;

**LINK**

Brian

[VannParticipant @vann]

Many thanks for the advice Brian,

I've been consulting the same reference source as you directed me to, and the description of back to back bearings on the smaller Fobco Star is why I wonder if the bearings on my 7-Eight have been installed incorrectly.

The niggle is that lathes co uk don't actually say what orientation the bearings are on the 7 and 10 Eights, Only that the nose bearings are a matched pair. The big drills are significantly larger than the star with more leverage and bigger capacity. If I had a better feel for the kind of end loads axial bearings will take, I would be happier.

lathes co uk also make the assertion that the gearbox bearings on the big drills were all steel and not fibre. This appears to be wrong as mine does have one fibre gear to quieten the high speed range and I see nothing to suggest that it didn't come from the factory this way so I can't take everything they say as gospel

Final point of interest – pairs of angular bearings don't seem to tolerate much inaccuracy in alignment but a face to face pair are more tolerant than a back to back pair (4 minutes of arc vs 2 moa according to SKF). If I change the arrangement, I'll go for face to face as I'm not confident in my ability to measure the assembly and determine if it meets either of these tolerances..

It appears that there never has been a manual for the bigger drills so it's proving an intereting exploration…

I'll take your advice about checking the bearings, thanks !

[Martyn HamptonParticipant @martynhampton97662]

Hi Vann

Came across your post looking for information on my Fobco 7/8. Did you resolve the bearing questions?

Thanks

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