Oilite Bearing with through oil hole

The Oilite bearing on the reciprocating arm of my power hacksaw was badly worn and I've finally got around to making the simple tool to pull it out of the casting (and push the new one in). As built (I assume) the arm casting has a 1/4" open oiling point on the top that passes right through the oilite bearing.

I'm fairly sure a good part of the machines wear is because no-one bothered to actually oil it (the motor bearings are also badly naggered) but it may well be that muck found its way into the hole too.

I've actually already inserted the replacement bearing but on reflection should probably have tapped the hole for some kind of cover/oiler first. However, I'm in two minds whether to drill through the new oilite bearing - or not. One option would be to use a small centre drill and make a small(er) hole (plus depression and then just make a brass cup/cover to hold some oil and keep out debris. The other is to use an oil nipple and push oil in under pressure with an oil gun (with no hole in the bearing). Either is probably better than the old arrangement but which would be best??

Regards,

IanT

Ian ... NO please don't drill the Oilite.

MichaelG.

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Picador had the right idea, with their Plummer Blocks:

https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=GB&NR=797066A&KC=A&FT=D&ND=3&date=19580625&DB=EPODOC&locale=en_EP

Edited By Michael Gilligan on 14/07/2018 16:24:11

Many of these sintered bushes never get lubricated during their lifetime due to inaccessibility. Instead, they rely on the reservoir of oil retained in the gaps within the sintered material. The porosity varies between products but around 15-20% is typical.

Handy intro from GKN here:

Note that when you press a sintered bush in place, the bore shrinks. You aren't supposed to try to ream them to shape as it damages the surface. Similarly, if you drill a hole, it could reduce the bearing surface and also risk distortion.

Some other stuff about lubrication of journal bearings here.

Murray

Thank you Michael - I get the general idea (I think)

Well the arm's too big to swing - but I could use my boring head to bore a 'channel' ring inside the arm casting I guess - probably wouldn't need to be too deep. Undoubtedly a fiddly set-up required but "if you are going to do something, you may as well do it best you can" (....says an Arch Bodger….)

Then just the motor bearings to sort - and the spindle is deeply worn (the late JS would have been busy welding on replacement metal long ago - but I'm not up to that kind of work I'm afraid - so I'll have to find another way to do it)

Regards,

IanT

Thanks Murray,

I made a tool to draw the new bearing in - and the 'pin' (1.25" dia) fits quite nicely in it - perhaps it is slightly worn too but it isn't scored (whereas the old bushing was). I had no intention to try and machine the Oililte - as I've read it "smears" the surface and stops the lubrication process - but I didn't feel drilling would have the same effect...

The machine will not be used so often - but perhaps a belt and braces approach won't hurt...

Regards,

IanT

Edited By IanT on 14/07/2018 18:24:52

Sorry to disagree with Muzzer as regards reaming an "Oilite" bush, but I had exactly this type of query when I refurbished my Super 7 countershaft. I found that it says on "Oilite"s own website that the bushes may be reamed with a sharp reamer.

Maurice

It was always my understanding that you can machine oilite but the cutting tools used need to be "very" sharp, sharp tools will keep the oilite structure open but dull tools will rub them closed. I also read that reaming is generally not recommended, however if its needed it can be done but again only with a very sharp tool.

Edited By Ron Laden on 14/07/2018 21:04:15

Although Oilite bushes can be reamed and turned using really sharp tooling it's not advisable except as a last resort. Sharp pretty much means sharp enough to shave with and there are depth of cut issues if you are to get a long term satisfactory result. Sintered materials are often unkind to tool edges too.

I've done it. Third try worked well enough to last a few years of home shop duties until the machine went to a new home. I seriously doubt if the bush performed up to specification tho'. That said I doubt if Mr Black & Mr Decker got the design right in the first place. In that application an Oilite bush should have lasted pretty much for ever on home shop duties. First couple of tries at machining were less than pretty. Fortunately I had about 50 to play with as part of one of Mr Whistons mystery surprise packages from the famous Cat-on-a-Log. Medium size one. Still working though it. Some of the stuff really is a mystery too.

Given that modern Oilite bushes are vacuum impregnated with lubricant I'd be surprised if applying oil via an external hole had any effect. Even with a fancy ring channel. I suspect the Picador patent applies to permeable bushes. An older technology than Oilite. If memory serves me right these had to be oil impregnated before use by soaking in a bath of (rather warm?) oil before installation. Larger pores so oil could be drawn through by capillary action. Something I've been told about by a usually reliable source, rather than used myself, maybe 45 years ago so plenty of time to get muddled up!

Clive

Edited By Clive Foster on 14/07/2018 21:05:32

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That's an interesting, and probably valid observation,Clive

... In defence, I can only quote from Bowman's website: **LINK**

http://www.bowman.co.uk/bearings/oilite-bearings-self-lubricating-bearings

MichaelG.

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Oilite® Special Lubricants and Additives

Standard Oilite bearings are impregnated with a highly refined mineral oil to ISO VG (SAE 30) having a high viscosity index and containing anti-oxidant, anti-rust and defoamant additives.

A wide range of lubricants are available to meet specific requirements within a temperature range of -60°C to 200°C, lubricant additives are also available to impart anti-wear properties in marginal lubrication conditions. Special additives are also available for use with various shaft material and finishes. We are also able to offer special oil to suit customer specific requirements.

Oilite® Storage

Oilite bearings can be stored for considerable periods without deterioration or loss of oil if kept in a metal or other non-absorbant container, at room temperature. Proximity to heat could cause oil loss by sweating, in which case recoiling is necessary before fitting. Soak in oil if storage conditions are in doubt. We are able to offer Oilite bearings in sealed plastic bags or boxes.

I think in days long gone, all oilite sintered bearings needed to be soaked in oil before fitting. I fitted a couple on a water pump fan shaft back in the 80’s. They are gravity fed with engine oil and the old ones were totally solid, behind, with sludge - which likely caused their failure. I had to bore undersized oilite bearings at the time.

At the time, I just drilled them, but I can be sure the bearings are lubed because there is always oil leaking very slowly and being blown back onto the engine block by the fan. It was a characteristic of the tractor from the time of original fitment with that type of fan shaft, but an improvement over the greasy-packing type of pump fitted to earlier examples.

I often bore and reduce the diameter of metric bushes with sharp tooling when refurbishing some old worn imperial size parts. Also do it the other way around modifying imperial to metric. This is usually when I have turned a shaft or bored a hole to clean up wear then fitted bushes to suit the sizes. I did a lot of work on an old Dennis lawnmower for a local football club along with a lot of other ground keeping equipment. So far all equipment has lasted over 5 years of regular use maintaining the pitch. They do now get oiled though which never happened before !

Thought about this overnight and I have decided to leave the bearing "as is" - e.g. with no hole.

Reading Muzzer's GKN document - it clearly states that these bearings are "self lubricating" and "require no maintenance". My power hacksaw will have a much easier life now than it had in Industry, so hopefully the bearing will last me out. An allied thought is that I've now made the tool required to extract/replace this bearing - and this was the most time consuming aspect of the job - not the actual bearing exchange. The bearing itself cost about £8 (inc. postage) and was available from a number of sources - so that's not a big deal either if I need to re-do this...

One other comment - Oilite bearings are currently available in a wide range of both Imperial (mine is 1.5" x 1.25" x 1" ) and Metric sizes, so the only reason I can see to have to machine them is if (like Chris) you really need a custom fit. Thank you everyone for your advice on this matter.

Regards,

IanT

Edited By IanT on 15/07/2018 10:47:11

I would ream your bushing to size and not drill an oil hole through it. Oil will soak into the bushing from the top, but dirt etc will be prevented from reaching the working surfaces. According to Oilite, reaming is OK, but not as good as single-point cutting. But for a low speed application like your saw, should suffice for the next 20 years or more of service in the home workshop.

From OiIite's own literature here **LINK**

Edited By Hopper on 15/07/2018 11:03:52

I think, from reading the original brochure, they are talking more about mass production scenario where holding an edge for thousands of parts may be an issue. For home use on a one-off job, I would use HSS.

Generally speaking, yes carbide can be sharp. Solid carbide end mill cutters and reamers are sharp as.

I would suggest that as the casting the bearing is in has an oil hole in it, the original bearing bush may have been a plain bronze one that has some time in the life of the machine been replaced with an Oilite Bush.

With the 1/4" oil hole, either make a little plug, or get a flip top oiler.

Ian S C

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Good logic, Ian, ... but inconclusive

The Picador 'Plummer blocks' were drilled for lubrication, but, as a warning, they were clearly marked [actually cast into the housing]:

DON'T DRILL OIL RETAINING BUSH

MichaelG.

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https://goo.gl/images/hBRhnP

Edited By Michael Gilligan on 15/07/2018 13:56:45

Regarding finishing sintered bearings to size, this might be of interest. I recall reading many years ago in a bearing manufacturer’s literature that the recommended method was to press through a precision ground steel ball. This was to avoid smearing the surface with a reamer which would destroy the sintered properties, as noted by others.

I recently replaced the Oilite bearings on the pulley of my Tom Senior mill. There are two adjacent bushes, one being flanged and the other plain. Although I bought both from the same supplier, the bushes seemed to be by different manufacturers. The colour of bronze was different and one had a wall thickness a thou or so larger than the other, resulting in a stepped bearing. I decided to try the ball sizing method and obtained a 1.1/8” steel ball. At first it virtually dropped through the bearing due to the working clearance. A quick calculation using the coefficient of thermal expansion of steel suggested that warming the ball to 100 degrees might be enough to provide the necessary increase in size. I boiled up the ball in water in a saucepan for 15 minutes then pressed it through using a drill press. A rod was mounted in the drill chuck after drilling the end with a large centre drill to form a conical seat. It has resulted in a very smooth but open surface.

Edited By Andrew Moyes 1 on 16/07/2018 09:29:55

Err... has no-one noticed that the original post is suggesting a radial NOT opening out the bore?

Such a hole will get additional oil to the bearing surface where it can replenish the bush as well, even if the drilled hole has 'smeared' walls.

Whether this is more effective than a blind hole to the side of the bush is a moot point.

Did anyone know that 'moot' has opposite meanings in Britsh and American English>.

A bit like 'table'...