Scaping bearings

[Howard LewisParticipant @howardlewis46836]

The surface finish of the shaft is important. A rough finish will allow oil to drain away, allowing metal to metal contact, leading to failure.

In automotive engines with pressure oil feed, the steel backed shell beatings, of various compositions, (Aluminium/Tin, Aluminium/Silicon etc ) with normal clearances, the shaft needs to be dimensionally correct to within 0.001" ( 0.025 mm) on diameter and have a primary surface finish of no more than 16 micro inch Centre Line Average.

At 18 CLA, the shell will begin to show a polish

At 20 CLA the bearing will begin to wipe (Localised melting ).

By 22 CLA failure is certain!

With Nitrided, or Tufftrided shafts, rather than Induction hardened, these limits become even more important.

Once failure begins, "healing" is MOST unlikely, usually the damage increases exponentionally. Often the root cause is impossible to find, because the damage to shaft, bearing, and housing is so extensive. Often the steel shell, if any is left, will have been blued and hammered to a thickness of less than 0.001" The whilte metal will have been distributed by the pressurised oil all over the surroundings, in minute flakes..

The "White Metal" bearing needs to be of similar finish, a variation of 0.00001" (0.00025 mm 0.25 microns! ) will show itself as a polished band on the surface of the bearing surface. More than that leads to failure..

This kind of failure can happen at speeds of 2,000 rpm or below, with rubbing speeds of as low as 1,500 f p m..

So shaft and bearing finish and clearances need to be correct to minimise the risk of wear or failure.

Howard

[IvyParticipant @ivy]

As I am not likely to be machining parts for Red Bull Racing or the aerospace industry any time soon and this lathe runs at maximum speed of 640 RPM I am going with Old Marts method.

I am experienced in engine repair and assembly but machining is just a hobby that I am not so good at.

Due to my stupid comparison the engine side of the discussion has really taken over and that was not really my concern but thanks for all the contributions.

[Howard LewisParticipant @howardlewis46836]

Don't worry, Ivy

We all learn as we go along, every day.

Experience allows us to recognise the mistake, the next time that we make it!

With a low speed, drip fed, fairly lightly loaded application you can afford to minimise clearances.

When Sentinel made expansion engines for British Oxygen, the large whitemetal bearings used to be hand scraped. Being a big, single cylinder engine, the pile of swarf on the floor was big!

For accuracy you need the spindle to be kept as closely aligned as possible anyway.

Howard

Edited By Howard Lewis on 28/05/2022 10:28:40

[SillyOldDufferModerator @sillyoldduffer]

Posted by Ivy on 27/05/2022 19:10:52:

Posted by old mart on 27/05/2022 18:47:05:

I would fit the bearings and after making sure they were not tight, just run them for a short while with plenty of lubrication. Then dismantle and look for tight areas and scrape then lightly and repeat. The design varies a great deal, from clamped and shimmed bearing halves, tapered designs which can be adjusted by axial means and also parallel surfaces which have bushes made like er collets which can be closed down by axial adjustment. Each style needs slightly different approaches. There are certainly no traces of scraping in the spindle and bushes of the Smart & Brown model A lathe. Any scraping like bedways get would be detrimental to a rotating bearing, only the rings of tighter contact require attention.

I was thinking along the same lines as you. I also saw a chap on youtube who fitted new bearings to his Myford ML7 and said no scraping was needed, he showed the results of the change including running temperature at the bearing caps. I am confident he knows what he is doing.

…

A chap on youtube eh? You can always trust the internet!!! Old Mart is much closer to the mark, his method is respectable. He tests and adjusts.

The problem with Youtube's 'he showed the results of the change including running temperature at the bearing caps' is it proves nothing. Even a sick bearing can pass that test. Unless a bearing is very bad, it's performance isn't measured by running a machine for a bit. The real test is how many running hours the bearing can do before it wears out and has to be replaced. Years.

Well fitted bearings last much longer than badly fitted ones. Takes time for the damage to appear – see Howard's post – and for a long time it's invisible, Bottom line, it's easy to fink a new bearing has been fitted satisfactorily, when actually it's a bodge.

It may not matter! As machines go lathes are lightly loaded and slow. And most hobby lathes aren't run for hours on end day after day. So if a bodged fix lasts longer than the owner he will never know or care that he messed up! He might even post a convincing internet video suggesting he knew what he was doing.

Kawsaki motorbikes are different! They're are ridden hard by millions of customers and fitting poor bearings soon becomes bleeding obvious due to excessive warranty failures and loss of confidence in the product.

Dave

[IvyParticipant @ivy]

A chap on youtube eh?

I didn't want to name him without his knowledge. There are lots of youtubers that really know their stuff and are happy to show it and discuss.

You can always trust the internet!!!

Isn't this the same internet?

[Tony Pratt 1Participant @tonypratt1]

If you post on YouTube then it’s in the public domain as intended, I think we are talking about Steve Jordan?

Tony

[old martParticipant @oldmart]

Ivy was right about starting an argument, wasn't he.

[Pete RimmerParticipant @peterimmer30576]

TBH I would not put too much weight on advice given by someone who demonstrates lapping in cross slide ways with loose abrasives. It might make good sense to the unwitting, but lapping is the very last thing you should do to finish any moving way.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Ivy on 28/05/2022 10:48:48:

A chap on youtube eh?

I didn't want to name him without his knowledge. There are lots of youtubers that really know their stuff and are happy to show it and discuss.

You can always trust the internet!!!

Isn't this the same internet?

I'm not thinking of anyone in particular, just noting that perhaps the majority of internet videos are flawed. It's because video makers mark their own homework and are easily pleased! As any fool can post a video on any subject, or he might be an 'influencer', it's best for viewers to watch critically. Question everything.

The best internet videos are peer reviewed and go through some sort of editorial process. Most don't.

The forum is different because it allows question and answer. Whenever anything is posted here that's ambiguous or wrong, other members can and do point the issue out. As a result the quality of forum advice is generally high, but you do have to read it all carefully and make your own mind up!

Dave

[IvyParticipant @ivy]

SillyOldDuffer / Dave.

I understand what you mean about some youtubers and I don't automatically assume the worst or best in people that's one of the reasons I asked here. Some don't communicate very well or at all, some are brilliant at editing, with all the doubt that adds and some make excellent teachers for the likes of me.

I acknowledged the bad comparison I made with the IC engines but unfortunately that took over and started to come across as a, "I know more about engines than you" competition. And I also know from other forums (motorcycle related and predominately American} that they can be very cliquey if you don't blindly follow the script.

My requirements are very crude by some standards and although Old Mart is the only person to offer an alternative to scraping I am sure his method will serve me more than well enough for the rest of my life. Fortunately I have another lathe that turns out good work by my standards so nothing ventured nothing gained.

[not done it yetParticipant @notdoneityet]

If the YouTuber was the person that Tony suggested, I would, like Pete, not take too much notice of his videos.

His main application seems to be as a paid ‘influencer’ to persuade people to buy a particular brand of rubbish. A lot of the lower 50% are likely impressed by his reviews.

[Neil LickfoldParticipant @neillickfold44316]

My Myford headstock is fitted very close to its bronze tapered bearing. The scraping like been said allows for the capillary action via the wick to lubricate the bearing. Its clearance is just enough for a very thin film of oil, that it actually runs on. Model enigins by comparison have very large cleanaces for the pin diameter, from 0.04mm to 0.08mm on diameter clearance on 5 to 6 mm pins.

[HopperParticipant @hopper]

Posted by Tony Pratt 1 on 28/05/2022 11:50:01:

If you post on YouTube then it’s in the public domain as intended, I think we are talking about Steve Jordan?

Tony

He is the guy who machined the top off his topslide to accommodate a different toolpost etc then when commenters pointed out he had weakened the toolpost stud anchoring area, he built up the lower side of the area with a dollop of JB Weld to "strengthen" it again.

I think his knowledge and experience are limited so I would check around a bit first before assuming an unscraped set of bearings is OK because they are not running hot or noisy and he says so. Five generations and more of millwrights/fitters have not been scraping bearings for the past 200 years for nothing.

There is real danger in getting engineering advice off YouTube. I have seen some shocking clangers, including by some of the most reputable on there. EG Blondie sticking a dial indicator on a job right next to the set up fixed steady to "check it's running true". Lots of Harley "gurus" doing the same thing with flywheel truing stands, putting the dial indicator on the shaft right next to the supporting bearing instead of on the end of the shaft. And the lathe chuck rebuilding guy who flogs the back plate off his chuck with a shifting spanner and screwdriver instead of using the provided jacking screws and tapped holes. When queried, his response was he used the shifter because his hammer was outside in the back os his truck. And even lifelong skilled machinists like Joe Pie do things like blow swarf with compressed air — enough to get you sacked some places I worked at. So it always pays to shop around for info.

Edited By Hopper on 28/05/2022 23:56:18

[PatJParticipant @patj87806]

My rough calculator for how much knowledge/skill a ytuber has is to look at how many glossy colorful images he has on the front of each video.

If it looks all splash and colorful, like some sort of storefront display, with lots of shiny bits, that seems to indicate a rank amateur who is only there for the views.

The more shiny videos they have, the less knowledge they seem to have.

Its like some sort of linear relationship in math(s).

Some of the least visually impressive channels have some of the best technical material.

I guess it is a matter of whether you focus on what your videos appear to look like from the outside, or the depth of knowledge your video actually contains.

Reminds me of what we use to call "sleeper cars" in high school.

The bright and shiny cars were always were the slowest.

The cars with somewhat of a rough paint job, and a few dents here and there were the ones to watch out for, since they often concealed a 500 hp Hemi or something like that, and would leave you very quickly in a very humiliating cloud of dust in an impromptu street race.

.

Edited By PatJ on 29/05/2022 01:00:34

[IvyParticipant @ivy]

There is real danger in getting engineering advice off YouTube

Trouble is as an amateur hobbyist with no more than CSE metalwork for experience and no access to real world help I watch lots of youtube and read forums if I get stuck on something. The alternative is to give up.

Someone mentioned Blondie, I think she is great, may not be text book or 100% in everything she does but always says, "this is how I did it", mistakes and all and that is a great help. This old Tony and Doubleboost are great entertainment too.

 

Edited By Ivy on 29/05/2022 07:54:43

[not done it yetParticipant @notdoneityet]

One particular instance I remember was of some idiot using a cheap plastic sandwich box as an enclosure for mains electrics – and with no cable restraints AND locating it outdoors!

[mgnbukParticipant @mgnbuk]

Due to my stupid comparison the engine side of the discussion has really taken over and that was not really my concern but thanks for all the contributions.

Not so much a stupid comparison, but trying to compare an example from one industry ( high volume, mass market, close tolerance products with a relatively low selling price) with another (low volume, niche market, close tolerance products with a relatively high selling price) – the needs of (or methods employed in) one industry do not necessarily transfer easily to another.

IIRC at the time I was at Boxfords (1980-81), they had a production capacity of around 2500 lathes a year – probably not a lot compared to Chinese mini-lathe makers today, but not inconsiderable for a UK maker at the time. They had a mix of manual & CNC machines to produce the parts & all the machines were hand fitted on an assembly line. There were bench fitters who put sub-assemblies together (headstocks, tailstocks, aprons etc.) and others who brought the sub assemblies together to get the required accuracy in the finished product. There were time impositions on the various steps – again IIRC , the fitter who fitted the tailstock to the bed & aligned it with the headstock (scraping the base of a previously assembled tailstock assembly to get alignment & centre height correct) was allowed 1/2 an hour. If tolerance stack-up meant that the fitter couldn't get it sorted in 1/2 an hour, that tailstock assembly went in the scrap skip ! I particularly remember that bit, as I "rescued" such a tailstock from the scrap skip and (over a lot longer than half an hour ! ) fitted it the the tailstock-less "bitsa" lathe that lived in the maintenance shop. That machine had been built up from parts rescued from the skip – starting with a bed that had a blow-hole at the tailstock end of the shears.

From what I recall of Myfords from visits during their open days, they operated along similar lines to Boxfords, (though the facility was obviously older) so not unreasonable to think that they would have built (i.e hand fitted) their machines in a similar way. Just the way it was, given the quantities produced

Did your bearings require "fitting" ? If you checked that your spindle didn't rattle or bind and the alignment with the bed was OK to meet your requirements, then maybe no need to break out the marking blue and scraper.

Trouble is as an amateur hobbyist with no more than CSE metalwork for experience and no access to real world help I watch lots of youtube and read forums if I get stuck on something. The alternative is to give up.

Another alternative is specialist publications, many of which were written when lathes like the ML7 were current but whose content is as relevant today as when they were written. Some of these are available as .pdfs online.

There will always be differences of opinion in forums & opinions on YouTube "experts" can depend upon the experience or background of the viewer – such is life.

Never give up !

Nigel B.

[IvyParticipant @ivy]

Nigel B.

Thank you for taking the time to share your experience.

I have several workshop practice books although I do sometimes find a demonstration can be worth several written articles quite often.

Ivy.

[Neil LickfoldParticipant @neillickfold44316]

Ivy, My friend was having his model engine big end bearings not lasting as long as he liked. I suggested that he honed them with a courser stone set, once he did that, the life has improved significantly. What it is all aimed at doing is finding a way to keep the parts separated by a film of oil. The better the oil retention, the longer the life of the parts. So sometimes very shiny is not always good. Pins and shafts last much longer with as fine a finish as can be achieved with that material and bushes last long with a course hone or a scrapped surface. In saying that, after the course hone, a very light hone to take away any of the low spots that will get knocked off by the first run are taken away. I call it the deburring of the honing. Even ground surfaces should be micro deburred if you want it to last. But people do like the look of the shiny ground finish.

Neil

[old martParticipant @oldmart]

I would steer clear of white metal and use bronze if I was making bearings for a lathe. They would need provision for lubrication and if the top half has a hole for oil, then an oil groove in the bore would be easy to produce. You can produce a helical groove in the bores of both bearing shells with a ball end cutter in a Dremel or similar. Not a stone for fear of leaving abrasive particals. A groove about 1/16" wide and 1/32" deep would be more than adequate starting at the oil hole and stopping just before the outside edge. Some split bearing shells have the grooves in an "X" running from the oil hole and continuing at the split line to the other shell half. My choice would be leaded gunmetal, it makes nice nuts and probably good bearings as well. Perhaps somebody could have a better bronze alloy to recommend for bearing material.

[IvyParticipant @ivy]

Posted by old mart on 30/05/2022 13:42:49:

I would steer clear of white metal and use bronze if I was making bearings for a lathe. They would need provision for lubrication and if the top half has a hole for oil, then an oil groove in the bore would be easy to produce. You can produce a helical groove in the bores of both bearing shells with a ball end cutter in a Dremel or similar. Not a stone for fear of leaving abrasive particals. A groove about 1/16" wide and 1/32" deep would be more than adequate starting at the oil hole and stopping just before the outside edge. Some split bearing shells have the grooves in an "X" running from the oil hole and continuing at the split line to the other shell half. My choice would be leaded gunmetal, it makes nice nuts and probably good bearings as well. Perhaps somebody could have a better bronze alloy to recommend for bearing material.

Old Mart, I was thinking of something from page 48 of the M-Machine catalogue? What do you think?

Although I am getting way ahead of my self at the moment. I was looking for advice on feasibility first.

http://www.m-machine-metals.co.uk/downloads/metals catalogue.pdf

Thanks again for your contribution.

Ivy.

[old martParticipant @oldmart]

I had never heard of M-Machine, but have now downloaded their pdf, thanks IVY. Most of the metal on p48 would do if the sizes you want are there. The Smart & Brown model A gets fed a plentiful supply of 5W30fully synthetic motor oil and seems to like it, after all, modern oils are light years ahead of what was available in the 1940's.

 You should see about getting the spindle reground first, let the grinding shop see if they think it is ok to do.

Edited By old mart on 30/05/2022 21:15:21

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