[modeleng] Re: Lubricating oils

Ron,

With really small bearings, you can take advantage of the excess 15W40. The 
basic rule is, the bigger the bearing (diameter) the thicker the oil. The 
smaller the bearing the thinner the oil. This is because the surface speeds 
are generally in the same range, but the clearances are shrinking as the 
bearing decreases in size. As the clearances decrease, and the RPM increases 
to maintain the surface speed, the shear stress of the oil becomes greater, 
and hence the pwer being absorbed also increases. This is counteracted to 
some degree by the heat generated by this process, which thins the oil, but 
not enough unless it is over heated. If the bearing is turning slowly, then 
you are often better of using a thicker oil. Very few 3.5" and 5" gauge 
loco's are driven at scale RPM. This is partly due to the scale effect of 
miniaturization. Basically, properties don't change, just the quantities. 
Therefore, things like the expansion rate of steam is the same, regardless 
of the size of the engine. THEORETICALLY, a miniature staem loco, can go 
just as fast as the prototype. Unfortunately, they can't due to ballancing 
dynamics, mass stability, etc. etc. They just fly of the track, before they 
come anywhere near reaching thier potential. Which brings us back to the RPM 
of operation. At 3/4" scale, the scale opperating speed is 1/16 of the full 
size. So assuming you are racing around the track at 5 mile an hour, which 
is pretty typical for what I have seen, then you are doing a scale speed of 
90 miles an hour..... Hmmmm..... I doubt whether many full sized shunting 
engines did that speed...... Full size speed here, was 50 miles per hour for 
goods services. That makes a scale speed of 3.125 miles per hour. That's a 
pretty slow walking speed.... If you are operating at full size RPM, 
approximately 300 RPM, then you are better of using a thicker oil than a 
thin one. The boundry film pressures are lower at 300 RPM than at 600 RPM. 
and hence the thinner oil used for 600 RPM will not generate enough pressure 
in the boundary layer to keep the 2 components apart. That's when wear 
starts.....

Slideway oil is good stuff, on your machinery. But, not always for 
everything else. Take the tacking agent for example. It "tacks" the oil, 
only after it has stood still for a while. It has no useful effect while the 
bearings are moving. If you let it sit and "tack off" and then start moving 
the bearing again, it imeadiately reverts to it's normal liquid nature until 
it stand still for a while again. So the tacking agent can make clean-up 
after running harder. But the other aditives are excellent, for our use, as 
long as they don't get to hot. I know that most of the tacking agent don't 
like heat.

I hope that gives you all more food for thought.


Cheers,

Phill.


----- Original Message ----- 
From: "Ron Head" <ronald.head@xxxxxxxxxxxxxx>
To: <modeleng@xxxxxxxxxxxxx>
Sent: Thursday, June 04, 2009 1:32 AM
Subject: [modeleng] Re: Lubricating oils


> Some interesting replies so far!
> The preference seems to lean towards heavier oils, perhaps with a 
> tackiness additive.  I was surprised to hear that some folk use steam oil 
> for everything!
>
> I've always been reluctant to use motor oil in anything other than a car 
> engine, as I don't know what effect the detergents have on bronzes etc. 
> Mind you, my current car is a diesel which uses the most expensive 
> synthetic oil imaginable, so I've got plenty of surplus 15W40 doing 
> nothing!
>
> I also have some Mobil Febis K68 slideway oil in my shop, which I use on 
> my lathe bed.  This has a tackiness additive, so it might be suitable for 
> motion....who knows?  Anybody tried it?
>
> Regards
> Ron
> MODEL ENGINEERING DISCUSSION LIST.
>
> To UNSUBSCRIBE from this list, send a blank email to,
> modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject 
> line.


--------------------------------------------------------------------------------



No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 8.5.339 / Virus Database: 270.12.52/2153 - Release Date: 06/03/09 
18:00:00

MODEL ENGINEERING DISCUSSION LIST.

To UNSUBSCRIBE from this list, send a blank email to, 
modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.

Other related posts: