[modeleng] Re: Lubricating oils

Not a problem Ron. Always glad to help or shine a light on something.

Oh, as an extra bit of info.... Did anyone notice that I made no mention of 
putting hardened axles into the Juliet? The reason is simple. An axle (or 
pin) that long will distort, when quenched, enough that the wheels would 
wobble unless it is cylindriclly ground afterwards. Even silver steel, which 
is the designated material, warps to some extent. Also, silver steel is very 
brittle, once hardened, and is fairly easy to break with an impact 
(derailment). Even though you would temper the axle from the centre, it 
would not lose enough of it's brittleness to be a guarrenteed item. Most 
other materials require professional hardening services to prevent 
distortion. Thee is one that is used in clock making, instead of Silver 
Steel, as it is not as brittle. Silver steel pinions have been known to 
break as often, 20 years after manufacture, as 5 months after maunfacture.


Cheers,

Phill.

----- Original Message ----- 
From: "Ron Head" <ronald.head@xxxxxxxxxxxxxx>
To: <modeleng@xxxxxxxxxxxxx>
Sent: Friday, June 05, 2009 7:20 AM
Subject: [modeleng] Re: Lubricating oils


> Hi Phill,
> Thanks - some very interesting points, and you have certainly given me 
> something to think about!
>
> Regards
> Ron
>  ----- Original Message ----- 
>  From: Phill Smith
>  To: modeleng@xxxxxxxxxxxxx
>  Sent: Thursday, June 04, 2009 7:39 AM
>  Subject: [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.
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>
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