model engineering mikes-models

Mike, 2024 (the alloy used in aircraft construction which is my
> > favorite for machinability, finish and strength) will always have
> > "mill marks"--printing that identifies it including the batch number.
> > 6061 is close to 2024 and is weldable. 7075 melts slightly higher and
> > is not weldable. All 3 machine beautifully and have mill marking,
> > "commercial" grades don't and may give problems with buildup on tool
> > edges. As to telling what you've got, all I can say is buy from
> > someone who knows what they have! ;-) But the allure of someone's
> > scrap box is irrestable to model engineers, in which case, telling is
> > hard. Guidelines:
> >
> > Look for mill marks (even if the number you want is missing, their
> > presence says 2024, 6061, or 7075)
> > Look for surface oxidation. The above grades have high mangenese
> > content and oxidize quickly giving a dull grey surface unless polished
> > ("alclad" is another matter I won't go into). Commercial grades
> > generally stay bright.
> > Read stuff from the amateur aircraft building groups. That's where I
> > learnt most I know about aluminium.

Ron gave permission for this information to be given but with a footnote
that says " this is a bare-bones treatment that ignores a lot of other
information, like heat treatment condition
quaifiers to the alloy designation, etc (there is no substitute for going to the
official, detailed data, once you know it exists!)"

Clarification of article on building the Mills 1.3cc diesel engine and the datum plug

I sent the following request to Ron for help building the Mill 1.3cc diesel engine. Ron's
reply is posted below my question......

> > On 3/4/08, Mike Freeman <mikefreeman2@msn.com> wrote:
> > > Hello Ron, you may not remember me but I am building the Mills 1.3cc
> diesel
> > > engine, which you describe in the American magazine Model Engine
> Builder'. I
> > > am also recording the event on my hobbies website mikes-models.com. I
> have
> > > put a lot of time into making the crankcase and before I commit myself
> to an
> > > action which may turn the work so far, into scrap, I thought I would
> clarify
> > > a couple of things with you if you don't mind?
> > >
> > > Firstly, the stage I am at is to bore the .5" bore in the crankcase
> ready
> > > for the cylinder liner. The face plate that arrived with my imported
> large
> > > variable speed lathe isn't running very true and my ML10's faceplate
> with
> > > my smallest angle plate on hasn't enough clearance, so I thought I could
> use
> > > the milling machine and boring bar to achieve the same end? If i
> checkthe
> > > centre position by co-ordinate' via my DRO's would that be accurate
> enough?
> > > It ma b a daft question but that's novices for you!
> > >
> > > The second and final question relates to the paragraph on page ten which
> > > deal with finding the datum point for the crankcase and I repeat it
> below in
> > > case you can't remember the exact wording.......
> > >
> > > "The object of this plug is to establish a datum line at a precise,
> known
> > > distance above the case centre line. To do this, measure across the
> > > circular diameter, than across the flat. Subtract half the measured full
> > > diameter from the second value and record this as your datum height"
> > >
> > > I take it that the than is a misprint and should be then? if so then my
> > > interpretation is that the diameter of the plug made to fit my
> particular
> > > crankcase is one measurement. The second measurement is smaller because
> > > this is another diameter but on which has the flat in it .i.e. minus the
> > > 0.192" mllled from the plug. Hopefully this is correct although I am not
> > > going further until I understand....... The reduction in height to the
> > > correct dimension is also done in the lathe in your build, would my
> milling
> > > solution be satisfactory in reducing the height?
> > >
> > > I am sorry this is such a long email ad I hope you don't mind helping me
> > > again.
> > >
> > > Kindest regards, Mike

Ron's, reply is given below..........

> > Date: Wed, 5 Mar 2008 08:26:23 +1000
> > From: enquiries@modelenginenews.org
> > To: mikefreeman2@msn.com
> > Subject: Re: Mills 1.3cc question
>
> >
> > Hi Mike
> >
> > Congratulations! You've found a real proof reading error: yes, "then"
> > is the correct word. Better wording might have been:
> >
> > "To do this measure and note down the full plug diameter (D) and the
> > distance from the flat to the opposite edge of the plug (X). The
> > distance from the plug axis to the flat is then calculated as X -
> > (D/2). Record this as your datum height."
> >
> > Milling the bore will work though you'll need to maintain a steady,
> > regular down-feed manually going in and out as it is important that
> > this bore smooth and not tapered.
> >
> > Re the plug, the cylinder boring task requres:
> > 1. making a parallel bore that is perfectly at right angles to the shaft
> axis
> > 2. ensuring that the cylinder bore axis in the same plane as the shaft
> axis
> > 3. facing the top of the case to be a very precise distance from the
> > shaft axis and perfectly normal to the liner bore.
> >
> > (1) is requred to minimise friction and ensure there is no binding in
> > the movement
> > (2) ensures there is no "de-Sax" which would offset the timing from
> symmetrical
> > (3) establishes the deck height to get the timing right and seats the
> > liner flange to provide primary compression.
> >
> > The problem with (3) is it requires measuring from a physical location
> > to a theoretical point in thin air, hence the plug with the flat that
> > is a known distance from the theoretical shaft axis in the crankcase
> > cavity (the "Datum").
> >
> > If you play with the Timing diagram calculators on the web site,
> > you'll find that shifting the deck height by even a couple of thou
> > will alter the timing several degrees, so we try to be accurate here.
> >
> > There is still a *lot* of latitude in the timing--which is good
> > because the gasket thickness and how much it compresses is going to
> > shift the deck height too. So try to hit the numbers, but don't worry
> > as long as you are within say 0.005 of it. Cumulative errors in deck
> > height and port cutting could shift the timing by 10 degrees or more
> > before you have an engine that is hard to start, or performs poorly.
> >
> > Feel free to include any of this email on your web site.
> >
> > cheers!
> >
> > Ron