Reference to the photographs will show that occasionally I got my ISO5RH and ISO3
doing the reverse tasks, probably because they were on the top slide at the time
I started a particular machining operation. Still, this shows that there are few
things in the workshop that are hard and fast and as a beginner I would recommend
not being overly concerned about such matters. I have an approach in my workshop
that says “ if it's working, it's working”.
Some pieces of steel will be needed for the fixtures and mandrels used, but as the
sizes are not critical you should have suitable pieces in the offcuts bin, otherwise,
you will have to purchase materials also.
Stuart provide all the materials required for making the engine but later in the
series I propose making the crankshaft from a single piece of steel rather than fabricated
from the separate pieces that are supplied. If you go along with my method you will
need a length of 1” x 3/8” steel, ideally, 230M07 but as this is not easy to locate
in small quantities then 070M20.
This is a subject that I know from experience causes some confusion for the novice
but I would say learn from experience and avoid tables that give speeds to 3 significant
figures. The lathe that I am using for this series, mentioned above, is highly thought
of but has just four speeds 250, 500, 1000 and 2000 rpm which surly indicates that
speeds are not that critical. Of course, a much lower speed would be ideal for large
intermittent cuts but only screw cutting is taboo at these speeds and this is easily
overcome by adding a hand wheel and turning the lathe by hand.
The important things to remember are-
1. When turning, tend to higher speeds as the diameter reduces.
2. With rotary cutters (drills, end mills typically), tend to higher speeds as the
cutter diameter reduces.
In practice though, speeds become much more critical as you approach small diameters,
try drilling a 1mm hole at say 100rpm and you are likely to end up with a broken
drill, or a bent part if trying to turn to that diameter on the lathe.
For this project then I can only give an indication of the speeds I used and these
should give a basis from which of those available on the users lathe to employ.
250 rpm was used for machining the castings, only increasing it to 500 rpm for boring
the centre of the flywheels
500 rpm was used for machining the brass and larger mild steel components
1000 rpm was used for the small diameter mild steel items, typically where reducing
diameters for threading 5BA. This speed was also used when small milling cutters
were in use.
2000 rpm was used for very small milling cutters, less than 4mm and small drills,
2mm and less.
With speed changing being a tedious task with the Hobbymat no doubt I deviated from
this ideal on occasions again indicating that speeds are not critical.
It is relatively unimportant the order you machine the parts, only where an external
diameter has to fit closely into an internal diameter is the order important as it
is normally easier to make an external diameter a fit in an internal diameter rather
than the reverse. However, whilst I will largely deal with a part at a time, the
one making the the engine should consider breaking from one part to another to avoid
continually changing from three jaw, to faceplate to four jaw and so on.
Drilling will in some cases best be done using one completed part as a template for
positioning the holes in another, in such cases I will comment on it in the text.
Otherwise, except where I consider some guidance is worthwhile, I will leave when
to carry out drilling and tapping to the discretion of the viewer.
Need for accuracy
Having mentioned accuracy of fit between an internal diameter and an external diameter,
a vitally important aspect of some parts is concentricity and alignment, many aspects
of the methods I propose being with this aim in mind. In much of the engine a rule
dimension will be adequate though you may want to match one part to another for appearance
Jigs, Fixtures and Clamps.
Except for very simple items, these are detailed in the drawings and any important
considerations are included but rather than making them all at the commencement I
would suggest each one is made when it is first required as its purpose will then
be understood. Should the mention of jigs and fixtures needing to be made cause some
concern Photographs 4 and 5 shows that there is nothing too daunting.