Mar. 2019

problem is that centre drills do not go down to the

very small sizes; 1/16” is fairly common, they do seem

to be made down to 0,5mm (0.02”) but below this you

are out of luck.

Where I have mainly seen the problem is in making

jets for carburettors where very small holes are

needed. Spotting drills are the other option but you

could still be left with the pip in the middle of the

conical starting hole. Maybe a clue to what should

work comes in the MSC catalogue where in the

spotting drill section they say: “designed for accurate

spotting on NC machines where a drill with less of a

point angle will be used for the drilling

application.” The NC part is not really relevant (does

anyone use straight NC machines anymore?) but

these things are made with a point angle as low as

600 so they leave a fairly gently tapered starting hole

and maybe there is a self centering action that takes

out any pip that starts to form? If you come in with a

drill afterwards that has, say a 1200 point angle, the

drill will hopefully contact the sides of the tapered

starting hole first and be guided sufficiently to not be

thrown off by any pip that is left. People who make

components with small holes on a commercial basis

must have found ways around the problem. (Maybe

having higher quality equipment than we can

generally afford helps somewhat?)

Bruce went on to talk about a couple of Joe “Pi”

videos on making wagon wheels. Firstly, with straight

spokes:

https://www.youtube.com/watch?v=Gbpe3qdQ0EU&p

bjreload=10

Then flared spokes:

https://www.youtube.com/watch?v=s0HfNx9FdRc

One of the general subjects that came up for

discussion was air bags in cars and some of the

lawsuits that have arisen because of faulty

design/manufacture. Something of an explosive

nature is needed to inflate them sufficiently rapidly to

protect people in a vehicle. (A device is used to

detect the rapid deceleration of the vehicle in a crash,

a computer decides whether it is appropriate to

activate the air bags, the bags then have to be

inflated before you hit the steering wheel etc., then

Stu’s Easton/Anderson Beam Engine

He then went on to talk about the difficulty of startingsmall holes. The same problems arise whether one isusing a drill press/mill, or when drilling the hole in acomponent rotating in the lathe. The difference is thatin a lathe you can see the problem more easily

because the drill “wiggles.” With inaccuracies in the

chuck (and the centering of the tailstock in the case of

a lathe) the axis of the spotting or centre drill is never

exactly on the rotational axis. Therefore a “pip” or flat

is left in the middle of the starting hole.

If a normal centre drill is used and the diameter of the

end is smaller than the drill one will be using, the

problem is not too bad. Assuming the centre drill is

held sufficiently rigidly, the small starting hole will be

slightly oversize with a flat at the bottom, but the

actual drill being used will follow the starting hole,

take out the flat and carry on as intended. The

Todd’s Burner

Stu Brownlow brought along his model of an

Easton/Anderson grasshopper beam engine from

1892. It has not been constructed so that it will work

on steam or compressed air but instead it is turned

over by a small battery powered motor inside the

base. The flywheel is smaller than the drawings call

for because of Stu’s equipment limitations. It is fitted

with the governor that he purchased ready made and

brought along to one of our meeting several months

ago. Although it would probably work as intended,

because of the electric drive, you just see the balls

going round, but it does not in fact control the speed.

Todd Michel is planning to get into the metal casting

business – hopefully being able to melt iron. As a first

step he has made up the burner for the furnace: This

has a supply for propane, an air atomized nozzle for

oil (diesel?) and a connection for the forced air

supply. There was some discussion about whether

preheating the air supply, using the hot gasses

leaving the furnace, would help get the higher

temperatures needed for iron.

The magnetic base dial indicator support:

The end of the

connecting rod has to be forked to go around the

pump and act evenly on both sides of the piston rod.

And, no, he confessed that he did not cut the gear that drives the crank himself.

He also brought along a dial indicator mount with

magnetic base and articulated support system that

allows great flexibility in how the indicator is used

Although not strictly show and tell, Tony also brought

along some rolls of emery cloth etc. that were surplus

to his requirements, to give away to anyone who

needed some. (Murray Bennell used to talk about

giving things to the needy, not the greedy!)

available with the magnet and Hall effect transistor

combined in one component where a gap is provided

between the two parts (see below.)

Tony’s Give-Away's

This works inconjunction with a steel disk that has slots in theperiphery. When the solid part of the disk is in thegap, the magnetic field is blocked and the device isturned off but when a slot enters the gap, themagnetic field gets through to the transistor and it

turns on. This is the Hall effect device I bought (on a

mounting bracket) and the slotted plate:

In the earlier systems, the contact breaker cut the flow

of current through the ignition coil to produce the

spark. In present systems the switching is carried out

using a special type of transistor. When you break

the current in an inductive circuit, in this case the

primary windings of the ignition coil, a high voltage is

produced on the primary side (several hundred volts

in fact.) This, when reflected into the secondary

windings, induces the very high voltage needed to

produce a spark (>10kV.) With a conventional

contact breaker, a capacitor is needed for the

arrangement to work. Without this, some current

continues to flow after the points open, resulting in

arcing at the points, a lower voltage being produced

on the primary side and not much of a spark. If a

transistor is used, the same arcing problem does not

exist and so no capacitor is needed. In the special

transistors designed for this purpose, over-voltage

protection is built in to prevent damage to the device.

I do have an experimental Arduino micro computer

and have toyed with the idea of using this to control

the spark timing. However, to get the engine running

I will content myself with using the Hall effect device

in conjunction with a slotted plate shown above to

provide the basic timing, then use the special high

voltage transistor to switch the current through the

ignition coil.

Meetings for the Rest of the Season

April 8th

May 13th

June 10th

Our Website

https://sites.google.com/site/bluewatermes/

John Lovegrove

After my shoulder surgery I had limited use of my left

arm and this put the kibosh on running the lathe and

mill in the workshop. I wanted to maintain some

progress on my Sealion and one on the items that

needed attention was the ignition system. Westbury’s

original design used a contact-breaker/capacitor/

distributor arrangement which was the technology of

the 60s when the engine was designed - but things

have moved on since then.

In the automotive world nowadays, solid state sensors

are used to detect the angular position of the

crankshaft. A computer takes this, calculates engine

speed then uses it, along with other information, to

determine when each spark should occur. It then

activates the ignition coils to fire the spark plugs. The

distributor has gone and individual coils are used for

each cylinder or pairs of cylinders.

For multi-cylinder model engines, the distributor

probably has to stay because there is a limit to how

small ignition coils can be made and using 4 of them

on the Sealion would take up a lot of space.

However, I did want to see what other aspects could

be updated.

The device typically used to detect crank position is a

Hall effect transistor. This is turned on when the

south pole of a magnet gets close to it. Therefore, if a

magnet is mounted on something attached to the

crankshaft and the Hall effect device fixed in an

appropriate position, it can be used to trigger the

ignition. In fact, more suitable devices are now