Jan. 2019
Bluewater Bulletin
Bluewater Model Engineering Society Sarnia, Ontario
Vol. 34 No.4 January 2019 Editor John Lovegrove
Our next meeting will be on
February 11th, 2019 @ 7:30 pm
Northern Collegiate Room 125, Indian Road, Sarnia.
The January Meeting
To give us a change in scenery the custodial staff put us in room 127 - something about working on the floor in 125.
Having settled into the new surroundings (family
studies room this time rather than French) we started with the Treasurer’s report: All is well, particularly after a few more “dues” were paid in.
Bruce started by talking about OX Tools with Tom
Lipton. (This is not to be confused with the OX Group that supplies tools to the construction industry.) He has produced a series of YouTube videos complete with a warning about not getting anything done in your own shop if you spend too much time watching them.
https://www.youtube.com/channel/UCZC9LGZLfyjrKT
4OZne-JNw
In particular this person has produced a video on
making a sensitive micro-drilling attachment and this includes getting the operating handle made using 3D metal printing (stainless steel + bronze binder.) This was sintered afterwards to increase the strength and the final cost was only $78.
https://www.youtube.com/watch?v=bVxOmh5cj_w
Discussion then followed about whether this approach would ever become mainstream, taking over from casting or machining from solid using CNC. Powder metallurgy has been around for a long time and components can be made by pressing powdered metal into moulds then sintering afterward. The technique is only cost effective for production runs long enough to justify the cost of the tooling, whereas
3D printing makes it viable for one-offs.
When I was still working there was always discussion about the huge stock of spare parts (for pumps etc.) that one had to carry in order to keep a plant running. The possibility mooted at the time was to have a library of print files available and use 3D metal printing to make parts as needed. I wonder whether it will ever happen? My main concern is whether you can get the same strength as you do with a made from- solid part. Holding good dimensional tolerances is also an issue (alluded to in Tom’s video.)
The damper piston and view through cylinder.
Someone we get to talking about regularly is Jo “Pi”.
He now has a video about using rotary tables on a
conventional mill:
https://www.youtube.com/watch?v=oQtO0VELAi8
Another person we have mentioned is “Clickspring”
from Australia. He is into clock making and this item
is about producing an attractive oxide layer on
bronze.
https://www.youtube.com/watch?v=Nksb2RCNsF0
Bruce moved on to the subject of lapping: Apparently
McMaster Carr supply some very nice miniature
barrel and needle’s eye laps (1/16” upwards.) They
will not supply into Canada but KBC carry many of the
same items:
https://www.kbctools.ca/products/search/laps?v=j&fac
et=%5B%5B%22catname%22%2C%22catname%22
%2C%22Barrel%20Laps%22%5D%5D
Bruce is very much into lapping at present, one
component in particular, the damping cylinder of the
Howitzer, required this technique to finish the ID.
Laps have to be made from a fairly soft metal (to hold
the abrasive.) They also need a tapered ID and be
split along one side so that they can be expanded.
He has made a tapered reamer (D-bit) to finish the ID.
Show and Tell
Bruce brought along the parts for his Howitzer. The
damper cylinder with internal helical grooves and its
piston with corresponding external helical flights,
are
the latest items to be produced. (I wrote up quite a lot
last time about what was involved.) As mentioned
earlier he had to make up a lap to finish the cylinder
bore and below are the components of the lap along
with the tapered reamer to create the bore:
The demand valve/carburettor
Also, a while ago, he bought one of the Wholesale
Tool cutter grinders that are a Chinese knock off of a
Swiss design (I also have one.)
The band saw roller guide assembly
Quality is not thatgreat and the collet holder used for holding end millsetc. was a very sloppy fit in its housing. He re-sleevedthe housing, made internal and external lapsand went to work. The result is a really nice smoothfit between the two components.
Tony Koolen has been working on a gas carburetor
for the Perkins hit-and-miss engine he has acquired.
There are problems with the existing carburettor and
the plan is to run it on propane which should make
things easier. Because it may be of more general
interest I have put together some information on the
subject below. Running an engine on gaseous fuels
requires a gas demand valve in addition to the normal
(BBQ type) regulator and the normal arrangement is
to have a separate demand valve and carburettor.
However, Tony found plans in Edition 24 of Model
Engine Builder that essentially build the carburettor
into the demand valve and this is what he has done.
The main problem he ran into was that the drawings
called for a number 0 “O” ring to seal around the gas
control needle. He made the component, ordered the
O rings (not a common size) but when they came they
were far too small for the groove shown on the
drawing. He has now modified the design, made a
new needle and is using a larger O ring (that he
already had in stock) located further up the stem (left.)
The original needle and specially ordered O rings are
on the right.
Don Hayes has been out buying stuff again. Below is a collection of spacer pieces/blocks/parallels he has acquired.
Tony has also re-built the guider roller assembly from
his band saw. The problem was that the original
construction relied on un-machined cast components
to support the guide rolls and castings being what
they are, there was a 2-40 misalignment of the rollers
with the blade. His fabricated support assembly has
now corrected this.
When air flows through the carburetor venturi the
pressure is reduced below atmospheric (Bernoulli
effect) and with the carburettor jet connected to the
gas demand valve, as soon as the venturi pressure
goes below atmospheric, gas starts to flow. For
model engines, some kind of needle valve is required
to adjust the gas flow to get the correct mixture
strength. One significant difference is that gaseous
fuels need a larger jet size than liquid fuels.
The critical components in a gas demand valve are
the diaphragm and valve assembly. It is not really
practical to make these one’s self but nicely made
commercial parts from Tecumseh are available
through Jerry Howell’s organization. Plans are also
available and making the body for the valve is fairly
simple.
If you look at full size gas engines (there are lots at
Coolspring) they essentially all have some form of gas
demand valve. Some are quite crude with a large
inverted can dipping into a slightly larger container of
water to form a simple gasometer type pressure
sensing arrangement. Through some levers,
movement of the can then operates a normal ¼ turn
valve to control the flow of gas from the supply to the
underside of the can and the engine so that pressure
is maintained just below atmospheric.
The carburettor on my Wyvern is designed to work
with either gas or gasoline (2 separate jets.) For my
early runs I used liquid fuel but thought that I would try
propane, so I bought a kit for the demand valve and
made it up.
The engine certainly runs more cleanly on propane
(less spark plug fouling.) I also find it more
convenient at exhibitions: Just connecting up one of
those small camping size propane containers is much
simpler (and safer?) than pouring gasoline into a tank
at the start of the show and trying to remove what is
left at the end.
Using gas, it should also be possible to obtain uniform
mixture strength over a range of throttle openings. In
any carburettor, as throttle opening increases, so
does the reduction in pressure in the venturi.
Therefore, the fuel flow through the jet will increase
with the air flow through the venturi. The problem
with a liquid fuel is that the flow characteristics are
different from a gas and in fact the fuel flow increases
more rapidly than the air flow. Therefore, in a very
simple carburettor using liquid fuels the mixture
strength increases with throttle opening.
In the days when carburettors ruled, elaborate
systems were devised to overcome this effect and
give a uniform mixture strength over the operating
range but repeating these in a model carburetor is
very difficult. People have been able to develop
reasonably successful small carburettors that
Running Engines on Gas
A gas demand valve is essentially the same as a
pressure regulator: There is a diaphragm to sense
output pressure and this operates a small valve that controls the in-flow of gas. In a normal regulator, the diaphragm is spring loaded and the valve essentially lets in gas at a sufficient rate to maintain a pressure force on one side of the diaphragm equal to the spring
force on the other. Therefore, output pressure =
spring load/effective diaphragm area. The difference in the case of a demand valve is that there is no spring acting on the diaphragm so the output pressure will be very close to atmospheric. There is a small spring in the valve assembly and the force from this has to be overcome before the valve opens. This provides enough bias so that the regulated output pressure is always at or slightly below atmospheric rather than at some set value above. It also means that if the engine is not running and there is no suction, no gas flows.
overcome most of the problems but they still become
somewhat complicated. Fortunately, with a gaseous
fuel, the flow characteristics are very similar to air and
so the flow through the jet should be more in
proportion to the air flow through the venturi. On this
basis, mixture strength should remain more uniform
with throttle opening even with a very simple
carburetor design. The carburettor part of the
combined unit Tony has made is as simple as one
can get – hopefully it will work.
Alibre Atom3D
Last month I mentioned the Alibre Atom3D solid
modelling program that is available for a 6 month free
trial through Model Engineering Workshop. (A 3
month free trial is in fact available to anyone.) I did
download this to see how well it works. There are
various tutorials one can follow to get started and
these provide a good introduction. I then tried doing
something of my own from scratch (the distributor for
my Sealion) and got somewhat frustrated until I
properly understood a few more of the key concepts.
As with other 3D solid modelling systems, one starts
with a 2D drawing (sketch) but the approach needed
to create that is vastly different from the approach
used in the old AutoCad program I am used to. So
there was a significant learning curve here.
For many objects, the approach then is to “extrude”
the sketch over a specified distance to form the solid
object that can then be modified in various ways.
One of the frustrations is that one can create a 2D
sketch that looks OK but this will then not extrude and
there are no error messages to say why. Eventually
you get to understand the subtle errors that can cause
this and avoid making them. I have dabbled with
Various versions of AutoCad Fusion but not for long
enough to become competent. The basic approach to
creating components is similar in Alibre but this has
far fewer commands available. I guess this is what
you get for a $200 piece of software rather than one
that costs many times more than that (if you have to
pay for it.)
Meetings for the Rest of the Season
February 11th
March 18th (11th is March break)
April 8th
May 13th
June 10th
Our Website
https://sites.google.com/site/bluewatermes/
John Lovegrove