Member postings for Andrew Johnston

See this link for what can be achieved on a medium size milling machine with a face mill:

Face Milling

The tests were done with depths of cut at the maximum recommended and a chip load set by the maximum the milling machine could achieve. Finishes were excellent on aluminium and steel at around one micron Ra.

On the Bridgeport I run a 50mm, 5 insert, face mill. On low carbon steel normally run at 800rpm and ~400mm/min feed and maximum DOC of 1mm without stalling the mill. Converting to imperial that equates to about 1.3 cubic inches per minute. That is about right as the Bridgeport has a 1.5hp motor, but with a varispeed head, which I suspect isn't overly efficient.

Andrew

It would be rather pointless (!) using points with a CDI system instead of a Hall effect device. However, if points are used the capacitor is not needed, as the points act as a trigger and do not see the inductive flyback voltage that can cause arcing in a conventional ignition system.

Andrew

I don't get hung about stock tolerances. Out of interest I've just measured some offcuts of 3/16", 1/4", 5/16" and 3/8" steel rod, all are between 1 and 2 thou undersize. That is perfectly acceptable for most applications with a reamed hole. Bearings need a gap for the oil film to work properly.

Tolerances are only of concern to me for precision stock, mainly silver steel and gauge plate. A couple of pieces of silver steel measured 0.03mm undersize.

If I really need accurate and straight then I grind my own, but a pretty rare occurrence:

Andrew

Most cold drawn/cold rolled sections are slightly undersize. They all have tolerances, and by being at the bottom end of the tolerance the manufacturer can save considerable amounts of material.

I don't buy kits, but in terms of stock any bright steel under about an 1" in diameter is bouight in a standard ~3m length. Above that I buy what I need. For hot rolled steel I buy the standard ~6m length. For brass/bronze I buy shorter lengths as needed.

For sizes I use a lot I keep several lengths in stock. For instance I keep stock of steel in 3/16", 1/4", 5/16" and 3/8" diameters plus 8, 10, 11 and 16mm AF hexagon as I am making most of the nuts, bolts and studs for my model engines.

I find it useful to buy more than needed as it allows one to mess up without having to buy more stock with the associated wait. Over time one buiids a stock of material which can often be used rather than buying new.

Andrew

The UK harmonised standard is brown, black and grey for phases, blue for neutral and yellow/green for earth.

Andrew

I would describe the action of the circuiit slightly differently to SOD.

Let's imagine that at time zero the points are closed, the full voltage is across the primary coil, but no current is flowing. The capacitor is shorted by the points, so holds no charge and hence the voltage across it is zero. At time zero plus a small amount a current will start to flow through the primary and points. The rate at which this current increases will be determined largely by the inductance of the coil. As we wait the current will build as 1 minus an exponential to an asymtote. The value of the asymtote will be V/R, ie, the applied voltage divided by the resistance of the circuit, due to the inductor and the points. So in the final steady state the value of the inductance plays no part in the final current value. In practice an ignition system will not allow the current to flow for anywhere long enough to allow the current to build to the maximum. The points normally open long before that. Usefully the first part of the current curve is almost a straight line, which makes the maths easier.

At a time after zero we have a current flowing in the primary and the points. If the points open without the capacitor the current will fall to zero and the voltage between the coil and points will rise in an attempt to maintain the current. This voltage is then amplified by the ratio of primary to secondary turns in the ignition coil to provide a voltage high enough to jump the spark plug gap. From a practical point the increase in voltage in the primary circuit may be enough to arc across the points, eroding same and radiating energy.

However, if we have the capacitor the current will continue to flow but into the capacitor, charging it up and creating a voltage across the capacitor. At some point the voltage across the capacitor will equal the applied voltage so no current will flow. But the inductance and capacitance form a series resonant curcuit. So on the way to the final stable DC state the energy will oscillate between inductor and capacitor. The voltage where the inductor and capacitor are joined can be many times higher than the applied voltage during this oscillation and is dependent upon the Q of the resonant circuit. As SOD says these oscillations die down due to losses in the components, mostly series resistance in the inductor. As the oscillations die down they decrease in amplitude until reaching a steady state DC value equal to the applied voltage.

Andrew

The primary purpose of the capacitor is to reduce arcing across the points as they open. This reduces erosion of the points, and also helps reduce radiated emissions. Adding the capactor, reduces dv/dt and hence peak voltage, as the points open. This might seem to be a bad thing as the voltage across the spark plug will be proportional to the voltage across the points as they open.

However the capacitor and coil primary inductance form a series resonant circuit which will oscillate when the points open. The voltage at the internal node of a series resonant curcuit can be much higher than the driving voltage, the value being dependent upon the Q, and this will be reflected in the voltage at the spark plug. In this way the loss of dv/dt is compensated for, at least to some extent.

The capacitor will carry the full coil primary current and the voltage across the capacitor will be plus and minus wrt 0V. So a ceramic or film capacitor will be needed. An electrolytic capacitor is unsuitable.

Andrew

Irrespective of tightening torque that will never hold a cutter, or work, properly. Looking at my 6mm diameter Pultra 10mm collet the holding length is 8 to 10mm.

Andrew

I would associate Hauser with jig borers and precision machine tools for the watch industry. So I'd assume you are pushing it beyond the limits expecting it to act as a normal milling machine with, presumably, a 6mm cutter.

Andrew

On my engines the crankshaft gears are steel, EN8:

The 2nd shaft gears, final drive pinions, and final drive gears are cast iron:

The bevel gears in the differentials are also cast iron:

Cast iron would be prototypical. I am building relatively large engines where tooth loads on the crankshaft gears tend to need medium carbon steels, but I suspect cast iron was used in full size.

I have used cheap gear cutters for experiments, but I'd be wary about using them for real gears. The ones I have never seemed to run true. I doubt that cutting a small number of gears, steel or cast iron, will blunt them.

Andrew

Languages are not a strong point, so I try to choose my words carefully so that they represent the picture I have in my head. I know that I have a tendency to be economical with words. When I was playing at being an academic I often got research papers back with a request to expand on the introduction before publication.

I read, and re-read, a post to make sure I understand it before posting a response. I also like to read the whole thread to make sure I am not simply repeating what has already been said, or asking a question that has already been answered. Of course that sometimes means that I am pre-empted by another poster, in which case I don't post.

Andrew

I didn't know that horizontal cutters were handed. Surely the required direction of rotation is dependent upon which way round the cutter is mounted on the arbor? My horizontal is happy running in either direction. I normally run cutters clockwise, looking from the front, with the work feeding from left to right.

Andrew

PS: In my previous post I forgot to add that for slitting saws there are those who use drive keys and those that don't.

I prefer to use slitting saws on my horizontal mill. On the vertical mill (with stub arbor) they tend to go walkies on deep cuts. On the vertical mill I limit cuts to shallow slotting, usually one pass. On the horizontal I am happy to take deep cuts, more than 25mm, normally in 5mm steps.

As mentioned above for deep cuts, as opposed to things like screwhead slots, coarse teeth cutters are needed. In this picture all the slitting saws are coarse, except for bottom right:

While I don't think twice about climb milling on the vertical mill I don't do so on the horizontal mill, at least not until I have fixed the backlash adjuster. For slitting saws I tend to run a bit slower than theory, for a 4" cutter around 70rpm. On the horizontal I use 4 thou per tooth as a minimum feed. Below that the cutters seem to chatter. As with all cutting tools they need to cut, not rub. Remember that even with a reasonable depth of cut on a 4" diameter cutter chip thinning applies. So what you get in terms of chip load is smaller than the theory. For steel i always run flood coolant on the horizontal.

I would have the outer support much closer to the cutter to minimise deflection, like this:

My horizontal mill was an impulse buy, but it has turned out to be very useful.

Andrew

Threading inserts come in a range of sizes, of which the most common are 11, 16 and 22. Coarser threads tend to use the larger sizes, but any given size will cover metric and imperial, and partial or full form, threads of all specifications. As standard I use size 16. I normally buy insert holders from Cutwel. I have one size 16 external holder and size 11 and 16 internal holders. When screwcutting small (less than ~12mm) internal threads I use form tools.

Andrew

+1, makes my A&S 2E look weedy.

Andrew

In general I use HSS taps and dies. However some older thread families, ME in particular, are only available in carbon steel. Which is fine as I mostly use them on brass. I think that HQS is simply a form of carbon steel. I use the Tap&Die company for ME threads, usually taps as I screwcut most external ME threads. The owner can be a bit mercurial. I used to buy from Tracy Tools but don't do so any more as I wasn't happy.

Andrew

Redacted!

Andrew

Edited By Andrew Johnston on 10/09/2022 21:18:04

For centrifugal governors the controlling force is proportional to the square of the angular velocity. Higher operating forces mitigate the effects of friction within the governor. For slow revving engines, such as a pumping engine, it is common for the bevel gear drive to the governor to be step up so the governor runs faster than the engine.

Andrew

Never worked for me, the soft solder is too weak. I'd agree with Bernard, use mechanical fixings. This picture shows boring bearings, but is equally applicable if the bearing stand and bearing cap hole is round:

Andrew

When turning the forces resulting from the shearing action are predominantly downwards.

Andrew