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Member postings for Clive Steer

Here is a list of all the postings Clive Steer has made in our forums. Click on a thread name to jump to the thread.

Thread: Controlling air
10/10/2020 10:20:11

You may consider using a positive displacement pump of known swept volume and controlling its speed to provide the flow rate needed and the pressure will sort itself out determined by the head of fluid in the tank.

Clive

Thread: Ball bearings and friction.
02/10/2020 09:44:14

I think the same general rules apply to chaotic pendulums as those for normal clock pendulums in that air and bearing frictional losses determine the system Q. Given the degree of freedom needed ball races are probably the the simplest bearing arrangement. However to reduce the effects of air friction, like the Shortt clock, the pendulum needs to operate in a low air pressure or vacuum environment which has its implications. So why not apply the same method of maintaining oscillation as a pendulum clock by giving the pendulum an occasional impulse. This can be done electro-magnetically, in a similar way to that being devised by SOD for his pendulum clock. For a conventional pendulum clock the impulse is usually provided on a regular basis with a defined amount of energy added to maintain pendulum amplitude and precise timing. However for a chaotic pendulum the impulse energy can be varied to give different levels of excitement to its movement.

Clive

Thread: Arduino Pendulum Clock Design - Comments Welcome
02/09/2020 14:32:58

Picking up on the point that the "pendulum" does not have a suspension spring but relies on the carbon rod flexing doesn't this make it more like a tuning fork than a true pendulum. If that is the case then the resonant frequency will be a function of the mass of the bob whereas in a true pendulum clock the timing is largely independent of the bob mass. In some ways the arrangement is a mono resonator whereas a tuning fork is a double resonator with mutual coupling although the "pendulum" support structure could form the other half. Tuning forks can provide excellent time keeping as shown by the Bulova range of watches.

Clive

Thread: Why is there no side relief on a wheel cutter
28/07/2020 09:45:44

All the clock/watch wheel and pinion cutters I've come across are form relieved and I have examples of those that have been sharpened. For very fine watch pinion cutters this must have been very difficult to achieve accurately and was probably done by the companies that made them as a refurbishment service. There are complicated machines, mostly Swiss made, that were solely designed to automatically cut the cutter profiles. I bought a box of machine parts at an auction to get the Schaublin vice in the lot and it took me about 10 years before I eventually found out what machine the parts belonged to and I still don't know which Swiss company made them but possibly Safag.

There is an excellent book by J M Wild on Wheel and Pinion Cutting in Horology and section 8 shows how the cutters are made and also how simple home made cutters can be made.

I have an early Petermann automatic pinion cutting machine and this would have three cutters mounted on the same spindle. The machine would automatically make gashing , profiling and finishing passes over the pinion blank for a fully manufacturing cycle and some machines had the capability to automatically load pinion blanks from a cassette. To see the machine check out Petermann on the lathes.co.uk site.

Clive

Thread: Manual control of CNC
19/04/2020 14:11:07

Most CNC machines have a manual positioning capability but this is usually a single hand wheel selectable to act on one axis at at time for positioning. There are few technical reasons why a CNC machine couldn't have a manual reversion capability using an arrangement of hand wheels similar to manual machines. These hand wheels do not need to be mechanical connected to the CNC machines ball screws as their function could be replicated electrically. Strictly speaking there may be no need for a computer if the electrical encoders are fitted to the hand wheels provide step and direction signals that can directly connect to the ball screw stepper motor drivers. However some CNC machines micro step the axis motors so the effective "gearing" between the hand wheel and axis movement may be too fine.

This might be a way to test the mechanics of a machine being converted to CNC before splashing out on an expensive computer and software or to check out a machine whose controller is unusable because of license issues.

Being able to use a CNC machine in full manual mode may help when a simple one off task doesn't justify the time investment overhead of CAD/CAM.

Clive

Thread: Electrical help please
15/04/2020 14:56:23

I see that John says the clock uses a variant of the Hipp toggle to control impulsing of the coil depending on the swing amplitude rather than at every swing. As the amplitude decays the Hipp toggle is triggered and an impulse is applied to the balance wheel. As mentioned before if the mechanical or electrical efficiency are not optimum then the impulsing will be too often giving a short battery life.

The mechanical efficiency ( Q ) is easy to check by doing the oscillation check. The electrical efficiency can be checked by holding the balance wheel at its neutral position and energising the coil. Then move the balance wheel either side of the neutral position and see what force is felt acting on the balance wheel. There should be a sweet spot just before the neutral position that maximum force is felt. When you know this position then check that operation of the Hipp Toggle acts slightly before this point. The lead timing is needed so that current can build up in the coil. Usually impulse is given only one side of the neutral position (top dead centre in engine terms) as any current flowing in the coil after TDC could retard the balance wheel and reduce efficiency

Clive

15/04/2020 14:29:03

With electric clocks of this type both the mechanical and electrical efficiency must be good if the battery is to last.

As an example the Eureka clocks will typically run for a year of a D sized cell and this has a 30 coil resistance.

To check the mechanical efficiency just set the balance wheel in motion, without the battery connected, and see how long the balance wheel remains oscillating. On the Eureka clock I have in for service I released the balance wheel from 120 degree position from the at rest position and the balance wheel final stopped 90 seconds later.

For good electrical efficiency the timing of the energisation of the coil must coincide with the magnetic pull produced by the coil acting on the balance wheel at the correct position of the swing.

I'm not sure about the exact design of the Wilding clock but on the Eureka clock the contact closes 30 degrees before the pole pieces are at their minimum distance and the distance is about 3 thousands of an inch. The coil/pole piece arrangement forms a reluctance motor in that force is generated between the pole piece and coil as the length of the magnetic field in the air gap is shorted. If the air gap is very small the inductance of the coil can be very high even for a very low resistance coil. A high inductance has the effect of slowing the rate of rise of electrical current when a voltage is applied so the effective current drawn may be quite low provided the duration of the coils energisation is short.

So for good efficiency the air gap between the pole piece and coil must be short, the timing of energisation should be short and at the correct point in the balance wheel position to give the greatest mechanical impulse to the balance wheel.

I hope this helps.

Clive

Thread: An Easter Tale of Cordless Batteries.
12/04/2020 13:41:21

If the cells in the batteries are Lithium and have discharged below about 2V as far as the charger is concerned their viability is questionable. So the charger checks each cell and if any are below the 2V min it will not continue with charging. Unlike NiCad/NiHi batteries Lithium batteries need complicated charging profiles including cell balancing and the chargers are not simple devices especially if they are designed for rapid re-charging where charging currents can be high. If discharged below the lower viability threshold voltage the cell can develop a number of issues that subsequent charging at high currents can cause fire and/or explosions which is a bad thing.

It may be possible to revive a cell by carefully charging it with a current limited( say 100mA) bench power supply to bring it above say 3V so the normal charger will see the cell as viable but care is needed.

If the cell shows any signs of swelling then the cell is definitely beyond recovery. I've noticed this condition in several phone and camera batteries where the device hasn't been used for some months. Although Lithium cells have very low self discharge rates they have protection circuitry that can worsen this and the devices they are fitted too may add a background discharge rate which could be just a couple of months.

The other Clive

Thread: Todays news -- well done
06/04/2020 10:21:28

I've seen references to Cover-19 being described as a Schrodinger virus.

One state is that one has the virus but possibly not showing any symptoms and therefore could unwittingly infect others.

The other state is that one does not have the virus and therefore have no immunity to the virus and susceptible to infection.

So until tested we both have and don't have the virus.

Clive

Thread: 2TB USB drives.
04/04/2020 00:48:46

I read about low cost USB memory sticks supposedly with high memory capacities actually providing write only functionality. So when you move files to the stick they can't be retrieved and effectively you lose your data. It is possible that such devices could also download other nasties that you'd prefer not to have on your computer.

Clive

Thread: DC-DC converter
29/03/2020 18:43:14

As has already been stated the callipers only use microamps of current so even an LM317 may be overkill. All that is required is a 10K ohm series resistor and 2 forward biased silicon diodes in series plus as Neil has recommended a capacitor across the diodes to suppress noise.

Clive

Thread: Can we have a really clear distinction between Silver Soldering and Brazing
21/01/2020 10:14:08

As already explained soldering and brazing are similar processes but performed at different temperatures. However the distinction may have arisen by the need to discriminate between different types of manufacturing process or equipment needed or take into account the trade or operative qualifications/training and possibly Union they belonged to.

Clive

Thread: VFD Question
10/01/2020 18:53:36

Picking up on the point about the maximum frequency that a nominal 50 Hz motor can be driven I've outline my experience with my lathe.

I have a Chipmaster lathe which I've modified by removing the variator but have retained the original 3kW 4 pole 1428 RPM motor which is configured in Delta for 240V working. I drive the motor from a 3 phase 7kW VFD which I operate from a 240v single phase supply. The VFD is programmed to have a max output frequency of 100Hz that spins the motor at 2800rpm and I have fitted a motor pulley to gives a spindle speed of 2200rpm. This works fine and produces sufficient torque at low speed for most of the turning I do whilst providing adequate higher speeds.

However the Chipmaster is capable of running its spindle at 3000 rpm so to try and get this I re-programmed the VFD max frequency to 150Hz but still couldn't achieve much more than 2500rpm which I was due to the motor's back emf and the supply voltage.

I next tried a 6 pole 980 rpm 3kW motor, fitted a bigger pulley but still couldn't get this motor to run at much more than twice its design speed confirming that the back emf appears to be the issue.

Therefore to get the higher speed I either have to drive a delta connected 240V motor from a 440V VFD or find a 110v motor and drive it from a 240V motor.

Clive

09/01/2020 01:20:42

Taking Andrews point about how a street is wired with 3 phase and each house is fed with a one of these phases it is likely that your neighbour either side of you may not on the same phase as you. So it may be possible to get a true 3 phase supply to your property if you can persuade you neighbours to throw an extension lead connected to their mains over the fence.

Although not a serious suggestion is this a possible safety risk as there would be 440v between the live of your house wiring and the live of the feed from your neighbours.

Clive

Thread: An interesting repair to an Hour Wheel
13/10/2019 13:37:09

I think this repair scheme, although not orthodox or elegant , should be high on the conservationists score as it neither adds nor subtract material from the original artefact and if adopted using modern super glue could be reversible with no lasting impact on the artefact. The orthodox repair usually required a slot or dovetail shape to be cut into the wheel and a single or multiple teeth usually donated by a similar wheel to be shaped to fit and soft soldered in place. Another accepted approach is to make and fit a new, signed and dated, wheel and leave the old one with the movement. If taken to the limit one could make a completely new movement and leave the old one in the bottom of the case where at least it won't wear out or need servicing again.

Unfortunately the value of long case clocks is so low that, unless they are family heirlooms, they are beyond economical repair. I think a sketch, similar to the well known one about a Norwegian Blue, could be written for long case clocks.

Clive

Thread: Jim Al Kahlili : Revolutions
01/08/2019 21:01:13

I think that the majority of roads that cyclists are likely to use are maintained by local council taxes and not from funds raised by the VED. Therefore since they are likely to pay council tax I feel they have every right to use the roads. A cyclist is an easy target for criticism which really should be directed towards planning authorities for failing to provide cycleways similar to those provided in Belgium and The Netherlands. New "relief" roads have recently been built near where I live but essentially provide access to land so more housing can be built. However none of the roads have cycleways. As the law stands at the moment cyclists are not allowed to cycle on footpaths but many main roads have associated footpaths which are rarely used by pedestrians and could be turned into cycleways making everyone lives safer. Blaming cyclists for using the roads is like blaming commuters for the trains being late.

Clive

Thread: Another scam
30/07/2019 17:23:39

I can understand that if one is persuaded to initiate a call to a premium number that one could be charged. However I'm not sure I understand how pressing 1 after a bogus introduction call would result in a charge to the receiver of the call unless the phone companies are in cahoots with the call initiators as they have to take your money and pass it to the fraudsters.

Also if the caller number can be so easily spoofed I feel that the phone companies aren't doing enough to protect vulnerable people. If the true address of a sender of an e-mail could be spoofed as easily as it appears the phone caller number can be then we could be in for a whole world of pain.

Clive

Thread: What mills have you had
21/07/2019 17:55:38

I started off with a BCA Mk3 which is now fully tooled and I still have. However needing a little more capacity but having limited space I bought a cheap Tom Senior off eBay. Big mistake as it needed quite a bit of work so moved it on. Bought a Boxford VM30 and fitted it with a Bridgeport M head to provide a Quill capability. Added VFD and DRO to make very nice and compact machine which is just right for the work I do.

Clive

Thread: Possible New Internet Scam to be Aware of.
22/06/2019 12:52:23

I must be missing some vital security knowledge regarding banking transactions. Even if a scammer obtains someones bank account details how do they persuade the bank to send them money from that account. I can understand an account owner transferring money because he has been persuaded to do so but not how a bank might transfer money to a "new" recipient without the account owners permission. Not everyone who has a bank account necessarily has on-line banking enabled so maybe this isn't their way in.

Clive

Thread: Model aircraft pilots angry over drone laws
07/06/2019 10:19:40

Like most new legislation and control mechanism put in place by Government following incidents the innocent and responsible are often affected the most whilst the criminals and those intent on causing harm won't even loose sleep over the matter. Given that a local Sussex enterprise was manufacturing illegal semi-automatic pistols in their workshop on an industrial estate the control of machine tools may need to be "licensed" so watch this space.

Clive

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