Member postings for Peter Cook 6

Thread cutting at over 2000 RPM sounds Interesting!

As Dave (SOD) says it mainly depends on what you want to do with the lathe, but it also depends on how deep your pockets are, and what level of precision you are aiming for.

A decent watchmakers lathe in excellent condition is expensive A second hand one is cheaper, but the bits come expernsive - 8mm collets can run £10 each second hand and you need one for every 0.1mm - and the precision is questionable.

Can I suggest - if you are in between the mini lathe or watchmakers lathe - that you look at something like a Sherline, Taig or with deeper pockets one of Cowells. They are a good compromise between the two.

My Taig (with an ER collet headstock and shop made power feed) works well and is safe enough with a graver (I would not want to use a graver with a 3 or 4 jaw chuck!) and I can turn up to 6" diameter using riser blocks if needs be. Many of the professional clock repairers use Sherline machines.

Sherline lathes use a similar approach. They use a key to reset zero

What has Model Engineering taught me

a) Enormous respect for those who do it to a far better standard than I can achieve, either professionally or as amateurs.

b) you can never have too many tools. The one you want just now is the one you don't have - and either have to get one, make one or get very ingenious with the one you have.

According to the 1901 census my grandfather started his working life as a rivet boy in the shipyards. If I understood correctly his role was to transport the red hot rivets from the furnace to the riveters!

Dave - you said "It also empowers folk who want to do everything 'by the book', no matter how costly or pointless." I once heard ISO9001 described as a mechanism to ensure that you could make the same rubbish consistently!

Edited By Peter Cook 6 on 08/01/2023 11:57:05

If you are printing them yourself, one trick I have used is to print (on the same printer, using the same substrate) a series of grids where each square in the grid differs from the next by a few steps on the RGB scale. Along one dimension alter R, on a second dimension alter G, then repeat with several grids each of which alters B.

If you use fairly coarse steps (say 5 or 10 points on the 0-255 scale for each one) you can then pick the square that is closest. Then repeat with smaller steps.

There is an issue using Pantone colours with Adobe

Adobe Just Held a Bunch of Pantone Colors Hostage | WIRED UK

Still doing the same today. I have several similar on various bits of Kit.

This one

Is from a BT Smart Hub. It was done so that (as Bazyle said) the packaging will fit through a UK letterbox.

But did you also take into account the difference due to gravity? I was only thinking about pendulum clocks, but general relativity also says that time shifts not only with speed, but also gravitational potential.

NIST registered differences in the passage of time between two high-precision optical atomic clocks when one was elevated by just a third of a meter How Time Flies: Ultraprecise Clock Rates Vary with Tiny Differences in Speed and Elevation - Scientific American

So the solar gravitational effects will also impact the timings - even of a balance wheel clock!

I suggest when Dave is having to apply these corrections in his counter logic we can consider that he has almost succeeded.

Assuming you are sticking to pendulum clocks in keeping with this thread

I think they should run faster! Gravity is stronger at night. The sun is on the opposite side of the earth to the clock, so It's pull is additive to the earth's gravitational field. During the day the sun's field should subtract from that of the earth as perceived by the clock.

As the period T = 2π*Square root of ^L/_g as G increases, the period T decreases. So at night T should be shorter than during the day.

Although that ignores the effect of the moon, tides and other variables. But the effect will be small!!

Thank you Dave, now I am a little clearer about what you are attempting. What confused me was the digression into PID control - a technique I learned (and forgot about) long ago, but all in the context of closed loop feedback control. So I assumed you were trying to close the loop electronically.

I will now drift away into silence to finish putting new springs into and cleaning a small Maji era Japanese clock. Its oscillator is a hairspring balance wheel, it's counter is clockwork as usual but the indicator and strike mechanism a little complex as they cater for the changing length of the "hours" with the time of year.

Good luck with the project, I will follow with interest.

Edited for typo

Edited By Peter Cook 6 on 23/12/2022 16:51:44

The teaching process is about the timing and length of the pulse duration.

If Dave can "teach" his clock so that the power pulse is sufficiently accurate that it delivers the power needed to offset losses, and starts at the point which ensures that the trailing edge of the power pulse is exactly aligned with the falling edge of the reference pulse, then my system doesn't need the reference pulse either.

No more "cheating" than any other mechanism used to get the pendulum to accurately match a GPS derived time signal.

As you said a few posts further back in the discussion about PID control to deal with long time constants, "The clock compensates on every beat". So every beat you are adjusting the power to keep the pendulum in sync with the time standard. I was just suggesting a different (and possibly simpler) way to do that.

Both approaches achieve the same end, adjusting the power pulse to compensate for external (temp, pressure etc.) or internal (friction, cyclic error etc.) variations in rate.

There is nothing to stop you measuring the stability of the power pulse length, and working to minimise its size and variability by tweaking the mechanical and environmental conditions.

Dave, for your next project. Now that you have a highly accurate GPS reference signal, and a switching mechanism to deliver a power pulse to the pendulum, rather than complex (PID) math to adjust the pulse timing have you considered using the lack of isochronism in the pendulum as an inherent feedback mechanism.

I assume the pendulum characteristics are such that as the power increases, the amplitude increases, and the rate slows (slightly).

The diagram illustrates the idea in a somewhat exaggerated form. The top line is the highly accurate signal used to deliver a square wave pulse exactly at the pendulum’s ideal rate.

The next three lines show the drive pulses from your sensing/switching mechanism under various scenarios.

A illustrates the ideal position. On each swing, the reference signal goes high before the switching mechanism applies power to the pendulum. The switching mechanism then activates and applies power which is turned off by the reference signal going low. The red area represents the power supplied.

B is the situation when the clock gets a little slow. The pendulum switching will occur slightly later relative to the reference signal. That results in a lower power delivery to the pendulum. Therefore, the amplitude decreases, and the clock speeds up a bit. The feedback continues to increase the rate until we get back to A.

C illustrates the clock gaining slightly. The pendulum switching then occurs slightly earlier relative to the reference signal. The power delivered increases, as does the amplitude and the clock slows down again until position A is re-established.

If it all works as it should, the pendulum rate will inherently lock to the falling edge of the reference signal*.

This is the mechanism, based on an idea from Derek Roberts, which Bryan Mumford developed into his Governor product for Eureka, Bulle and other antique battery clocks. Frank Roetsky makes a similar device.

PS* If the pendulum characteristic is the other way round  - increased power increases the rate, and Bryan suggests there are  Eurekas that do this, then the mechanism still works except the the pendulum locks to the rising edge of the reference signal.

The method does work well. I have one of Bryan’s units and one of Frank’s on a couple of Eureka clocks and both keep time to within seconds per year.

Edited By Peter Cook 6 on 22/12/2022 12:39:04

Sorry Dave, I think Pin 2 AND pin 3 are both detected EVERY time (at least up to a certain speed). It's just that your ISR3 code (which happens second) overwrites the Least significant bit in VALUE which has been set every time by ISR2 which runs first.

Your code executes as Loop - ISR2 - ISR3 - Loop.

When it gets warmer in the workshop I will see if I have a suitable frequency source and have a go.

Dave I think there is a problem with both your code and your understanding of the interrupts. If I read the Arduino documentation correctly, if two interrupts arrive simultaneously, then they are processed in priority order. Pin 2 has a higher priority than pin 3, so in your test Interrupt 2 should get processed first which sets Value equal to 1, when that ISR is finished the interrupt on pin 3 is executed, which sets Value equal to 2 -- overwriting the bit set by interrupt 2 and making it seem as if the pin 2 interrupt is being ignored.

I also think that the problems you are seeing at over 5khz are the result of the serial print process being interrupted. 115,200 baud is about 10,000 chars/second max. You are sending 15 - 20 chars per print. Once the serial print buffer fills Serial Print waits until there is room in the buffer - so once the buffer fills each serial print will be taking 100 microseconds per character printed. At 10khz interrupt rate you are almost guaranteed to get the print process interrupted and the data corrupted.

A more valid test would be to have each ISR increment a separate counter each time it is executed, then in the main loop simply compare the two counters.

If both interrupts are being serviced properly the two counters should remain in step. When they differ, you have found the limits.

PS if an interrupt on 2 arrives while the interrupt on 3 is being serviced, then it simply gets queued until the one on 3 has completed.

Edited By Peter Cook 6 on 17/12/2022 17:47:30

The only thing I watch for, through the vehicle in front, is the brake lights or indicators of the ones further forward. I don't find privacy glass obscures them significantly especially if the car in front is driving so close to the one in front of them that I can't see the lights directly. Cyclists, pedestrians, deer, pheasants etc I infer from the deviations (swerves!) of the vehicles further forward, and I see them down the outside of the one in front.

Peter G.

I accept "...of absolutely no importance..." but not silly - which the Oed defines as "having or showing a lack of common sense or judgement; absurd and foolish." None of which would apply to your question, as you so eloquently explained.

Or better still have the government privatise it in the least useful way (e.g. Rail, Water, Energy etc.)

Mike - in defence of GP's. A friend who chairs the local surgery's patient liaison committee told me recently that the surgery is getting three times as many requests for appointments than they did in the year pre-covid. Why - they are not sure. The local population might be up 10% but not 3X, so people are requesting many more appointments.

I wonder if it's anything to do with the relentless barrage of media cover of any and all aliments - all of which recommend that if you have the slightest symptoms you should see a doctor.  I wonder how many surgeries are currently buried in children with coughs and/or sore throats which would have been treated at home - but now need to be seen because of the publicity surrounding Strep-A. 

Edited By Peter Cook 6 on 11/12/2022 15:07:30

No such thing as a silly question, if you want to know ask. It's just a question of asking the right source.

The Encyclopaedia of Science Fiction SFE: Identity Transfer (sf-encyclopedia.com) gives

"An old woman's and a young woman's brains are swapped in Edgar Rice Burroughs's The Master Mind of Mars (1927 Amazing Stories Annual; 1928). "