Member postings for John Haine

It is star connected.

Joe, why should the divide by 5 jitter? Easy to make a synchronous /5 circuit where the output changes state every 5th edge, there's no reason why it should jitter surely? Existence proof: have a 3-bit register clocking the output of a 3-bit adder, force the adder output to be all 0s when the register state is binary 4, then the next state will be binary 0. So the register value cycles through 0, 1, 2, 3, 4, 0.... on successive clock edges.

I looked at the Neo/Lea M8T datasheet, it seems to say that the max frequency programmable is 10MHz.

1.8.2 Timepulse and frequency outputs The NEO-M8T and LEA-M8T modules provide two time pulse outputs that can be configured in rate from 0.25 Hz up to 10 MHz by message CFG-TP5. Time pulse alignment can be configured to UTC or GNSS time according to the standard used in signals being received or to an alternate standard where inter-standard calibration data is available (from the signals themselves or by aiding). The time pulses are generated on edges of an asynchronous clock; for pulse rates below 2 Hz, the exact phase of the TIMEPULSE output is reported before each pulse in the TIM-TP message. ☞ Times reported in navigation messages such as NAV-PVT report the time of the preceding pulse.

However, it also has this intriguing paragraph:

1.8.3 Time mark The NEO-M8T and LEA-M8T modules can be used for precise time measurements with submicrosecond resolution using the external interrupt pins (EXTINT0 and EXTINT1). Rising and falling edges of these signals are time-stamped to GNSS or UTC time, counted and the results reported in message TIM-TM2. The reference time is the same as set for TIMEPULSE with CFG-TP5.

Which means that the device will do the whole job I think!

Which one have you ordered please Dave?

And since the picPET can be clocked at up to 20 MHz this will work beautifully but give a slightly smaller time increment, which isn't a problem. Nice!

Storing tool offsets is actually invaluable!! Being able to take a tool in its holder, clamp it in the QCTP, select the tool number on the DRO, and have it display the turning diameter straight away, is just so convenient. Yes you have to set up the offset table but after that the offset for a given tool only changes when you sharpen it. The thread pitch "feature" comes for free with any DRO. I would definitely go for the DRO option.

Thanks for all the info, lots to go on. I've also asked a local rewind place for a quote, but overall it looks like a fairly straightforward job to do myself. And I think we are definitely intending to use a VFD rather than a capacitor Kluge.

Thanks for the links Joe. Some I had seen, they all look useful. I am trying hard not to get sucked in to being a time-nut any more than I have to, I'm mainly interested just in making accurate pendulum clocks - but how do I know how accurate?! I assume my cheap eBay OCXO is a lot better than my pendulum but how to check?

Hi Joe, no I don't think I did. I use one of Tom's picPETs (a pP07) to time both edges of the pulses from the BDC opto. The pP is clocked from a 10MHz OCXO, non-disciplined but likely to be a lot more accurate than my clock!

I assume the OP has an engine but it lacks the cutting frame - you can see from the PF Tools picture that it is just bolted in place. Presumably the OP's was parted from its frame at some point so it needs replacing.

As it's been a couple of weeks I thought a quick progress report was due.

• I finished the time logging system and got some initial Pi logging software working the w/e of the 4/5 Feb. That was logging the time of each swing, i.e. every second, but the results were difficult to process since the two swings are slightly different lengths as measured. Anyway the results were good enough to see the effect of the Turkey earthquake on amplitude and rate.
• New logging software installed last Tuesday and ran for nearly 5 days but I found the pendulum nearly stationary early in the morning of the 5th day. I'd noticed before that occasionally when I was working near the clock it would "forget" which side was left, which meant that the impulse actually slowed the pendulum down! This time I also found that there were no pulses coming from the optos and finally found the bad contact in the DC supply to the LEDs.
• As I had to restart the clock anyway I made another software update. Now the Pi for each cycle generates a record that has the acquisition time based on a "paper clock" that has the average period of the real clock; the error between the "clock time" based on the integrated measured period and the paper time; the period itself; amplitude averaged over the two opto pulse lengths; temperature, pressure, and RH.
• The reason for choosing the parameters and format is so I can directly read the data into either of two free software packages for analysis: TimeLab and Stable32. Both easy to find on the web, and recommended in Tom Van Baak's writings. I can't say I'm anything more than a novice with either, but they seem reasonably easy to use and can compute things like Alan Variance with a button push. I'll also use R-Studio to extract regression data. So far there hasn't been much variation in atmospheric conditions against which to correlate! I think I'll also add an LDR to look at ambient light levels to see if there's any systematic affect on the opto precision. Would also be good to log supply volts!
• I did manage to get a nice plot of time drift out of Stable32 from the week's worth of data but now I can't work out how to get it back!

Would be good to know where they came from Tony*. But HH coils are quite easy to make and you have the advantage then of a predictable flux density so the current needed can be calculated. But if I ever make another one I might well buy two of those coils...

* https://willys-hifi.com/collections/audio-inductors-air-core ?

Traditional cutter frames have point and cone bearings probably because they were easier to make, but some kind of rolling bearings would be better these days. I suspect that generally wheel cutting engines have fallen out of favour because small vertical mills will do the same job with the addition of a dividing head, plus a whole lot more. One approach that might work for you would be to use a small headstock such as the Peatol or Sherline ones which can be bought on their own and work fine as milling spindles.

https://taigtools.com/product/complete-headstock-with-er-spindle/

There's a book called Spindles by Harprit Sandhu in the workshop practice series that apparently has a design. You can 3ven get the book from Chronos!

Those numbers sound pretty good to me. Cutting a longer bar may well show up some taper but that's also a function of how well set up the lathe is, there could be some bed twist which could be removed by levelling. Also do you expect to support the bar at the end away from the chuck? Lots of ways you could get apparent errors due to the process not the machine.

Those numbers sound pretty good to me. Cutting a longer bar may well show up some taper but that's also a function of how well set up the lathe is, there could be some bed twist which could be removed by levelling. Also do you expect to support the bar at the end away from the chuck? Lots of ways you could get apparent errors due to the process not the machine.

From my reading of the book(s), though Shortt suggested the "raised cosine" design to FH-J after thinking it up whilst listening to Frank presenting at the IEE (in 1910?), it was described as only a theoretical idea. Actually there's no particular reason why a raised cosine should be better except that it starts and ends very gently and builds up in the middle then "fades away". But the actual shape hardly matters for a high Q pendulum. I'd decided to make my pallet by profiling anyway so needed some shape, and having read the book I saw it as an interesting challenge to adopt Shortt's.

Thanks Clive, that's encouraging!

Thanks John, that's helpful.. I know the basics though have never tried it. Do you have any specific experience with a Brook motor please?

A friend in the village has acquired a 60s vintage Wadkin cabinet saw, a very nice bit of woodworking kit. It has a 2hp 3ph Brook motor which is star connected.

I was wondering if anyone here has specific experience of finding the star point on these motors please? In particular just how much dismantling is needed to get at it.

Edited By John Haine on 13/02/2023 13:35:49