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Member postings for Robert Atkinson 2

Here is a list of all the postings Robert Atkinson 2 has made in our forums. Click on a thread name to jump to the thread.

Thread: Ml2
06/05/2021 21:19:37

I had problems removing the spindle from my ML2. The issue turned out to be somone had tightened the pointed grub screw in the bullgear away from the intended recess and raised burrs on the spindle. not much you can do about it other than brute force or miving the spindle / gear positions back to where they were and using some kind of long end cutting tool down the grubscrew hole to remove the burrs.
Mine scored the front bearing on the way out.

Robert G8RPI.

Thread: IT Travails
05/05/2021 21:57:50

WiFi at 2.4GHz and 5GHz DOES NOT reflect off normal glass as used in domestic premises. It will be reduced by wirer glass or infrared reflective glass. Thisi s why some car windscreens stop GPS working.

The over mains network extenders can cause significant radio interference.

Robert G8RPI

Thread: motor control
05/05/2021 17:52:09

What Roger B says.

A permnent magnet motor will will run at a speed proportonal to the voltage across the windings and draw a current proportional to the load (torque) applied. The apparent voltage across the widings drops with load due to brush gear and winding resistance which is why they slow with loading.. Running in parallel with fixed, rated, voltage will give full speed and maximum torque. Putting the same two motors in series across the same supply will in theory give half the speed and half the maximum torque (twice the internal resistance that limits curent) so 1/4 power. In practice the motor resistance is too low to limit the current (motor on full voltage can draw much more current than rating if overloaded) so in series you can still pull full current without overheating the motor so can normally get full torque at half speed so half power. Practically it is just a simple two speed system. With modern electronics a PWM controller will give a much better solution.

Robert G8RPI.

Thread: Repair It? Wossat Mean, Like?
04/05/2021 21:32:20
Posted by Bazyle on 04/05/2021 18:19:08:
Posted by J Hancock on 04/05/2021 14:18:25:

Now that is real, 24hr/day 'reliability', only achieved by rugged design and available spares.

Indeed having and needing the spares. No menion of how much that repair and maintenance cost.

<SNIP>

Anyway the real problem is not just production cost paring but the lawyers. For each new product we have to make the 12v power supply connector incompatible with all our other products or go to the expense of having each combination of interchange requalified at costs of around £50k per set.

What sort of equipment? Most manufacturers buy 3rd party fully, normally word wide, approved external power supplies so they don't have to bother with the multitude of mains certifications. Even medically certified (low leakage current) one are available. Only thing I can think of is ATEX approved equipment.

Robert G8RPI.

Thread: Pond filter with UV lamp
01/05/2021 10:41:32

Hi,
Annual lamp changes are pretty conservative. Normal flourescent tube life is 20 to 60 thousand hours depending on source and a lot of loss of output is due to the phosphor coating which of course the UV-C tubes don't have. If on 24/7 then a 2 year life is almost certanly OK.

Covid 19 might bring down the cost of 269nm LEDs due to large scale production for sanitation robots but recent research indicates that surface contact is not a significant infection route for Covid.
Even then they are not as efficent as the fluoresent tubes. Thatypical small "8W" 16mm dia 288mm long tube produces 2W of UV-C output for 7W electrical input.

www.osram.com/ecat/PURITEC HNS UV-C-UV-C lamps for purification-Ultraviolet lamps-Industry-Specialty Lighting/com/en/GPS01_1028570/ZMP_4021034/

In comparison a LED consuming 3W electrical input only produces 0.05W UV output.

https://docs.rs-online.com/edb9/A700000007304392.pdf

This would be 120W of power input for the same output as a 7W input tube. About £100 a year more to run on electricity consumption. I don't see tubes being replaced any time soon

Robert G8RPI.

30/04/2021 16:26:25

I've done some reseach on UV sterilisation (there is a patent on the subject out there with my name on it). The required waveband is has been mentioned UV-C which is wavlengths below 280nm The "classic" UV fluorescent lamps emit mainly on the mercury "line" t 254nm and are very effective. Note that even these have quartz glass tubes rather than normal glass as UV-C will not pass through normal glass.

You can get UV-C LEDs. The 285nm LEDs are not technically UV-C. Most common are 275nm so just in the UV-C band and not very effective. Even these are not cheap. One off from a reputable source is £2-3 for a <5mW LED. .
The only LED's that are really suitable are the 269nm ones. These are very expensive, over £100 for a single 50mW LED from a reputable source. You would need abot 100 of these to replace a single 8W 254nm tube.

The conventional UV-C tubes are very efficent, probably more than an LED, stick with what you have.If you want to run off solar find an old caravan or similar 12V fluorescent lamp that has the same size white light tube and use the inverter out of that

As others have said some wavelenghts will actually promote growth of things you don't want so buying a cheap LED unit from an unknown seller could be wors than nothing.
Anything with a plastic cover is not going to work, UV-C will not pass through it.

Robert G8RPI.

Thread: Problems trying to sell-on a 'Swiss' Army knife
28/04/2021 20:48:40
Posted by Michael Gilligan on 28/04/2021 20:28:01:
Posted by Robert Atkinson 2 on 28/04/2021 20:21:56:

Knives other than table knives are banned on ebay UK. The bayonet linked to was on the USA ebay site.

.

But the Swiss (sic) Army Knife that I linked was on

https://www.ebay.co.uk/itm/333976808820

MichaelG.

It's been removed.

They don't do it instantly unless it is very clear in the description. I didn't report it.

Robert G8RPI.

28/04/2021 20:21:56

Knives other than table knives are banned on ebay UK. The bayonet linked to was on the USA ebay site.

Enforcement is patchy but they will take down knife listings. What I find funny is that military equipment is also banned but they have caegories for militaria and military vehicles. Quote<

"The following or similar items are not allowed:

  • Ordnance, military weaponry (such as grenades and landmines), ammunition and related parts, and most military vehicles including aircraft and ships, even if it has been made "unserviceable" or has been "de-militarised" or "de-milled"
  • Articles or services specifically designed, developed, configured, adapted or modified for a military application."

And if you go to selling categories "Cars, Motorcycles & Vehicles > Military Vehicles Change category"

Go figure.

Robert G8RPI

Thread: Finding a penknife
28/04/2021 20:05:36

UK knife law is a bit of a mine field, especially if you add in "going equipped". My "everyday carry" (EDC) is a Leatherman Charge Ti. I've carried a Leatherman for about 25 years, The Charge has two knife blades both under 4" and locking. The blades can be opened one handed. It is illegal to carry this in public in England without a good reason. As I'm no longer working as a "hands on" engineer I'd rather not have to argue the need to carry it in court. So I have cut off the locking tabs for the knife blades. The saw and file blades still lock. I tightened the pivot bolts so the blades are now effectively friction locked. I have unmodified Leathermans to carry when justified and even a TSA approved Micra that I can carry on commercial aircraft.

Rober G8RPi.

Thread: Covid, DNA and Fred
25/04/2021 21:17:35

Unfortunatly we are not holding on to engineering in biotech. I once worked for a small british company who were world leaders in some of the automatic instruments used in genome sequencing and research. They floated on the stock exchange and a few years later were taken over by a big American group and a couple of years later the UK operation was closed down. The only sign of their name with the American company is on their list of patents (may name is on a few of them too). I moved back to aerospace.

Thread: Laptop with a SD card slot
12/04/2021 18:08:53

Rant on:

This moving to 2x USB C wth one taken for power and no CD/DVD/Blueray just seems to be a plot to push us into using "the cloud" and streaming services. Trouble is you then don't have assured access to your data and don't own the music or movie. Then they have killed the "old tech" off I bet the costs of the alternatives go up.

Rant off:

Robert G8RPI

Thread: Remote Control For Mitsubishi VFD
07/04/2021 19:13:21

No ,

Meant a 24V NVR, powered from the PC terminal and contacts to the safety circuit.

Addressing Bobs comment, while using dual circuit stops is best practice, it depends on the machine. A Failure Modes & Effects Analysis (FMEA) would be carried out and severity of failures addressed. The level of protection will depend on the hazards and use. For a non CNC lathe or mill used by a skilled operator a dual circuit protection system would not normally be required. If you did a safety analysis on a chain saw as a new invention it would never be allowed!.

One particular failure mode of most E-Stops is that the switch module fits on the back of the button assembly and it's actuator has to be pressed to open the contacts and stop the machine. If the switch block is not fitted or falls off for some reason the E-stop wont work, dual circuit or not. The only mitigation for this is testing the E-Stop, but the switch block could drop off as you reset it. I've looked for a fail-safe E-Stop but never found one.

Robert G8RPI.

07/04/2021 12:59:26

You could use a 24V no-volt release start / E-Stop module. These a re cheap enough. Arrange the guard switch(es) to drop out the no volt coil and one contact to the VFD.

Robert G8RPI.

Thread: Mystery Mains Connector
06/04/2021 21:11:57

OK don't bin it, "dispose of in a legal and environmentally friendly manner" with extreme prejudice devil

Being PTC based means it will maintain temperature but is no indication of the quality of insulation, It is very difficult / expensive to achive good thermal conductivity and the electrical insulation, including creapage and clearance, required for a class II (double insulated) appliance. I would be VERY suroised if this iron met the required safety standards. it is cheaper to use an earth wire. This was probably designed for 100 /115V


The UK importer probably went of of business so they didn't have to give refunds. Several of the items on the archived webpage clearly would not meet european safety standards e.g. 2 bar electric fire.

Robert G8RPI.

Thread: Call me cynical / Call me thick ... but
06/04/2021 19:15:58

Tell me about it. 6 GPSDOs, (one Rubidium), 4 other Rubidium oscillators, LF off-air standards, GPS receivers, crystal oscillators (some cost thousands of pounds when new) about 10 frequency counters including HP 5370B and Philips PM6654, the list goes on....

Robert G8RPI.

Thread: Electric motors
06/04/2021 18:51:19
Posted by John Haine on 06/04/2021 11:17:01:

Nice machines. My recommendation would be small 3-phase induction motors with variable frequency drive; or single-phase but they would be fixed speed.

An excellent UK motor supplier is Parvalux - I have one of these on my Quorn (single phase) and a 3 phase on a Unimat:

img_20181127_172122697_hdr.jpg

Photo shows motor and drive. The drive is available from Newton Tesla who give excellent support. This would be the right sort of motor for both your applications. Not the cheapest but very nice for some nice machines.

Hi John,
Nice lathe, but unfortunatly the inverter installation is very poor and potentlly dangerous.
1/ No strain relif on the power leads.
2/ One lead  has its ground lead unter tension. If the lead is pulled this could come off. If the motor earth comes off with it it could possibly touch the live terminal next to it and making the motor case live even if not running.
3/ Mounting is wrong. The front panel and thus channels through the heatsink, should be vertical for proper convection cooling.
4/ You appear to be using the front panel controls for normal operation. They are only intended for initial set-up and maintenence.
5/ The drive should be in an enclosure.

1/ & 2/ are the most important and should be addressed. The heatsink is probably common to higher rated models and is probably OK at the power and duty cycle you are running.
As a minimum you should really have an external emergency stop rather than relying on the front panel controls.

If it is a personal item with no one else able to access it then the condition is purely your concern. But you have posted pictures that others may copy so I feel obliged to point out the issues so they do not take it as an acceptable example of VFD installation. Nothing personal.

Robert G8RPI.

Edited By Robert Atkinson 2 on 06/04/2021 18:53:33

Thread: Mystery Mains Connector
06/04/2021 18:20:50

The lead is probably stiff because it is cheap and nasty heat resistant cable. The connector is non-standard. This is because you should not be able to use a non heat resistant cable on a heating device ( hence difference between C13 computer leads and C15 kettle leads). Using a different lead by modifying it or the iron will reduce its safety.

A bigger concern is the sole plate of the iron appears to be metallic This would almost certainly need a 3 core earthed connection. I would bin it and by a travel iron from a reptutable manufacturer. While this one does have a CE mark, the label is clearly not compliant and the website does not exist.

Robert G8RPI.

Edited By Robert Atkinson 2 on 06/04/2021 18:21:27

Thread: Call me cynical / Call me thick ... but
06/04/2021 17:55:45
Posted by Michael Gilligan on 06/04/2021 15:22:14:
Posted by jaCK Hobson on 06/04/2021 11:31:11:

Isn't it just saying how a second is defined? So the new definition of using the frequency of some alternative atom is found to be more consistent under different conditions.

Like a foot used to be the length of someone's foot but as they change a bit from person to person, a more universal definition has been chosen.

An inch might have been the width of a thumb but got redefined to make it be easier to map onto metric.

Temp scale has had a few changes, some quite recent.

.

I have no problem with that situation, jaCK ... but my question was a little more philosophical

If we currently have a definition of the Second ...

how can they claim to have measured it more accurately than that ?

MichaelG.

.

[quote] Researchers used three atomic clocks to measure time accurately down to the quadrillionth of a percent [/quote]

Edited By Michael Gilligan on 06/04/2021 15:35:08

The actual experiment was more about different means of time transfer, fibre optic vs direct ( free space) laser than the actual references themselves. The problem is that it takes time to transfer the time from one place to another. Even in the time of clockwork noon at Greenwich was signalled by both sound and visual signals as sound takes too long to travel. Thransferring time long distances relied on radio but even this has delays. When HP desigined the 5061A "transportable" cesium beam frequency standard in the early sixties the enabled "flying clocks and accurate time transfer around the world.
https://www.hpmemoryproject.org/news/flying_clock/celebration_01.htm

Robert G8RPI.

06/04/2021 14:57:08
Posted by Andrew Tinsley on 06/04/2021 14:40:36:

If the selected atom outputs light at a given frequency then the higher the frequency then there are more subdivisions of time available and hence greater potential accuracy..

Ignore Roberts quip re difference in gravity and hence frequency if his oscillator is upright or on its side. However time does alter depending on gravity. A satellite born atomic clock will give a different time to one on the ground . This has to be taken into account for GPS location otherwise the system will give an incorrect result.

Andrew.

It was not a quip, the oscillator I was refering to is a quartze one (HP 10811D based) and it has a detectable change in frequency when turned on its side or inverted.

Robert G8RPI.

06/04/2021 12:50:04

In my home workshop I can measure time to 20 picoseconds for one off events, much better for something that can be averaged. Thats 2x10^-11 or 0.00000000002 s. Thats good enough for most practical purposes. Light travels about 6mm in 20 ps.I can measure frequency to over to 25 GHz (2.5s10^10). I have 4 atomic frequency standards, but like most time nuts I mostly use GPS based clock. I have several of those with 3 different models running 24/7. You need three because if you only have two and they are different you don't know which is right nerd
I built a precsion quartz oscillator at over the weekend. I can easily see the effect of gravity on this e.g. the frequency change when you turn it on its side, +1 G to 0 G

Robert G8RPI.

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