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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: 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.

Thread: Flash Steam
04/04/2021 18:33:16

The Inspiration steam car holds the record at139.8 mph set in September 2009. Designed by Glynne Bowsher who also designed signifcant parts of Thrust 2 nd Thrust SSC. Bodywork was by Mike Horne also of the two Thrust car teams. Glynnne is a long time steam train enthusiast.

Robert G8RPI.

Thread: strange 240v pump 'switching'
04/04/2021 13:55:53

Almost certainly the pump is overhating causing a thermal trip to cycle and previously stated by Stuart and David. If it's 10 years old just buy a new one.

Robert G8RPI.

Thread: Tyre Guage DRO - capacitance issues?
04/04/2021 12:01:27

Hi Peter,

Your earlier comment sounds correct. The lights are generating interference an you are an antenna bringin it close to the DRO. The mill body is acting as a "ground" return capacitively coupled to the DRO. By touching the mill with one hand you and the mill are at the same voltage and the interference has no effect.

I thought it was the other way around with th milll body being the intererence source and you the ground, bu the end effect is the same. The "metallic" cse version my well sort the problem.

Robert G8RPI.

Thread: Magnetic bases - stored on or off?
03/04/2021 21:17:08

If not stuck to something ferrous they should be OFF. This 1/ preserves the magnetisim (less important with modern magnets but who knows what is inside a given base), 2/ It stops the base picking up stray bits of swarf etc.

Likewise magnetic chucks should always be off when not in use. A third reason applies to chucks, safety. They are powerfull enough to cause injury if they "grab" a tool or workpiece with your hand between them.

Robert G8RPI

Thread: Tyre Guage DRO - capacitance issues?
02/04/2021 21:26:20

Does it work OK if the mill is turned off at the socket? Fully unplugged at the mains?
I think the problem is interference with the mill bodywork being noisy. Your body is providing a return path.
You could also try firmly grasping the pillar with oe hand while pressing the buttons.

Robert G8RPI.

Thread: Advice acquiring single phase motor for Elliott Pillar Drill
01/04/2021 17:57:07
Posted by John Haine on 01/04/2021 10:46:00:

**LINK**

Less than 65 squids.

I do have a spare 3/4 HP single phase motor as it happens, off the Myford VMB that I fitted with a 3-phase motor.

How long do you run a drill in one go, a minute or so max? I doubt EMC will be a problem.

Slow speed and reverse are wonderful on a drill, for tapping!

That inverter is awful.
1/ 220V rated, UK is nominal 230V, typically 240V. This DOES matter especially if design is marginal anyway.
2/ Case looks like cheap polystyrene with heavy heatsink supported by self tappers through the side.
3/ No rear cover, PCB connectons exposed.
4/ Mains input and motor connections have no strain relief and I can't see separators either.
5/ No EMC protection.
6/ Non UK seller so possible customs / support issues.

EMC affects other people, not just you.

Robert G8RPI.

Thread: 1.1 kw brushed motor Torque
30/03/2021 21:58:33
Posted by JasonB on 30/03/2021 18:45:10:
Posted by Dave Halford on 30/03/2021 17:46:42:

Lets put it this way if you do something silly and overload a variable speed unit the smoke comes out pretty much instantly, the same thing happens if you forget to turn the speed to zero every time you switch off. The belt drive one will grunt a bit and may pop the mains plug fuse at worst. + the slower you go the more torque you get with belts

Not in my experience of running variable speed mills and lathes for 14years

Overload breaker just trips on my machines, switch off to reset it and good to go again

Never turned the speed down to slowest/zero just leave it where I want it and press the green/red button.

I think Dave is talking about the simple speed controls used on cheap machines from the far east with DC motors. These have little or no protection.

Robert G8RPI.

Thread: Gluing Aluminium
30/03/2021 21:25:18

To add another option, toughened acrylic adhesives such as loctite F246 or 330 work well and are easy to use. You put an activator on one surface and the "glue" on the other. Some manouvering to adjust is possible for several seconds but it set up to holding strength quickly enough to hand hold it. Note the activator may be sold separately.

Thread: Opto interrupter precision
27/03/2021 16:22:03

Blooming forum, Just typed a long erply and lost it.

Short version:

sensor optotransistor ran from same regulated supply as the comparator so not much variation and the signal and set point are ratiometric.

Arming is so circuit can tell the difference between nothing in the opto and the target slot. Basically the sequence is:

A/ Nothing in optocoupler, photo transistor "ON" - not home
B/ Solid part of target enters optocoupler, photo transistor "OFF" Circuit "arms"
C/ Slot in arget aligns with sensitive axis of optocoupler, photo transistor "ON" - in home position.

As a bonus step B is used to switch the speed of the axis during homing to a slower speed allowing faster more accurate homing.

You don't need the arming for a pendulum detector. If you have trouble screening the pendulum from ambient light, a long, curved target that obscures the slot throughout the swing, with slot or hole a trigger point, will help because it will block ambient light as well as the LED.

Robert G8RPI.

27/03/2021 13:33:23

They can be even better with some additional electronics and a slotted target. I did some work years ago to look at replacing expensive high precsion home sensors on a instrument in production.
We used a target with slot in the middle. The obscuration as the target entered the slot "armed" the circuit (We used a PIC microcontoller but a dual flip-flop and bit of logic will do) and then the narrow slot gave the actual home position. The coupler LED had constant current drive and the output was fed to a comparator with accurate reference. The sesor was shielded from ambient light. The target was thin laser cut stainless steel to reduce alighnment issues.
We were getting sub-micron repeatability. Measurement was using a Rennishaw ML10 laser interferometer. I could easily measure thermal expanssion of the 100mm long test rig if I moved the reflector from one end to the other.

The most important things are keeping ambient light off the sensor, keepng LED current constant (using just a resistor is not good enough with a 5V supply due to variation in LED Vf with temperature. A resistor is OK with a suply > about 9V) and using a comparator on the sensor output. A logic chip with schmitt trigger input is OK.

Robert G8RPI.

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