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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: Aircraft General Discussion
02/12/2019 19:28:52

Thrust SSC had a Martin Baker ejection seat rocket motor mounted "upside" down in the nose. The intention was that if the nose started to lift it would fire keeping it on the ground long enough for the hydraulic ride height control to jack the rear end up and generate aerodynamic downforce and drag. The test firing was pretty impressivebut diddn't sound like a sonic boom. The main seat "gun" cartridges might sound a bit like it though. I've worked on a Skyvan (a 3A) and several 330's and 360's It's no coincidence that Shorts were asked to build the Miles Aerovan a couple of years before staring work on the Skyvan. It's was more a case of what not to do rather than copying it.

Robert G8RPI.

01/12/2019 20:49:01

We used to hear the tail end of Concords supersonic runs up the bay of Biscay all the way in Christchurch on cool quiet evenings.
And I did of course hear the booms from Thrust SSC back in 1997. The car went supersonic 5 times. One of these was unintentional. The car was to run to a predetermined indicated airspeed which should hav been just below Mach 1, There was however a clear boom. The first suspect was the airspeed indicator calibration (which was my responsibility, I built the speedometer and Mach meter for the car) but it turned out that when calculating the target speed they forgot to allow for the affect of altitude on Mach number. The Black Rock desert is at about 3900ft above sea level.

Robert G8RPI.

Thread: LPG heater- fumes
30/11/2019 19:53:59
Posted by JA on 30/11/2019 19:38:43:

From what I read 1 unit of energy in, as electricity, produces 4.5 units of energy, as heat. Energy is just energy, whether electrical, thermal or anything else. This contravenes the First Law of Thermodynamics.

The World would kill for such a device.

I have nothing against heat pumps, at all. Given the right conditions I would consider one.

JA

Edited By JA on 30/11/2019 19:42:25

No,

1 kW electrical energy input PUMPS about 4kW of ambient energy from outside to inside. about half the input electrical energy is also transfered so in heating mode you get 4.5kW of heating. an outside looses 4kW. Cooling mode only gives ((in this example) 3.5 kW of cooling.

No magic, works just like a fridge.

Robert G8RPI

30/11/2019 18:57:20

The clue is in the proper name - heat pump These transfer energy from one unit to the other with a delta in temperature. They are more efficent when heating indors because a proportino of the electrical input is converted to heat nd adds to the wantd heating. I've had them in two homes now. Hitachi in last about 15 years ago and Daikin in the current. The Daikin will work below -20 outdoors.

Highly recommended.

Robert G8RPI.

Thread: VFD off the bay
28/11/2019 21:55:22

A genuine Huang Yang VFD is OK, but many of the ones on ebay etc are clones or fakes.

With these types of cheap clones and fakes (not just VFDs) they save costs by not including components that do not affect basic operation but often have a safety or protection function. These include overheat and overload detection, filtering transient protection etc. They also often use under-rated componens like DC bus capacitors an output transistors. This means they work with nominal supply voltage and less than full load but may not perform or fail if fully loaded. Poor quality components and shoddy construction can also lead to electric shock and fire hazards. When operaing machine tools even a minor shock can have severe consequences as muscle contraction or reflex may result in body parts touching moving prats or sharp tools. I saw someone get a really badly cut hand from a stationary but sharp cutter on a bridgeport because they were changing the lamp in the work light. They pulled away because it was hot (power was off) but the effect was the same.

Robert G8RPI.

Thread: which lathe?
28/11/2019 07:29:21

If you want to turn thin wall bearings accurately then how you hold them is important. Make sure that the lathe you buy can accommodate a collet chuck of suitable size. The SC2 will take one

**LINK**

**LINK**

The collet chuck can also hold an arbour to mount the bearing while you turn the outside diameter.

Robert G8RPI.

Thread: Colchester Student Mk1 Won't Start
27/11/2019 07:33:00
Posted by Richard Kirkman 1 on 26/11/2019 20:03:27:
Posted by Phil Whitley on 26/11/2019 18:23:24:

Hi Richard, mine is definitely a Mk1, but looking at the levers on yours I would say it is a very early mk 1, I do not have the "safety apron". If you can hear the contactor pull in when you press the front lever down, and the switch for the main motor is set to on, then it should run, stupid suggestion, the chuck guard doesnt have a safety switch on it? The main contactor is pulling in, and usually the safety switches are wired into the coil circuit, but who knows if a second contactor has been added. Turn OFF and disconnect the power, and with a multimeter, see if you can test from the contactor to the reversing switch, and from the reversing switch to the motor. This does depend on whether the reversing switch is before the contactor or after it, but I suspect it is after, it is a start anyway!

Phil

I'm getting quite confused with all these terms. Specifically which part is the contactor, is it this part? And if its not this part, what is this part and what does it do and why?img_20191125_125101.jpg

Or is it this part at the back. The piece that says limit switch has a pin that moves up and down when i switch the lathe on from the lever on the front and makes a click as it goes into place. But, I'm not too sure what noises i'm looking for?

And no, there isn't a switch on the chuck guard. Also, i have access to the motor round the back so I am able to check if it buzzes but i have not done so yet.

Thanks

Edited By Richard Kirkman 1 on 26/11/2019 20:04:37

Hi Richard,

The item pictured with 3 contacts separated by grey (asbestos?) insulation panels is the contactor. The contacts don't look great. If you can hear this clunking with the start lever operation the PC40 is powering it.

Do you have a multimeter / test meter? You really need to get into some fault finding.

First thing would be to check the contactor contact resistance you can do this with it unpowered by manually closing it , pushing down on the brown (Tufnol) insulator that carries the moving contacts and then checking the resistance across each contact.

Robert G8RPI.

Thread: VFD off the bay
26/11/2019 21:28:41

I seem to have upset some people with my comment about not buying from far eastern companies.

I did not say ebay or Amazon were far eastern or not to buy from them. I said "I would not recommend buying ANY mains powered device from any far eastern supplier on ebay, amazon bangood etc."
If you do, you are the importer and responsible for complying with relevant regulations. The VFD on ebay linked to by Brian H clearly does not meet CE requirements just from the photographs. It does not matter that you are not selling the unit or using it for business, you have to comply with the regulations. If injury or property damage results from the use of the item you could potentially find your insurance invalidated. I admit that this is highly unlikely to happen but it could. Apart from the legality issue, a large number of mains powered items sold by these sellers do not meet safety standards and many are downright dangerous.

I'm a professional electronics engineer and stand by my recommendation.

Robert G8RPI.

Thread: It's Myford Jim, but not as we know it!
26/11/2019 12:37:45

The lawnmower is the result of a stupid requirement in many ISO9000 quality manuals that all suppliers and subcontractors are ISO9000 approved. Many "advisors" who "helped" people get accreditation when ISO9000 first came popular used pre-made manual templates with "find and replace" for company name, business type etc. By requiring suppliers and subcontractors to be approved they made more business for themselves. First thing I changed as QM for a ISO 9000 company was to change this to "all suppliers and subcontractors shall be formally approved by the company" with a process that graded the criticality of supplier and level of review accordingly. If they had ISO9000 AND appropriate scope then we didn't have to audit them ourselves.
Got one at the moment with AS9100 (aerospace) approval where their scope is "design and make our widgets". As there is no recognised standard or specification for their widgits it is meaningless but as long as they follow their process they are compliant.

Robert G8RPI.

Thread: VFD off the bay
26/11/2019 12:09:05

I would not recommend buying ANY mains powered device from any far eastern supplier on ebay, amazon bangood etc. I would definitely not buy a VFD from one.

You can have little or no confidence that it meets applicable safety requirements (Low Voltage Directive EMC Directive etc) or that it even meets it's specification. Buy a branded unit from a UK (or possibly EU) supplier. If nothing else you will have some one to complain to. If they don't have a proper UK address don't bother.

Robert G8RPI

Thread: flypress bench
23/11/2019 09:53:20

Sounds about right size but even so I'd reccommend attaching it to the wall as security against it toppling, Either directly or by a strap or chain. Or bolt the feet to the floor.

Robert G8RPI.

Thread: Float indicator in water gauge glass
22/11/2019 12:26:16

I think we have gone off on a tangent...

I think Mick's issue is that the sight glass does on go LOW enough so there is still some water in the boiler when the glass is empty. This is of course the safe situation. If I'm correct then yes adding a float that sits on top of the water will give you some extra range equal to the height of the float above water. Some vintage aircraft used this technique, even going so far as to have the float completely out of sight with just an attached index wire showing in the tube. This also works for an overhead tank with the tube full of fuel and the wire sticking out the bottom of the tank and the float on fuel surface above.

The problem is that you have introduced a significant failure mode. If the float sticks you will run the boiler dry. Probably best to just put up with the reduced running time.

Robert G8RPI.

Thread: Loctite
12/11/2019 18:17:22

Did I religiously check the expiry dates on "consumables" when I was quality manager for an aerospace company - of course I did.

Did I then take it home a few days before it expired - well if I'd waited until it expired the company woyld have to pay to dispose of it as chemical wastedevil

Edited By Robert Atkinson 2 on 12/11/2019 18:21:40

Thread: Inverters and stop switches
11/11/2019 07:37:12

Those who say they cannot see how disconnecting a running motor will damage a VFD do not understand high power electronics. When the current though a coil (inductor) changes there is a voltage developed that is proportional to the rate of change. For disconnecting a motor, that large motor inductance can cause enough voltage to case arcing at the disconnect contacts (and possibly feed back into the drive causing issues) but more importantly for drive damage the inductance of wiring and even transistor internal connections on the drive side can cause voltage spikes high enough to cause damage. Yes you can design to account for these but don't bet on a cheap no name inverter having such protection. This does not mean every drive will fail the first time you disconnect it the magnitude of the spike and ability to cause damage depends on (among other things) the mains voltage, load, speed, temperature and most importantly the exact timing of the disconnect in relation to the load current.

I note that the drives direct advert that was linked to says they are "special" in respect of switching loads and also that they need to be rated at FiIVE to EIGHT TIMES the actual load. So for a 1hp motor you need 5 to 8 HP inverter with presumably a suitable input supply. Most electronics will take mose abuse if you only run them at 20% of their design rating.

Robert G8RPI.

Thread: Drilling big holes (in tiles)
09/11/2019 16:39:43

For cutting I'd suggest a diamond core drill rather than a hole saw. Difficulty is holding it in position. Make sure the drill has a clutch, if the bit snatches it will break your arm without.

As an alternative could you cut a slot in a toothed pulley, slip it over and clamp on and then use a belt to turn the pulley? To be fancy a slot half way through on one side could engage with one side of the valve handle. maybe even a shaft and drve pulley across the top of the "wall"

Robert G8RPI.

Edited By Robert Atkinson 2 on 09/11/2019 16:40:19

Thread: Inverters and stop switches
08/11/2019 21:57:00

That application makes some sense, being a secondary interlock after the motor has stopped and VFD output is off. It's not putting an E-Stop in series with the motor. Probably more cost effictive than using a safety rated VFD.

Robert G8RPI.

08/11/2019 20:17:39

I've never seen a switch between a VFD and motor on an industrial installation. Can you give an example?

08/11/2019 18:19:22

As stated putting any switch between the VFD and motor risks damaging the drive. Apart from this most E-Stops are not adequately rated for this.

Havig a faulty system that starts when it should not is not a got reason for fitting a switch in the motor. The root cause should be identified and fixed.

Robert G8RPI.

Thread: Lathe chuck guards - how many folk use them?
08/11/2019 12:45:11
Double post

Edited By Robert Atkinson 2 on 08/11/2019 12:45:39

08/11/2019 12:45:05
Posted by ChrisH on 07/11/2019 00:05:13:

<BIG SNIP>

Remember also, whether in your own shed on your own or in the firms shop, an accident only ever happens due to there being an unsafe action taken or unsafe condition existing. It therefore the responsibility of all of us to ensure unsafe conditions do not occur, neither do we take unsafe actions, however we operate our machines or provide for our own safety.

Have a nice day!

Chris

The problem is that you say you have taken that first "Unsafe action" - removing the guard- in your workshop. You also seem to be advocating removing guards to others.
Assessing the suitability of guards should be part of the machine selection process. If it's not suitable get the vendor to fix it or look elsewhere.

Generally in industry it is insurance assessors that drive good behaviour regarding guards and the like. If they refuse cover you can't legally work (at least in the UK if you have employees or public access to your business) Note that even in the home workshop removing guards could have accident or life insurance implications if the worst happens and they find guards were removed. Not very likely but some insurance companies seem to be looking for any excuse to reduce a settlement or increase a premium.

Robert G8RPI.

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