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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: Single phase to 3 phase motor conversion.
03/06/2020 18:42:02

Well that circuit applies 180 degrees to two phases (should be 120) and about 90 to the other. not an ideal situation.
The capacitor that reads in nF range is faulty. The 8uF are about right, tolerace is tpically +- 10% and normally under. Note that it's not just capacitance and basic voltage rating that matter when replacing. It must be rated for motor starting applications.

Robert G8RPI.

Thread: Surface Plate & Height Gauge recommendations
02/06/2020 13:15:36
Posted by Barrie Lever on 02/06/2020 12:39:26:

Dave

I keep looking for a CMM but no luck yet, will update if I am successful.

B.

Work threw one in the skip last year - literally crying The Rennishaw touch probe was still attached but smashed up aginst the edge of the skip.

Thread: Arduino/Stepper Motor Dividing Head
02/06/2020 12:48:31

Part of the UI problem is related to the "Maker" approach to electronics where things are built from ready made modules like Arduinos, stepper drivers and serial LCD and switch modules. This makes it easy but limits variation and customisation. Unfortunatly it does not build understanding of the basic principals or skills. I've seen electronics magazine projects using breakout boards and screw terminals so you don't even have to solder.

The ME version would be making a loco from ready made bogies, boiler. cylinder and valve assemblies from different manufacturers. Better than nothing, but not good.

Robert G8RPI.

Thread: Soldering Iron
31/05/2020 16:20:59

What sort of "small jobs"?

If electical / electronic I'd recommend a temeperature controlled iron in the 30-50W power range.
My personal choice has been Weller for over 30 years. Always liked the TCP series where the temperature is set by a alloy pellet with the correct curie point at the end of the bit. I don't like the new two part tips though.

Problem is decent ones are expensive and a lot of the cheaper ones are cheap nd nasty.

Robert G8RPI.

Thread: Machine Tool Peripheral Hoists
31/05/2020 10:11:06

I do note that the standard SkyHook tool post mount has a dovetail to fit directly on a large quick change toolpost. It is the youtuber (Adam Booth) who has had it modified to go in the slot of the tool holder.. The Dovetail mount is probably OK on a big lathe, but the tool slot with two set screws is just not an acceptable design. There is just too much leaverage trying to roll it out. As a minimun an adjustable "foot" opposite the lug that goes in tool post to react rolling forces into the cross slide or mill bed woud be a worthwhile improvement.

Robert G8RPI

Thread: VFD speed control fault
29/05/2020 17:17:31

This is most likely to be a failed or failing electrolytic capacitior. Less likely is a resistor failure. I assume there is no circuit available for the internals of the VFD so a bit of detective work wil be required.
Before you do ANY work on the VFD, Uplug it and leave for a least 10 minutes before touching anything. Disconnect it completley before attempting to open it up. You will have trace the connections and components on the 10V terminal. Look for buldged or leaking electrolytic capacitors r verheated resistors.

You could use an external 10V supply but the failing supply could still be used internally. Worst case thi could result in an uncontrolled overspeed condition.

Where are you located?

Robert G8RPI.

Edited By Robert Atkinson 2 on 29/05/2020 17:17:47

Thread: Earthing Issue on new machine
29/05/2020 10:50:15

Hand held appliances with properly implemented Class 2 (double insulated) protection are safer than similar Class 1 (Earthed) appliances as an undetected insulation breakdown is less likely than an undetected earth conductor fault. A second breakdown of the basic insultion is required in either case to cause a hazardous condition.
For Class 2 items with exposed conductive parts like your drill there has to be a minimum amount of insulation between these and any live part. It is possible that your old drill was indeed a crossover product that incorporated the Class 2 levels of insulation but retained an earth connecton. A "belt and braces" approch.
Safest of all is the "110 Volt" (actually 55 V - 0 - 55 V) power tool system which give a maximum of 55 V to grorund and 110 V between terminals.

Robert G8RPI.

29/05/2020 08:14:20
Posted by Brian Morehen on 28/05/2020 17:59:20:

This is a interesting question , If your motor is not attached to you lathe IE Mounted as a seperate unit it is quite possible that the only connection to the lathe may be your drive belt, This willl not provide any earth connection very easy to over look? You can buy a Plug for 13amp socket which has its own built in protection together with a manual reset in the event of a power failure , If you are using 3 Phase then more important because off the extra voltage to get a Electrician to check and test with a Megger for a Insulation test of either 500 volt or 1000 volt , Your Life is worth more than this simple test .

Take Care and check your equipment is safe for all .

Once remeber asking someone where is your earth connection its that lead there in the bucket of earth.

Take care Bee M

If the lathe tool has NO electrical equipment, including switches, lights DRO's etc, mounted on it and the only connetion to the motor is an insulating belt there is no requirement for the Lathe to be earthed. It is still good practice though. It's the fault current path that matters. If the motor was mounted on the same metal stand as the lathe but not directly on the lathe then both the motor case AND the stand must be checked for earth continuity, but the lathe would not have to be. If bothe the motor and stand are earthed there is no series fault path to the lathe. In practice of course the lathe would almost certainly would also have some earth path to the stand due to it's mounting.
Plug top earth current protetive devices are usefull but a modern consumer unit "fuse box" with protection built in is best. A socket with built in RCD is better than a plug type. Exmples are

https://www.mkelectric.com/en-gb/Products/WD/surface/MetalcladPlus/Switchsocketoutlets/RCDprotected13amp/Pages/K6231ALM.aspx

https://www.mkelectric.com/en-ar/Products/WD/white/logicplus/switchedsocketoutlets/RCDprotected/Pages/K6211WHI.aspx

Note that there are two types of RCD socket, Active and Passive. You should use an Active type for machine tools etc as the trip on mains failure so act as an additional no-volt release preventing unexpected re-starting.

Passive types should be used for things like freezers that must re-start automatically.

Robert G8RPI.

Edited By Robert Atkinson 2 on 29/05/2020 08:14:45

29/05/2020 07:51:15

Hi Emgee,

1/ I knew what you ment, but "Class 1 PAT" is not clear.

2/ I sver said anything aout the supply (that does come under installation test) I described the means of connection. If the connecton to the supply has a plug it is considered "portable" as far asr PAT goes, if it hasn't got a plug it's fixed and PAT does not apply. Typically a physically fixed machine with plug would have longer times between inspections than something movable with a fixed connection rather than a plug (these are rare but not unknown).

28/05/2020 17:35:36

There is no such thing as a "Class 1 PAT" defined by regualtion. Indeed there is no such thing a defined PAT.

There are Class 1 APPLIANCES these are those with a protective earth.

Portable Appliance Testing is normally considered to cover any electrical applance which plugs in. This includes industrial plugs, not just 13A ones. Fixed equipment regarding electrical testing applies to the supply, not the mounting of the equipment. Thus a Mill that is bolted to the floor but has a CY cable and a Commando plug going ito the wall is "portable" but pistol drill wired to a switched fused outlet is not.

A 20A earth bond test on a piece of electronic equipment will NOT damage it unless the equipment is faulty or test is carried out incorrectly. I've done or witnessed dozens of these on "portable" equipment that contained lots of electronic including servo drives.

A insulation test on a piece of electronic equipment will not damage it as long as the equipment is not faulty and test is conducted properly including selection of appropriate test voltage. A "Hi-Pot" (high potential breakdown test) does have a good chance of damaging electronic equipment but they are not appropriate to routine in servce testing.

There is NO legal requirement to carry out PAT.

Robert G8RPI.

I said don't get me started on PAT angry 2 (especiallty not " PAT Testing" which is testing a test)

 

Edited By Robert Atkinson 2 on 28/05/2020 17:49:28

Thread: Arc welding rods
28/05/2020 16:45:57

Hi,

Heated quivers for welding rods normally run at 80-100 degrees C. Any increase above ambient and dew point, which ever is higher will help, but to activiely drive moisture out you need to be in the higher range. I bake mine in the oven and then store in a sealed metal container (old munition case).

Robert G8RPI.

Thread: Method of joining for chuck key?
28/05/2020 16:38:35

The X-ray suggestion was tounge in cheek. No metal will completely stop X-rays so thicker or denser metal just needs more exposure. But you rapidly get into unrealistic times. Dental X-ray generators are at least 70 kVp and the thickness of brass that will reduce the intensity of 70kVp by a half is only 0.01mm. 10 half value thicknesses is normally considered to reduce it to negligble levels so yes a dental machine is unlikely to do the trick but it depends obn the sensitivity of the sensor. Older dental X-ray units were lower energy 50-60kVp which on the face of it seems safer, but it isn't. The lower energy means longer exposure and the dermis absorbs more energy at the lower kVp. (its actually a spread of energy and on dental machines a aluminium disk is used to filter out the lower end of the spectrum.

Robert G8RPI.

28/05/2020 12:51:19

The part of of the shaft inside the handle may be square, splined or similar (or even threaded) with small round post at the end that was peened over.

An X-ray would reveal a lot, how friendly is your dentist?

Robert G8RPI.

Thread: Earthing Issue on new machine
28/05/2020 12:41:37

Yes, PAT is Portable Appliance Testing. Don't get me started on that topic disgust

There are two reasons for unplugging accessories, to protect them during some tests and to stop any possible parallel earh connection masking a fault until the day you run the machine with the accessory unplugged.
An earth bond test shold not damage an machine. The potential problem is when people do insulation tests intended for 3 pahse motors on 240V electronic equipment.

Robert G8RPI.

28/05/2020 10:39:14

On another general thread a DRO issue was traced to a faulty safety earth on a new machine (not the DRO). The earth connectin was a ring tag onto a painted panel resulting in no earth. The machine came from a known UK supplier.

It is clear that in this case there was a design and or manufacturing issue as well as lack of testing.

This type of issue is hidden until another fault occours. then it could cause electrocution, fire or injury caused by pulling a hand away due to a mild shock and contacting a rotating part or sharp cutter.

While the other case was a particular make model, this could apply to any machine tool new or used.

Even if a check carried out with a multimeter shows low resistance to earth, this does not assure adequate earthing in the event of a fault. Ad a proper earth path has not been designed in, a stray connection through a burr of single wire strand will show low resistance but could fuse in the event of an insulation failure leaving the machine live, The only adequate test is a high current bonding test. This measures the resistance with a high current, typically 20A for equipment with a 13A plug, appled for at least a second.

A check with multimeter will pick up gross errors and I strongly recommend that owners of small machines carr out at least this basic check before first use, if they have been moved or modified and ideally every couple of years.

BASIC EARTH CHECK.
1/ Unplug machine, including any accessories like lights, DRO's etc.

2/ Using a multimeter select the lowest Ohms range (or auto)

3/ connect the test probe tips / clips together and note the reading. It should be less than 1 Ohm. For a analog meter zero the meter.

4/ Connect one meter lead to the earth pin of the mains plug.

5/ For each main exposed metal part of the machine connect the ther meter probe to it and check the meter reading. If an auto-ranging meter make sure it is still reading Ohms and not kiloohms or Megohms

6/ subtract the reading noted in 3/

7/ If the result is more than 0.5 Ohms the machine may be faulty and should not be used until properly inspected and tested by a competent person.

The main parts to check are the control box, Bed or main casting, Motor casing if exposed and spindle. Items like control handles should be checked but only ones that might become live are critical. For rsample a mill Quill feed wher the drive goes into a housing that has wiring in it must be grounded, but a cross-slide handle is not critical because athe bed and slide, or chuck, would have to be live first. If getting someone else to check, make sure they are competent, in my experience most individuals offering "PAT" testing services are not competent to check a machine tool .

Robert G8RPI.

Thread: Sodium Nitrite
25/05/2020 13:43:55

So it looks like suppliers are taking the easy way out on EPP reporting and only selling to companies even for reportable substances.
In theory they should sell to the public and only report it if the transaction is suspicious. By only selling to companies they remove the need to judge if a transaction is suspicious. Basically they are applying the EPP prohibition to every chemical on the list They don't even say you can buy them if you have an EPP licence (you can't get an EPP licence for Sodium Nitrite becuse it not restricted DOH). The easy way out is to set up a business to use it.

Thread: Chipmaster vfd
25/05/2020 09:59:46

I agree with Simon, NDIY's description, while correct (bar the minor issue that 220 V P-N is 380 V P-P not 425 V) for a lot of the 3 phase motors on smaller machine tools, is not the whole story .

It's important to realise that the voltage rating of the individual motor windings does not change between star and delta connections. Think of Star as series connection and Delta as parallel. This is easier to understand if you think of a single phase motor with two 120V windings connected in parallel for 120 V. It's easy to understand that if you connect the two windings in series it will run on 240V at the same power, you just multiply by two. For a multiphase connection the indivudual winding voltage rating is the Delta (phase to phase) voltage and the Star voltage is the winding voltage multipled by the square root of the number of phases which is 1.732 for 3 phase. Hence a 240 V winding voltage motor needs to be wired Star for the UK standard light industrial 3 phase supply of 415 V phase to phase. If a 240 V winding motor is wired delta the phase to phase voltage has to be 240 V which is non-standard and would give a phase to neutral voltage of 138 V.
It is much easier for a single phase input VFD to generate 240 V phase to phase (138V P-N) than 415 V.
The reason small motors are designed to be wired star (240 V winding voltage) is because fewer turns are needed making it cheaper to manufacture (with big motors the thinner wire of a 415V winding becomes an advantage). It's a lucky coincidence that it allows simpler and cheaper VFDs.

Robert G8RPI.

Thread: Sodium Nitrite
25/05/2020 08:35:50
Posted by Michael Gilligan on 24/05/2020 23:58:49:

I need a small quantity of Sodium Nitrite, for an entirely innocent purpose

Hi,

Camlab is a UK chemical supplier who will happly sell chemicals to private individuals (as long as they are not restricted). They eventake PayPal. They list Sodium Nitrite at reasonable cost.

https://www.camlab.co.uk/sodium-nitrite-pure

Unfortunatly it's on back order at the moment.

Robert G8RPI.

Thread: Model Turbines
24/05/2020 20:48:39

Hi,

My background is electronics so I tend to look in that direction for solutions. A brushless DC would act like a 3 phase alternator so a little harder to instrument. Known propellors are a useable solution and are used to check full size aircraft engines. These are normally special item with short blades and are called "club" propellers as they look more like clubs than blades. There is a document on their calibration here:
https://www.casa.gov.au/files/003pdf-13
(I'm in aviation)

Robert G8RPI.

24/05/2020 15:45:43

Have you though of using a small brushed DC motor as a dynamometer?
With a variable load you can check the power at various speeds and torque. The Torque is directly proportional to current regardless of speed. You can calibrate the motor / Dynamometer torque constant at stall using the weight / lever arrangement while supplying enough power to keep it balanced. A current reading gives you thedivied by the torque give you the constant for that motor. Using a brushed DC motor as a dynamometer you can get a pretty good estimate of the static or running torque and power. Most accurate is to meaure the speed and torque and do the math. Simply measuring the electrical power (V x A) will give a slightly lower figure but you can compensate by allowing for the voltage drop caused by the DC resistance of the motor.

Robert G8RPI.

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