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Member postings for Mike Poole

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

Thread: Reactive power loading
10/03/2013 18:14:53

I think this explains why electricity suppliers do not like poor power factor and charge major users for poor power factor. From E. Hughes Electrical Technology.

11.22 The practical importance of power factor

If an alternator is rated to give, say, 2000 A at a voltage of 400 V, it means that these are the highest current and voltage values the machine can give without the temperature exceeding a safe value. Consequently the rating of the alternator is given as 400 X 2000/ 1000 = 800 kVA. The phase difference between the voltage and the current depends upon the nature of the load and not upon the generator. Thus if the power factor of the load is unity, the 800 kVA are also 800 kW; and the engine driving the generator has to be capable of developing this power together with the losses in the generator. But if the power factor of the load is, say, 0.5, the power is only 400 kW; so that the engine is developing only about one-half of the power of which it is capable, though the alternator is supplying its rated output of 800 kVA.

Similarly, the conductors connecting the alternator to the load have to be capable of carrying 2000 A without excessive temperature rise. Consequently they can transmit 800 kW if the power factor is unity, but only 400 kW at 0.5 power factor, for the same rise of temperature.

It is therefore evident that the higher the power factor of the load, the greater is the power that can be generated by a given alternator and transmitted by a given conductor.

The matter may be put another way by saying that, for a given power, the lower the power factor, the larger must be the size of the alternator to generate that power and the greater must be the cross-sectional area of the conductor to transmit it; in other words, the greater is the cost of generation and transmission of the electrical energy. This is the reason why supply authorities do all they can to improve the power factor of their loads either by the installation of capacitors or special machines or by the use of tariffs which encour­age consumers to do so.

Mike

Thread: Rotating Table
17/02/2013 13:27:12

I have found that electronic equipment can often be "repaired" by unplugging and simply replugging circuit boards and multi pin plugs. I found that on many occasions a diagnosis would be made and a board exchanged for a spare but when the faulty board was tested by reinstalling it was Ok. Despite having gold plated connections atmospheric pollution is able to force the connections apart creating a fault, the removal and replacement wipes the connection clean and normal service is restored. A soft pencil eraser is excellent for cleaning edge connectors. Pollution also causes problems with relays and contactors carrying low voltage low current signals. The uninitiated are amazed when a thump on a control panel chassis fixes a fault, this is usually followed by replacement at the next maintenance opportunity.

Mike

15/02/2013 14:36:33

If you cannot fix it with a hammer you have an electrical problem.

Thread: Myford 254 Electrical problem
11/02/2013 13:09:13

Hi Olly,

I would check that the overload unit is set to the full load current of the motor and if you have the equipment and knowledge to use it, check the actual current the motor is pulling under the load you are applying.

More details of your lathes motor control would be helpful i.e. is it single or three phase, does it have an inverter?

Mike

Thread: Inexpensive Chucks
06/02/2013 23:32:32

It would appear that TOS are a Slovakian company.

Mike

Thread: myford super 7 clutch
20/01/2013 14:52:43

If it has never worked I think you will need to dismantle it to check the ball bearing and push bar are fitted. If you have a manual there is a sectional view of the clutch and setup procedure, together with the exploded parts diagram you should be able to see how it works with a bit of study.

Mike

20/01/2013 14:37:50

What is wrong with it?

Mike

Thread: Swarf vaccum cleaner
02/12/2012 19:59:17

I have too have a Wickes/Earlex and it is great for swarf and wood shavings from thicknesser or router, I even hoover the lawn with it after an outdoor wood session as the mess from indoor wood activity has to be seen to be believed.

Mike

Thread: Rapidor Saw
28/11/2012 16:05:13

My Rapidor wears its original paint is pale green with creamy suds tray and the lettering on the bow also cream. It was built in 1974 and I suspect followed the trend for machines to change from grey to pale green as earlier rapidor machines seem to be grey with red features. The drive system seems to be an indicator of vintage. My machine was manufactured by Alexander of Dudley and has a compact drive motor gearbox made by Newman Motors. The older machines were made in Manchester by Edward G. Herbert of Atlas Works Levenshulme. The drive systems on older machines seem to vary quite alot with some having a clutch, perhaps for drive from line shafting?

Mike

Thread: The Greatest Mechanical invention
10/10/2012 10:01:52

The lathe gets my vote, it is the mother of all machine tools and can be powered by a man,water, steam or electricity or any other power source you can think of.

Mike

Thread: Switch for Myford ML7
08/10/2012 13:11:22

Hi Charlene,

I have uploaded a diagam of this starter to help my explanation. The diagram shows the 3 phase configuration with overload unit but the single phase version is a small variation. The supply should be connected as follows Live (brown) to 5L3 and Neutral (Blue) to 1L1. Connect the motor live to 6T3 and the neutral to 4T2 on the overload unit, insert a wire from 2T1 to 3L2. Connect the two free wires that have tinned ends to terminals 95 and 96. Check that the thin wire of the two free ends is connected to coil terminal A2. Check or insert a wire from 1L1 to coil terminal A1. The two most important wires are the earths, these must be connected together and an earth point is usually provided in the starter.

If you do not want the overload unit connect the motor live to 6T3 and the motor neutral to 2T1, the link from 2T1 to 3L2 will not be required remove the thick free ended wire from the red button and insert the free end of the thin free ended wire.

If you wish to use a remote stop button move the wire that comes from terminal 14 on the contactor from the red button to the bottom of the green button, remove the short link from the red to green buttons and wire the two leads from the remote stop one to the bottom connection of the green button and the other to the top connection of the red button.

I would advise you to have your handiwork checked by a competant person.

Mike

teb1116217.jpg

07/10/2012 21:28:22

Hi Charlene/Norman

The remote stop for knee or foot operation is a good idea, Colchester had a foot stop/brake on some lathes, very nice to use. A foot stop on a pillar drill I would consider essential especially if like me you don't always bolt the vice down, a jam up can be very difficult to let go of to hit the stop with your hand.

Mike

07/10/2012 21:11:45

hi Charlene,

The starter you have purchased should be suitable for your motor, the overload unit is an optional item and will fit inside the enclosure. Toolstation sell these starters and the overload units, their part number for the overload is 44178 to suit your motor. They also sell mushroom head buttons for remote stops. The stop button on the starter is raised and the start button is flush so a panic fumble for the stop should find it even with out looking. The siteing of the starter should be considered for ease of use and so you will not be in line with the chuck on start up , if the work should leave the chuck for any reason it could hit you. The figures quoted on your starter are the ratings of the contactor and as it is rated up to 4hp is quite ok for a smaller load. The overload is the important item for motor protection and they should be adjusted to suit your motor the unit mentioned has a range from 2.8A to 4.2A and usually they are set to the lower value when you get it out of the box. If not set to 3.7A you may have nuisance tripping. if the overload ever trips do not be tempted to turn up the overload, you either are oveloading the motor or you have a fault, turning up the setting will eventually result in smoke and be expensive.

Mike

Thread: What is SWG?
23/09/2012 10:39:20

Hi Bob,

The table in your first link would appear to not be SWG.

Mike

21/09/2012 19:04:50

Standard Wire Gauge. The sizes are readily available from data books or google.

Mike

Thread: Converting a Myford ML7-R to variable speed
14/09/2012 05:47:15

I have an inverter fitted to my ML7R and can recommend it. It is of the flux vector type so maintains good torque at low frequencies. A tacho is useful to check your speed. I think the belts should still be adjusted to roughly the speed you need and then using the speed adjstment to optimise cutting. I have a foot mounted 1hp motor and this is not a problem as the ramp up to speed is smooth and the motor runs much smoother than a single phase motor. I felt it was worth arranging the drive to have forward and reverse and a slow jog and a rapid speed selection to enable a fast return when screwcutting and the leadscrew sync dial cannot be used.The acceleration ramps if reasonably gentle should not unscrew the chuck if reverse is directly selected but beware of cutting in reverse if using a chuck.

Thread: Brightening old tired metal
06/09/2012 20:42:13

Ajax is still available in the UK.

Mike

Thread: Dormer drill bits
06/09/2012 19:43:51

I have Dormer drills marked SKF from some years ago when they were SKF Dormer. They are now part of Sandvik and I think no longer manufactured in the UK

Mike

Thread: Dormer fastloc collets
24/08/2012 22:42:22

Hi,

I have a fastloc chuck and a clarkson, the colletts are interchangeable.

Mike

Thread: Wiring power cable to new motor
12/08/2012 22:53:37

This motor should be supplied from a motor starter to give overload protection and no volt release, wireing direct to a supply will not protect the motor in the event of a stall or sustained heavy cutting. A fuse large enough to survive the start surge will not protect the motor from overload, a proper overload set correctly should trip before the motor has cooked. The no volt release is for your safety, in the event of an interuption to the supply the machine will not restart while unattended. If the NVR is not installed then when power is restored this could cause damage to the machine if self acting feeds or screwcutting are engaged. The first thing most people do when plunged into darkness is not turn the machine off with the switch you now cannot see but check if the neighbours are in the dark aswell and then find the torches and candles, if you or someone else returns to the machine and power is suddenly restored you may have your fingers in a dangerous place, the no volt release will have turned the machine for you and will wait for you to restart it.

Mike

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