Member postings for Robert Atkinson 2

How about a joint connector nut

www.screwfix.com/p/joint-connector-nuts-m6-x-17mm-50-pack/83521

www.screwfix.com/p/joint-connector-nuts-m6-x-12mm-50-pack/83501

Robert G8RPI.

On the linked page, Inverter drive Supermarket, remember that like many suppliers they are providing information that supports the product(s) that they are selling. This particular page looks OK. However, note that the mechanical power available running a 400V Delta motor at 50Hz/1.73 (29Hz) is THE SAME as running it at 50Hz. The difference is the available torque. If you are also changing the machines gearing then it's 6 of one half a dozen of the other. If the gearing remains the same then it depends on the machine type. It may even be worth considering running both settings one for work that needs high speed (50Hz) and one for high torque for mills and lathes.

Robert G8RPI.

Simon and Andrew have pretty much nailed it except K is absolute temperature (Kelvin), the multiplier for thousands is k (lowercase).

Ahh, VAR's some early turbine aircraft actually had VAR meters so the flight engineer could ensure limits were not exceeded.

Robert G8RPI.

I've come to the thread late but OMG what a confusion. Lot's of good info, some "simplified electrical" and some just wrong.

One key point that seems to be missing is that (assuming same speed) the output power of a motor is determined by the torque. The torque is directly proportional to the CURRENT in the windings. If the current required to provide the load torque is less than the available current the motor provides the required power at the output (note this could be an overload and damage the motor). If the available current is less tthan the requirement the motor will slow and stall. A much better way to consider motor rating is the maximum torque and speed not power.
The above applies to any motor, 3 phase, single phase, universal including DC. For permanent magnet motors the magnet field is an additional limting factor.
Note there is NO mention of voltage. Voltage does not affect the available power IF enough current can be drawn. Voltage applied to a motor sets two parameters - A/ the off-load current (and thus speed for a DC motor) and B/ the maximum available current and thus (indirectly) available power.

So what controls the current? Well according to mr Ohm's law, Voltage divided by resistance for DC. We are mostly talking about AC but if we simplify things its Voltage divided by impedance (AC & DC resistance).

For a given frequency (speed) the impedance of the motor windings is fixed. This sets the stalled current. So what set the running current? That is the apparent voltage across the windings divided by the impedance. This apparent voltage is the applied voltage less the "Back EMF". This is the voltage developed by the the current flowing in the motor and opposes the applied voltage. It decreases with the load on the motor. At no load it is equal to the supply voltage and no current is drawn (This is a gross simplification, there is always some load, bearings windage etc so some current. and ignores phase relationships beteen voltage and current in coils). As load increases the Back EMF decreases and the current increases. The voltage rating of the motor is that which limits the input current and power (and thus output power) to the rating of the motor (set by the amount and quality of the iron and copper in the motor). For AC motors this includes the frequency. Too much current will overheat the windings due to rsistive losses.
The impedance of the motor is directly proportional to the frequency applied (all else being the same) so if you halve the frequency the impedance will halve and the current will double. This is why when running at reduced frequency (speed) the VFD reduces the voltge proportionally to keep the currrent the same. The available power reduces not becase of the reduced electrical input but because of the reduced speed at the same torque. You cannot exceed the torque rating of a motor without overloadding it and causing damage. If you increase the frequency (speed) the VFD increases the voltage to compensate for the increased impedance. This means you can get MORE power from the motor assuming you don't exceed the mechanical ratings (mostly bearings and centrifugal forces) or the voltage rating of the electricl insulation. Some "inverter" rated motors allow for this in their design. So ideally yous hould run a motor as fast as possible. 60Hz is OK for most normal motors.

So;

1\ you do not need to limit the upper frequency when running a motor at less than its rated voltage. Running a higher voltage rated motor (e.g. delta) with at lower speed and maximum available voltage allows you to get more torque out of it so keep the voltage up.

2\ The ratio of line to line and line to neutral is always root 3 (1.732) for a 3 phase system (five phase is root 5) so 230V/440V is not possible.

Robert G8RPI.

I know is obvious, but you have tied turning it both ways?

Robert G8RPI

Steve, how is the adaptor initially installed in the chuck? Is it screwed in from the front (jaw) side or the back side? Is the section in the chuck fully threaded? I could assume its not fully threaded and goes in from the front , but assumptions are not a good basis for sound engineering.....

Robert G8RPI.

I watched a few episodes of "repair shop" but had to stop. I have a couple of problems with it. First they are not passing on knowledge in particular details of materials used. e.g. a ceramics expert doing a repair with clearly two different adhesives but not a clue as to what type they were or why. Another using a "special solvent" on a motor in a plastic toy again with no details or even a warning that many solvents would destroy the plastic. secondly they show lots of poor practices, bodges, misuse of tools etc.

Back on topic my everyday watch is a 20 year old Breitling Aerospace (the old, compact thin titanium design not the modern chunky "jewellery" bought with my small part of the legacy of a relative who was an amateur horologist. The minute hand fell off last month. No sign of a broken staff so just need putting back on as far as I could see. As it was due a battery it was put in for a service and estimate (factory repair). This came back when I was out of the country for work and included repair, service, new crystal and case polish at just under £900. I would have said no thanks and done it myself but SWMBO said OK. Guess that's my birthday present sorted.

Robert G8RPI.

Robert G8RPI.

Report them to ebay. They are not supposed to list multiple copies of the same item. There is a limit of 10. There is a "Report item" link on every listing. This comes under listing practices.

Robert G8RPI.

The bigger problem is companies don't want or can't actually fix things. They uust want to replace "modules" or sell you a new one. This means owners of those items that can't be replaced are forced to pay high prices. Recent examples

My car has a worn bearing causing noise in 6th gear. It's a known problem (M32 'box). bearing are in the end cover so easy to change I talked to my local garage nd they won't do it. They will only fit an exchange garbox. I'll go bck and negotiate them re-moving nd refitting the gearbox with me taking it away and doing the bearing myelf.

A friend asked me to look at a Singer sewing machine that the local repair shop said was not repairable. I quickly found that the flying hook drive gear had broken up, This is a polyurethene gear with a metal hub. New gear cost £3. The problem is it is press fitted to the shaft flush to the bottom of the hook so getting the old hub off is an issue, but I just split it with a cutting disk in a dremel and pressed the new one on.

As to labour costs, near me there are a Jaguar and Ford Dealerships on the same site. The Jaguar labour rate is twice that of the Ford but a Jaguar X type is basically the same car as a Ford Mondeo,,,,,,,,

If your existing punch works OK other than centering would it not be easier to make a set of slides that fit in the slot and have coin sized holes to center them under the punch? to might have to block one side of the slot in the block to give a register to push the slide against. I guess it depends how many different size coins you deal with.

Robert G8RPI.

Hi,
Take an impression of the threads (spindle as well as back plates) with plasticine or similar and measure the pitch across several threads with a magnifying glass and digital callipers. This will give you a good idea of the pitch. Then slice through across the threads with a sharp blade and compare them end on for thread form.

Robert G8RPI.

There are many different grdes of ATF. All have lots of additives. Personally I would not recommend them on a lathe with bronze bearings. The additives in many transmission oils can degrade yellow and white metal bearings.
SAE 32 oil is cheap ad readily available in small quantities as jack oil, e.g.

https://www.halfords.com/workshop-tools/garage-workshop/trolley-jacks/halfords-hydraulic-jack-oil

but a branded hydraulic oil like Nuto 32 would be preferable.

Robert G8RPI.

You could try heating the 1/4" bar to expand it and then let it shrink onto the carbide.

Robert G8RPI.

I've not looked at inside a cheap VFD (the photos are often enough to identify CE non-compliance), but have looked at lots of cheap power supplies. Most of these have lacked EMC components, had unqualified fuses (if any) and worst of all had poor basic electrical safety, for example unsuported solder joints on mains connections, weak cases, inadequate spacing / insulation between mains and low voltage. They "work" but are one failure away from electrocuting someone. VFDs may not have the direct, un-earthed connection to the user of a power supply but can still be dangerous. The Schneider ATV12 looks like a good unit. It might be twice as much, but the difference is less than the cost of filling your car, is it really worth it? I would not entertain a cheap unbranded far eastern VFD personally.

Robert G8RPI.

Sorry I made a typo. KW instead of kW is not a typo, it is a common error i expression of units. Not as bad as M instead of m and vice versa though
On the point of setting up the VFD to suit the motor, that is fine if can do it given the quality of the manuals. And if you do, yes the electronics will be lightly stressed but if you buy a decent VFD you don't have to de-rate it to 20%. The is also the point that you will only be using 20% of the dynamic range of the control system. For example if it uses 10 bit conversion there is a total of 1024 levels over the full range. Limiting it 20% will only use the 256 streps. the 8 least significant bits, down in the noise. Thiss reduces the performance. Using a drive with adequately rated components preserves the dynamic range. If you are using a bigger VFD to rive multiple mtors then you loos the benefit of overlod protection.

Robert G8RPI.

Edited By Robert Atkinson 2 on 26/12/2019 21:03:47

If the 5kW (KW is KilogramWatt) drive is not set up properly for the 1kW motor it will not provide protection against overload and will supply enough power to burn out the motor.

Rant ON

It's not just safety compliance that some drives lack, it's interference (EMI/EMC) as well. Many drives and most of the cheap ones need external filters and chokes to meet EMI/EMC and the manulas say this. As a proper filter can cost as much, if not more than the drive they are often omitted. I dosn't stop it "working" but affects others.

Rant OFF

Robert G8RPI.

There is another issue with the cheap far eastern electronics (not just VFDs) - compliance and safety. Most of the items I;ve seen, particuarly mains powered ones, do not comply with relevant safety and interference requirements. Even units sold through UK suppliers can be non-complaint. one trick is to get the unit tested with all component needed for compliance fitted and then leave them out on production units. This can be seen as empty or linked out component loactions on he circuit boards. While fire and shock hazards are obvious, interference is more subtle. It could be obvious like blocking the workshop radio, but you could also be affecting emergency service radios or safety critical navigation sytems. It also works the other way a non compliant unit could suddenly start, stop or change spee because of interference from radio transmitters or other no-compliant equipment.
Yes, I know this hardly ever happens but if it does you could have a wrecked machine, serious ingury burnt down house or worse.

Unfortunatly enforcement of the regulations is virtually non existent and there are hundreds of hazardous items sold every day. Even well publicised fatalities due to mains chargers does not sem to have stopped it.

Rant over.
Robert G8RPI (proper CE compliance is part of my day job)

Well Starrett still list them under precision metrology tools. The only thing that I can see as precise is the top and bottom faces are ground, presumably flat and parallel. For non-precision, non-marking work I use a ice hockey puck. Thesse can be cut and drilled to accomodate odd shaped work pieces. They are made from filled hard rubber which is "dead", high friction and won't damage cutting edges. Pretty cheap if you are in North America and not bad prices from the usual online retaillers. Make good pads for trolly jacks too.

Robert G8RPi.

Hi Richard,

If the unit is faulty and they can't even look at it for 28 days go in and request a refund Tell them it's obviously faulty or not fit for purpose. a 28 day wait for them to start looking at it is un reasonable. As a consumer in the UK you have rights. If it is less than 30 days since it was delivered or picked up you can demand a refund for faulty goods

Robert G8RPI.

We are in the Tea Room so that's OK.

I just can't  relate using the internal frequency calculation of the GPS to steer an external loop. I can find no information on the granularity or accuracy of the NAV-CLOCK message, but have not looked that hard. The noted ~10^-10 stability seems a couple of orders worse than the "bare" OCXO. The construction and finish is great by the way.

Robert G8RPI.

Edited By Robert Atkinson 2 on 23/12/2019 12:41:46