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: VFD - which is best please ?|
Why did you say this? Are you just trolling?
EMC is not just about you. It's mostly about affecting others. How do you know that you are not interfering with aircraft navigation? Emergency communications? For example can you be sure that if an ambulance parked outside your VFD would not stop their datalink system or upset their ECG machine or other equipment?
I will not be posting pictures of my workshop as it is far from pristine and I would not want people to think what I do in my personal workshop is an examples of good practice. I have enough training and experience to assess the risk to me and put appropriate mitigation in place. My acceptable risk to myself is higher than I would expose others to either directly or by giving advice.
Happy new year and stay safe,
As I've said before, you can chose to do whater you wish in your workshop but please don't recommend unsafe practices to others who may not have enough understanding of the risks involved. If, as you imply, you have done this sort of work as part of your employment you should know better.
David J and Mike P. Thank you for the posts. Saved me saying it.
There is another side to all this. At some point there will be an accident and the "ambulance chasers" or an insurance company will come after either the supplier of substandard kit or someone who gave poor advice. We all have moral and legal responsibility for athe advice we give. Additionally I have professional responsibility.
I was trying to avoid this thread but I have to respond.
Emgee. A VFD mounted without an englosure is unsafe / unacceptable for a number of reasons. Firstly as Ian McV says the IP rating is not suitable for a workshop environment. Secondly the cable connections generally do not have adequate protection from contact or adequate strain relief. Thirdly the installation manual will (on better drives at least) tell you it has to enclosed. The safety and approval of the drive depends on following the instalation requirements. Note that these drives are components not equipment. They have to be correctly incorporated with other item to make a finished system. The supply of them assumes that the equipment they are incoprorated into is designed and constructed by competent persons. Note that this does not include the average electrician. In theory the completed equipment should be inspected and tested for compliance with the machinery, electriacl and EMC safety directives. Few people do this even for commercial kits.
As Andrew J says there is no correct answer to the original question. ANY VFD choce will be a compromise. I'm sure Andrew was going to say this in his next installment but the VFD should adjust it's output voltage with frequency to maintain the rated current and torque. Not setting this correctly is one cause of poor low speed performance. Of course even if you maintain the current and torque halving the speed halves the power.
I do not like the cheap far eastern drives sold on ebay and the like They are generally poor quality. Most of the ones I've looked at are clearly not UKCA (CE) compliant just by looking at photographs and reading manuals. Saying that they are "made by omron" or what ever is just nonsense. It's been discussed for mechanical items that thes low cost manufacturers will build to the cost / quality the customer wants. The same applies to electronics. The cheap ones leave out parts not essential to basic operation. This includes interference (EMC) limiting components and over current / voltage protection parts. Even the basic electronic components from reputable OEMs are variable cost / performance. Capacitors are a classic case. You my have a basic requirement of 100uF 350V but do you want 85 deg C or 105 deg C temperature rating? 1000 hour life or 10,000 hour? Al else being equal a 105 deg 10,000 h capacitor will last much longer. And this is without basic improvments like de-rating for voltage and current.
If you have to ask the question of what drive to buy you probably should be buying a preconfigured kit or paying a competent person to do the work for you.
This will not be a popular answer but it is factually correct.
PS must type faster several other comments came in while I was typing.
Edited By Robert Atkinson 2 on 31/12/2021 12:48:19
|Thread: Suitable Metal for Electro-magnet Levers|
Use steel. If there is not a lot of force to pull it off put a thin nonmagetic (plastic aluminium etc) shim on the electromagnet to maintain a small gap. I'd expect maxium force in the contact positionfor you application so shim should not bee required.
Do your "solenoids" have magnetic cores? I read the original post as they had. If they have fixed magnetic cores technically this makes them electromagnets, not a solenoids. A solenoid has no fixed magnetic core and the moving part is normally Iron. This works because there is nothing ferromagnetic for the core to stick to if it retains magnetism. The moving part attracted to an electromagnet, the armature, is normally made from a material thati s harder to magnetise. This is typicall steel.
Some supporting data from Eclipse
" The armature plate may also be known as a keeper plate. An electromagnet or electro-permanent magnet always needs a ferromagnetic surface to clamp onto – the ferromagnetic surface required is generally a mild steel or ferromagnetic stainless steel. "
Note that iron is more easily magetised than steel. It is also more easily de-magetised which is why it is used for transformers. As the holding electromagnets are DC they will not demagetise the armature (moving part). This will eventually result it it sticking even with the electromaget de-energised.
The armature should be STEEL not iron.
Steel. Mild is OK but when doing this sort of application in the day job we used gauge plate. We had it electroplated but the environment was fairly agressive. Don't go too thin, the force will be reduced.
|Thread: XY Table, or XZ gantry?|
A X-Y table and Z gantry takes at least 50% more X width. All else being equal the Z mounting will be less rigid. However as there is no change in load point it is easier to predict any flex and it will be consistent regardlesss of XY position.
|Thread: mill conversion|
|Thread: Myford vfd|
Those almost certainly use a "universal" burushed motor. much simpler to control. Not as smooth torque as a 3 phase. Brushed motors are sometimes used on small lathes but a 3ph and VFD is much better.
|Thread: Pin-hole in oil pan - which product to patch it?|
If it is a reasonably flat surface and the leak is slow try this approach.
|Thread: Lock nuts / Jam nuts - MEW 311|
Whatever way fitted a pair of plain nuts provide only minimal locking against vibration. There are much better technical solutions. The only justification to use two nuts is historical accuracy. That being so, fit them as they were on the original design. If you need locking use a tab washer, split pin or modern solution.
|Thread: Machining Plastic|
If it is recycled it ia almost certainly thermoplastic and may melt. Nothing wrong with using normal metal cutting coolant or minimum concentation soluble coolant. No more risk to mill than cutting metal. Fast feed rates help too.
If you have lot to do it might be worth making a jig with stops for a circular saw. A custom "table saw" with 3 ganged cutters on a spindle might be worth considering as you have a lot to do.
|Thread: Digital Caliper - again, sorry|
I bought one of ARC Eurotrade's lower cost ones and am very pleased with it.
|Thread: Etch Primer life|
Any 2 part paint is unlikely to keep for very long once mixed. Putting in the fridge will help. Some 2 part materials can be frozen once mixed to stop them curing. This is used for some ircraft sealants.
The Phoenix website says 3 hour pot life. Closing the lid will make no difference to this.
|Thread: Metrotropolitan Vicker Single phase motor|
There are other examples of "inside out" induction motors. However most of these have the inner part with electrically connected windings stationary and the outer rotating. This means they need no brushes. A well known type is by PAPST (now EBM-PAPST). These are shaded pole types and connonly used for fans
OK, A picture is worth a thousand words.
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