Member postings for Bob Jepp

Just been over to our local Axminster Tools ( Nuneaton ) to look at bench drills - I thought that I should let everybody know that they are going through a re-branding exercise over the next couple of weeks and are selling off ( at a massive discount ) machinery and other products. I purchased a bench drill that was priced at £230 for £120.

The manager said that the offers would be on the web site later this week or next week, but he expected to have sold out of most of the reduced product before the offers hit the web - do we need any other excuse for some new gear in the workshop !

Bob

Download the instruction manual from :

https://gb3a.mitsubishielectric.com/fa/en/dl/8113/M_FR-E700SC_A_UK.pdf.

On page 3-14 is a table showing the control circuit specifications for input circuits. The bottom two lines detail the requirements for the control of Safety Stop S1 and S2.

Quote :

" S1/S2 are safe stop signals for use with in conjunction with an approved external safety unit. Both S1/S2 must be used in dual channel form. etc... "

Page 3-24 provides the manufacturers suggested method of connection of the 'approved external safety unit ' in fig. 3-15 ( other 'approved external safety units ' are available from other manufacturers ).

Since the manufacturers specifically state that "S1/S2 are safe stop signals for use with in conjunction with an approved external safety unit", it would appear that the drive does not have the capability to perform the dual channel integrity checking.

Should we do what the manufacturer tells us ? Having been responsible for the risk assessment, design, building, commissioning and testing of hundreds of control systems for machine tools, robots and industrial automation over 40 years, I am not brave enough to depart from the manufacturers instructions. In industry, such control systems must conform the the latest legislation - at home, it's your choice, unless of course someone else is injured by your equipment in which case you will be liable.

Dave is quite correct in saying that we do not HAVE TO be 100% compliant with Health and Safety at home or in industry but the risk of injury is always there, the responsibility is yours.

Dave also says " Anyone aware of a VFD starting a machine unexpectedly due to a fault? " - this is not the point - the point is to reduce the risk to an acceptable level. Software controlled equipment is defined as unsafe with the exception of devices specifically designed, manufactured and certified for that purpose ( simplistically, such devices must be designed in a fail safe manner and must contain two completely separate systems even to the extent that some devices use a totally different design for each of the systems, different components and different software ).

"an old lathe switched at the mains socket with no NVR or safety interlocks at all." don't cause much trouble except when you have a power failure, fiddle with the machine/chuck/motor and happen to have your hands in the machine when the power comes back on again.

So, we need a realistic approach - the choice is yours ! I have dealt with second-hand machines for many years it is quite acceptable to buy and use a second-hand machine in whatever state you find it, but in industry we are covered by the Provision and Use of Work Equipment Regulations ( PUWER ) under which we are compelled to carry out a risk assessment on the equipment before allowing our employees to use it ( it has to pass the risk assessment - obviously ). This is supposed to ensure that any safety issues are dealt with before use.

At home, we are not covered by any of this legislation unless we 'substantially alter the machine' - oh yes, we just fitted an inverter ! in which case a competent person must re-assess the machines safety.

What to do and where to pitch our changes to the machine - well, I would suggest that there should be no shortcuts. Health and Safety say we are expected to 'take all reasonable steps' to ensure that the equipment is safe to operate - there is a discussion whether cost comes into the 'all reasonable steps' as excess cost may limit the 'reasonable steps'.

When we consider a normal bench drill, milling machine etc. without electronic control, we conclude that the single channel on/off system is adequate ( Start button, Stop button and NVR ), but there again, there is no software controlled device in the equation.

What would I do, the $64,000 question ! Having risk assessed the machine, I would go with my assessment - I would investigate the "re-start after a fault" situation and make my decision then ( if the drive does not restart automatically then the safety relay COULD potentially be left out, but I'm not advising that without the risk assessment ).

Lastly, Dave, in Fig. 3-15 the Emergency stop button is shown ( centre left ) - to add more safety interlocks just add them in series with the Estop contacts. The safety relay will complain if you don't have the wiring correct.

Bob

Just reading the comments regarding an NVR - again, this compromises the comcept of the dual safety circuits by degrading the safety system from a double to a single circuit. Any device connected to the safety inputs should be CE marked. There are specialist safety relays whose job it is to make guarding safety safer - they most definitely are not cheap ( something like £100 upwards depending upon the level of safeguarding required ).

Bob

Inverters are a complexed, software controlled motor drives. As such, we must understand that the drive may fail either without any power to the motor or with full power to the motor ( or anywhere in between ). Since the inverter is under software control, either failure mode is possible and the standard Start, Stop, Forward an Reverse controls which also pass via the software may become inoperable. To prevent unsafe situations, safe shutdown inputs are sometimes provided, generally preventing the output stage of the inverter from driving the motor, preventing power transfer by disabling the output devices.

So, lets look at the safety issues surrounding inverters on machinery :

• Your lathe motor is directly connected to the lathe chuck via a system of belts, pulleys, gears and shafts, therefore any unexpected starting of the motor will result in potentially dangerous rotation of the chuck - imagine should the chuck start turning whilst using the chuck key - potential injuries could result in loss of fingers, hands or even arms.
• Equally, un-safe opening of change-wheel guards etc. also exposes the user to similar hazards should the motor start without warning.

According to the diagram posted by William, he is expecting to find door switches and an external Emergency Stop fitted to his machine.

The reason for the provision of two parallel safety circuits ( PC to S1 and PC to S2 ) is to reduce the affects of potential failures in the safety circuits - i.e. there are two chances of detecting a failure rather than one therefore the door switches and Emergency Stop should form part of these twin parallel circuits.

OK, so lets look at the requirement for safety switches on machinery :

• Safety switches should have two independent electrical circuits ( one for each safety loop ),
• Safety switches should be forcibly disconnected when the guard is opened ( or Emergency Stop pressed ). This ensures that the contacts of the safety switch are forcibly opened even if the switch contacts were welded closed due to a fault.
• Doors should be fitted with a 'tongue in the slot' type safety switch or a suitable mechanical cam to force operate a roller type limit switch. Note that the limit switch must be a safety type switch and that micro-switches generally do not conform to the safety requirements.
• Emergency stop switches manufactured and CE marked ( yes we know the Europe issues and the comments about China Export markings ) by reputable manufacturers will provide dual safe contacts.
• Safe operated switches providing two electrical circuits may still fail because their fixings may come loose allowing the switch to fail to operate. This is the subject of another whole massive set of legislation.

Finally, one should provide two identical loops from PC to S1 and PC to S2 ( this is the reason that the drive manufacturer provides two terminals ) - looping the two safety inputs together defeats the purpose.

One final note regarding the safety circuits, the inverter should not re-start after the safety circuits are completed following a safety stop but must be provided with a manual method of re-starting i.e. a Reset pushbutton or maybe the Start button to be pressed again.

Finally, to address Robert Atkinson 2's comment regarding the integrity of Emergency Stop switches, it is generally accepted that designers of industrial control systems will incorporate a suitable monitoring relay which is specifically designed to detect such faults ( and many others ). The Mitsubishi manual details such a system a few pages on from the normal connection drawing.

Sorry to drag this out, but our safety is of the utmost importance.

Bob

I had a quick look at the Mitsubishi manual for the FR E729S inverter. The wiring diagram shows details of the safety circuits which show dual inputs S1 and S2 for the safety stop. It is intended that each device in the safety system should be provided with two electrically independent contacts ( closed when safe and open when unsafe ). Each circuit ( PC to S1 and PC to S2 ) should contain one of the dual contacts in each circuit. The intention is that there is two identical safety circuits which normally operate together hence giving two chances of a safe stop - operating only one circuit ( such as in the case of a mechanical failure ) causes a lock-out until both circuits are opened.

PLEASE, PLEASE make sure that the principles are adhered to - they are there to keep us safe ( even if they are a little more difficult to understand and implement ).

The method used at Colchester Lathes was to black anodise the whole dial and then skim the dial surface, removing a small amount of material and leaving the blacked engravings.

Bob

Mine is Kempe's - 1984.

Bob

The use of inverter drives in industry has been very common for many years - I think I've been using them for 25 years or so.

Whilst the integration of inverter drives requires some degree of expertise, it is not beyond the reasonably skilled engineer ( legally known as a competent person ) assuming that they read and can interpret the supplied documentation, which is usually quite sizeable ( most inverter drives also come with a quick start document to allow knowledgeable people to short-cut reading the whole manual ).

Integration of the controls for an inverter drive will be covered within the manuals, but beware that one will have to change some parameters to get these controls working.

The primary issue - in industrial and domestic installations, is to make sure that the device is safely installed. Electrical installation must be carried out by a competent person who will understand the wiring requirements although from my experience, it is unlikely that they will understand the implications of guard closed limit switches and emergency stop push buttons. It is insufficient to connect these safety devices to normal digital inputs to the inverter drive since they pass through the software which runs the drive and are therefore considered to be UN-SAFE.

As discussed on several threads, it is possible to implement the standard no-volt method for removing power from the supply terminals to the drive and in some cases ( see the manufacturers data book ), it may be permitted to place the disconnect between the inverter output terminals and the motor. One should note that it may be necessary to feed-back an additional contact of the disconnect to shut down the drive.

Generally, disconnection of the infeed power will shut down the drive, but one must understand that there will be some stored energy within the drive and therefore the motor may run-on for a time even though the emergency stop has been actuated - an unsafe condition. Disconnecting the output of the drive from the motor can cause premature failure of the output electronics of the inverter rendering it faulty.

Since these issues have become really important in industrial installations, inverter manufacturers has added safety rated inputs to the inverter which disconnect the output power from the motor within the inverter rather than externally - such inverters allow repeated safe stopping through emergency stops and guard safety switches without risk to the user or the device.

Many inverter manufacturers provide units with the safe stopping facility and anyone looking to implement an inverter drive on a machine should contact the manufacturers for advice ( I would add that inverter manufacturers who are active within Europe will provide CE marked products - those from more doubtful sources might suggest that CE stands for China Export ).

Drilled some holes in the cylinder support of an Elmers Open Column engine - 7BA clearance last weekend. When deburring the holes, I noticed that they looked quite large on one side of the component ( the top side whilst drilling ), and a lot smaller on the other side, Closer inspection of the holes showed that they were considerably oversize except for the last fraction of a millimetre where the drill broke through.

Looking at the drill point through an eye loupe revealed that the geometry was far from normal ( couldn't see enough detail without the loupe ). Although the point was in the centre of the drill and the point angle was similar on both sides, the Lip Clearance Angle ( according to the Presto cutting tool pocket book ) was wildly different one side to the other, in fact on one side there was more than sufficient clearance but on the other side, the cutting edge was below the flank causing that side to rub and, according to the book, causes exactly the symptoms I've seen in my holes.

Looking at all the drills in the set ( a budget set of number drills - long since forgotten the origin ) gave me a tally of roughly a third with incorrect lip clearance. Whilst I can probably just about re-grind the points on drills down to about No. 31 or 32, I find it too difficult to go any smaller, so a new set of Dormer drills were procured ( and inspected through the eye loupe - perfect ).

The other issue I've been having is with the actual drilling machine. Whilst I use a spotting drill to locate the holes from the readout on the Chester 626 mill, I find the spindle control has too little 'feel' with smallish drills, so I invested in a Sieg X0. The first real model engineering task for the X0 was drilling the hornstays / pedestal ties of my O gauge Josie clearance for 10BA. I found the speed of the drill very difficult to adjust - even on the low speed pulleys, which caused the tiny parts to become far too hot to handle. In addition, the drill seemed to struggle - only about a 1.8mm drill. I checked the speed with a tacho - should have been 0-3600 rpm was actually 0-7500 - no wonder the components got hot and there was very little power to make swarf.

I stripped down the drive motor and pulleys to investigate and the motor legend plate says 230V ac 150W and 18,000Rrpm - I wonder if the variable speed drive is only a half wave unit which may explain the top speed and the poor speed / power control. I spent some time looking to see if I could track down a lower speed motor as a swap-out, or maybe add a second stage pulley reduction but it doesn't seem that practical a solution.

Has anyone else on the forum got one of these machines and experienced similar issues and hopefully got some ideas ?

I’m up for a meet up - Rugby is quite near Neil I think.

Neil /

Quite agree - I've done it both ways around !

I think that there is a more important issue here than drawing board versus CAD - having worked in industrial automation for the last 25 years, I fear that the understanding of what is drawn has slid away from us.

At school, I started using the board and tee square at 11 years old, being taught by Mr Turbin - an experienced draughtsman turned teacher. I started work as an apprentice and wasn't allowed to go on the board until the third year, having completed the training schools first year and some time on the shop floor.

I've just completed a project with one of my customers whose 3D CAD operators, whilst very capable on the computer, don't have the practical experience and therefore make silly errors claiming that 'it looked alright on the CAD' !

Any method of producing drawings is great, as long as one can pass over the intended information - what do I do, well a lot of scribbly sketches on scrap paper, some pencil drawings in 3D and 2D & 3D CAD - using the appropriate method for the job - as long as the information is easy to follow. My favourite - a quick 3D pencil sketch passes over ones ideas as quickly as anything.

Bob

Thanks guys. I've manages two ME's today so far, and read the forum 3 or 4 times !

Bob

Collapsed in the workshop on Sunday - no warning, just my wife asking me what was wrong ! Sitting in hospital with all the fantastic medical attention is good - at least I'll get chance to catch up on the ME reading backlog !

Bob

Trying to decide what vehicle to go for - it seems that petrol is more expensive to run and higher carbon emissions, diesel cheaper to run ( it seems that recently designed vehicles have particulate filters and adblue ) and hybrid cars are extremely expensive and nowhere near as economical as the manufacturers claim.

Quite agree about the apps - can you believe that you need a smartphone app to fold down the rear seats in a Land Rover - BUT - heated steering wheels - the best thing since sliced bread ( had mine on tonight driving back from Tesco's ) !

Thanks Dave, now I'll have to let you into a secret - I have risk assessed my lathe and reverse engineered the circuit diagram only to find out that the 'so called Emergency Stop' in no way conforms to the legislation.

The stop side of the inverter, which included the guard safety switches, are open contacts which close when the Emergency Stop is pressed - a serious no-no in control systems. Needless to say, it's on the list of jobs to address - but I haven't as yet come up with a solution as the inverter is Chinese and I'm not understanding their manual too well !

Just a little explanation of the no-no :

Safety contacts should be normally closed and open when the device is actuated - Why ? - well several reasons :

• Firstly, should the wire fall off, the circuit will shut down,
• Secondly, should the switch fall apart, failing in the open mode, the circuit will also shut down and
• Thirdly, should the switch contacts weld closed, the actuation of the mechanical part of the switch will forcibly disconnect the circuit ( albeit leaving the device permanently damaged, but better than an injury - eh ).

Using standard European Approved Emergency Stop push buttons will provide these safeguards, but, limit switches for guard interlocks are not so easy to specify correctly as the safe operation of the switch depends upon the correct mechanical application of the switch as well as the electrical aspects. Just take a moment to think about a limit switch applied to a safety guard - on my milling machine, there is a belt guard safety switch which is depressed when the belt guard is closed, relying on the spring inside the switch to operate the mechanism when the guard is opened - what happens if the spring fails or the switch jams ?

Bob

The original posts regarding the starting and stopping of an electric motor on machinery - the machine will need the following :

1. A disconnection device which will default to OFF should the power fail and,

2. An overload detection device to switch off the motor in case of overloading,

The terms used in the previous posts should be understood as follows :

DOL :

The terms DOL ( Direct On Line ) refers to a device which starts the motor directly from the supply - i.e. no other device controlling the motor current.

NVR :

No Volt Release refers to the function whereupon the starting device will automatically drop out should the power supply fail and will remain off until the start control is re-actuated.

Normally, the disconnection device relies on an electromagnet to hold in a ( or several ) switch contact(s). The electromagnet is powered from the supply via a Start push button and is held in by a closing contact of the device together with a Stop push button.

These devices may be found at a number of our suppliers, I personally have used some devices from Axminster ( just because they are the most conveniently located supplier - no other reasoning ) which incorporate the Start and Stop push buttons as well as the NVR. Regarding overload protection, a correctly rated fuse is the absolute minimum requirement although various other specialist motor overload devices are also available.

Make sure that you do a risk assessment ( sorry - had to mention that ). You should consider the following and, in addition, any other pertinent points :

1. Conveniently located start and stop button ?

2. Once started, does the motor turn off AND STAY OFF if the supply is switched off and then on again ( NVR ) ?

3. Do you require any additional Stop devices such as guard safety limit switches of extra Stop buttons ( must be normally closed contacts in series with the Stop push button?

4. Have you incorporated an overload device which will shut down the NVR when it trips ?

OK, sorry about that, on to the inverter controlled motor - Lets be clear about the meaning of an Emergency Stop. Emergency Stops must safely remove energy from driven devices. With inverters, there are several ways to do this :

1. A disconnection device between the power source and the inverter,

2. A disconnection device between the inverter and the motor,

3. An inverter with built in safety outputs,

Considering each option :

1. A disconnection device ( NVR ) between the supply and the inverter is generally considered to be the safe option, but, the inverter will retain some charge at power down allowing the motor to continue running for a short time. Your risk assessment will tell you whether this is acceptable - industrially this method is going out of favour,

2. A disconnection device between the inverter and the motor potentially has the capability to remove the load from the inverter whilst running at 'full whack' causing a catastrophic failure of the inverter. This is obviously not good although some inverters are capable of withstanding this and others may or may not have a special input to feed back the status of the disconnect device to shut down the inverter when the NVR switches off,

3. Inverters with safety outputs are becoming increasingly the way to go. They incorporate two dedicated inputs whose job it is to shut down the outputs of the inverters in a guaranteed safe manner. Inverters incorporating these safe outputs need to be specifically selected,

So, the difference between Stop and Emergency Stop is that Emergency Stop must remove power from the motor in an approved safe fashion - again ( sorry ) your risk assessment should ask the question "When is Stop safe enough ?". If you are putting your hands into a lathe, maybe holding a chuck key, do you want to rely on the inverter to stop the rotation of the chuck ?

Just bear in mind that all modern inverters rely upon software to drive the motor - the basic principle of safe design is that software can fail and Murphy's Law says that it will always fail in the most un-safe way possible.

Bob

Edited By Bob Jepp on 01/04/2017 22:56:02

Lets get back to the topic !

Many years ago ( I'd hazard a guess at 35 years ), I bought a Toyo ML210 micro-lathe - it's very similar to the C0 machine in many respects except for one major point - its Japanese. I used the machine for many years making lots of small parts for a Tich, a 2' scale Clayton Steam Lorry and a plethora of other items and, I can say that the engineering of the machine was typically Japanese ( very high quality ).

A couple of years ago I decided that I needed some additional tooling for the machine, but due to the fact it has been out of production for many years, I couldn't find what I needed. I decided to buy a new small lathe and having visited both Arc and Axminster, decided on the Axminster C0 ( I liked the colour ).

On a previous forum post, I commented on the engineering standards of the Axminster C0 - it was dreadful - I didn't need another project, so I returned it and got my money back ( I didn't even get to cutting metal ).

I've since bought a new Cowells ME90 - I spent some time talking to Colin Childs at Cowells - he said all the right things about the quality standards he works to, and I am so impressed with the machine.

So :-

Toyo - was about £60 when I bought it - really good value for money - still got it, still works well,

Axminster C0 - enough said, got my money back on it,

Cowells, fantastic machine, but it should be at just over £3000.

Why the Cowells, well, apart from the quality, it has back gear, a full screwcutting capability and a common design M14 threaded spindle nose. I have one criticism - the MT0 headstock and tailstock tapers - very difficult to get tooling to fit this unless you go back to Cowells.

My two boys bought me a selection of imperial sized end mills to replenish my stocks ( from Arc ), wife bought me a solid gold lens hood for the SLR ( must be solid gold at the price - surely it can't just be plastic ! ), a magnifier / lamp from the Midland ME Exhibition and a MeArm robot kit.

Although programming robots is my trade, I am fascinated by the underlying motion control software which I know almost nothing about, so, as the MeArm can be controlled with an Arduino i'll be able to experiment.

My oldest lad ( he's over 30 year old ) had a Lego Technic Bucket Wheel Excavator kit - a huge model and so complicated, loads of gears and shafts - a fully working model ( kept him quiet for two days ! ).

Had a day out shopping on Wednesday - dropped in to Arc as my brother-in-law ( visiting for Christmas ) wanted some bits and pieces and was greeted cordially by Ketan, his good lady wife and had the usual lengthy chat during which we put the world to rights - came away with a bag full of assorted stuff.

I don't do Fusion either - it's Autodesk Inventor for me.

I use a Logitech something or other ( legend long since worn off ! ) with a scroll wheel for zooming etc. and forward and back buttons.

Absolutely essential - I find as I haven't mastered the standard mouse in 3d yet - a 3DConnexion Space Navigator ( the basic one - it was cheap at about £40 when they first came out ) for pitching, rolling, yawing and XYZ panning - once you get the axis set as you like them it becomes so intuitive.

Bob