Member postings for Simon Williams 3

My Mother, having brought up five of us, re-discovered her creative roots and took up Batik printing. In her case she was interested in drawing pictures of birds, animals, landscapes in Batik.

She discovered that the beautiful quality linen resulting from washing draughting cloth made a superb material to carry the wax resist, and took the dye reliably and with an excellent resolution so she could get the detail she wanted.

IIRC she washed quite a lot of this linen, having been given a roll of it by an interested neighbour who no longer had a use for it. Washing out the conditioner (gelatin?) was easy enough, but she found that the only easily available solvent for removing the wax resist after each stage of the dying procedure was petrol. Needless to say Father, who smoked heavily, was not allowed in the kitchen on those days!

I still have my Father's collection of Graphos pens, if they are of interest to anyone as historic memorabilia please PM me and we can discuss further.

Regards to all

Simon

Crikey Muzzer, that's quite an analysis there! I think I'm going to laminate it and put in the back of my Machinery Handbook. Thank you for that work!

Rgds Simon

Mmm. Interesting little snippet there, thank you Emgee. I wonder what I've got! Are these gears common with a Student I wonder?

On a related but parallel matter, I had a sort through the change wheels I've squirrelled together, and realised I have some of 16DP which match the originals supplied with my Mk 2 Bantam, but I've also bought some with 14DP without realising they were different, sold to me as suitable for "The Bantam".

Both have the same splined centre. Could it be that the Mk1 had 14DP wheels?

I've got a hope that I can mix and match them, provided the same DP's mesh. With the centres being the same I can in theory put one of each DP on the idler spindle (say), and use the corresponding meshing gear on the g'box and on the mandrel. Bit of a faddle, but needs must. Always supposing they are the relevant no of teeth of course. I've yet to try this experiment!

Any thoughts? Simon

Hi there,

Try Lever A = position T (value1)

Lever B = position 5 (value 12)

The formula in the handbook now becomes 224/19x12x1 = 18.6667/19

Multiply top and bottom by 3 and you get 56/57. You were always going to have to have 57 in there somewhere!

so the train becomes Driver / Driven = 56/120 x 127/57.

I've taken this from the handbook for my Mk 2 Bantam, I assume the Mk 1 has the same gearbox ratios.

Try it carefully on a scrap piece before committing to the real thing!

Muzzer - could you please check my arithmetic!!!

Rgds to all

Simon

Edited By Simon Williams 3 on 30/04/2016 11:26:32

Colin - thanks for the correction over the RCD - yes if there is a path to earth on the load side of the inverter it must upset the balance in the rcd, so it trips. Only if the inverter output was truly isolated from the supply would this not be true, and of course that's not the case. I've just been reading the Telemecanique Application notes for the Altivar range and they agree. Of course.

You've got me thinking now about the braking of my drive. Re-reading the user manual for the drive in question (Ativar 18) I realise that it can do both DC injection and braking resistor, but at this moment my brain is refusing to co-operate in understanding what I've set up. It was a long time ago and the user manual is a bit vague. Or maybe it's me!

I have got a braking resistor connected, and my scribbles in the margin say it should be 68 ohms/36 watts, though it's not entirely clear why except that this appears to be the value taken from TME's catalogue of the proprietary item. But that's irrelevant, because on looking closely I realise that the resistor fitted is actually 6R8. So I'm not too sure if this is doing anything! Checking the resistor confirms this value.

If I'm trying to stop a big inertia, I get an overvoltage error on the display of the drive, which trips out and then the load just spins down. You must be right though, if the drive will accelerate the load it can stop it, but it doesn't. I guess that could be a number of reasons, not least I've cooked the braking circuit. I'll try it with a 68 ohm resistor as soon as I can get one.

I'd imagined that the drive went into current limit on acceleration so it just extended the ramp time, whereas on braking the drive actually aborts. I'm wondering now if the braking resistor is actually doing anything useful! If I measure voltage across the braking resistor during deceleration what sort of voltage am I expecting and for how long?

Said drive is a fairly ancient TME Altivar drive, type ATV18U41M2 (2.2 Kw), motor is 3 ph 4 pole 5.2A FLC 1.1 Kw (oops - I said earlier it was 2 HP, apologies, no wonder it doesn't like the top speed!) connected for 230 v in delta.

Motor rating plate says Hydrovane on it, but that's what I scrapped and kept the motor, I'm fairly sure it's actually Leroy Somer.

Rgds Simon

Colin - thank you, and I'm very intrigued by your "part speed 400 volt" motor approach, this looks like a very elegant answer to the star/delta problem, and I'm looking forward to trying it out.

"Single speed motors and inverter drives are not always expensive" - I've got caught by initially buying a (Oriental) motor that was plainly not VSD compatible, it's torque just fell off a cliff as I went above or below 50Hz, and buying another motor (Weg) cured the problem. For all I got both motors at good prices it was still a bit of an expensive lesson to learn! Should have asked the experts...

The RCD thing was initially about would an RCD on the supply side of an inverter trip if there was a fault downstream of the electronics. I can't imagine it would. The business about whether the drive would trip the supply RCD was a different thing. Certainly I've got that problem here, and have sidestepped it by feeding my shed from its own source. SWMBO put her foot down with a firm hand when Eastenders went off three nights in a row. AFAIK that's about the initial charge current into the transfer capacitors.

As for DC braking, I've come from an industrial drives environment where the HSE wanted to see DC braking on unguarded or poorly protected rotating spindles such as drilling machines, lathe chucks and the like. For my conversion of my Bantam lathe I found that to give an acceptable stop time with the difference in inertia between a 10 inch 4j chuck at 1000 revs or a 5 inch 3j the braking resistor didn't really do the job.

I've got several small sub kilowatt VSD's which use DC injection to stop the spindle (vert' mill and a pillar drill) - these work a treat but of course the inertia is so much less. For the purposes of this thread the point of the discussion was "don't disconnect the motor from its drive while it's rotating".

Best rgds,

Simon

I've already tried the VSD route in similar circumstances albeit on a Mk 2 Bantam. I took the original two speed motor off and replaced it with a single phase one, but didn't like the crash start stop, so changed it for a 2 HP 4 pole motor with a VSD to match. I couldn't put the original motor back  IIRC because it was a 400 volt motor and didn't have the terminals for the necessary connections for 230 volts. I never imagined (as I have since seen here) diving into the motor and finding the star point connection.

The VSD is configured to give soft start and DC braking to stop; you can't do this if the VSD is supplying other stuff as well as the lathe main motor.

Even though the original motor was 3HP my 2HP works well, except in high speed top gear (2000rpm) when it will only start if the gearbox oil is warm. So 2HP is marginal, but for the limitations of the supply to my shed I'm happy. I run the low range speeds with the inverter giving 50 Hz, and the high range at 100 Hz. I'd love to know if someone has tried running the low range at 25 HZ and the high at 50 Hz because this way the motor should be more efficient and might be man enough to pull the top 2000RPM speed, but it's a laborious experiment to try. The beauty of the frequency based speed change is that no switching of the motor connections to the inverter is needed, and as has been said above this is a no-no.

Looking at the commentary above about RCD's the concept of current balance isn't really the place to start. The internals of an RCD measure the vector sum of the current passing through the device, provided all of the out-flow current and all of the return current is passed through the sensor the total current taking account of direction and magnitude will always be zero. With a single phase device this explanation reduces to the one above about the current in the two wires being balanced, but with a three phase RCD the sum of the currents in all four wires (including the neutral if it is used) always sums to zero. If there is a bypass path around the sensor inside the RCD for the current - supply or return - then the vector sum of the currents is no longer zero, and out pops the trip. So the three phase load doesn't have to be balanced.  "Balanced" means that the magnitude of the current drawn on all three phases is the same.

The inverter may have other ideas, as most won't tolerate gross imbalance in the load applied to them, it gives 'em indigestion .

Pedantically, an Earth Leakage Circuit Breaker is a different animal, and for these purposes is obsolete. However the industry tends to use the two terms interchangeably, but what you need is an RCD (Residual Current Device).

And thanks to Nicholas Farr for picking up the point about a 110 volts site transformer is really a two phase 55 volts source, with the centre tap connected to earth. The concept here is that (according to historical editions of the wiring regs) 55 volts is (nearly) a safe touch voltage. As I remember it, that isn't to say that you can't get a shock off it, and in unfavourable conditions I guess it could be lethal, but it is low enough not to cause involuntary movement. There is still a contradiction in the 17th edition in that 24 volts is deemed to be "Safety extra low voltage" but 55 volts is acceptable on a construction site because the safe touch voltage is 50 volts - as used for calculating earth path impedance criteria.

My recollection is that provided you don't apply enough volts to the skin to break down the skin resistance you would be very unlucky to get enough current to pass though the heart to cause fibrillation starting from a 50 (55!) volt source. The same is not true of cows, IIRC, which is why the regs have special requirements for farm buildings.

To return to the original post, I guess the answer is that the original two speed motor is unsuitable (without a lot of modification) for running on an inverter, the choices are either to go single phase (clonky!) or a single speed motor and corresponding VSD (more money, but a very nice machine results).

HTH Simon

Edited By Simon Williams 3 on 27/04/2016 19:58:30

Edited By Simon Williams 3 on 27/04/2016 20:09:56

My Apologies. So it shall be.

Simon

Isn't there a problem with the component values for the 555 timing circuit?

The values as shown and as per the link MichaelG added show R1 = 1M, R2 = 3K3. This gives a mark space ratio of about 300 to 1.

A 555 can't do this. You can go to about 100 to 1 (but not with this basic circuit) but 300 to 1 is going too far.

Why does the reset pulse have to be short?

Simon

Edited By Simon Williams 3 on 21/04/2016 23:49:24

John - thank you , fair comment.

I have!

Rgds Simon

That's the complexity leaking out.

Come on chaps, I don't know enough about the innards of an Arduino chip to know if the answer is as simple as ditch the diode, feed the reset I/p with an open collector and rely on the pull up resistor inside the A' chip. But some of you jolly clever chaps must do.

The OP was asking for help in his hour of befuddlement. I don't feel we've maintained our high standards of brotherhood in adversity here.

Edited By Simon Williams 3 on 21/04/2016 22:52:08

Sorry John, but this OP isn't ready for CMOS static sensitive stuff yet.

The same essential functionality exists with the 555 - so the original question stands. How do you implement a reset with a 555? There are other ways to do the same job, but that wasn't the question.

Equally the point that he is adding complexity for the sake of may be correct, but - with respect - is irrelevant. The OP wanted to learn how to do this stuff, and asked why does it not behave as he expected. He can build an entire Heath Robinson panorama of unnecessary complication - and learn much as he does it. But it is nice (and ever so much more rewarding) if the lights come on when you expect them to.

Rgds to all

Simon

I say chaps, have we not fallen into the trap of "if you want to make it complicated ask an expert"?

I get the feeling that the OP is more than somewhat bemused at the extent of the expertise this spotlight on the intricacies of safety circuits has revealed. But it isn't answering the original question.

At risk of lecturing all and sundry, for which I apologise, the OP made his risk assessment, identified the hazard, and devised some control measures. Other solutions exist.

So to focus on making sure that the control measures are effective, how do you reset an Arduino with the output of a 555?

My cursory glimpse at the equivalent circuit of the 555 output stage shows a pair of npn transistors connected between the supply rails. I fancy one needs to think about the leakage currents through the base bias resistors to be sure that pin 3 will actually go properly low.

Alternatively - and more simply - should not the Arduino reset input be fed from an open collector output? Minds other than mine understand the intricacies of these things better than I do.

For my part I like the idea of not allowing the microprocessor in the Arduino to suicide itself in times of peril. If the innards have gone doolally, then exterior means to bring the Express to a safe halt are indeed prudent. That goes back to the next stage of the risk assessment - have the implemented control measures reduced the risk to an acceptable level?

Rgds to all Simon

I've got a scrap Bridges drill here. Do you want it for the fasteners. Easiest if I strip it and post you the debris. If interested PM me with name and address and I'll get my Black and Decker electric screwdriver on charge...

Rgds Simon

Drill a hole right through one end of the slot as your first operation, ideally with a long slot drill (i.e. two flutes) in the mill with the table stops set for the ends of travel. Now use plenty of suds to wash the swarf you make as you cut the remainder of the slot down the hole you just made and out of the way. It's nigh on impossible to keep a slot as deep as this clean of swarf if you go in blind, and it makes a.big difference to the finish if you keep chumping on swarf and may break the cutter.

You can blow the swarf out with the airline, but it's messy, noisy and inefficient.

Interesting my predictive text failed at "swarf". What use is that to an engineer!

Rgds Simon

I'm just wondering if you have the half nut engagement adjustment set too deep. The half nuts have an adjustable stop by means of an allen screw and a spring, if this was allowing the half nuts to clamp down on the thread instead of just engaging it this might give you the symptoms you describe.

HTH Simon

Edited By Simon Williams 3 on 16/04/2016 17:07:21

I'd hate to think that we've dissed TIG to the point of it being pointless. It is a very versatile process, capable of welding almost any combination of metals (within reason), and giving excellent results from the point of view of appearance (a good stainless weld is indeed a pretty thing) and function (but only if you know how!)

That "know how" is a problem, but is surmountable - or at least I hope it is otherwise I'm wasting my time! The cost is an issue, and here it isn't just the cost of the equipment but also that the cost of the gas is cruel. You can buy some very neat all built in inverter based TIG welders, (and incidentally get a useful stick/ MMA welder in the bargain) for not a lot of money - typically less than these arc controllers seem to go for. But the cost of the gas is significant, and the rods are also not cheap because you need a wide variety of them to work with a wide variety of metals, such as us model makers and home machinists like to play with.

Having said all this, I like the TIG because there is nothing quite so useful at welding small items together. MIG is good, but clumsy if you are looking at something on the scale you can hold in one hand. Gas (Oxy fuel) is also useful, but the cost of running it has got really out of order.

If Andy would like some advice on the most cost effective way of tackling the issue of sourcing shielding gasses for TIG I'm sure we can pool our knowledge. For my part I've given up on BOC and Air Products (UK based) and I'm now on the system where you "buy" the deposit on a cylinder, and pay for the refill as and when you want it. It's still expensive, but it seems to be the best deal in town for the amount of gas I want to use.

Rgds to all Simon

Don't take this as the gospel word, because I'm still fairly far down the bottom of this learning curve... However my understanding is that pretty much any DC welder will be usable as the power supply for DC TIG welding, but you need the ancillary bits and gismos around it to make it work.

In this instance you need a TIG torch and a source of shielding gas. This machine doesn't seem to have the controls for the gas built in, so the gas goes direct to the torch, and needs to be controlled somehow by the trigger. The other thing is that the welder you have doesn't have an on off switch, so the torch is always live, neither (AFAIK) have HF start feature so you will have to use it scratch start (I.e. the electrode is touched to the work piece and then dragged away quickly (but not too far!)

All this, and the inherent difficulties of learning to TIG weld (it's not as easy as the guys on Youtube make it look) mean that this isn't, I don't think, the place from which to start. Just getting the electrode contaminated will frustrate you for days - so I think a beginner has got to start with a more expensive but more controlled machine and concentrate on the technique. Once you've got good at it and understand causes of weld faults then make it more difficult by using equipment which is more difficult to control and set up (but why would you want to!!!!)

You can buy a TIG torch on ebay which has a trigger controlled valve which will turn the gas on and off, you may be able to remote control this welder via that four pin plug on the front panel, if you get past that you will almost certainly get demoralised because scratch-start almost inevitably contaminates the electrode and then you have to stop and grind it clean and so on and so on. Then there's the little matter of hand-eye co-ordination... As they say in these parts - "If I was you wouldn't start from ere!"

If you want to TIG weld buy a TIG welder. It's quite an expensive facility to have in your workshop, but it's very useful.

PGK-

My central heating boiler is rated at 17Kw, runs about 7/24 of the time. Sounds to me like 8 Kw should be plenty for a bit of silver soldering, provided you can direct it into the metal and not lose a significant proportion on global warming.

Simon