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Member postings for Simon Williams 3

Here is a list of all the postings Simon Williams 3 has made in our forums. Click on a thread name to jump to the thread.

Thread: Electric motor ratings
09/01/2020 23:13:32

Let's untangle some of the folklore from the technology here.

Motor as above is plated for 550 watts OUTPUT, ie mechanical power delivered at the motor shaft. It absorbs 5.1 amps times 230 volts = 1.17KVA to achieve this NOT kilowatts. KVA is a measurement of reactive power, not to be confused with real power measured in KW i.e Kilowatts.

This tells us something about the efficiency and the power factor imposed on the supply. Estimate max mechanical efficiency is say 70%, then power factor at full load is approx. 0.67. Power factor of a single phase motor will drop quite noticeably at part load, may get down to 0.3 while the measured line current (now highly reactive) drops only slightly.

Motor will run slightly faster than the quoted full load speed of 1425 rpm at part load, but not much. Estimate 1470 RPM at no load. Motor will never attain synchronous speed (1500 rpm) - it can't - but this slip factor is largely what controls the power factor the motor presents to the supply. This is with the motor running at service speed (duty point on torque/speed curve) in equilibrium with its applied mechanical load. This motor is continuously rated - which might be what the CR stands for - but it would have to be marked as such if not rated for continuous duty .

This motor will take multiples of its 5.1 amps quoted full load current briefly while starting. A typical figure for a three phase motor is that it will take about 7 times full load current in the first few milliseconds after it starts, for how long this continues depends on the Inertia of the motor and its load. But you'd better let it spin up the full speed pretty quickly or outgepouf und smoken mit ze blitzen. Maurice's 'scope traces show this effect and quantifies it nicely.

A single phase motor is even worse to start electrically, so budget on say 9 times full load current as starting inrush, get it over and done with as soon as possible. What makes single phase motors so treacherous is that this starting inrush is likely to be limited as much by the upstream supply impedance as the characteristics of the motor. In other words the supply wiring and contacts are often the limiting factor and are getting hot during the inrush event.

Whether non European manufacturers actually conform to the same standards is anyone's guess - the machine could only be (legitimately) CE marked if they do.

HTH Simon

Thread: Gluing glass
04/01/2020 16:59:42

Thank you both for your expert attention -

Bill, it's going to take ages to dismantle the meter from the instrument and I don't know if I can do so without the complications of co-lateral damage. But I may well face this and take you up on your kind offer thank you. I'll be in touch.

MichaelG as ever thank you for your encyclopaedic knowledge of the internet and the expertise therein. I'm doing my homework even as you read this!

Best rgds Simon

04/01/2020 16:21:56

Good afternoon one and all, and best wishes for a Happy, Heathy and Productive New Year

Some while ago I had a windscreen chip and crack repair done, which included bleeding adhesive into the crack. If the adhesive is clear and has the same refractive index as the glass, then the repair is invisible.

I'd very much like to use the same technology to repair the glass of the VU meter of a vintage portable microphone mixer. Any suggestions what is a suitable potion, and where do I buy it please? Is the UV curing Loctite used for sticking rear view mirrors to windscreens the right sort of stuff?

Best rgds, and as always many thanks in anticipation

Simon

Thread: Precision 10MHz reference Oscillator.
22/12/2019 23:08:05

Impressed? That's not the half of it. What a neat project - congrat's Joseph.

Greetings of the seasoning

Simon

Thread: Machining a 70mm hole in steel
22/12/2019 23:04:36
Posted by petro1head on 22/12/2019 22:08:14:

To be honest not too bothered about the finish for this job but I get your point

Gas Axe. Definitely.

22/12/2019 09:38:05

Gas axe.

No, just allowing my agricultural background to take over.

Depends on how big the 65 mm (which I assume is material thickness) block is, also depends on how accurately you want to keep the hole diameter and surface finish -

First choice - quickest and most accurate - 4 jaw in the lathe, pilot drill, boring bar. First reserve first choice substitute face plate for 4 jaw.

Second choice if the block is too big to swing - milling machine and boring head. Slow and less accurate, or at least less reliably accurate in my hands, than the lathe

Third choice (getting rougher by the minute) pilot drill, holesaw in a mag drill, from both sides. Pushing the limits of the technology, but it'll go.

Fourth choice , yes the gas axe

Fifth choice - sub it out to someone with bigger machinery that I've got

Season's greetings all

Thread: Three phase Variac Internal wiring
15/12/2019 19:36:03

Ah hah, cunning!

How did you calculate the saturation voltage?

Rgds Simon

15/12/2019 18:56:20

Robert - thank you - I think you have confirmed the answer I'd thought. I'm more than slightly bemused how such an item came to be in this country, though the chap who gave it to me did work for a while in Canada. Why would he have brought this great lump home - we may never know. Unfortunately he's asked me to loan it back to him to run some antique 120 volts (American) Christmas lights - I've got to go and see him on Wednesday and break the news that this ain't going to work.

As for the suggestion of a swapsie, that might not be as far fetched as it sounds as I have family in Peterborough. I'll send you a PM and we'll see if we can work something out.

John - my test set up with a filament lamp works perfectly - provided I only put 120 volts on the input terminals. My input voltage comes from the big transformer, the tappings on this are such that I can only try 100, 120 0r 210 volts or stick the mains on it directly. With 120 volts on the input terminals of one section as a single phase auto=transformer I can twiddle the dial and alter the dimness of the lamp completely as one would expect.

I was curious to see if my theory about the saturation of the core leading to loss of control of the self inductance and thus input current met with any approval within the community. I tried it at first on 230 volts input but realised the current was ridiculous, so I'd imagined I'd got a shorted turn. But then I tried it on 120 volts and the current was sensible that scotched that theory. Besides,. all three sections behave the same.

So many thanks for your help, and season's greetings to all.

Simon

15/12/2019 15:12:48

Good afternoon, and thanks for the help so far. Firstly a picture of the whole gismo, just to show it is a three phase unit.

dsc_2149-1.jpg

The transformer right of picture is my "source" - it has a selection of secondary windings which means I can vary (to some extent) the input voltage to the variac under test. The scratty looking desk lamp is just a suitable load, and was diconnected when I was doing the "no load" current draw tests.

Here is a picture of the terminal arrangement for each of the variac elements:

dsc_2150-1.jpg

If you look closely at the solder remnant on the tags, you can see that the original wiring was connected to a tap on the winding, not the top end. Just as John says I thought if I connected to the end of the winding I could apply anything up to 234 volts and bob's yer mother's brother. Not so.

Here's another close up of the terminals for each stage - this time of the middle section so my test wiring isn't obscuring the legend.

dsc_2151-1.jpg

And lastly a better picture of the user interface terminals propped against the chassis -

dsc_2152-1.jpg

15/12/2019 12:57:04

Hi Bill, I didn't explain enough - I have three variacs stacked on a common frame, with the rotors connected mechanically to a single knob. I'll post another picture of the whole assembly later.

The terminal board (with extra extensive safety features!!!!!!!!) has a single input neutral, and three coloured line input terminals coloured red yellow and blue. Adjacent are mounted output terminals also coloured red yellow and blue, with a single black neutral that I would assume is connected to the input neutral as the whole thing is only ever an auto-transformer.

The photo above shows the top half of the terminal board with the red and yellow input and output terminals, also the black neutrals. Again, I'll put some more photo's up later.

So it's a three phase variac if I connect it to three phases - which I don't have! I had some idea to split the assembly 'and end up with three single phase variacs, but that won't fly because of the issue over the input voltage.

15/12/2019 11:56:07

Good morning all, and Seasons Sunday Greetings.

I have been given a three phase variac, but it's not all it seems.

Firstly the details:

dsc_2148-1.jpg

That little identity plate shows it as type no RB2L-G3M

Input 208 volts 50/60 Hz

Output 0 - 234 V 5A

When I stripped the covers off to discover if it was safe to energise, I found the wiring to the input and output terminals had been cut. I've freed up the mechanism and cleaned it and now have energised it but have run into a problem with the applied voltage.

If I apply 50 Hz volts at 115 volts to one of the three sections of the transformer across the windings. the static no load current is about 130 mA. I can vary the output voltage with the position of the slider all exactly as I would expect a Variac to behave.

If I increase the input voltage to 210 volts the static no load current hikes up to over 6 amps, and the magic smoke appears as the windings overheat. Turn it off and have a rethink!

If that input voltage figure is to be interpreted as 208 volts line to line connected in delta that would correspond to 120 volts line to neutral in star., which gets me into the envelope where the thing seems to be happy. Is that what the nameplate means?

I assume what is happening with my 210 volts applied directly across one of the transformers (ie star connected) is that the core is going into saturation, and thus the inductance of the transformer plummets and the current isn't controlled by the self inductance of the winding. Anyone got any better ideas?

Thanks as always in anticipation

Best rgds Simon

x

Thread: Myford Super 7 Metric thread cutting gears
12/12/2019 00:01:33

Hello Moderators, here's an oddity

According to the "latest forum posts" the last entry in this thread is from Brian. timed 11/12/2019 09:24:48.

But that isn't what I'm seeing above.

Uh?

Simon

10/12/2019 17:44:59

So - Thank you guys for your kind and positve vibes, and it all turned out well if I do say so myself.

Here's the picture I took of the two gear clusters I made before sending them off to sunny Denmark:

dsc_2143-1.jpg

As before, I have made the smaller gear on a stub, then a second gear cut as a plate wheel is soft soldered onto the stub. This time I made them out of EN32B, 'cos that's what I had.

Pleased it turned out well, and thanks for the encouragement off camera from Jesper and from Brian.

Season's greetings all

Simon

Thread: Case Hardening
05/12/2019 09:49:46

Good morning all,

Not sure case hardening is really about absorbing carbon into the surface layer of the parent at all. My understanding is that it is actually a nitriding process, which is why you don't need to quench the treated part to get a hard finish layer. Or do you need the carbon to capture the nitrogen into solution?

So bone meal has nitrogen in it, as does anything cyanide flavoured, but simple barbecue charcoal isn't (I think) going to do the whole chemical/metallurgical/structural alteration.

Any metallurgists?

Best rgds to all

Simon

Thread: Back saw for cutting steel and brass?
27/11/2019 14:35:12

Hello all, interesting question.

First observation is that you'll never get a pretty slot using a saw with set on it. So using hacksaw blades whether they're wavy set or a normal wood saw with side set ain't going to cut it, if you'll excuse the pun.

The slotting file is the right tool, and I seem to remember correspondence from Ketan a few months ago saying he'd bought some - inadvertently - and were they of interest. Might be worth a call. A slotting file is a thin file with no teeth on the faces, but teeth on the edges so it cuts sideways - or downwards if you hold it on edge.

A razor saw has also been mentioned - that's what the top saw in this pic' is:

xxx

dsc_2141-1.jpg

 

That's an Exacto razor saw, and it will cut brass but the blades aren't very hard and you'll lose the teeth pretty quickly. It's really intended for cutting wood, particularly balsa or similar.

The bottom one is a jeweller's backsaw - if you can find a source of good quality blades it'll cut anything a hacksaw would, as it's designed for cutting 9 ct gold which is pretty hard. The blades are removable from the brass back, and usually double sided, but beware of cheap and nasty blades they won't last as well as the razor saw. My Dad was a silversmith, we used to have periodic expeditions shopping for this sort of stuff round the Hockley Hill area of Birmingham, but I've lost touch with this over the last thirty years and I don't know where to buy these blades. I remember the good blades were expensive, but the cheap ones were absolutely useless!

The backsaw willl give you a good groove to guide the slotting file and remove the majority of the metal, but the blade on this one is only 0.35 mm thick so you need parallel cuts or follow with a narrow file to get a slot which looks in proportion. You used to be able to buy blades of different thicknesses.

HTH Simon

Edit - MichaelG has - as oft before - pipped me to the post about ARC's slotting files.

Edited By Simon Williams 3 on 27/11/2019 14:36:30

Thread: Myford Super 7 Metric thread cutting gears
26/11/2019 22:04:14

Brian, Jesper, good evening

I've spent a happy few moments with my trusty calculator and come up with the followingpresentation1.jpg

Sorry it's a bit small, I've had all sorts of fun and games converting a table in Word into a format the forum can accept.

Obviously my table only shows the pitches where the 29/16 or 31/17 gear is relevant. The error figure in the last column is the pitch error in mm per revolution compared with the nominal "correct" number. Of course we're quibbling about microns here, and arguably the limiting factor is the wear in the lead screw and halfnuts. But that just explains why the traditional 127 tooth gear isn't necessary.

Using a 31/17 gear consistently gives a greater error than the 29/16 gear I chose. I can't take the credit for that as I didn't do the analysis at the time, though it looks like we came to the right conclusion nevertheless.

Best rgds, let's post this and see if it's legible!

Simon

xxxxx

26/11/2019 12:03:01

My my my, thank you Brian for those warm words, JS did most of the thinking I just followed his instructions!

As ever your ingenuity in finding an alternative answer amuses me no end. I'm currently planning a house move so my playtime in my shed is somewhat curtailed, but I'll sit and work out what the error is for the useful range of threads doable on the Myford by using a 17/31 cluster as a comparison.

Your point about wrecking the internal gears of the gearbox is well taken - as is EGA's observation of the warning in the handbook. I'd just note that if someone is contemplating cutting coarse threads there is plenty here in the forum about using a mandrel handle to circumvent this problem.

FYI Jesper has been in touch and we have agreed I will supply copies of the 16/29 and 17/30 cluster gears I made for myself directly to him. I'm looking forward to hearing his M62 x 1.25 thread has come out right on the second visit.

And just in passing, I only got involved in this whole saga because I wanted to cut a 20 mm x 2.0 pitch thread in a nut to fit the U2 collets on my Deckel grinder. I was intent on making a U2 variant of JS's ER32 collet blocks for milling a hexagon on something. I'd cut 13 TPI and got good results - the collet closed up and all was well, but my interest was piqued by having read about the 33 tooth gear idea, so I made one but couldn't fit it. JS explained I was barking up the wrong tree, and the rest is history.

I'll publish a error table shortly, it's only a few minutes work with a calculator.

Best rgds Simon

Thread: Colchester Student Mk1 Won't Start
25/11/2019 20:23:19

Richard -

Have you got a neutral connected to the switch gear - I think I'd expect the contactors to need a neutral to the coil, not be connected line to line. But if they are line to line the point above about being connected to the transformed input phases and not to the false phase is valid. What voltage is your converter actually applying, and is it three phase at all?

If you are not familiar with machine electrics that might sound like gobbledegook, so can you tell us where you are, maybe someone with the relevant expertise can assist "hands on".

Good luck, you need a competent sparks used to working with industrial machinery. Keep your fingers out of the birds nest, them wires bite!

Thread: Myford Super 7 Metric thread cutting gears
25/11/2019 20:01:21

To continue my saga:-

We've worked out how to play tunes on the gearbox output ratio to achieve a much wider variety of TPI or pitch settings that the original set by altering the input mandrel gear. It's only fair to say that this is the essence of Brian Wood's book, and far be it from me to steal his thunder.

The difficulty we've created for ourselves is that the input (mandrel) gear for the MK1 S7 QCGB is this all in one double gear. The Mk 2 lathe has a demountable driver gear so (within reason) you can fit any standard change wheel to it and play even more tunes on the TPI chart.

So the two compound gears I made were as follows Here is a picture of the standard 30/12 set on the left, and my 30/17 set on the right.

xxxx

dsc_0538-1.jpg

I made it out of bronze because it is made in two parts - a 17 tooth gear cut on a stub shaft, then a 30 T wheel soft soldered onto the stub of the smaller gear. Besides , it looks pretty and I can recognise it easily in the drawer full of change wheels.

So the same principle applies to the gear I christened the 16 -1/2 tooth gear, which was a bit of a joke between me and the late John Stevenson. I don't have a photo of it, but it looks exactly the same as the bronze one above except the small end is cut for 16 teeth, and the larger one is cut for 29 teeth, but on a blank of the same outside diameter as a 30 tooth gear. This ensures that it meshes correctly with the existing tumbler gears - there's no adjustment on the centre distance - but runs at the speed of a 29 tooth gear - it's only got 29 teeth so it runs a bit faster (as a driven gear the smaller it is the faster it runs).

So far so good, but where do you buy one? Well, I only know one answer to that - simply there's the one in the picture in a drawer in my shed and I'll make a duplicate if you are interested. If so send me a PM and I'll explain further. I'm not too clear on the etiquette of touting for business openly on the forum - mod's please note I make no direct charge and all of the money goes to charity. It's such a specialist application I don't think anyone is making them commercially but if anyone with the technology fancies their chances be my guest. Indeed if Jesper knows anyone who can do this locally please have a go! Not sure if 3D printing technology is up to this, but some day someone will try it out.

So I hope that answers the questions remaining, if not let me know what's not clear and I'll try and fill in the gaps.

Good luck, and the arithmetic and more details are in the two threads referenced above.

Ooh, and Brian's book goes into much more detail, with pictures and set-up tables and I recommend it.

Best rgds Simon

25/11/2019 19:33:19

Jesper - good evening. Firstly my apologies for not picking up your questions sooner, I've been out of touch for a day.

So, if I may I would like to summarise what we think we know, and answer your question about obtaining the requisite gear.

I believe we have established that you have the older type QCGB, that's what the photo's of the lathe indicate, and the fact that you have a 30/12 cluster gear in the gear train on the mandrel gear suggests the same. What we don't know for absolutely certain is whether the lathe cuts the threads as indicated on the gearbox label. It's just possible that there is a mismatch here, and the gearbox cuts either twice or half the threads per inch that is indicated. This of course is when you are cutting an imperial thread such as 20TPI. The label inside the gear cover sows a seed of doubt in my mind, and I would just like to be sure we know where we are starting from before telling you what to do next. Can you try cutting a thread with the gearbox set up for (say) 20TPI - it needs only be a scratch pass to prove the gear train - and confirm that it is 20 TPI that you get.

I chose 20 TPI because it is the same thing as 1.27 mm pitch - and if the M62 nut you were trying to make is only fairly short you may find that using a 20 TPI thread instead of 1.25 mm pitch gives acceptable results. After all the error is only 0,02 mm per revolution - so if your nut is 10 mm thick the thread error is still only +/- 0.08 mm.

However, we can do better. ASSUMING the gearbox IS the old one, the gear train you have identified starts with a 30 tooth gear with a 12 tooth gear married to it to make a compound gear. This gives the thread per inch selection as per the label on top of the gearbox.

If we change the 12 tooth gear for say 18 teeth we'll get a different set of TPI values for each position of the gearbox selector levers. In this example the gearbox output is speeded up by 50%, so our 20 TPI setting will now cut 13.3 (Edit - I got this wrong in my initial post - it's less TPI because the lead screw is running faster.  OOPS!)  TPI. Using other input gears gives us control over the threads on the workpiece over and above the "normal" (standard settings.

One such choice is a 17 tooth gear. If we change the 12 tooth gear to be 17 teeth, and set the gearbox levers in the positions for 24TPI we get 16.94TPI, which equates to 1.499 mm pitch. The arithmetic is simple pro-rata gear ratios, but work it out in TPI and then convert to mm pitch last.

So that's a nice accurate answer for 1.5 mm pitch. also 3mm, and 0.75 which is an oddity but it shows the principle. How do we go about getting 1.25 mm pitch.

Do the same arithmetic, and you find you need a 16-1/2 tooth gear. Now whatever I've said before, I haven't worked out a way of making a single non whole number gear. But it isn't a single gear we're working with , it's a compound pair. The other gear of the compound pair was always 30 teeth, giving a 1 : 1 ratio with the chuck, but it doesn't have to be.

16-1/2 : 30 is very close to 16 : 29, so if we change the input gear to be 29 teeth meshing with the tumbler gear, and now 16 teeth driving the otherwise standard gear train going down to the gearbox input we get jolly close to 1.25 pitch. And 2.5, also 0.625, another size we're likely never going to want!

Enough for a moment, this post is long enough already, I'll continue in a second instalment.

 

Edited By Simon Williams 3 on 25/11/2019 19:37:41

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