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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: What solenoid to use?
15/10/2019 19:55:57

Try googling "belimo actuator" for a wide range of damper actuators - essentially a motor driven crank that turns trough 90 degrees. Other variants are available but looking at ebay at the moment there seem to be quite a few on offer around the £25 to 30 sort of mark.

HTH Simon

Thread: Tingling from Myford Super 7
11/10/2019 14:29:15

I know I keep banging on about this, but the idea that there might be enough resistance in the earth path to allow any item within the installation to reach a voltage sufficient to experience a tingle needs de-bunking, as it flies in the face of everything the Reg's have to say about earthing.

Sure, the earth path will have some resistance, but the installation must be such that the potential reached by any exposed conductive parts (metalwork) is always below the safe touch voltage, even under fault conditions (whilst blowing a fuse). Safe touch voltage is usually deemed to be 25 volts RMS, that won't give a tingle though the actual requirement is that anyone touching an exposed metal surface must not be given sufficient shock to cause an involuntary movement.

This places some pretty tight constraints over what earth path resistance can be accepted, and rightly so.

Cows being very susceptible to electric shock there are specific additional requirements for livestock pens, farms etc.

11/10/2019 11:17:27

As has been said before, you have two faults.

The leaky cable under concrete is fault 1, but you still have to find fault 2 which is the inadequate earth connection to the frame of the lathe - and possibly other loads. Please don't ignore the second fault!

HTH Simon

Thread: Bright EN24T steel vs Black EN24T for cutting gears
08/10/2019 22:26:44

As alluded to above, I assume it doesn't need saying that you don't want to let your nice sharp involute cutter anywhere near that nasty black mill scale. It'll knock the edge off the cutter quicker than you can say pickle.

There, I've gone and said it now...

Thread: Tingling from Myford Super 7
07/10/2019 17:08:01
Posted by Maurice Taylor on 07/10/2019 15:03:59:

If your house is wired using PME system ,there could sometimes be a potential difference between the earth you’re stood on and the earth your lathe is connected to, possibly giving a slight tingle.

Best advice is isolate it and get a qualified electrician to check it.

Well, I'm not saying it can't happen, but it would be a strange and significant fault in the supplier's PME system to allow sufficient potential difference between neutral and earth to be detectable by the "tingle test".

The point of PME (parallel multiple earth) is that there are many paths of cross connection between neutral and earth; all of them within a zone would have to fail simultaneously to get a "tingle" as described. Not to mention a few house fires....

No. Go looking for a failed or broken earth connection. The last one I did was caused by the earth pin socket pin not making contact in the socket outlet (13amp socket at the wall).. The machine earth bonding was all connected together but the whole lot was floating from the house earth because the earth pin didn't connect. In that instance the motor was connected to a VSD so that was the cause of the leakage current. If I've understood correctly there is only switchery in this application, so there is no excuse for enough leakage current to cause the symptoms as described.

But that's not the whole problem in this case, you've got a second fault (earth leakage current) as well. Come what may you need an adequate earth connection and this is absolutely a text book example of why.

HTH, do let us know how you manage to resolve this.

Good luck Simon

07/10/2019 12:58:17

Turn it off at the mains, unplug it or isolate it or whatever it takes to make sure it can't be energised. Without wanting to get too melodramatic, this is a potential (no pun intended) emergency and you MUST isolate it. NOW.

The symptoms you describe are of two separate unrelated faults. Firstly you have an earth leakage fault of some kind, and sure that Dewhurst switch is a likely suspect, so are the motor internals.

You also have a second fault, in that the frame of the machine (lathe, switch etc) is not earthed.

My suggestion is that you get someone with experience of looking for these two faults to have a look, as you need some specialised test equipment and the knowledge to use it and interpret the results. If you are in the West Glos area send me a PM and I'll gladly help.

As Robert has said, is is very definitely something you should be worried about.

Isolate it and call for expert help.

HTH Simon

Thread: Universal Joint Alignment
02/10/2019 22:29:13

Thank you Neil, not least for correcting my silly but very annoying spelling mistake.

I'm more than somewhat confused by this now - Neil you are right in quoting the link you have used, and it says what you say it says, but...

Along side the text is this picture, which kinda speaks for itself.

330px-cardan_shaft.jpg

There is also another paragraph later which says :

A double Cardan joint consists of two universal joints mounted back to back with a center yoke; the center yoke replaces the intermediate shaft. Provided that the angle between the input shaft and center yoke is equal to the angle between the center yoke and the output shaft, the second Cardan joint will cancel the velocity errors introduced by the first Cardan joint and the aligned double Cardan joint will act as a CV joint.

(My italics)

Duh!

x

02/10/2019 21:12:59

Hello good evening, and my thanks to all those who have taken the trouble to respond.

I've sort of got the answer I was expecting - I haven't done the maths but I would expect aligning the yoke parallel would give the best cancellation of the angular velocity variations. However here is a re-print lifted straight out of the parts list for the machine in question.

metrac rear pto shaft 001.jpg

Which clearly shows the yokes at right angles. Don't know why.

I've had this shaft out on a previous go-round, and I'm pretty sure its got a master spline so it will only assemble as shown. I think I'm going to have to just accept that I don't understand.

Many thanks once again for everyone's interest.

Best regards Simon

Thread: Thread Cutting on Myford Super 7
01/10/2019 12:25:08

Ah Hah! That'll do it!

Many thanks Tom for the update, it's always nice to know how these things resolve themselves.

Now we're looking forward to some pictures of the EIP (engine in progress) pretty please

Best rgds Simon

01/10/2019 10:16:36

Tom, good morning.

24TPI isn't a fine feed within the meaning of the phrase in this circumstance, and you don't need to reverse the 17/57 gear pair on stud A to get it. Reversing this gear gives you the range of fine feeds as marked on the gearbox label, but we're talking about a few thou per rev (13 down to 1) such as you would use in turning a parallel surface.

If setting the top lever to centre, and the sliding handle to third from the right doesn't get you 24TPI there is something else wrong. Could you let us know what thread your scratch test showed, maybe we can reverse engineer the cause from the symptoms.

dsc_0529-1.jpg

Handily my picture happens to be taken from the very angle that lets the top lever obscure the 24TPI setting on the label.

What thread have you actually cut, and if it is very fine indeed is the gear on stud A already reversed?

Otherwise can we have a picture of the gear train from the mandrel down to the gearbox input gear cos' the explanation's there somewhere.

HTH Simon

Thread: Universal Joint Alignment
30/09/2019 19:44:03

Good evening all. and a jolly wet one it is too.

I have been spending some time recently rebuilding a tractor, and have come to servicing the PTO shaft from the front mounted transfer box to the rear splined take off. The shaft is a simple cardan shaft with spider type universal joints at each end and a central sliding spline. The two end points run in fixed bearings and are on parallel axes.

The yokes of the two UJ's are presently assembled at right angles on the floating centre shaft. My (limited) research suggests it is normal to align the two yokes so they are parallel, to minimise torsional vibration. OK it's a tractor and a 540 rpm shaft is hardly a precision application, but what is the logic of this?.

Does it matter, and why?

Looking forward to some advice, so many thanks in anticipation

Best regards Simon

PS (edit) Just pressed the go button and noticed the spelling mistake in the title.  Please Neil/Jason could you add the missing "r" ?  Many thanks

 

Edited By Simon Williams 3 on 30/09/2019 19:45:22

Thread: Are there any left?
21/08/2019 22:09:54

Thank you Robert, in a previous existence I passed through Nottingham maybe two or three times a month, and frequently stopped in to see what delights Anchor could tempt me with. These days I need to make a day of it to go there, so I'm pleased to hear they made it albeit on a survival kit regime.

Their museum was something to behold, and I'm sorry to hear it was lost. Such is life.

I was seriously tempted by the the jet engine (a Gnome if I remember right) but it was a bit (quite a bit) more money that I wanted to sink. Nevertheless, what an experiment!

Rgds to all

Simon

21/08/2019 20:37:52

Rolling back to John Haines' post above, Anchor Surplus had a nasty fire about two years ago. Are they back up and running again?

Rgds to all,

Simon

Thread: Anyone good at fault finding with amplifiers here?
18/08/2019 00:45:08

First suspect is dried out and leaking electrolytics, but TR203 base to emitter voltage at 0.8+ volts says it's cooked. Doesn't necessarily say why. TR 205 is also off or nearly so, 2.4 V across R211 doesn't look right.

Shouldn't need a matched pair for TR203/204 (edit correction 201/202) to get a stable and usable system, though it may be needed to get the distortion/noise spec. If you want to borrow a distortion meter I've got one.

That 21 volts negative on TR203 collector looks wrong, (80 v or so across R209) confirms that TR203 is not a happy bunny. Looks too far negative, should be nearer mid rail. But TR201 and 202 are nearly completely off, as revealed by + 67V on their collectors. Long tailed pair like this (even if upside-down) should have collectors mid rail or thereabouts. Can't hurt to pull C204 and replace it. Ditto C201 is suspect.

Keep us posted as to progress, do.

Best rgds Simon

edited for correction in italics - though the same is true of TR203/204!

Edited By Simon Williams 3 on 18/08/2019 00:51:42

Thread: Arkwright Scholarship
16/08/2019 21:16:46

My thanks to all of you who took the time to answer, as ever some excellent ideas have come out of this. I am looking forward to the experience of having a willing and eager apprentice albeit only for a couple of days. I may even sweep the floor before we start.

Although the suggestion isn't directly connected to those ideas detailed above, this exercise has broadened my mind and I think I can find him something to do related to his interest in competitive archery. Either that or possibly following the suggestion above about some kind of third hand or PCB manipulation gadget. We shall see.

So thanks again for all the expertise and suggestions.

Regards to all

Simon

15/08/2019 22:39:42

My nephew has been awarded an Arkwright Scholarship.

His father, realising that his son has had little or no experience in workshop practice (though he's totally buff with an Arduino) has asked me to show him the fundamentals of cutting metal. And welding it back together again.

I'm totally OK with that, except that I would like to give him a lathe-work exercise that meant something and wasn't going to be bunged in bin 13 in a year's time.

When I did something similar (a long long time ago) I was given a drawing of a simple spindle, with diameters and shoulders and lengths, and had no end of fun showing I could do it better than anyone else in the class. I was that sort of teenager, Sorry!

My confreres made a plumb bob to take home. I could do this, and it's the best suggestion I've got so far. But my nephew knows about things like angles and pendulums (pendula?) and will have written the software for a digital angle gauge before I can say vernier protractor.

Any suggestions for a "take home friendly" example piece I can set him? I want to be able to spend not more than a day on this, and then spend the second day morning with a mig welder and in the afternoon we're going to "do" metrology.

It's taken me 60 years to get here, and digest it into 2 days???? What Are The Young Coming To?

Ideas please?

Rgds to all

Simon

Thread: Centec 2A riser block
14/08/2019 20:02:23

Gary, good evening and thank you indeed for putting the pdf files of the dovetail dimensions up for us to see. Most helpful.

I've just got a tractor engine to rebuild and then maybe I can back to this project.

Best rgds Simon

13/08/2019 22:39:24

Ooops - misinformation alert!

Sorry folks, Automills come as Mk1 and Mk2, not A.B.C etc.

My apologies.

Simon

13/08/2019 22:21:30

Gary - I would be very interested to see a copy of your drawings, and I have sent you a PM with details.

I have two Centec Automills - an "A" and a "B" - and the vertical head without the quill. This fits directly onto the Automill (A) but not the type B as the dovetail in the column is wider. I'm sure you knew that but others less familiar with the marque may wonder what the difference is.

I bought a lump of EN1A leaded a little while ago to make a riser/adaptor block - the job would be immensely easier with the drawings to hand.

Best rgds Simon

Thread: Start of Tom Senior refurbishment.
11/08/2019 23:50:20

Hi again, serial number on mine is V3485, making it 1974 vintage, Your s/n at 2961 is a whole lot earlier, does this mean that Mr Senior decided to ditch needle rollers for the driven pulley and go to a bronze bush as an improvement? It does seem to indicate that my assumption that needle rollers and a spline drive is later is wrong!

Interesting stuff, what!

Like the spindle/quill.

Rgds Simon

Keep taking the tablets (out to the shed).

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