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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: Myford Super 7 Metric thread cutting gears
24/11/2019 14:18:55

Ah ha!

Hello again Jesper, and thanks for the pictures. You obviously sussed out how to load them!


The plot thickens! Because the label you show from the inside of the gear cover isn't the right one! That label belongs with the standard Myford metric banjo kit, which was marketed to go with the NEWER gearbox, not the one you and I have got. The 2:1 gear reduction factor has to be taken into account.

So here is a picture of the label inside the cover of the gearbox I have.


If you have followed the links I showed earlier you will have realised that this is irrelevant, as using the 17 or 16-1/2 compound input gears sidesteps this problem.

HTH Simon

24/11/2019 13:06:23

MichaelG - thanks for your contribution, that's a very neat solution to the problem. However one of the main advantages to using substitute gears on the mandrel and retaining the other (standard) gears taking the drive to the gearbox input gear is to retain the availability of the fine feed function.

Brian and I examined the pitch error introduced by using 17 and 16-1/2 tooth gears, I'm happy the error is insignificant and within the normal working tolerances of the single point screw cutting technique.  There is a summary table in one of the threads referenced which lists the theoretical error.

There's nothing not to like, apart from the intricacies of making these compound gear sets.

HTH Simon

Edited By Simon Williams 3 on 24/11/2019 13:07:45

24/11/2019 10:19:50


The explanation is in the two threads I have referenced.

No, I haven't worked out how to make a half tooth - well not intentionally anyway. The key to this is that the gear cluster is either a 17 : 30 or alternatively 16-1/2 : 30. as a compound pair. You need both sets to achieve the whole range of standard metric pitches for the sort of sizes a Myford owner might encounter.

16-1/2.: 30 is almost exactly 16 : 29, so that's what I made. John Stevenson worked out for me how to make a 29 tooth gear on a 30 T blank so it would mesh correctly with the tumbler gears. Details are in the two threads referenced above.

Works a treat, and I'm fairly certain that's what Jesper needs to solve the pitch error problem he has encountered.

Rgds Simon

24/11/2019 09:33:51

Good morning Jesper, hopefully Brian Wood will chip in shortly, can I suggest you need a copy of his book "Gearing of Lathes for Screwcutting" which covers this in detail and answers the questions you are asking. Copies usually available from Arc Euro and also Amazon.

Essentially you need the magic gears, but I suspect from the date you have the early version of the quick cutting gearbox, the difference is a 2:1 reduction in the later box which means for you that you need a 17 and a 16-1/2 tooth gear on the mandrel to cut accurate metric threads, not the 34 and 33 tooth gears. If you can work out how to post a picture of the right hand side of the gearbox we can determine which gear box you have, and hence which gears are needed.

[Edit:  the 30/12 cluster gear in the gear train you have described in your initial post confirms that we're dealing with the older style gearbox.]

The 16-1/2 tooth gear sounds mighty odd, but don't worry all will be explained. You might like to do a bit of back ground reading on the subject here:

QCGB1 should take you there


QCGB2 links to it.

To post a picture you have to upload a JPG to a site album first, then reference it in your post. So , log in, go to Albums on the header and start a new album giving it a suitable name. Now up load your picture in jpg format, it helps if the file size is sensible but I think I've read that the forum software sizes the file anyway if needs be. Now you can write a forum message, and include your picture by using the little camera icon in the message header. This opens a screen where you browse to the picture you want to include in the album you just started, and then pastes it into your message for the rest of us to see. Hope that makes sense. and if I've missed anything out please could those with more knowledge correct my summary.

Hope that helps, this is a subject with plenty of reference stuff on the forum, so I'm sure we can sort out the problem you have encountered.

Best rgds Simon



Edited By Simon Williams 3 on 24/11/2019 09:42:53

Thread: Inverters and stop switches
06/11/2019 20:06:30

Simple factual answer to the question as stated - "could the e stop be wired into the single phase supply" is "Yes!"

But the question deserves some more thought than that, and the pro's and con's of putting an E Stop in the supply need a bit more consideration.

Firstly, my apologies if I've missed the relevant post, but I don't think I've seen what sort of machine this is. This arises because I think the proper answer to your question needs a rudimentary risk analysis to inform the design decisions. If the machine is something nasty and dangerous, then the risk of injury is offset (controlled) by being able to stop the machine quickly, and switching off the mains supply won't necessarily give you the optimum control. If your arm is in the mangle then having an active machine braking function activated by the emergency stop would probably be a good idea.

If the hazard is of the machine going berserk because of the inverter losing control then shutting the mains off is your only option. For the milling machines and lathes I have in my shed I think this is a very unlikely that a modern good quality inverter is going to go doolally, so I have the E Stop function as a stop signal to bring the inverter to zero frequency and with DC braking if appropriate. The inverter stays energised so it can do what it needs to do to effect a rapid stop pf the offending machine.

So the short and simple answer to your question is "Yes" - you can connect some sort of E Stop functionality to remove the mains supply from the machine motor, but my preference is to use the extra control facilities of the inverter to give me a quick stop function and for this I leave the supply on the inverter but tell the inverter to stop the machine. There's a big red latching button on the machine within reach, and if I bang it the machine comes to a stop whichever way it is configured.

Horses, as they say, for courses.

Hope this helps Simon

Thread: Pulley flank angles - help !
30/10/2019 17:32:29

Another vote for 34 degrees or something close from me.

I've read that the included angle is (slightly?) dependent on the radius of the vee pulley groove - the tighter the bend the less the included angle. Whether it's significant and to what extent the default 34 degrees figure needs to be modified is very likely something Mr Fenner's drawing office keeps in a safe place.

I've made Z and A section pulleys of a variety of diameters using 34 degrees included angle and been happy with the results.

HTH Simon

Thread: AVO 8 Mk2 meter wire size
30/10/2019 17:25:12

Hi Roger

I've got a Mk3 in the shed, and it's been sat on a shelf for about 30 years. I pulled it down to admire it not long ago and realised that the needle was sticky. Pulling the back off shows very fine iron filings aggregated to the magnets in the coil gap.

On one of the radio/electronics forums I was advised not to take the magnets off the movement, as cycling them through the magnetic remanence path of removing them and replacing them will change their strength. These are red eclipse pot magnets before the days of rare earth.

It may be an old wife's tale, but if so it's well entrenched in Avo folklore that removing the magnets is a one way trip.

If you know different or have a cunning work-around do tell!

Best rgds Simon

Thread: Lifting A Tom Senior Light Vertical
17/10/2019 21:59:50

Good evening again, looking for some advice please.

I am planning a house move, and included in my goods and chattels is a Tom Senior Light Vertical.

The question arises of how to pick it up safely. I don't like the thought of putting a sling around the cast iron bar at the top of the machine where the head is attached - all of the weight has to be carried by those two little castings clamping the head. Or am I being over-cautious? Having the casting crack would be the end of Mr Senior.

I moved it on a pallet the last time, but of course it's top heavy.

Any thoughts?

Thread: Limiting pressure to a gauge
16/10/2019 22:32:51
Posted by vintage engineer on 16/10/2019 21:39:22:

I am rebuilding a 1910 5 litre petrol engine. On start up the oil pressure peaks at 70 psi but the running pressure is 15 psi.


Is this because the oil is viscous when it is cold, or perhaps the engine is a bit tight yet and will slacken off when the running in process is complete.

Cure the problem, not the symptoms.

I'm uncomfortable with the idea of dumping oil flow back to sump during start-up, that's when you most need the oil in the bearings where it belongs. High pressure on start up suggests the oil isn't getting where it needs to be - or at least not in the quantities it should. I'm assuming the oil pump is a positive displacement device so the rise in pressure indicates a restriction in the flow around the engine. If it is actually caused by the oil being a bit thick and treacly when it is cold then there are other oils to choose, at least for the running in phase.

I'd fit a higher scale pressure gauge as a temporary measure and see how this problem develops as the engine hours accumulate.

HTH Simon

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.


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)



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.


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

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