Myford Super 7 - electrics/motor

Hello,

I’m new to the hobby and have bought a Myford Super 7 based on the huge following, availability of spares and it was the right price!

There was a n issue with the switch and it came supplied with a Dewhurst reversible switch. On investigation, the previous owner has bypassed the switch and the power runs direct to the motor, controlled by the plug socket switch. It works but not ideal by any means.

I think the motor is an aftermarket job, Delco CS 28170. It has three power inputs, earth, positive and a negative.

I’m now looking at wiring in the Dewhurst but none of the literature I can find aligns to what I own!

Any advice on how to proceed?

Thanks,

Chris

Google doesn't seem to have any direct link for that motor, and anyway aren't they mainly a car electrics supplier?

Please could you post some photos of the motor and switchgear so we can get a better idea of what you have?

My Super7 came with the Myford fitted single phase motor which was a dog to be honest. Replacing it with a decent 3phase motor and VFD has transformed the lathe..

Welcome to the forum Chris. How post photos described here.

First step is to identify the type of motor, for which pictures will probably be necessary unless someone recognises the Delco part number. As the motor could be old, it's Sherlock Holmes time.

Particularly useful is a photo of the terminals inside the terminal box, which should have a removable cover. If not, the motor will be hard to reverse because reversing is done by swapping over one of two pairs inside the cover. The exact wiring depends on the motor - there are about 4 different types.

I'd put the Dewhurst in a museum, or sell it to a Myford enthusiast who wants an authentic look. They weren't particularly good switches when new, so replace it with a modern one.

If the motor can't be reversed and it matters to you, John's suggestions is a good one - replace with a 3-phase motor and VFD, kits available with instructions. You get smoother running, speed control, and reverse.

Dave

Chris

Important to remember the chuck is screwed onto the spindle so if when fitted with a reversing function careful use is essential, you don't want the chuck coming from the spindle when spinning.

Some Myford users have modified the chuck retention so it is more secure, searching the Forum should bring up the post.

Emgee

Welcome to the party Chris !

The dewhurst is easy ! Top left is No1 Live in, No2 Start winding, No3 Neutral, No 4 unused. Top right No5 run winding, No6 Start winding, No7 Run winding, No8 unused.

No 2 & 6 may have to be swapped for the switch to show right ! There are many colour codes and terminal names so tell us what you have and it should be easy. Best wishes Noel.

Hello,

Thank you for all the kind responses and words of advice. I’ve uploaded a few pictures of what I think are the key bits.

I bought the lathe from a deceased estate so welcome any information anyone has on it. First stage is sorting the motor/switch out though then more daft questions will follow!

Thanks again,

Chris

Before you spend/waste any time wiring in the ancient Dewhurst switch, carefully inspect the contacts inside the switch. They commonly burn out and become unusable over time. That is quite possibly why the previous owner bypassed the reversing switch.

You don;t really need reverse on a hobby lathe. I have used my old Drummond lathe for over 50 years without it. I have reverse on my ML7 but have never once used it. The only time you might really need reverse is if screwcutting metric threads on an imperial lathe.

You might be better off to leave the reversing switch until later and carry on without it. Wiring in a simple stop/start push button switch (available online cheap) would be a good safety thing though. As a beginner there is plenty more you need to do and learn first before really needing reverse.

Thank you again.

I got the Dewhurst with the lathe, that’s the main reason for attempting to use it. I’m not actively looking to reverse the motor currently as that’s well outside of my current abilities. So I’ll follow the advice here and avoid for now.

In terms of the motor, what’s the view?

Thanks,

Chris

A close inspection would seem to show the start windings are tapped from the run windings - this being so then reversal in simple terms is not possible. But it appears to be only 1/4 Hp ? if so then it is to small, n S7 should have a 1Ph 3/4Hp or 3Ph 1/2Hp. Wire it up as shown on the cover with out the reversing switch and play with it.The important thing is to make sure it has a good earth connection.  The machine will not take heavy cuts and may not run at top speed but will give valuable experience. DO NOT overload the motor or you will quickly cook it ! When money is available look for a secondhand 1ph motor, there should be many about as everybody changes to VFDs with 3Ph. If there is plenty of money then you may consider a VFD, though I have 2 S7s and have no intention of changing. WHY VFD ? Variable speed, handy bit in no way vital. Reversal of direction, on a lathe with a screw on chuck ? Smoother drive, theoretically correct ! A very complicated electronic kit with plenty to go wrong and need setting up, unlikely to be happy in a damp shed. Costly, new motor and unit ! You must choose ! Good luck, Noel.

Edited By noel shelley on 08/05/2023 10:58:34

Welcome to the forum.

I have had my Super Seven for a number of years and have not used reverse mainly due to the chuck being screwed on to the spindle nose. When run in reverse there is the chance of unscrewing the chuck. If you ever do need reverse please be very careful if using a chuck or backplate. A collet would be safer but just be careful.

A number of years ago my motor burnt out and i bit the bullet and changed to a three phase motor and vfd. The cost was similar to a quality single phase motor but it has transformed the lathe machining performance.

As there doesn't seem to be a capacitor it is presumably a motor where the start winding just has a high resistance compared to the run winding to give some phase shift. With only 1/4 hp the lathe is definitely underpowered. And apart from anything else the mains cable looks old and horrible and ought to be replaced!

I fitted a 3ph motor to my S7 only partly for variable speed, but mainly to get smoother operation. With the single phase motor the higher speed range on the motor pulley was essentially unusable as the lathe vibrated so much. Going to 3ph has transformed the machine, much smoother and quieter. Single phase motors inherently have lumpy torque.

The Capacitor is shown in the diagram and can be seen in the picture of the motor ! Noel.

I agree reversing this motor is likely much more trouble that it's worth.

Only three terminals in the box and a diagram showing the start winding is tapped into the run winding mean this design isn't simple to reverse! Unlucky: it's more usual for the both ends of the start winding to be brought out to terminals, and these are easy to reverse once the terminals are identified.

The photo is blurred, but as Bazlye says, ¼HP is the bare minimum power for a lathe of this size. ½HP or ¾HP is more usual. 1HP is a shade too much poke, and more than 1HP unwise because of the high wear rate and risk of damage when the lathe is crashed.

That a Super 7 won't run in reverse isn't a huge problem, and many owners with reverse avoid doing so because it risks unscrewing the chuck. Lathes with bolt-on or cam-lock chucks do forward and reverse equally well, which is very useful at times, but not essential.

The machine will work plugged into an ordinary mains socket, but this is bad practice today. It's usual to fit a combined Emergency Stop / No Volt Release switch. Various, styles such as:

The big red emergency stop button is wonderful if the operator gets caught in the works, especially if wifey has to rush in and cut the power. NVR stops the lathe restarting unexpectedly after a power cut - a common cause of accidents. Look for NVR on the internet - widely available from Amazon and others.

Dave

The 1/4HP motor will be enough to get you started for the time being. As Noel said, it might struggle with the S7's top speed due to the high pulley ratio, or with deep cuts (say 100 thou etc) at higher speeds. It is the rubber mounted version so should run smoothly. Looks like it has been a bit of a quick add-on after the original reversible 3/4HP motor died.

Can someone explain how any of the many earlier model engineers using Myford 7 lathes with a single phase 1/2 or 3/4 HP motor were able to build such accurate and functional models ?

Emgee

Edited By Emgee on 08/05/2023 11:33:04

The same way their predecessors with treadle machines did; by operating within its limitations.

A VFD driving a 1Kw 3 phase motor won't make a good Myford any more accurate, but it will be nicer to use and a bit easier to consistently achieve good results - like tweaking the speed slightly to make the drill cut better.

By the superhuman greatness of all things Empire and ancient. Kings in golden carriages and Manx Nortons and all that.

And by rubbing a block of wood against the chuck to control its movement.

One thing for sure, you need to tidy up the 3 core cable and according to the diagram in the terminal box lid the motor is not reversible. Not to worry as it is rarely needed if ever at all, I've had my lathe about 30 years and never had the chuck wind off or attempt to wind off. But do get yourself a No volt release device as pictured by Dave for your personal safety. The Dewhurst switch contacts are just not man enough to be used as the ON / OFF, they work well as a direction switch in conjunction with proper motor starter, selecting direction of rotation when the motor is stationary. Regarding the motor size many small cuts often, you learn to live with it, just enjoy the hobby get making swarf. Later you might pick a bigger motor if its actually needed, and when time / money comes, fit an inverter and 3ph motor. John

I fitted a very similar looking motor carrying an AEI Houston label to mine, three phase with a VSD but 2 pole to rev the old girl up a bit. Very successful, until a small but persistent spiral of swarf managed to make its way through the ventilation hole next to the terminal box.

Sparken blitzen mit ausgepouf.

It needs its ventilation but you might like to cover the hole.

HTH Simon

PS I wouldn't question 1/4 HP - yet. Plenty of umph to get into trouble, run it and learn its limits for a while.

I've had a super 7 with a 1/4 HP motor on it, the machine was 3 phase when I got it cheap and very secondhand and a smaller single phase motor was all I could find secondhand and afford at the time ( well before inverters were widely available). It did struggle with the top two speeds, in order to use them the machine had to be run for a while to warm up. I used it for a few years like that and never did change the motor for anything bigger, it was obviously underpowered really, but perfectly useable with care and sharp tools. The top speeds were only used a few times to drill some tiny holes in brass, I'd be inclined to just put a new cable and switch on it and use it until a suitable motor turns up, even with the small motor on it should have around the top speed of an ML7 available, and look what fantastic things have been built on those over the years.

In the interests of not starting another round of lathe wars I should point out that fantastic things have been built on Mini lathes,Chesters, Warco's Boxfords, Raglans, Drummonds and a host of others!

Just noticed the motor protection device is called a Thermotron, straight out of Dan Dare! (am I showing my age again!)

Edited By Dave Wootton on 08/05/2023 13:19:50