Myford Metric Lathe Leadscrew

The first reply to the OP from Rod Jenkins answered the query correctly. The lead screw is 8tpi - unless since the demise of Myford at Beeston I'm pretty certain there was no such thing as a totally metric Super Seven.

I converted my original imperial S7 to metric many years back and tried to source a metric leadscrew at the time - obviously to no avail. I have the 21 t gears as Noel suggests and they have proved more than satisfactory when metric threads have been cut (not often it has to be said!)

Rod has it in one

Tug

Some, mostly older and higher quality brands, dies have a tapered end and a flush end where the threads come full to the face of the die with just a small chamfer on the very first tooth.

But I did notice using a borrowed set of CEI dies yesterday that they have the long lead-in taper on both ends. Possibly to spread wear on cheaper carbon steel dies by sharing the work between two ends over time?

Hi John just to answer the lathe is without quickchange gearbox but it has the full set of metric change gears so quite a lot of work to switch between threads if say making an adaptor. On the other hand it's also got the full imperial range. The tailstock has metric scale and so do all micrometers.

Edited By Nick DoubleYa on 30/12/2022 13:05:07

Myford-metric or name it imperial-metric is accurate enough for model enginering but it is not metric. Niko.

Niko,

I can't disagree with you from a pedantic viewpoint. However, if you look at the calculated results (Actual) of the Myford thread cutting chart, could a metric lathe of similar size cut a more accurate thread?

Regards,

Rod

Of course you are right Rod, but raised metric I was learned to use a 127 change wheel, its how I still do it. Niko.

There is a 127T gear available for a Myford 7 Series (I had one, but never used one so don't know if it would fit inside the gear cover.

That should give an exact conversion from Imperail to Metric, or vice versa.

My lathe (Not a Myford ) has a gearbox. and uses a 120 / 127T compound as an idler so can be used in either configuration.

Although as Rod points out, an error in the 4th place of decimals is of little consequence. How many times can we screwcut to that degree of accuracy /precision? )

An error of that magnitude might only become evident on a LONG thread, if the Leadscrew is of equal or greater accuracy..

Howard

All a bit moot when the leadscrew on a hobby lathe is not accurate to even 0.025mm when made. They are just a mass produced rolled thread so no great accuracy. The gear ratios are the least of the worry!

Not forgetting to throw in possibly 50 odd years of wear on the Myfords leadscrew

You would also see the length of the thread change by some of those errors in Rod's chart if you cut it in the depths of winter and then measured it in summer

Edited By JasonB on 31/12/2022 07:37:22

S7 leadscrew is screwcut not rolled thread, for what it's worth.

I'm not sure about this and seem to remember Myfords used threadrolling.

Can anyone elaborate?

A murky subject. I have a book published about 1930 aimed at British purchasers of industrial lathes. Quite interesting for many reasons, and it it points out many reasons for avoiding the domestic product of the day. For example, it suggests the British practice of joining a long queue to buy an expensive well made manual lathe intended to last 60 years is daft at a time when Johnny Foreigner is making rapid progress with automatics. The author was right: manual lathes are rarely used in production today, having been supplanted by hydraulics, cams, numerical control, CNC, and machine centres etc. Factories full of manual lathes disappeared after WW2.

Anyway, pretty sure the book mentions almost all British lead-screws at that time being made by a specialist Bristol firm, unfortunately not named. I think the better ones are made by rolling and grinding, not by screw-cutting. Rolling increases strength and grinding provides accuracy. Makes sense to me: lead-screws are common items, and it would be financially unattractive for even a big firm to make their own. Myford might have made their own lead-screws, but I think it unlikely.

Does anyone know what was made by Myford in-house? I'd expect them to have machined bought-in castings, fabricated things like the compound-slide and tool post, and then assembled finished lathes from many other bought in parts. Brooks Compton motor, Dewhurst switch, BICCC wiring, Pratt Bernerd chuck, Timkin bearings. ICI paint etc. Unlikely I feel they made belts, gears, oilers, fasteners or anything in the tool kit, such as spanners and the oil-can. The firm designed and produced an excellent affordable lathe, but I think they only did the important things they needed to be good at in-house, and didn't waste time and money producing components available cheaply from other suppliers.

Dave

I don't know about Myford's production method for their leadscrews, but I do know that Boxfords were cut on a Jowett "thread whirler" - basically a thread milling machine - in the early '80s when I finished my apprenticeship there.. Broadbent lathe screws were made by a specialist company in Brighouse - Halifax Rack & Screw - who also whirl threads. Another of the suppliers I used in a later employment whirled screws for Parkson milling machines.

I fitted my S7 with a new leadcrew sourced from the Myford spares outlet when I fitted it with a screw cutting gearbox. It may be possible to get some clues on how it was manufactured from a close inspection - the tailstock end has seen no use since I fitted it.

My fords did seem to make a lot in house, from what I recall from looking around the works at a couple of their open days. They certainly made gears (large gear cutting area) and a lot of small turned parts. They had a HES Somua CNC lathe with a bar feed that was making the solid style S7 leadscrew handwheels in large quantities from bar stock during one visit - remembered for two reasons. One was the French HES Somua lathe, which was a rare beast in the UK & the other was the large stillage of finished handwheels alongside it, which appeared to hold far more components than there were lathes in build in the fitting shop. I seem to think that they also made most blacked screws & fastners in house, as most of these (on my mid-60s S7 at least) are non standard.

Nigel B.

I think it was John Stevenson who posted about remembering the thread rolling machine at the Raglan lathe factory that was used to make their leadscrews. In house production was probably cheaper than buying in if they were making enough lathes.

And thread rolling was certainly much cheaper than screwcutting, because you start off with a smaller diameter piece of stock (cheaper) and the thread rolling process pushes the metal out of the roots, up to form new peaks that are larger diameter than the original stock. Plus there is no swarf (wasted material that cost money) generated. And it was way quicker. You would roll the thread on a leadscrew in less than the time it takes to make one pass when screwcutting, which on a long, thin, flexible thing like a leadscrew would be considerable, especially back in the days of HSS tooling. And it would take a skilled machinist to screwcut a leadscrew, whereas any day labourer can feed bar stock into one end of a thread roller machine and out the other.

Either way, I can't see a mass produced screwcut leadscrew being any more accurate than a mass produced rolled leadscrew. Both would have variations greater than the tiny amount in Rod's gear chart above.

Edited By Hopper on 31/12/2022 13:30:39

Edited By Hopper on 31/12/2022 13:41:04

PS, although Myford claim a precision for their leadscrews on their inspection sheet of plus or minus one thou per foot, which is pretty darn good.

On the subject of Tumbler Gears and 34T + 33T "Metric" screw cutting gears for Myford lathes.

Can anyone inform me whether Stephen Tracey is still around and still frequenting this forum?
- I believe Stephen used to make and sell the two Tufnol Tumbler replacement gears.

This is very interesting:

.

Edited By Michael Gilligan on 08/04/2023 14:52:28

Martin Cleeve describes a method of picking up a metric thread over short distances in his excellent 'Screw-cutting' book which every model engineer should possess. If I recall correctly, it requires the use of his saddle stop which, IMO, should be made and fitted to every Myford lathe. I have fitted a collar and spring on the stop rod to act as a buffer when screw-cutting or traversing up to a shoulder which is worth considering. I made a similar design of saddle stop which lives at the rear of the tailstock and uses the pre-tapped holes for the taper-turning attachment to hold it in place. With a stop available at either end of the saddle's travel it is easy to set a predetermined distance for picking up a metric thread, as per Cleeve's instructions.

Also, I have seen mentioned in this thread, reversing the lathe. Nothing wrong with that, except you must take precautions to prevent the chuck un-screwing. It will un-screw no matter how gentle the reversal is made and the chuck should be held in place with a drawbar screwed into a disk which sits behind the jaws and in front of the mandrel nose. Obviously, this only applies to lathes with screw-on chucks.

Edited By Chris Crew on 08/04/2023 15:37:00

Indeed he is. I am that man.

Please PM me if you (or anyone else) would like to progress this.

I have recently supplied Myford with Tufnol gears for the S7/ML7R.

They are also available on eBay under the same user name that I use on this forum.

I also supply the 18T & 20T equivalents for the ML7.

My best regards,

Steve.

Hello Steve,

Thank you for replying to my query about Tumbler Gears on a Myford Super 7.

Have you ever considered (or actually made) your tumbler replacement gears with Oilite Bronze bushes in the bore?

If so was the inclusion of the Oilite bush effective in reducing heat build up at the tumbler gear bore under high speed (high RPM) application?

The reason I ask is that I recently acquired a relatively new Super 7 (that was held in storage for decades) and experienced a problem when turning the OD of a medium length & medium dia steel shaft at high RPM and while using machine feed rather than manual feed.
It is unfortunate that you need to run the Leadscrew to obtain machine feed on the Myford and therefore one or both of the tumbler gears needs to be engaged under load.
* However after turning for some time I noticed considerable heat build up at the bore of the tumbler gear.
- It is now evident (by gear removal and replacement) that the oilway to that gear was partially blocked by some of the original wax coating from when the machine was new and therefore that gear bearing was not receiving proper oiling, only partial oiling. Luckily no damage was done. However, I believe that if an oilite bush was included in the tumbler gears their bearing areas would not have heated up nearly as quickly as did the Tufnol material running directly on the steel Pin. Also, a suitable oilite bush of 5/8" x 7/16" x 3/8" long would add minimal cost.

What are your thoughts?

Since then I have thought about making a variable speed DC + Geared drive unit to rotate the leadscrew independently from the handwheel (tail stock) end and thereby eliminate the need for the gear train to be engaged at all when turning at high RPM's. Experiments in design and development of this drive unit will begin soon.

Regards, Barry

Edited By Barry Dyson on 10/04/2023 07:35:57