Myford Metric Lathe Leadscrew

[Roderick JenkinsParticipant @roderickjenkins93242]

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

[speelwerkParticipant @speelwerk]

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.

[Howard LewisParticipant @howardlewis46836]

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

[HopperParticipant @hopper]

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!

[JasonBModerator @jasonb]

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

[John HaineParticipant @johnhaine32865]

Posted by Hopper on 31/12/2022 03:02:55:

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!

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

[egaParticipant @ega]

Posted by John Haine on 31/12/2022 09:08:46:

Posted by Hopper on 31/12/2022 03:02:55:

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!

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?

[SillyOldDufferModerator @sillyoldduffer]

Posted by ega on 31/12/2022 10:55:47:

Posted by John Haine on 31/12/2022 09:08:46:

Posted by Hopper on 31/12/2022 03:02:55:

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!

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

[mgnbukParticipant @mgnbuk]

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.

[HopperParticipant @hopper]

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

[HopperParticipant @hopper]

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.

[Barry DysonParticipant @barrydyson71148]

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.

[Michael GilliganParticipant @michaelgilligan61133]

 

This is very interesting:

.

 

MichaelG.

.

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

[Chris CrewParticipant @chriscrew66644]

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

[Steamer1915Participant @steamer1915]

Posted by Barry Dyson on 08/04/2023 12:23:54:

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.

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.

[Barry DysonParticipant @barrydyson71148]

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

[Pete RimmerParticipant @peterimmer30576]

Posted by mgnbuk on 31/12/2022 12:25:44:

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.

Nigel B.

They must have progressed in the '80's as the 1979 Boxford drawing I have for cross-slide screws certainly specifies a blank dimension for thread rolling.

 

Edited By Pete Rimmer on 10/04/2023 08:41:46

[Neil LickfoldParticipant @neillickfold44316]

As you have a Myford lathe, it will have a hand wheel . This can be used if you don't have a thread dial to engage the halfnut at like zero . Older machines have a lot of backlash in the system. So reversing so that you have plenty of time to take up the backlash . I hold my hand on the carriage wheel to drag it and to take up the backlash in the system. Also make sure that you have the halfnut engaged at the same level. I fully engage the halfnut handle each time. There has been alot of good tips in this thread.

On my lathe as I added a VFD, I have added a microswitch that allows it to stop quite quickly . I have mentioned this as a 3phase motor and VFD allows for easy reversing and variable speed for other situations etc. ut something to be thinking about for later down road.

[Steamer1915Participant @steamer1915]

Posted by Barry Dyson on 10/04/2023 07:35:06:

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

Hello Barry,

I haven't done anything along the lines of fitting Oilite bushes to the Tumbler gears. I see no reason to. I think in many respects you have answered your own question when you state that there was clearly a lack of lubrication.

I have done a lot of work over the years at elevated speeds on my S7 and never had any issues with overheating of the tumbler gears. Correct lube is the answer…

Best regards,

Steve.

[egaParticipant @ega]

That lack of lube may have been due to the use of grease rather than oil.

[Barry DysonParticipant @barrydyson71148]

Hi Ega, Yes use of grease decades ago could have been the cause of the poor lube problem.

Hi Steve,
I agree that proper oiling is working better now but don't agree that one should require the use of the full gear train to achieve a simple feedrate during high rev turning operations.
Also at high speeds polymer bearings are affected much more adversely from overheating than oilite bronze is on steel.
And running the full geartrain seems like too much overhead for such a simple feed requirement during high speed turning and facing operations.

IMO the real function of the geartrain is to deliver accurate pitches for screwcutting at much lower revs when less bearing (bush) heat is being generated.

Are you in the business of making and selling the 33T and 34T "metric" screwcutting gears as well as the tumbler gears? – I could do with one of each of those.

I'll continue the trial of a Variable Speed DC + Geared drive unit driving the leadscrew for an improved feed function when turning and facing at high RPM, – which is often.

Thank you,

Regards, Barry

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