MYFORD S 7 BELTS ?

Made in 1969 my much neglected Myford super 7 has started to slip its belt. The original belts have done sterling service for 53 years but it's now time to change them. I have looked for threads on this subject to no avail, though it has cropped up numerous times So ! The headstock belt is A29.5 ( A 780) but the motor belt size I cannot find, one scorce says 3/8" which would indicate Z section and an inside length of 34.5", an odd way to size a belt, So is it a Z34.5" before I order one can anyone confirm my assumption ? I WILL NOT be using link belt ! Noel.

PS just found an old myford parts list that says M33.5 (Z870) So may be sorted !

Edited By noel shelley on 09/06/2022 13:48:58

I took my damaged/worn out one to the local bearing, pulley, you mention it dealer, and they supplied me with one for about £7. Maybe much more now, but worth a try. John.

Noel take a look at this supplier 

**LINK**

H

Edited By Harry Wilkes on 09/06/2022 17:04:43

Mine is an Optibelt as recommended by Myfords at the time (about 40 years ago) that I had the bed reground.

Part No Z870

I'm using this link belt off eBay, seems to work well enough, cheaper than Fenner, and far better than either the black or white plastic link belts from RDG
https://www.ebay.co.uk/itm/174456949982

Bill

I got mine 2 years ago from Myford near halifx. Not expensive & good quality.

Steve.

Would be surprised ikf it was a Z section (A very badly worn A? )

You should be able to find some one in Kings Lynn who could supply suitable replacements.

The argument in favour of using a link belt for the secondary is that it avoids disturbing the Headstock bearings

I heard Roger Warren give just that advice to someone else, years ago when I was looking to buy a BH600.

If all else fails, based on limited dealings with them, I have found Anglia Bearings, in Sturrock Way, Peterborough to be helpful. Although this means quite a long journey form you.

Howard

I get belts bearings etc from simply bearings. On line, by return service and as long as you haven't run it they will swap belts if you order the wrong one. Size for S7 is well known tho?

Are you sure its the belt? Have a good look at the condition of the pulley/s involved. Your belt may be bottoming in the V of the pulley due to wear there. Don't be tempted by link belts if you use top speed on a Myford S7. It won't fit, but otherwise go for it if you want.

+1 for Simply Bearings, always had good service from them, and they are not expensive. No connection other than as a very satisfied customer.

Rob

My ML7 has Z section pulleys on the primary drive from motor to countershaft. But an A section belt works ok, just rides a bit high in the V groove. Does not slip at all. (Inadvertently tested by starting up with back gear engaged and drive dog in place still!)

I replaced the primary belt, motor to clutch, with a link belt .The first thing I noticed was a reduction in over all vibration. That reduced further after the 3phase motor and DRO was installed. I have another for the secondary but still have not installed it yet. I have noticed recently some rubber build up dust at the top of the top pulley and cover. So soon it will need to be cut free and the link belt will be then be put in place.

Why did Myfords opt for Z section for motor to countershaft and A section for countershaft to spindle?

(I have never felt sure which of these should be called "primary".

I assume the answer has to do with the power being transmitted but I would welcome an informed comment.

Gentlemen ! I will collect what I believe is the right belts this morning supplied by Hayleys an national bearing and transmission specialist in Kings Lynn. Having found an old myfords spares list, whilst I knew that the secondary belt was an A 29.5, the primary belt was the question ! It is stated as Z870 and that is what I've ordered. I fail to see how a likn belt will transmit power more smoothly than a continuous belt ? Maintaining tension on a link belt is a challenge and on multi step pulleys not easy, at high speeds their mass also can cause issues. Once you understand the workings of angular contact bearings and their setting then changing the secondary belt is no problem and as mine has not been touched in 53 years it will do no harm to reset them.

Put simply, The primary belt is transmitting speed, the secondary is transmitting torque.

The primary belt IS Z section and 870 long the secondary is A section and 780 long ! ( according to Myford)

Why did Ian Bradley not mention setting the headstock bearings in his book on the S7 ? The early (1960s) Myford handbook was not very clear and only a later version clearly laidout the correct proceedure, which is not hard at all provided you understand what your doing. So changing the secondary belt is not difficult. The only thing you need is a pair of slightly alered ER 32 C spanners to set the adjusting rings !

To all who have replied, thankyou, I will report back when the job is done ! Noel.

A link belt might bend around those small diameter pulleys like the one on the motor better than a solid V belt perhaps? I use AX profile "cogged" belts with the notches that let them flex around small pulleys for this reason. Can;t say there is any noticeable difference because I never used the lathe with the old belts on it. But I think maybe some people notice a smoothing out after fitting a link belt simply because their old ancient belts had taken a "set" from sitting unused in one position for long periods, and they do harden up with age regardless of use, so could run a bit rough.

Ega -- I always assumed the lathes followed motorcycle practice where primary drive is from motor to gearbox, ie the first step in the drive train.

Edited By Hopper on 11/06/2022 12:37:28

I see what you mean and thank you and Hopper for your helpful comments.

I agree that the S7 spindle adjustment procedure is not difficult but it is time-consuming and there are other claimed advantages of the link belt.

Myfords clearly thought the Polyvee belt was superior; however, I understand they need to be run at higher tension and would have doubts about the effect of the oil which is bound to get on them.

I agree that a link belt does not seem to have any advantages, but I have only reported my findings. My conclusion is that the frequency that it vibrates at when running is obviously different to a continuous belt. On some machinery at our work, they have recently changed to linked belts and are having less issues with some of their machines. The Z section link belt I went for was the twist link system, so does not have the mass of the metal lock pins with the belt. It does look to be flimsy and I did wonder how well it could even be working. I have lad the link twist belt on for over 10 years now. It is made from linking in the pressed sections into each other that makes a funny looking weaved belt.

I just looked it up, mine came from Fenner drives, and is called the power link twist belt series.

I'm another fan of link belts - at least for the primary belt (motor to countershaft). Its possibly reduced torque transmission capability isn't a problem here. The increased damping of the link belt dramatically smoothed the drive. The original belt (in fine condition) thrummed annoyingly, with the vibration being easily felt by a hand on the headstock. Changing belt tension (within reasonable limits) didn't stop it, but the link belt did. Beware low-quality link-belts, of unknown provenance, however!