Poly V Belt Conversion

[StyxParticipant @styx]

I have the drawings and Poly V belt from Hemingway Kits for the primary drive conversion for the Myford S7 and I was thinking of using aluminium for the conversion instead of buying the castings. Can anyone see any problems with using aluminium? ie belt grip or possible lack of flywheel effect from using lighter materials.

Any thoughts would be appreciated.

Steve….

Edited By Steve Sedgall on 11/12/2013 13:37:53

[StyxParticipant @styx]

[ZiggarParticipant @ziggar]

i too have looked at this kit for quite some time now and wondered the same thing. Would it be possible to use ali instead of the cast iron suggested.

far easier to machine and obtain than the cast. also a bit cheaper. cleaner to machine. no dust to clean up.

So im watching this with more than a little interest. I hope there are some good answers to mull over

Z

[NJHParticipant @njh]

I 'm just wondering why you are seeking to change to poly V ?

If it is to obtain smoother running then have you investigated link belts? My S7 was rough and noisy in the high speed range so I replaced the primary belt with a link type. Super smooth and quiet at all speeds now. The secondary drive belt is still a traditional 'V' type at present but that too will be changed for the link type when the time comes.

The belt is shown here

Cheers

Norman

[michael sansomParticipant @michaelsansom56931]

Hi Steve I have not done the myford conversion but have done the poly belt conversion on the Warco VMC milling machine using aluminium for the pullies and have had no problems at all . MIKE SANSOM

[oldveloParticipant @oldvelo]

Hi Steve

Go for it with "Poly Vee" belts and aluminium pulleys I can recommend them as all metal working machines in my workshop have them.

Instead of castings you can use ali discs 12 mm thick bolted together to flanged boss bored to fit the shaft size.

Looking at Normans excellent photo this seems to be a viable proposition.

EDIT Looking again at the photo Maybe the large pulley is to big to be turned on a "Myford" so a proportionate reduction in diameter may be used.

PJ  "Poly Vee" will run on a 20 mm pulley much tighter than a "Vee Belt".

Eric

Edited By oldvelo on 12/12/2013 19:05:45

[StyxParticipant @styx]

Hi All,

Thanks for all the tips, I have started machining the motor pulley and hope to have that finished soon. I have the use of a Colchester lathe so machining the larger pulley shouldn't be to much of a problem. I will post some photos in my albums when it is done.

Steve….

[ZiggarParticipant @ziggar]

i didnt realise that the motor pulley was part of the deal, nor does it say anything about it on the hemingways website. unless you mean the countershaft pulley.

either way, im looking forward to regular updates from you on this. lots of photos and updates as you go along

good luck with it

Z

[Steve WithnellParticipant @stevewithnell34426]

I used a Contitech "Poly V" belt for a mod to my lathe. PJ610/240. The grooves on the new pulleys were cut with a 5/8 BSW tap as a tip from John S. Following John's post there was a number of posts pointing out everything that was wrong in the match between the profile of the tap and specified profile of the Poly V belt.

Fact is, the grooves were a doddle to cut this way and the belt is still in good nick years later. Maybe a trick worth considering.

Steve

[John OlsenParticipant @johnolsen79199]

I thought this was a conversion for the secondary drive, eg from the countershaft to the spindle. Anyway, for what it is worth, I have done the equivalent conversion on my ML7, so if anyone was wondering, it is possible, although it is a bit of a squeeze. (I did do four speed steps.) I did mine because I was tired of the pullies overheating and letting go on the spindle…the ordinary V belt gets very hot, which tells you that the drive is not very efficient.

John

[StyxParticipant @styx]

Hi John,

The conversion I am doing is for the primary drive. Hemingway also do a final drive conversion as well.

Hi Ziggar,

You need to machine a new motor pulley and modify the clutch pulley. Hemingway supply castings for these but I am making them from aluminium.

Hi Steve,

Thanks for the tip about using a tap to cut the grooves but I have ground up a carbide grooving tool with the 40 degree angle.

Pictures will be posted in my albums when I start machining.

Steve….

[ZiggarParticipant @ziggar]

do you have a link to the kit you are referring to because all i can find is the kit for the main 4 step pulley arrangement between the countershaft and the mandrel

Thanks

Z

[StyxParticipant @styx]

Hi Ziggar,

If you go to the Hemingway web site and download their latest workshop catalogue, W180, you will find the Poly V conversion on page 36.

Steve….

[ZiggarParticipant @ziggar]

thanks for that

i always thought that the catalogues would simply reflect the website contents

seems i was wrong

off to hemingways site i go

Z

[oldveloParticipant @oldvelo]

Hi Steve

Following your posting with interest being a "Poly Vee" fanatic

Pleased to see "Thanks for the tip about using a tap to cut the grooves but I have ground up a carbide grooving tool with the 40 degree angle.

Near enough good enough not for me. The enemy of the best is not the worst but the good enough.

Eric

[Steve WithnellParticipant @stevewithnell34426]

For me I'm afraid, Pareto always wins.

The belt has been in service for over five years without issue, never slipped, spun off.

However, I'd agree that the good enough that's not is a problem.

The irony is, in another forum I've just been accused of being a perfectionist…

Steve

[ZiggarParticipant @ziggar]

unfortunately i only have the one lathe available [the S7] so wouldn't be able to do this conversion
although the other one is still a likely candidate at some time in the future

it would be a nice touch if hemingways were to offer a pre machined pulley if wanted/needed

perhaps something for them to think about ?

 

 

 

Z

 

 

 

 

Edited By Ziggar on 16/12/2013 18:13:43

[NJHParticipant @njh]

Hi Guys

Further to my previous post can someone please tell me the advantages of poly V belts? I've had a look at the Hemmingway site which lists the conversion kit but just what advantages do these belts have? What problems do you have at present with the conventional set up? ( I'm always looking for presents for my wife to get me!)

Norman

[Michael GilliganParticipant @michaelgilligan61133]

Norman,

Regarding the advantages …

I was going to refer you to this thread … but I see that you were a contributor!

If you care to follow some of the references, then I'm sure you will become a convert.

MichaelG.

.

Edit: Inserted the opening line

Edited By Michael Gilligan on 16/12/2013 19:42:09

Edit: Corrected typo.

Edited By Michael Gilligan on 16/12/2013 19:44:48

[NJHParticipant @njh]

Thanks Michael

I'd quite forgotten that ! However, whilst I. Can see an obvious advantage for a flat belt drive lathe like the ML4 I'm at a bit of a loss to see the advantage for a V belt drive like the Super7. The only problem I've had with mine is noise and vibration in the high speed range but this was cured by a belt change as shown above.

Regards

Norman

[Michael GilliganParticipant @michaelgilligan61133]

Norman,

I suppose the best summary is that, by design, the Poly Vee acts exactly like a set of matched Vee belts of very small section. This means that the efficiency of the drive is massively improved, because the "contact patch" is bigger, and the bending stiffness is much lower than an equivalent single Vee Belt.

The concept was derived from the use of multiple Vee Belts to drive high power compressors, etc.

… Most definitely worth exploring.

MichaelG.

.

Edit:  Here is a classic use of multiple single Vee Belts

Edited By Michael Gilligan on 16/12/2013 20:41:04

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Poly V belts are an improvement on simple V belts in M7 series lathes not particularly because of the multi v format but more because they are much thinner and more flexible .

On standard M7 lathes the V belt is very stiff and does not engage pulleys properly unless belt tension is quite high .

Poly v belts wrap around pulleys much better and belt tension can be optimal and not excessively high .

Improperly tensioned belts cause numerous problems of vibration and torsionwise instability – one of the ( several ) reasons why parting off can be problematic – and can also cause erratic spindle alignment leading to accuracy problems .

MikeW .

PS: To this day some very high quality lathe makers stick to thin section flat belts for spindle drive – essentially for same reasons as above .

Edited By MICHAEL WILLIAMS on 17/12/2013 00:08:04

[NJHParticipant @njh]

Thank you Michael and Michael !

Interesting. I bought my S7 S/H and little used It had been stored for some time and, as I posted above, the high speed range was very noisy and rough. I thought this might be due to the primary belt having become mis shaped by being in one position for all that time. The belt did seem to lack flexibility when I removed it. As you can see I replaced it with the link belt and this cured the problem – super smooth and quiet now at all speeds. To date I've not changed the secondary belt. Now one of the advantages you say that the poly V has is greater flexibility and this I think is true too of the link belt. At present I don't have a problem with parting nor do I experience lack of power – but then my interest tends towards smaller things so I guess I don't stretch the machine much! Before going down the Poly V route maybe I should first change the secondary belt to link type also and see what difference that makes.

Those of you fitting the poly V mod please post and let us know of your experiences in fitting the mod and your assessment of its effectiveness.

Regards

Norman

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi NJH ,

Fitting link belt is in many ways equivalent to fitting poly V belts .

If you have link belts on primary and secondary drive I doubt whether fitting poly V belts instead would be any further advantage .

Some swings and roundabouts though – poly V belts probably do give the smoothest drive but link belts can be fitted to lathe without modifying lathe and without having to remove spindle .

MikeW

[John Stevenson 1Participant @johnstevenson1]

You can get greater speed ratio's with Poly vee belts in places where space is limited because the smaller pulley can be a lot smaller than the one needed for a v belt or even a link belt.

On small pulleys with a vee belt you get a lot of non contact. Link belts don't suffer as much but are placed in a situation where wear on the pins takes place leading to premature failure.

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