Poly V Belt Conversion

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

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.

Thanks all.

John you say ....... " wear on the pins takes place leading to premature failure."

I must say that when I viewed the link belts I did wonder about that ( I'm assuming here that you refer to the belts with metal pins). Now the links on the belt I obtained are formed so that they slot into each other with no metal pin. ( see photo above) It was not my choice especially - that's just how it arrived. So far it has not had a great deal of use and it appears that the tabs don't actually contact the pulley. Have you come across this type and should I expect that the life of this too will be short ?

Cheers

Norman

I use the type of belt with the tags that fit through the slots, on the primary drive of my BH 1326 Taiwanese lathe, this is a some what larger machine, using B section belts, mines been in use for about 15 years.

One of the advantages of the Poly V belt is that it is narrower than the original A section belt, and the pulley has no rim, so an extra speed can be incorporated in the same space. Ian S C

Norman,

I don't think there is any problem when the link belt replaces a vee belt on existing pulleys.

My remark was aimed at fresh designs that need to use smaller pulleys. Without dragging the Poly V design bible out I reckon from memory that a 6 rib J series belt on a 38mm pulley [ 1.5" ] is good for close to 2 HP.

Thanks John

An interesting and useful thread. I think I'll put the conversion on hold for the time being - and find something else for my wife to indulge me with this Christmas !

Norman

I have finished the motor pulley. Please see my albums for photos.

Steve....

Very nicely done, Steve

Just one hint for others ... a Parting Tool blade makes a very convenient blank for the single point form-tool.

MichaelG.

I have finished machining the new Poly V pulleys and hope to fit them to the lathe as soon as I have found the small circlip that hold the pulley in place. I have put a series of photos in my albums if you would like to view my machining methods.

I will post more photos of the completed installation soon.

Steve....

Fitted the new pulleys to lathe last night and had mixed results when I switched it on. On the slow speed position it was quiet and smooth but on the high range the belt was vibrating and noisy. I will do some investigation work at the weekend. Any thoughts on what could be the problem would be appreciated.

I have added a photo of the installation in my photo album.

Steve....

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Steve,

After all your careful work, that must be frustrating.

My best guess would be that you have a slight mis-alignment of the two pulleys ... This may be more noticeable on the high range, because the belt is well-wrapped round both pulleys.

Is it safe to let the pulleys "float" a little on their shafts ? ... if so, that would allow them to self-align.

... If this works, then you will need a shim, or a skim, somewhere.

MichaelG.

Is the tension on the high speed pulleys enough, perhaps try changing tension. Ian S C

Tension in a poly-v belt should be enough to cause 1% stretch between two marks made with the belt slack.

Neil

It looks like its been a few months since the last post by NJH. I am curious of your take on your new primary drive on your Myford. Were you able to work out the virbration at high speed.

What is your take on the poly-vee belt conversion since you have it completed and had time to use it for a while.

Is this worth the investment?

Hi David

It was Steve Sedgall who carried out the poly V conversion to his primary drive and it seems that he has made no more recent posts on the forum since the one in this thread on 10th January. My own conversion on my S7 was just to change the primary V belt for a link belt and doing so got rid of all my problems with vibration. I note that there is a conversion kit for the secondary drive but, as I'm getting on with the existing set up OK, I think I'll give it a miss!

Regards

A great picture.

I have had one of these belts on my Myford since 2006. I only put it on the outer like you have done as I was not sure of the life or consistency of these belts. When the spindle belt starts to look sad or slips, it will be cutting it off and be replacing it with the sectional belt. I got a piece for the job, but have not got to replacing it yet.

I just could not get over how much it reduced vibration and the surface finish improvement.

The spindle belt was replaced with a Gates belt that has the notches to allow it to bend around the pulleys easier. It has lasted way longer than expected. That belt was replaced back in 1996 or so when I rebeded the front bearing and replaced the rear bearings.

I have not experienced the spindle belt slipping, and do not see the need for a poly Vee belt. But I am also not against anyone making such changes. Each to their own.

Neil

I used poly-vee belt on a Centec 2B to drive the vertical head, that was over twenty years ago and I believe it is still working. I also used taper wedge bushes to secure the pulleys that were machined from dural discs. Regarding the use of multiple vee belts, they must be a matched pair. A friend had a strange noise on his lathe that was eventually found to be due to the belts not being matched, and them creeping relative to each other over the pulley Ensure that belts come from the same batch if you need a pair or more.

ivan

Another point of reference for poly vee drives. In a previous job I worked in a team on a project with Gates (who invented the vee belt apparently) and Ford Motor Company to implement a "belt starter generator" system on a 2.0L diesel Transit (Google "HyTrans Hybrid Transit". This used a modified alternator as a motor to start the engine rapidly without needing to use the slow, noisy starter motor.

The poly vee belt had only 6 or 7 ribs and the crank pulley was only 5 or 6 inches diameter. The engine could be cranked up to idle speed within half a second or so to start the engine, even with the vehicle cooled overnight to subzero temperatures.

This was a belt system that was properly designed by a reputable supplier and was rated for a normal operating lifetime. Gives you an idea just what these systems are capable of.

Murray

I'v been looking for it but can't find it, a thread that included poly - v belts and pulleys, the grooves were done with a thread chaser (wrong angle but OK)? 11 tpi.

Ian S C

Ian,

Here it is ... in a post by JohnS.

MichaelG.