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Small polyflex belts

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mark brockley09/09/2017 12:32:28
17 forum posts

Has anyone else had problems with the modern drive belts used on new lathes ?

Just under 3 months ago I replaced a small lathe with a brand new bigger machine. It has a bigger swing than my ML7 but is about the same length of bed. It is driven by a gates 5M710 belt .

Within 1 week this belt snapped after only a couple of hours. I was sent a replacement and I purchased a second at £16 !!!!

The lathe hasn't been used in 3 weeks due to health but the last couple of days its been used for just over an hour.

The V belt is cracked in 2 places and only held together by the fibber reinforcing .

Niels Abildgaard09/09/2017 12:52:47
429 forum posts
159 photos

I cannot help You but isn`t it a pollyflex belt rather than a poly-V as used on washing machines?

mark brockley09/09/2017 13:14:08
17 forum posts

Yes your right they are pollyflex not sure about them on washing machines but guess they will be

JasonB09/09/2017 13:24:35
22750 forum posts
2653 photos
1 articles

Does sound a bit of a short life, have you checked tension? My lathe uses the exact same belt and I replaced it after about 8 years as it was squeaking a bit but still good enough to keep as a spare. Maybe try one from a belt or bearing supplier as they are readily available at good prices.

Neil Wyatt09/09/2017 13:28:58
19033 forum posts
734 photos
80 articles

This is odd, those belts usually last years.

It may be that you have the tension set too high, especially if you have fitted a new belt.

I don't know the correct tension, other than they need much less tension than old style cotton reinforced belts.

Tension calculator here


Edited By Neil Wyatt on 09/09/2017 13:30:40

mark brockley09/09/2017 14:56:48
17 forum posts

The lathe has a ''clutch'' lever to de tension to start and then tension it up for running. I do think it is tight so with the new belt I bought I am leaving it in the start position as it is not slipping and to me feels tight enough.

I will contact the company next week but am disappointed with things so far.

I will check out the tension calculator cheers.

Hopper10/09/2017 04:09:33
6397 forum posts
334 photos

Belts are like bearings: The more expensive brand name items are good quality and last for years. The cheap Chinese generic items have a wide range of quality and durability. Some are OK, some are not. You might try to source a good quality belt from manufacturer such as Gates etc.

oldvelo10/09/2017 05:31:24
295 forum posts
56 photos

Hi Mark

Is this the belt type on your machine "Gates 5M710. PolyFlex® 8902-0710 V-Belt - 5M Section, 3/16 in Top Width, 27.95 in Outside Length, Polyurethane Material "

What is the motor power on your lathe as this size seems to be big enough for nothing bigger than around 1/8 hp. unless on very large diameter pulleys with very high peripheral speeds are used.

Polyurethane belts do not perform very well when excess slippage occurs when used as a clutch.

Being a convert to "Poly Vee Multi Rib Belts I ditched Vee Belts on my machines where ever possible and have run them trouble free for several years now.

Broken belt suggests that it is being used to attempt to transmit a high torque loading on a very small belt cross section.

This MAY help better prices LINK   and in my VERY biased opinion a good deal



Edited By oldvelo on 10/09/2017 05:40:40

JasonB10/09/2017 08:24:09
22750 forum posts
2653 photos
1 articles

Where did you get the 1/8hp figure from. As I said above the belt on my lathe is a 5M and that has a 1hp motor with a very small did pully on it.

Mark, what lathe is it and are you sure the lever is a clutch and not just to reduce tension when changing belts?

Neil Wyatt10/09/2017 11:01:08
19033 forum posts
734 photos
80 articles

The polyflex belts are supposed to take much higher powers than conventional v-belts but the process of working out how much power one takes is (probably deliberately) made very complicated by Gates, when all you need is a a speed/power graph with some lines to show different minimum pulley diameters.

Ed Duffner10/09/2017 11:13:42
840 forum posts
94 photos

May I suggest (if not done already) checking the pulleys for proper alignment and any burrs or anomalies which may be wearing away the belts.


Hopper10/09/2017 12:04:21
6397 forum posts
334 photos
Posted by JasonB on 10/09/2017 08:24:09:

Mark, what lathe is it and are you sure the lever is a clutch and not just to reduce tension when changing belts?

Ah, you might be onto something there. It does seem like harsh duty for a small section belt.

mark brockley10/09/2017 16:13:00
17 forum posts

I did check the pulleys for burrs and polished them. The lathe is a Chester 920. The first belt just snapped with no warning at all just a noise like a rifle going off.

This second belt has 2 splits in it I will try and get a pic of it.

I will get in touch with Chester and see what they say as I have only had the lathe 3 months.

JasonB10/09/2017 16:36:14
22750 forum posts
2653 photos
1 articles

As I thought that is not a clutch it just slackens the belt to make pully changes easier. If you say it runs in the "neutral" position then probably too tight when tensioned.

SillyOldDuffer10/09/2017 18:05:26
8692 forum posts
1967 photos

If the belts are snapping because they're too tight, that may be doing you a big favour. An over-tensioned belt (or motorbike chain) much increases the risk of damaging the pulley and motor bearings. And bearings are much more painful to replace than a belt!


JasonB10/09/2017 18:38:23
22750 forum posts
2653 photos
1 articles

Talking of tight belts, the instruction manual for the 920 suggests a 5M730 belt yet mark say 5M710 which would make for a very tight belt.

It does also say slackening the idler can be used as a clutch which I have notheard of before on teh 920 machines

mark brockley11/09/2017 13:00:09
17 forum posts

That's an interesting point Jason the instruction manual supplied with the machine has no information on belt size !! and looks different than the link you have given.

I have been informed that belt sizes changed and have had to e mail customer services with the problems I am having.

Will see what they say.

John Rudd11/09/2017 16:31:27
1450 forum posts
12 photos

I've had a 9 x 20 since 2005.

It uses 5m730 belts.

The manual may have been rewritten since, but on my lathe there is a label inferring that the lathe should not be started with tension on the belt ( the 'clutch handle lowered towards the rear of the machine'

There is a clutch, which is only effective when used on the lowest speed ( unless the springs have become weakened)

I have several spare belts sourced from Beeline Engineering ( google ) at a lower cost than the vendor.

There maybe some tension adjustment if the clutch assembly can be slackened and repositioned, but this is constrained to a degree by the tension of the primary drive belt from the motor pulley.

Fowlers Fury11/09/2017 17:41:13
406 forum posts
91 photos

About 20 years ago I dumped the standard 2ndary V-belt on my S7 and replaced it with a Brammer multi-link belt. Apart from not having to dismantle the mandrel etc to install/replace such a belt, the lathe runs very much smoother at higher speeds. The belt is not tensioned too much and will slip in the event of a dig-in yet never slips with fairly deep continuous cuts.

I checked some while back for the availablity of a replacement on the Brammer website but it seems the exact type is no longer listed. Instead the "Nut-T link" belt seems closest. The d/loaded pdf contains a wealth of information on belts as well as illustrated pages of faults and causes of breakage and splitting etc. Well worth a look IMHO.


"Nut-T belt"


John Reese11/09/2017 22:43:34
1035 forum posts

I had a drill press that used a polyflex belt. The drill press was purchased in the late 70's and the belt lasted until about 5 yr. ago. I replaced it because of wear. The motor on the drill was 3/4 hp. If your belts were failing that fast I would suspect they were counterfeit polyflex.

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