# 9X20 Drive belt breaking.



## Stockyj (May 15, 2017)

I have had my second-hand lathe for about 8 weeks now and have broken a few belts, the belts in Australia are $20 so getting expensive.

Ist break parting jam
2nd starting with 4 jaw chuck with tensioner engaged.
3rd can't remember
4th just started it without much load with the tensioner engaged, second highest speed.

Is this normal, it is a hassle to disengage tensioner every time stop and start to measure etc.
I have loosened tension on spring and have now set the tensioner so there is a slight slip.
Is there something else I can do..

Thanks


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## RJSakowski (May 15, 2017)

I have run belts for years without breaking.  I did break one recently but it had been in service for forty years.  Two thoughts: 1. inferior belts 2. running too tight.
You might want to check your pulley alignment too.  Misaligned pulleys can cause a sideways stress on the belt.


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## Dave Paine (May 15, 2017)

I have V belt drives on my metal lathe and milling machine.  The metal lathe has the original belt on the spindle which dates back to late 90's.  I have not replaced this since it looks to be in decent shape and I would have to remove the spindle to replace.

I replaced the motor belt when I got this second hand lathe in 2014.  The original belt was showing signs of wear.

I got my second hand milling machine a few months ago.   The original belts were from 2000 and badly worn, parts of the cloth outer were coming off, but no signs of breaking.

I replaced my belts with cog style belts.  The pulleys are smooth, but I like the cogged design since it can flex easier.  The cogged style is often seen in automotive applications.  It is possible the smaller diameter on a pulley is causing too much flex with your belts.

http://www.vbelts4less.com/V-Belt-Specs_ep_45.html
http://www.vbelts4less.com/V-Belt-Specs_ep_45.html
If your belts keep breaking, perhaps try what we call in the US a link belt.  An example to illustrate.  This type of belt is more expensive but if a link breaks, it is easy to replace.  These work well in the machines where I have these installed.  A bit more air noise, but they do not take a set, so good for machines which are not used often.

https://www.harborfreight.com/vibration-free-link-belt-43771.html


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## T Bredehoft (May 15, 2017)

Unless you need considerable tension on your belt, you might try leaving a bit of slack, so the belt slips under heavy load, thus avoiding breaking. My MK2 Clausing slips every time I engage the motor with the spindle locked. Its' the original belt, from the '60s. I have a replacement on hand but haven't needed it yet.


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## Bill Gruby (May 15, 2017)

If you are talking about the spindle drive belt the answer is yes it's normal for a start up with the idler engaged. Those belts are thin. I try to never start the lathe with the idler engaged. Toooo much stress is applied to the belt.

 "Billy G"


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## Stockyj (May 15, 2017)

The belt on this lathe is a 5mm X 710 thats (5mm wide) its tinny.
I think the new gates belts are not as good as the older ones the first belt that broke was old and made a break pop, but the new ones just break no noise.
I am not aware of any alternatives any ideas??


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## savarin (May 15, 2017)

I've broken two of the skinny belts since I bought the lathe.
If you leave the tension handle on it will stretch the belt.
Where do you get them for $20?
I'm certain they are way more than that here.


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## markba633csi (May 15, 2017)

Are these v-belts or round section?  Can you post the Gates part number?  I don't see how you could break Gates belts that often, if they are in fact Gates. 
The smallest v-belt I know of is a 2L size which is 1/4" wide.  
Mark S.


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## Bill Gruby (May 15, 2017)

I have only broken one since I got these 2 years ago. This seller ships world wide for $3.00


http://www.ebay.com/itm/5M710-GATES...hash=item58f06c2c85:m:msI7Q7iWDvWAim097mKkcQg

 "Billy G"


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## savarin (May 16, 2017)

same company I use Bill, very happy with them


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## Stockyj (May 16, 2017)

The gates belt is a 5M710 some machines have 730.
I managed to buy a PK3710 that ia a multi rib belt same diameter. I have sliced the 3 ribs so I now have 3 belts the vee angle is slightly steeper but seems to work OK have run it for quite a while will see how it goes. This is a cheap alternative and appears to be a stronger belt.


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## 4GSR (May 22, 2017)

The 5M710 belt and a couple other 5M sizes, I use them on my K O Lee tool & cutter grinder, too.


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