# Lathe Belt Slipping



## rogerl (Aug 8, 2020)

I have a 11 in South Bend Lathe with the motor in the cast iron base under the lathe. The lathe was my dads and it had a leather belt on it. I had to cut the leather belt to disassemble the lathe to get it out of the basement and into my shop. When I reassembled the lathe I bought a synthetic drive belt from Albino Industrial belting. I am noticing that the spindle is slowing down when I take heavier cuts. The belt is slipping on the head stock pulley. The pulleys are very clean and shiny. The belt seems tight. Do I simply tighten the belt more? I do not want to over tighten the belt and have the glue joint fail. Another option would be to put some belt dressing on the belt to make the belt and pulleys little more sticky. The web page for the belt say not to use belt dressing. Any information would be great.

Roger L


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## benmychree (Aug 8, 2020)

Tighten the tension until it does not slip (tight within reason).


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## Ulma Doctor (Aug 8, 2020)

i bought a synthetic belt inexpensively, i'm sorry i did 
i'll be switching to a serpentine belt inverted next


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## rogerl (Aug 9, 2020)

How do you splice the serpentine belt?

Roger L


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## gonzo (Aug 9, 2020)

I have had a lot of problems with a synthetic belt slipping. Finally I got a new non green belt and have not had any trouble at all. I love it even if the new belt cost me $75.


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## markba633csi (Aug 9, 2020)

Roger, try going over the cone pulleys with alcohol and maybe the belt too; it may help a bit.
I believe folks are splicing serpentine belts with cyanoacrylate (crazy) glue with a tapered lap joint. Possibly also stitched with nylon thread.
-Mark


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## Ulma Doctor (Aug 9, 2020)

rogerl said:


> How do you splice the serpentine belt?
> 
> Roger L


as Mark said above, stitched together high test braided fishing line


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## rogerl (Aug 9, 2020)

I went over the pulleys and belt with alcohol. There was some oil on the pulleys and the belt. When I looked at the inside of the belt the rubber portion of the lap joint was coming loose. I wiped it down with alcohol and put on some rubber contact cement. I clamped the joint together and am letting it dry over night. Tomorrow night I will see if I still have the slipping problem. If I do I will increase the belt tension and see what happens.

Where do you find serpentine belts long enough for the lathe? I might go that direction if this belt continues to slip.

Thanks for the replies.

Roger L


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## Ulma Doctor (Aug 9, 2020)

rogerl said:


> I went over the pulleys and belt with alcohol. There was some oil on the pulleys and the belt. When I looked at the inside of the belt the rubber portion of the lap joint was coming loose. I wiped it down with alcohol and put on some rubber contact cement. I clamped the joint together and am letting it dry over night. Tomorrow night I will see if I still have the slipping problem. If I do I will increase the belt tension and see what happens.
> 
> Where do you find serpentine belts long enough for the lathe? I might go that direction if this belt continues to slip.
> 
> ...


 a cummins diesel serpentine belt Is what i got


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## graham-xrf (Aug 9, 2020)

Ulma Doctor said:


> i bought a synthetic belt inexpensively, i'm sorry i did
> i'll be switching to a serpentine belt inverted next


Yes - you can use a ribbed belt inverted. The difference is the minimum radius for the small end is more than if used non-inverted. From my (recent) digging, I gather you can use a serpentine belt non-inverted, ribs up against the pulley, and expect more friction - something to do with friction being related to the reaction pressure under the contact.
These are called "V-flat" drives.

These belts are used in cars to drive alternators, and air-con compressors, and so run over various ribbed and flat pulleys. You can considerably increase the torque by increasing the wrap circumference using idlers. Wherever possible, they are supposed to go on the slack side of the drive, allowing the idler tension to be considerably less.

Also, an inside idler must be larger than the smallest pulley in the system.

For me, it is to be a 8-ribs serpentine from cone pulley to cone pulley, I I have yet to get to the joys of splicing the V-flat serpentine, I have more belt than I need, so I think I might try a "practice attempt" first.

Easy enough to find quite low cost "new old stock" on eBay.


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## pontiac428 (Aug 9, 2020)

graham-xrf said:


> Also, an inside idler must be larger than the smallest pulley in the system.



I've never heard that, why is it so?  And which do you call the inside, one that touches the inside of the belt, or is it inside the wrap if placed outside the belt?


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## graham-xrf (Aug 9, 2020)

pontiac428 said:


> I've never heard that, why is it so?  And which do you call the inside, one that touches the inside of the belt, or is it inside the wrap if placed outside the belt?


Whatever route a pulley takes, turning back on itself at times, it is a two-surface thing. If you took it off the drive system, and spread it into a circle, there is an "inside the circle" and an "outside the circle".  "Inside" is the surface in contact with the driving pulley surface. That definition persists everywhere, but I get it that what is in your mind is when a serpentine belt goes around a pulley, then wraps the other way around an idler to come back out

I think the answer to your question is related to what happens when starting up. A ribbed V-belt drive pulley can be quite small, and if the belt wraps a pulley even smaller, the tensions around it might be on both sides, unlike the driving pulley, where the tension on the "slack" side might reduce to near zero.

The vendor manual I found will have a lot of stuff you don't need, but it is the most complete guide I have found, with all the formulae, advice, for almost any arrangement.


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## pontiac428 (Aug 9, 2020)

Interesting.  I wonder how Detroit and Osaka have been getting away with running such tiny idlers.


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## graham-xrf (Aug 10, 2020)

pontiac428 said:


> Interesting.  I wonder how Detroit and Osaka have been getting away with running such tiny idlers.


Oh yes! My first reaction was "Huh? Really?".
I thought that too!


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## Charles Spencer (Aug 22, 2020)

I've got to give a home town business a plug. Hudson Belt Company, making leather drive belts in Worcester for the last 160 years. 





						Leather Drive Belts | Hudson Belting
					

One of the ONLY remaining Leather Drive Belt manufacturing company. Our belts are sold throughout US and are unmatched in quality and price.




					www.hudsonbelting.com


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## MrWhoopee (Aug 26, 2020)

I replaced the leather belt on my SB Heavy 10L with a serpentine belt.





						D&D PowerDrive 700K8 Simplicity Manufacturing Replacement Belt, Poly, 8 -Band, 70.75" Length, Rubber: Amazon.com: Industrial & Scientific
					

D&D PowerDrive 700K8 Simplicity Manufacturing Replacement Belt, Poly, 8 -Band, 70.75" Length, Rubber: Amazon.com: Industrial & Scientific



					www.amazon.com
				




I tried several different methods of splicing; cyanoacrylate, hog rings, and wire lacing. The cyanoacrylate would not bond, the other two splices failed in a relatively short time. I finally tried Shoe Goo.


			Robot or human?
		

It has been the winner, providing a very tough, flexible bond. I glued a test piece and have not been able to break the glue joint. On the belt that I received, the flat side is quite slick while the grooved side almost feels like it has "grit" embedded in it for grip. Shoe Goo will not bond to the slick side. I run my belt with the grooved side down, it will stall the motor before the belt will slip.

My splices are 2 in. flat lap, no angle cuts or anything fancy. I ground the laps on my disc sander with an 80 grit disc, grinding down each end until the reinforcing fibers are fully exposed, being very careful not to compromise the fibers. I had one belt fail because I had not been careful enough and ground into the fibers.

Replacing the flat belt with a serpentine belt makes a huge difference. I highly recommend it.


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## graham-xrf (Aug 26, 2020)

MrWhoopee said:


> I replaced the leather belt on my SB Heavy 10L with a serpentine belt.
> < Re: Shoe Goo .. >
> It has been the winner, providing a very tough, flexible bond.
> 
> ...


By some kind of co-incidence - I happen to be getting to grips with exactly that right now!
Same here, except my one is called "*Shoe Fix*"  - water resistant - bonds leather, vinyl, rubber, canvas.
It threatens to have quite the aroma - Naptha, Acetone, Ethyl Acetate highly inflammable - do not inhale, etc.

The other is B-7000 "Jewelry glue", also with all the claims. (I still think the precious stones should never rely on a glue)!  Both kinds dry in about 10mins, and need 24hours to get to full strength.

Basically following what you are saying to do. It is to be test pieces first - but nearly there!


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## AmericanMachinist (Jan 28, 2022)

MrWhoopee said:


> I replaced the leather belt on my SB Heavy 10L with a serpentine belt.
> 
> 
> 
> ...


Hi Mr. Whoppee,

Is your serpentine belt with the Shoo Goo still holding a couple of years later through use?  I am debating whether to use a serpentine belt or one from https://albinoindustrialbelting.com/drive-belts-faqs

It seems like the reviews on whether the Serpentine belts last the test of time are mixed.

Thanks


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## MrWhoopee (Jan 29, 2022)

AmericanMachinist said:


> Hi Mr. Whoppee,
> 
> Is your serpentine belt with the Shoo Goo still holding a couple of years later through use?  I am debating whether to use a serpentine belt or one from https://albinoindustrialbelting.com/drive-belts-faqs
> 
> ...


Yes, still holding just fine. I have switched to Goop, which is a slightly more fluid version of the same thing. There are multiple flavors of Goop, but I don't think it really matters.


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## Illinoyance (Feb 1, 2022)

The synthetic belt on my 19K kept slipping.  I sprayed contact cement on the inside of the belt while the lathe was running.


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