I need to take a belt to this lathe

Shotgun

Shotgun

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Craftsman Commercial 12x36 one day started trying to walk the floor if I tried to go above 1,000 rpm.
I've been living with it by keeping it slow, but recently found a claim that different length belts would cause this problem.
I checked, and sure enough, one of the belts was tight while the other had several inches of play.

The loose belt sit deeper in the groove of both the top and bottom spindle.
The printing on the tight belt is clear. "4L540 Goodyear FHP". The printing on the other is barely legible, but I think it is the same.
I'm not able to measure the V grooves, but the belts measure the same width and thickness.
My lathe was modified by a PO so that the 1Hp motor drives the spindle directly, and it appears that the weight of the motor may be used for tension.

So now for the guessing what happened.
I'm going to go with the loose belt was slipping all along. There was a slight difference in diameters of the pulleys initially, but over time the grooves for the loose belt have been ground down. . . resulting in it sitting deeper in the grooves. . . resulting in more slippage, then more wear. This also caused the belt to heat up and oxidize the printing on it. These belts are AT LEAST 12 years old.

The fix?
Swapping belts is a PIA, but I'm up for that.
Is there a better belt selection than this Goodyear? Rotate the spindle by hand, and they sound like wet sneakers on a basketball court.
Does it make sense to replace the belts if the Vs are damaged? How can I tell if the pulley Vs are damaged?
 
Didn't follow everything, but link belts are a great option. Especially if your lathe is like mine where replacing the belts requires tearing apart the spindle. They do stretch over the first week, so you may need to pull a few links later on. They are not supposed to take a set which is nice.
 
I believe you can buy matched belt sets.
 
Continental makes good belts, though I don't know if they offer matched sets or not.
 
You might look at a different belt construction, those with Aramid or Kevlar (4LK540 or 4L540K) may be less likely to stretch or deform. If the pulleys are small than a cogged type belt will bend easier and stay more uniform. Seems like the options are somewhat limited in that size, I also prefer to purchase from a belt dealer than say Amazon/eBay, the latter often have old stock that can be less flexible or returned stock. You may need a new motor pulley if V V's are worn. Also sounds like your belts are probably hardened and glazed. Link belts also may be an option, hotly debated subject.
www.royalsupply.com

Gates 6854 PoweRated 4L540K Light Duty V-Belt 8423-6854

6854 Gates PoweRated v-belt 4L540K 54 inches in length x 1/2 top width. Gates product ID 84236854
www.royalsupply.com
 
I cut off the loose belt. It was glazed really bad. All the squeaking while running went away, and I ran it up to he max it could give 1850rpm, and she ran smooth as glass.

I did find a couple extra markings on the tight one. 0198, and a series of monotonically increasing number 067 to 069. I'm thinking it is January, 1998 as the date of manufacture, and the other numbers mark where they were in the hose that it was cut from.

I'm going to pull the spindle and put in new "4L" belts. Looking for a couple of the highest quality, that is cogged and kevlar reinforced. I could do the link belt, even have one on hand that I could use; but, my experience with them is that they're noisy. I'd prefer this repair outlast me.
 
Do I really need two belts? Follow along with me for a second.

Atlas modified the 12" lathe to use two belts due to problems they had with slipping. But, that was a while ago, and belts have improved. I've got a 1Hp, 3phase driving mine through a VFD. Nice, smooth power. The bottom sheave is 2.5", and the top is 3".

Here is a link to a belt guide from Grainger.


The type A belt can handle 1.69Hp on a 2.6" sheave. The AX can handle up to 2.25Hp. These numbers can't be taken directly. The video below explains the corrections that need to be made. But, at 1750, the RPM stated is close enough to mine, and the Hp rating so far in excess of what I am able to produce, that I think I can just take one belt off the shelf and use it. Then I don't have to worry about the issues involved with matching belts.

Am I missing something?

 
The late models of the Atlas 12" did not all use the same belts. The bench models with a 4-speed conical pulley on the spindle use two different 1/2" nominal section FHP v-belts. The cabinet models used a total of four V-belts. The motor belt and the belt that connects the two 4-step cone pulleys are still 1/2" section FHP belts. The two identical spindle belts are "A" section A42 "Multiple V-Belt" belts, not 1/2" section FHP Belts.

I don't normally comment whenever someone mentions using link belts but I do not recommend using them for anything other than what they were originally designed for, which was for temporary emergency repairs in a heavy production environment not involving running in both directions. Anyone who insists on attempting to re-start that argument will simply have their posts deleted.
 
If I’m understanding the one set of pulleys are worn ? Then I would think even a matched set would have issues. Maybe a single belt until you find it slipping .
 
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