1340GT: Advice on how to get belt tension correct?

[andrewgr]

Any tips/tricks/advice on how to get the tension on the belt correct?

 

[pacifica]

By balancing the sheaves, changing to a gates cogged belt direct from gates and reinforcing the stand I was able to almost eliminate vibration that occurred at about 655 to 700 rpm. Belt needs to be towards the loose end of tension. That's about 1 to 1.5" of slack. Added benefit is the belt will slip if you are over extending the lathe. Maybe extend the life of the bearings.

I measured the vibration with an indicator on a stand separate from the lathe and get slightly less than .001" from 655 to 700 and about .0003" at the other rpms.

 

[RJSakowski]

The amount of slack will depend on the distance between the pulleys.A common method of setting the tension is to deflect the belt with a "moderate amount of force and note the deflection. The problem is, what is a moderate amount of force. There are devices which will measure tension by using a spring to apply force to deflect the belt between two arms at a set distance.

Amazon.com: ABN Belt Tension Gauge - Universal, 10 lbs Specification, Easy to Read: Automotive

Buy ABN Belt Tension Gauge - Universal, 10 lbs Specification, Easy to Read: Timing Belt Tools - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

 

[andrewgr]

The amount of slack will depend on the distance between the pulleys.A common method of setting the tension is to deflect the belt with a "moderate amount of force and note the deflection. The problem is, what is a moderate amount of force. There are devices which will measure tension by using a spring to apply force to deflect the belt between two arms at a set distance.

Amazon.com: ABN Belt Tension Gauge - Universal, 10 lbs Specification, Easy to Read: Automotive

Buy ABN Belt Tension Gauge - Universal, 10 lbs Specification, Easy to Read: Timing Belt Tools - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

I've looked through the manual, and it doesn't give a value for what the correct tension should be. This being the case, how would I use the Belt Tension Gauge? Are you aware of anywhere that gives a recommended number to be shooting for?

 

[RJSakowski]

I can't say. The proper tension will depend on use. The type of belt, concerns for bearing wear, pulley sizes, and torque requirements all come to play. A loose belt will slip and eventually glaze the belt. A tight belt puts stress on the bearings and causes temperature belt failure.You might find some guidance on the websites of belt manufacturers.

Belt Tension Calculator

For standard & micro v-belt types, determine the proper tension for manually tensioned belts with Gates Belt Tension Calculator.

www.gates.com

https://www.daycoproducts.com/stuff/contentmgr/files/3/1378ea57bf6d09e5f72ce92bb8eff3ce/documents/belt_tension_recommendations__rev._4.18.13_.pdf

 

[xr650rRider]

I wouldn't overthink it too much. Clean the sheaves with de-greaser as the sides of the belt do all the work. If your running a VFD, the weight of the motor is nearly enough tension. It won't slip on startup as the VFD accelerates on a programmed ramp to speed. No VFD, you'll probably hear the belt chirp when in high gear on startup. Too tight it's hard on bearings so just apply a little force to motor and cinch it down.

 

[andrewgr]

If I get it too tight, is there a risk of any permanent damage to the machine, other than the belt wearing out more quickly (or breaking)?

 

[xr650rRider]

Again, too tight is hard on bearings, bearings in the motor or bearings in the headstock side. DON'T use a pry bar to push down on motor and it will be fine. The further apart the sheaves are, then the more deflection the belt can have for same amount of tension, so deflection in belt at low speed setting is different than high speed. Again if the lower pivot isn't locked down, the weight of the motor plus just a little force with hand is plenty tight. If it doesn't slip with just weight of motor, then that's tight enough.

 

[Ischgl99]

You can also break the shafts by over tightening the belts. The excessive force over time can create a crack in the shaft that leads to failure. I had a customer that ignored his mechanics advice on a small motor and tighten the belt so tight he could play the guitar with it, didn’t take long for an expensive shaft to fail.

Follow the advice given in previous replies and you should get long life from your machine. If you want a number for your tension, I believe Gates has a tension calculator on their website.

 

[andrewgr]

Again, too tight is hard on bearings, bearings in the motor or bearings in the headstock side. DON'T use a pry bar to push down on motor and it will be fine. The further apart the sheaves are, then the more deflection the belt can have for same amount of tension, so deflection in belt at low speed setting is different than high speed. Again if the lower pivot isn't locked down, the weight of the motor plus just a little force with hand is plenty tight. If it doesn't slip with just weight of motor, then that's tight enough.

Okay, this is what I did, so I guess my intuition wasn't too bad. I'm more worried that I have too little tension, rather than too much-- I have experienced the belt slipping, but I've only spent a couple hours actually making chips, and I've never used a lathe before, so I'm perfectly willing to believe that I was abusing it as I tried my first parting job, and that it should have slipped. If it continues happening, maybe I'll try a tad more pressure on the motor before locking it into place.