Belt experts, are 3V and 3VX interchangeable?

[Joe Jensen]

My SCMI jointer had a 3V-425 belt on it that was shot. Grainger sold me a 3VX-425 which is cogged, but the same size. They claimed the cogged version was a step up. They did not have the 3V series.

The jointer uses the weight of the motor tension the belt and it has a spring to prevent the motor from lifting. The new 3XV belt slips when the motor starts. I've programmed the VFD for a .8 sec soft start, and it now starts without slipping.

Is a 3VX interchangeable with a 3V? I've searched the web, and the have the same dimensions, but the picture of a 3V shows that sides slightly concave. The sides of the 3VX belt they sold me are straight.

On a side note, this is an amazingly small belt for a 3HP tool.

[Chris Padilla]

The belts on my 1990 Toyota pick-up are rather small for a 4 banger! ;)

[Joe Jensen]

The belts on my 1990 Toyota pick-up are rather small for a 4 banger! ;)

Actually the belts on a car only drive a few smaller loads. Not sure how many HP, but it's not like it's the whole 4 banger :)

[Charlie Plesums]

I don't know the specs of the 3V425, but the 3VX425 is a high power belt... multiple HP for many sheave sizes. On the scale of belts that I have learned about, the VX series is the highest power capacity.

On my MiniMax machine (a SCMI subsidiary) the 5 hp jointer planer is driven by two 3L500 belts. They are rated fractional HP, so I wonder how two fractional hp totals 5 hp. When they dissolved, I replaced them with 3VX500 belts which are working perfectly, and have not dissolved.

[Ben Martin]

Actually the belts on a car only drive a few smaller loads. Not sure how many HP, but it's not like it's the whole 4 banger :)

Haha, I build "big yellow machines" as a day job, it takes 120HP just to turn the radiator fan on our machines, now those are some belts!!

[J.R. Rutter]

Joe - I routinely replace V with VX when it is time to replace them.

[Joe Jensen]

Well, I cleaned the pulleys (the alcohol was clear after, and the white rag to dry was clean) and they weren't dirty. Interestingly, the motor side is where it's slipping and the motor pulley diameter is maybe 2X the cutterhead diameter. With the .8 sec soft start programmed into the VFD and it starts fine, but this is puzzling and not right.

[Steve Rozmiarek]

Haha, I build "big yellow machines" as a day job, it takes 120HP just to turn the radiator fan on our machines, now those are some belts!!

That must be the BIG iron from Peoria?

[Tom Klass]

Joe, You are better off with the cogged belt and it would be a direct replacement. The cogged belt is better for smaller pulleys easier to go around the smaller radius. where I work most of the machines have been replaced with the cogged belt they hold up much better esspecially when the belt needs to go against an idler pulley less stress on the inside webbing also less noisy.
good luck, tom

[Ben Martin]

That must be the BIG iron from Peoria?

Nope, from Aurora, IL. We make Wheel Loaders and Excavators here. I used to work in Peoria though.

Here is a pic of the machine I was talking about, it is our second largest BTW.

[Rod Sheridan]

I don't know the specs of the 3V425, but the 3VX425 is a high power belt... multiple HP for many sheave sizes. On the scale of belts that I have learned about, the VX series is the highest power capacity.

On my MiniMax machine (a SCMI subsidiary) the 5 hp jointer planer is driven by two 3L500 belts. They are rated fractional HP, so I wonder how two fractional hp totals 5 hp. When they dissolved, I replaced them with 3VX500 belts which are working perfectly, and have not dissolved.

Hi Charlie, fractional horesepower motors are loosely defined by having an output of one horsepower at normal shaft speeds ( about 1800 RPM) this means the torque value is a fixed maximum number, or having a frame size equal to or smaller than a 1 HP open motor of normal speed.

So a 2HP motor at 3,600RPM would be fractional since it would have a horsepower at 1,800 RPM of 1 HP. (Same torque, half speed).

The definition of fractional horsepower also includes motor frames 56 or smaller, so a 5 HP 3,600 RPM could be fractional if its frame size is 56 or smaller.


The same thing exists with belts, which are speed/force rated devices.

A belt with higher speed will transmit more power for a given force. So a belt rated fractional could indeed be used for several horsepower if the belt speed was high enough.

For a jointer or planer, the multi-horsepower motor may be running at very low belt force, with very high belt speeds due to motor speed and pulley diameter.

Regards, Rod.

[Charlie Plesums]

I appreciate the lesson, Rod. Makes me feel better about the OEM belt on my costy machine. However that OEM belt dissolved (or should I say, those two OEM belts dissolved) under normal use, and the VX belts are going fine several years later. So I only feel a little less cranky.

[Dennis Ford]

Interestingly, the motor side is where it's slipping and the motor pulley diameter is maybe 2X the cutterhead diameter. With the .8 sec soft start programmed into the VFD and it starts fine, but this is puzzling and not right.


You are correct, there is something wrong here. Is it possible the belts are contacting the bottom of the groove instead of (or in addition to) the sides? Any slippage should show up on the smaller pulley. I have seen machines where the motor pulley and driven pulley did not fit the same size belt. If that is the case, one or the other will have to be replaced to get maximum power transfer ( you might not actually need maximum power transfer).

[Charlie Plesums]

...
The jointer uses the weight of the motor tension the belt and it has a spring to prevent the motor from lifting. The new 3XV belt slips when the motor starts. I've programmed the VFD for a .8 sec soft start, and it now starts without slipping.....

I have never had any luck setting belt tension by the usual "so it deflects 1/2 inch" or whatever method. (Is that 1/2 inch when a kid squeezes it, or 1/2 inch when an 800 pound gorilla squeezes?)

Finally I learned ... if a belt squeals/slips when the motor starts, it is too loose (but no problem other than a little wear if it is a little squeal). Then I started really levering my shaper belt tight - no squeal, but found the belt turned inside out. MiniMax explained that the tension was too tight. I also found that once a belt had turned over, it was shot... it kept turning over even under minimal tension, and had to be replaced (it now also has a 3VX belt). I accept that the "1/2 inch deflection" may be too complex for me to handle, so I work with the new rule, "just enough tension to eliminate the starting squeal."

My old contractor saw had the traditional motor hanging out the back with the weight providing tension for the belt, and there was nothing to do to change the tension. But my old 6 in jointer claimed to set the tension by the motor mounted on a sloping panel. In that case, the slope may have contributed to the tension, but I could also add or subtract tension as I tightened the motor mount. If your jointer is like my saw, then the VFD solution (or tolerating a small squeal) may be the only solution. By playing with your mount and spring you may be able to get a little more tension so you don't need the soft start.

[Joe Jensen]

I have never had any luck setting belt tension by the usual "so it deflects 1/2 inch" or whatever method. (Is that 1/2 inch when a kid squeezes it, or 1/2 inch when an 800 pound gorilla squeezes?)

Finally I learned ... if a belt squeals/slips when the motor starts, it is too loose (but no problem other than a little wear if it is a little squeal). Then I started really levering my shaper belt tight - no squeal, but found the belt turned inside out. MiniMax explained that the tension was too tight. I also found that once a belt had turned over, it was shot... it kept turning over even under minimal tension, and had to be replaced (it now also has a 3VX belt). I accept that the "1/2 inch deflection" may be too complex for me to handle, so I work with the new rule, "just enough tension to eliminate the starting squeal."

My old contractor saw had the traditional motor hanging out the back with the weight providing tension for the belt, and there was nothing to do to change the tension. But my old 6 in jointer claimed to set the tension by the motor mounted on a sloping panel. In that case, the slope may have contributed to the tension, but I could also add or subtract tension as I tightened the motor mount. If your jointer is like my saw, then the VFD solution (or tolerating a small squeal) may be the only solution. By playing with your mount and spring you may be able to get a little more tension so you don't need the soft start.

There are two settings for the spring tension. I tried the tighter one and it still squeals on startup. I now think it's most likely that I am supposed to have a metric belt, even though the one I removed was a 3V. I'll call SCMI on Monday to find out.

[Joe Jensen]

Update:
==============

I spoke with SCMI today. The Parts guy looked up the belt, and it IS supposed to be a 3V belt. I have a 3VX which should be better. The pulley is clean, sanded it a little too, so I know it's clean. Maybe the new belt from Grainger is somehow defective, but it feels just like a new belt.

SCMI had a service tech call me and the first tech did not know about that specific machine. He is having someone with expertise on that machine call me, but there is no way to increase the belt tension.

The last option is to order the 3V belt from SCMI...joe

[Charlie Plesums]

Parts guys are nice friendly warehouse people who can look up a part number in the manual and find the part for you from the shelf. They are not machine experts.

There is no way I would replace a 3VX belt with a 3V belt, but it is your machine.

How do you release the tension to replace the belt?

[Joe Jensen]

Parts guys are nice friendly warehouse people who can look up a part number in the manual and find the part for you from the shelf. They are not machine experts.

There is no way I would replace a 3VX belt with a 3V belt, but it is your machine.

How do you release the tension to replace the belt?

It's easy to get a 3V. Based on my online research, the profiles for 3V and 3VX are the same dimensionally, but you may be right.

The motor mounts to a cast iron plate that swings on a shaft. The weight of the motor and plate tension the belt. There is a medium tension spring that pulls the motor down and the belt a little tighter. I think the spring is there to keep the belt from jumping off the pulley when the motor starts. The way the machine is designed, there is no way other than a much heavier spring to put more tension on the belt.

[Charlie Plesums]

...
The motor mounts to a cast iron plate that swings on a shaft. The weight of the motor and plate tension the belt. There is a medium tension spring that pulls the motor down and the belt a little tighter. I think the spring is there to keep the belt from jumping off the pulley when the motor starts. The way the machine is designed, there is no way other than a much heavier spring to put more tension on the belt.
I am grasping at straws, but is the shaft that the plate swings on well lubricated?

[Joe Jensen]

I am grasping at straws, but is the shaft that the plate swings on well lubricated?

Sadly yes. I'm going to try a 3V, but all the experts tell me that a 3VX is an upgrade to a 3V :confused: