Northfield Jointer Throwing Belts

[Malcolm McLeod]

I don't understand why the single phase motor would have a sudden drop in RPM's...

The big-brain folks haven't weighed in, but I would assume that as the planer is stopped and initially begins slowing, the run winding is a 'generator' load. When it slows further, the centrifugal switch closes, the start winding and the start capacitor are connected back into the circuit - but now as (sudden) additional LOADS on the inertia of the cutter. System slows down (suddenly)?

I still think the sheave's ctr-ctr distance, belt's rigidity/flex/stretch/slack, and the above change in load all combine for belt slap - - and 'un-wrap' ( I'm paying attention, Mr. Coers). I'm just not sure about the most efficient fix.

[Jerry Bruette]

Are the motors both the same frame size? If not how was the motor mount modified to fit the 3HP motor?

I'd like to see a picture of the sheaves to determine if they're worn.

I don't think 37 1/2 c-c is a long belt, I've worked with drives that are way longer than that. Shorten the c-c dimension and you have problems with wrap on the sheaves w/o changing sheave diameters.

I googled a picture of the jointer and don't see how you'd shorten the c-c dimension of the drive without major modifications.

I'd buy some new brand name belts and make sure they're installed properly and tensioned maybe a little on the tight side and give it another go.

[Rob Sack]

Did Northfield spec the motor too? What brand is it. Sounds like a 3600 rpm two pole motor. Northfield used that hp on their 12" jointers but it was a direct drive large frame design. in a single phase motor, I'd want 5 hp or at least an 1800 rpm 3hp and different pulleys. I know this isn't your problem with shut down but if you decide to swap, do it right. I find NOS good 5 hp three phase motors all the time for under $600 delivered. I even find TENV vector duty motors ( $1500 new and a big step up from normal ) for $500. I don't like single phase much so I don't have a lot of experience with them on a large jointer but it could be a problem specific to this motor. Most 3 hp 3600 rpm motors are made to a price point and not the greatest piece of engineering on the planet.

As to the vfd wiring, there are codes that say you should run an input 250% of the rated output so that is the information you will get when you ask. I know a 30 amp circuit will work and you are not likely to ever hit FLA on a 5 hp motor on a jointer unless it is in the 20" wide range. Dave

Northfield did spec the motor, which is a TEFC Baldor 3 hp - 3600 rpm motor, along with the pulleys and belts. From a performance standpoint, the machine works perfectly. I have never been able to bog it down. The original motor is a 5 hp, 3 phase, 3600 rpm motor with a 5/8 in. double pulley.

[mreza Salav]

On my 3-5HP motors typically the belt is tight enough that you cannot put the belt on without loosening the motor mount. I am still thinking that if the pulleys are aligned and the belts are not damaged and properly chosen then it must be the insufficient tension on them. I'd try to loosen motor mount, use a long screw driver or something similar to put extra tension on the belts and tighten the bolts at the same time.

[Rob Sack]

First of all, I want to thank everyone for their suggestions. As far as the motor specs., Northfield lists on their website that the standard motor for their 12HD jointer is a 3hp/3600 rpm motor, which is what I have. The desired cutter head speed is 4500 rpm. My current set up has a 4490 rpm cutterhead speed. After talking again with Northfield, I am going to try changing the belts and pulleys to 5/8 and see if the extra stiffness will solve the problem. If this doesn't work, I guess my only other alternative is to go back to the original 5 hp/3 phase/3600 rpm motor with a VFD and bring in a new 50 amp circuit, or just live with the belt situation as I have for many years.

[Paul Haus]

This kind of remind me of something on the farm growing up. Had a elevator that would throw a belt at times on shutdown. I found some scrap stuff that one was a shaft that had a pivot on one end, a pulley sticking out from it on one side and an adjustable weight on the other end. I welded up a mount and put it so the pulley just rested on the belt and adjusted the weight so it kept tension on the belt, nothing more. The belt would whip a little on shut down and this kept the belt more stable during shutdown and did nothing else while the elevator was running. It wasn't fancy, it wasn't special but it did work. Just a thought.

[David Kumm]

Baldor is as good as it gets in the small motor world so I'm leaning to belt tension too. I have motors that you can instantly change from forward to reverse with a load and don't throw the belt but it needs tension or an idler. Dave

You also don't need a 50 amp circuit to run that machine from single phase. If a 3 hp motor works fine and you decide to swap back, a good 3 hp output vfd will run the 5 hp motor. The vfd will allow a slower ramp up to cut down inrush. I'd add a braking resister for $100 and use the vfd to slow the head down within 5-10 seconds. Opening that porkchop guard and seeing the head still turning is scary. I tend to be absent minded so will never leave a machine that has not stopped. Dave

[Bill Dufour]

My general guess is the belts have worn and stretched. It is time to move the motor and tighten the belts . Are you sure the motor is parallel to the jointer head?
Bill D

[Mark Wooden]

Sounds t me like the motor brakes hard and fast and the cutterhead inertia is whats throwing the belts. The cutterhead is probably heavier than the motor armature also. I wonder if there is a way to delay or slow the braking in the motor.
JMHO

[Mel Fulks]

Not much….but I remember an old jointer that was bought by the shop I worked in. We couldn’t keep the jointer belt on and we brought in
an “expert” . The belt had to have a twist in it to stay on. We were trying to run it without the twist.