Northfield Jointer Throwing Belts

[Rob Sack]

I have a 1953 Northfield 12HD jointer. It has been a great machine with one exception. I got it with a 5 hp three phase motor. I swapped it out with a new 3 hp Baldor single phase motor and Furnace starter. It works fine except on shut down. Something happens to the motor that causes a brief shutter that throws the belts. The folks at Northfield suggested that this is characteristic of single phase motors. They also recommended I use double 3/8" belts when I did the motor swap. Once running the belts work fine. I asked them if I could switch to 5/8" belts and pulleys in order to stop the belts being thrown at shut down. They are suggesting against it. I don't remember why. They are now suggesting I put the original 5 hp/3 phase motor back on with a vfd. I wouldn't mind doing this, but I don't know the condition of the 68 year old motor, a proper name brand vfd will cost close to $1,000.00 with tax and shipping, and the vfd will require a 50 amp/220 volt circuit, which I am capable of providing, but it's a big job. This seems to be a very expensive and labor intensive way of preventing the belts from being thrown. The current 3 hp motor works great and I have yet in all the years I have owned the jointer, been able to bog it down. I've adjusted the belt tension and checked the pulley alignment. The distance between the motor shaft and the cutterhead shaft is 37 1/2 " OC, making for long belts. Any suggestions? What about idler pulleys to reduce the flex on the long stretch of belts?

[Kevin Jenness]

Have you been to the motor shop? Could be a problem with the centrifugal switch, definitely worth having it checked out.

[Richard Coers]

What's a furnace starter?

[Brian Runau]

I would not use an idler pulley, not really their application. Speed might also be limiting factor. Brian

[Paul F Franklin]

What's a furnace starter?

I suspect OP mean a "furnas" starter, it's a brand name.

[Paul F Franklin]

When does it throw the belt? Right when you shut it off, or a little while later during spin down?

[Andrew Hughes]

That’s a weird one . My first thought is the belt isn’t the correct side for the pulley. I’ve ran odd sizes before on my Davis and wells table saw and never had one come off it’s a single phase motor. It would have to be very far off in sizes
Good Luck

[Rob Sack]

What's a furnace starter?

I meant Furnas brand manual starter for the motor. I really could use a Spellcheck for Woodworkers app.

[Rob Sack]

When does it throw the belt? Right when you shut it off, or a little while later during spin down?

It will throw the belt 8 to 10 seconds after shutting down the machine. There is a slight click and the motor drops into a lower rpm range. At that point the belts vibrate momentarily and more often than not, one or both will either flip over upside down, or occasionally fall off the motor pully.

[Michael Schuch]

I have a 1953 Northfield 12HD jointer. It has been a great machine with one exception. I got it with a 5 hp three phase motor. I swapped it out with a new 3 hp Baldor single phase motor and Furnace starter. It works fine except on shut down. Something happens to the motor that causes a brief shutter that throws the belts. The folks at Northfield suggested that this is characteristic of single phase motors. They also recommended I use double 3/8" belts when I did the motor swap. Once running the belts work fine. I asked them if I could switch to 5/8" belts and pulleys in order to stop the belts being thrown at shut down. They are suggesting against it. I don't remember why. They are now suggesting I put the original 5 hp/3 phase motor back on with a vfd. I wouldn't mind doing this, but I don't know the condition of the 68 year old motor, a proper name brand vfd will cost close to $1,000.00 with tax and shipping, and the vfd will require a 50 amp/220 volt circuit, which I am capable of providing, but it's a big job. This seems to be a very expensive and labor intensive way of preventing the belts from being thrown. The current 3 hp motor works great and I have yet in all the years I have owned the jointer, been able to bog it down. I've adjusted the belt tension and checked the pulley alignment. The distance between the motor shaft and the cutterhead shaft is 37 1/2 " OC, making for long belts. Any suggestions? What about idler pulleys to reduce the flex on the long stretch of belts?

A 20amp 240v circuit should be more than enough for a 5hp VFD. The last Chinese 5hp VFD I purchased was about $100. The Last Hitachi 5hp VFD (SJ200) I purchased was a little over $200 (Used SJ200 off ebay). Not much need for a fancier WJ200 Hitachi VFD on a jointer. A 68yo 3ph motor is still practically a baby, I have a ~100yo 3ph motor with its original bearings running on a Chinese VFD just fine. 3ph motors will way outlast most single phase motors.

I have no clue why the single phase motor is causing the jointer to throw belts? Are you sure the pulleys are lined up correctly? Are you using the original motor pulley off the original 3ph motor? I might try a link belt. How is the motor tentioning the belt (a photo or two might help). But I would go with the original motor and a Chinese VFD.

[Kevin Jenness]

It will throw the belt 8 to 10 seconds after shutting down the machine. There is a slight click and the motor drops into a lower rpm range. At that point the belts vibrate momentarily and more often than not, one or both will either flip over upside down, or occasionally fall off the motor pully.

The click definitely sounds like the centrifugal switch. Does the motor vibrate at that point?

[George Makra]

Chances are you have damage belt already I would replace your belts. Once they've rolled there's a good chance that the cords have been damaged and they will continue to roll off. Next take a straight edge and make sure that you are aligned from sheeve to sheeve. Then I suggest you check the tightness of the belts the belts I don't know what the span is between the motor and the top sheeve. But I can say that you probably should have about a 1/2 inch of deflection it's been a deflection on the belt mid span.

You don't have to look at the electrical it has nothing to do with the belts rolling off. It's like saying your car doesn't start and you check the air pressure in the tires.

You are hitting a harmonic on slow down and that is causing your belt to jump off but but you already have some issues that are allowing the belts off.

[Ronald Blue]

Explore getting a banded V-Belt. They are one piece with 2 or more Vee's. Here is a link to an example. It's guaranteed they won't flip over. In my experience once a belt "turns" over it is no longer dependable. That may be why you are having more issues after tightening. We had an application that ran 5 belts side by side. They seemed to even when "matched" to never all tighten evenly. Switched to these and belt issues became a non factor.

https://www.vbeltsupply.com/banded-wedge-wrapped-belts/3v

[mreza Salav]

I agree with George. Things I'd look at are:
- not enough tension on the belts and/or wrong size belts.
- making sure the pullyes are coplanar.

Single phase/3phase should have nothing to do with this, unless the motor is damaged and makes extra ordinary vibration.

[Rob Sack]

A 20amp 240v circuit should be more than enough for a 5hp VFD. The last Chinese 5hp VFD I purchased was about $100. The Last Hitachi 5hp VFD (SJ200) I purchased was a little over $200 (Used SJ200 off ebay). Not much need for a fancier WJ200 Hitachi VFD on a jointer. A 68yo 3ph motor is still practically a baby, I have a ~100yo 3ph motor with its original bearings running on a Chinese VFD just fine. 3ph motors will way outlast most single phase motors.

I have no clue why the single phase motor is causing the jointer to throw belts? Are you sure the pulleys are lined up correctly? Are you using the original motor pulley off the original 3ph motor? I might try a link belt. How is the motor tentioning the belt (a photo or two might help). But I would go with the original motor and a Chinese VFD.

This solution certainly is cheaper and much less labor intensive. However, the folks at Wolfautomation, which is a highly regarded supplier of quality VFD's, recommend a supplying electrical circuit twice amperage of the motor plus 50%, bring the total to 42 amps, hence a 50 amp circuit.

[Rob Sack]

I agree with George. Things I'd look at are:
- not enough tension on the belts and/or wrong size belts.
- making sure the pullyes are coplanar.

Single phase/3phase should have nothing to do with this, unless the motor is damaged and makes extra ordinary vibration.

The pulleys are coplanar, they have been checked with a precision straight edge. The belt tension has been adjusted to within 1/2". The belts were sized by Northfield when I did the motor swap. This had been going on since the belts were new, so I don't think the issue is worn or damaged belts. Northfield agrees. the reason for switching back to the 3 phase motor, and thus requiring the VFD, is that the 3 phase motor will not have the sudden drop in rpm's on shutdown, like the single phase motor. Again, this is according to Northfield.

[mreza Salav]

Most non-production machines have single phase and it is not normal for belts to jump. Sudden drop in rpm is not reason enough for belts to jump off pulleys. I would try to increase the tension on pulleys further and test. Do you feel vibration on the whole machine during shut down?

[Andrew Hughes]

The pulleys are coplanar, they have been checked with a precision straight edge. The belt tension has been adjusted to within 1/2". The belts were sized by Northfield when I did the motor swap. This had been going on since the belts were new, so I don't think the issue is worn or damaged belts. Northfield agrees. the reason for switching back to the 3 phase motor, and thus requiring the VFD, is that the 3 phase motor will not have the sudden drop in rpm's on shutdown, like the single phase motor. Again, this is according to Northfield.

This makes more sense to me. My jointers head will spin for 5 mins after I hit the stop button. There’s so much mass coupled with the oil bath bearings the first minute it doesn’t sound like it’s turned off.
I could see a single phase belted motor not able to keep up with all the mass in motion.
My machine is direct drive 3ph.
Good Luck

[Michael Schuch]

This solution certainly is cheaper and much less labor intensive. However, the folks at Wolfautomation, which is a highly regarded supplier of quality VFD's, recommend a supplying electrical circuit twice amperage of the motor plus 50%, bring the total to 42 amps, hence a 50 amp circuit.

You might question them about this. This is very contrary to my experience with VFD's. Due to the soft start feature of VFD's 3 phase motors draw considerably less current on start up than single phase or three phase motors on there respective native circuits with a motor starter and no soft start. The soft start feature dramatically curtails the initial inrush current of starting the motor which is the max current most motors will ever draw. This can be easily seen with a clamp on current probe and a multimeter like a fluke set to capture the maximum amperage reading.

Having over a half dozen 3 phase machines running on VFD's and having shared experiences with hundreds of other wood workers, metal workers and home machinists the advice they gave you makes no sense for real world applications. I think you either misunderstood them or were not talking to their "A" team engineers. A 5hp VFD would trip an error and shut down WAY before pulling even half of that current. It simply isn't possible for a 5hp VFD to pull that much current. A 50amp 240v single phase circuit for any 5hp motor makes absolutely no sense.

[Richard Coers]

If all engineering leads to the length of the belts being a problem, then the cheapest fix would be to add a jackshaft between the motor and head. Doing some research and worn pulley grooves shows up. How old are the pulleys? Plus more reading; http://vbeltsupply.blogspot.com/2013/01/v-belt-jumps-off-sheave.html https://www.seiffertindustrial.com/belt-failure-wear/

[Malcolm McLeod]

You might question them about this. This is very contrary to my experience with VFD's. Due to the soft start feature of VFD's 3 phase motors draw considerably less current on start up than single phase or three phase motors on there respective native circuits with a motor starter and no soft start. The soft start feature dramatically curtails the initial inrush current of starting the motor which is the max current most motors will ever draw. This can be easily seen with a clamp on current probe and a multimeter like a fluke set to capture the maximum amperage reading.

Having over a half dozen 3 phase machines running on VFD's and having shared experiences with hundreds of other wood workers, metal workers and home machinists the advice they gave you makes no sense for real world applications. I think you either misunderstood them or were not talking to their "A" team engineers. A 5hp VFD would trip an error and shut down WAY before pulling even half of that current. It simply isn't possible for a 5hp VFD to pull that much current. A 50amp 240v single phase circuit for any 5hp motor makes absolutely no sense.

^Agreed, FWIW.

From the handy motor handbook:
5hp/230VAC/3ph motor pulls 15.2 full load Amps, and a VFD will have to provide this from the 'back-end' of its circuit.
The front end would be receiving 230VAC/1ph, so it needs more amps to reach that same 5hp. The book says 28Amps. Or, you can multiply the 3ph load X ~1.7 (or square root of 3) and get roughly the same input value.

You need a 30A feeder to the VFD; exactly how I feed my 5hp DC.

Like others, I can only speculate about the belts. What V-series are the belts? 30? ...50? The center-to-center distance on the sheaves would give me pause for smaller profiles (30s or 40s), even tho' they'd likely carry the HP. I have seen much longer used, but in my world they are usually higher HP and quite large profiles (50+).

IMHO, the multi-V 'band' idea holds promise.

When you kill power, the cutter block - a large over-running load - begins driving the motor, rather than the motor driving the cutter. The motor turns into a generator. A 'tension reversal' in the belts occurs whenever this drive<>driven relationship changes. There may be enough stretch & so slack in the relatively long drive to throw a 'kink' in the belt when tension reverses. And off it comes.

I don't know exactly how, or if, a 1ph motor behaves as a generator, relative to the centrifugal switch cutting in/out; maybe one of the Sparkies can opine? But, I bet the switch adds to the 'kinks'. Might be interesting to get a slo-mo video of the belt during this transition...??

For background, my dad and then I ran his 12" 5HP/230V/1ph planer for (40?) years. It had 4ea VX-30 belts (not a band), on ~24" centers, and never threw one, nor did they ever require replacement.

[Malcolm McLeod]

If all engineering leads to the length of the belts being a problem, then the cheapest fix would be to add a jackshaft between the motor and head. Doing some research and worn pulley grooves shows up. How old are the pulleys? Plus more reading; http://vbeltsupply.blogspot.com/2013/01/v-belt-jumps-off-sheave.html https://www.seiffertindustrial.com/belt-failure-wear/

...Careful with this idea. The change in geometry may require either more belts, or larger profiles to convey the same Hp, as there could be less belt engagement of the drive & driven sheaves.

Edit: Re-read OP - - What diameter is the smallest sheave currently? Might be able to just increase the diameter of both sheaves (to maintain proper ratio)? :: You'd need longer belts, but have more engagement of the belts in each respective sheave?

No clue why vendor doesn't like larger belts. This should reduce belt slap (aka my reference to kinks above).

[Roger Feeley]

Are the belts tensioned using the weight of the motor or is everything bolted securely. I wonder if the profile of the belts are such that they get pinched in the pulleys.

[Richard Coers]

...Careful with this idea. The change in geometry may require either more belts, or larger profiles to convey the same Hp, as there could be less belt engagement of the drive & driven sheaves.

Edit: Re-read OP - - What diameter is the smallest sheave currently? Might be able to just increase the diameter of both sheaves (to maintain proper ratio)? :: You'd need longer belts, but have more engagement of the belts in each respective sheave?

No clue why vendor doesn't like larger belts. This should reduce belt slap (aka my reference to kinks above).
Engagement is not the proper term for belts and pulleys, that is for gears and threads. Degrees of wrap and v-belt cross section are the variables used in horsepower capability calculations for a v-belt system. I designed v-belt drives on small track type tractors at Caterpillar. Adding a jackshaft will not necessarily reduce degree of wrap if the pulleys are the same size as the pulleys on the motor and shaft.

[Malcolm McLeod]

Engagement is not the proper term for belts and pulleys, that is for gears and threads. Degrees of wrap and v-belt cross section are the variables used in horsepower capability calculations for a v-belt system. I designed v-belt drives on small track type tractors at Caterpillar. Adding a jackshaft will not necessarily reduce degree of wrap if the pulleys are the same size as the pulleys on the motor and shaft.

I assumed you meant converting 2 sheaves to a 3-sheave delta-shape with a given belt passing across all 3; now assume you are recommending 2 belts to do this (:: a v-shape) - - so I stand corrected. Semantically AND comprehendingly.:confused:

[Brian Runau]

I saw the post about belt wrap and it made me think. I wonder if the ratio between pulley sizes is to high. There is a min dia pulley size for drives depending on the profile of the belt etc... If the ratio is to great you might not have enough belt wrap in the smaller drive pulley and a shock load might cause this to jump off the pulley.

Brian

[Jerry Bruette]

The pulleys are coplanar, they have been checked with a precision straight edge. The belt tension has been adjusted to within 1/2". The belts were sized by Northfield when I did the motor swap. This had been going on since the belts were new, so I don't think the issue is worn or damaged belts. Northfield agrees. the reason for switching back to the 3 phase motor, and thus requiring the VFD, is that the 3 phase motor will not have the sudden drop in rpm's on shutdown, like the single phase motor. Again, this is according to Northfield.

I don't understand why the single phase motor would have a sudden drop in RPM's vs a three phase motor. After you stop supplying electricity to either motor don't they stop being the driver and become the driven? I would think that the three horse motor would have less mass than the five horse and would be easier to override with the cutter head.

When you put the new belts on did you loosen the motor and put the belts on or did you run the belts over the sheaves while the motor was bolted tight?

The problem could be badly worn sheave grooves. The sides of the grooves should be flat and not cupped.

I'll assume that the sheaves are coplaner in a parallel and angular plane.

[Rob Sack]

I saw the post about belt wrap and it made me think. I wonder if the ratio between pulley sizes is to high. There is a min dia pulley size for drives depending on the profile of the belt etc... If the ratio is to great you might not have enough belt wrap in the smaller drive pulley and a shock load might cause this to jump off the pulley.

Brian

The pulleys and belts were spec'd by Northfield when I first did the motor swap. The motor pulley is a double 3/8 in., 5 1/2 in. diameter. The cutter head pulley is a double 3/8 in., 4 1/4 in. pulley. The belts are always thrown from the larger motor pulley. And in reference to a previous question, the motor and jointer do not shake when this happens. But it does make the belts vibrate, sometimes considerable.

[Brian Runau]

The pulleys and belts were spec'd by Northfield when I first did the motor swap. The motor pulley is a double 3/8 in., 5 1/2 in. diameter. The cutter head pulley is a double 3/8 in., 4 1/4 in. pulley. The belts are always thrown from the larger motor pulley. And in reference to a previous question, the motor and jointer do not shake when this happens. But it does make the belts vibrate, sometimes considerable.

So they specified a drive that would I increase the motor speed to the cutter head? In industrial applications they decrease the speed to the driven pulley in order to increase the torque being transmitted. Brian

[David Kumm]

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

[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' (:cool: 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.