Northfield Jointer Throwing Belts

[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...ff-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...ff-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.

[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