Thread: Using VFD to lower RPM on large woodworking bandsaw just a bit....

32 inch wood vertical bandsaw, supposedly only 2 hp, turns at such high speed that vibration is a slight issue. Wondering if via VFD the rpm could be fine turned to reach a more harmonic speed ? And would a 2 hp capacity VFD be large enough for a 2 hp 32 inch bandsaw ?

Originally Posted by Milacron

32 inch wood vertical bandsaw, supposedly only 2 hp, turns at such high speed that vibration is a slight issue. Wondering if via VFD the rpm could be fine turned to reach a more harmonic speed ? And would a 2 hp capacity VFD be large enough for a 2 hp 32 inch bandsaw ?

Generally yes to both, presuming 3-phase all-around and a 'good brand' of VFD.

De-rating, however, is generally pretty cheap insurance in the lower HP ranges, so I'd look at 3 or 4 HP units and see if the higher rating actually cost enough more to matter.

Bill

Originally Posted by thermite

Generally yes to both, presuming 3-phase all-around and a 'good brand' of VFD.

De-rating, however, is generally pretty cheap insurance in the lower HP ranges, so I'd look at 3 or 4 HP units and see if the higher rating actually cost enough more to matter.

I wonder if motor physical size would matter ? This is on an older Northfield bandsaw where the Louis Allis motor is as large as a modern 10 hp motor...probably due to it's slow RPM (866) as well as battleship construction. 6.8 amps at 220 volts. Already have a new EMS G5U-21P5, 2 hp VFD, so would be nice if that would work. On nameplate for output of this EMS is "CT (150% OL)= 8.0 amps"

The other question is, should the saw magnetic starter be abandoned and turn saw on/off via the VFD only ?

The older motor will likely have a lower temperature insulation class. That could limit the range you'd try to get from your motor, but shouldn't be a problem in your case; since you'll probably run it in range more like 70 to 100% of full speed.

Don't know if you just want to cut contours or do some resawing. 2hp is plenty for most uses, but 3 or more could be useful if you have 12" or more under the guides for resawing. All of which is to say that a 3hp VFD sounds about right and (as suggested above) is cheap enough. It will also let you add a 3hp motor should you want it.

You'll want to ditch the magnetic starter.

Not sure of the pulley arrangement on this, but if vibration is the sole issue you might try a link belt and perhaps a different motor pulley.

If there are well positioned factory ON/OFF controls that look appropriate and you want to retain them, don't 'ditch' the mag, use it as a contact closure for the logic buss on the frequency drive.

This wasn't the gist of the thread but it's pretty simple to balance bandsaw wheels using small dollops of epoxy putty as weights...I have done it several times and achieved perfect, vibration free balance when running.

Back on the topic of the thread, a frequency drive has the ability to brake the saw to a faster stop, not to mention a ramped start. Some shops don't want the operator to leave the machine while it's still turning...the DC brake on the drive would address this if it were a concern which it may not be.

Stuart

FWIW, this wasn't my saw but a friend of mine. They got to looking closer this afternoon and found a set screw ever so slightly loose that secured the upper wheel to the shaft, tightened the screw and now it runs so smooth the want of the VFD has evaporated. Still, I'm glad for the info ... I have a 20 hp resaw I might be inspired to add a 30 hp VFD to (that I used to use as a phase converter 12 years ago)....mostly for the "soft start" possiblities and braking.

Just remember that with a VFD, as you lower the speed, you are lowing the HP. But on something like a band saw, if your teeth make fewer passes through the material (lower speed on the blade), each tooth then starts contacting the wood longer, which INCREASES the load on the motor. So as you LOWER the motor HP, you are effectively RAISING the load HP requirement. Any over sizing of the motor goes right out the window very fast.

Originally Posted by Jraef

Just remember that with a VFD, as you lower the speed, you are lowing the HP. But on something like a band saw, if your teeth make fewer passes through the material (lower speed on the blade), each tooth then starts contacting the wood longer, which INCREASES the load on the motor. So as you LOWER the motor HP, you are effectively RAISING the load HP requirement. Any over sizing of the motor goes right out the window very fast.

I cut wood, non-ferrous, and even steel. Just change the blade to suit the application.

This is 1 hp on an 18 inch saw, (motor the size of a 10hp unit ;-) but the Siemens VFD does everything a guy could want in a vert. band saw with respect to blade speed. Since FEED RATE determines the Horse Power requirement, the Motor sizing is a moot point unless production requirements dictate otherwise. I've yet to run out of power when the correct blade in good condition is fitted.

cheers

Originally Posted by Milacron

I have a 20 hp resaw I might be inspired to add a 30 hp VFD to (that I used to use as a phase converter 12 years ago)....mostly for the "soft start" possiblities and braking.

Whether that 12 years is when last used or when first used, the age - perhaps older yet - is worrisome. The most critical bits - electrolytic capacitors - are subject to calendar-aging as well as in-use-aging, largely from ripple. On gear expensive enough, or rare and collectible enough to justify it, there has long been a habit of putting the critter on a controllable power source and 're-forming' similar such capacitors. Or just replacing them all, which is a PITA even when not terribly expensive. And it CAN be expensive.

Have a look at the online published flat-rate refurb prices of the outfits who advertise DC Drive and VFD repair. There is precious little trouble-shooting or fault analysis time involved. Most of the fee is down to cost of known limited-life components and the labour to de-solder and replace.

Even if a top-brand and lightly loaded when it WAS in use, having sat idle will not necessarily have extended its life, so a VFD of that vintage has fairly high odds of failure by now.

Same applies to the bargain find of an older high-grade VFD - whether used or even NIB or NOS. Bit of a dice-roll, they are.

Bill

Originally Posted by thermite

Whether that 12 years is when last used or when first used, the age - perhaps older yet - is worrisome. The most critical bits - electrolytic capacitors - are subject to calendar-aging as well as in-use-aging, largely from ripple. On gear expensive enough, or rare and collectible enough to justify it, there has long been a habit of putting the critter on a controllable power source and 're-forming' similar such capacitors. Or just replacing them all, which is a PITA even when not terribly expensive. And it CAN be expensive.

Have a look at the online published flat-rate refurb prices of the outfits who advertise DC Drive and VFD repair. There is precious little trouble-shooting or fault analysis time involved. Most of the fee is down to cost of known limited-life components and the labour to de-solder and replace.

Even if a top-brand and lightly loaded when it WAS in use, having sat idle will not necessarily have extended its life, so a VFD of that vintage has fairly high odds of failure by now.

Same applies to the bargain find of an older high-grade VFD - whether used or even NIB or NOS. Bit of a dice-roll, they are.

The 30 HP VFD is a GE and probably 14 years old by now. I dunno...I have the impression from past experiences that electrolytics were simply made "better" by the early 90's going forward...but it will be interesting to see. That VFD has probably 3 hours use on it total, so if it fails soon after reawakening I'll have a pretty good idea of why.

Originally Posted by Milacron

32 inch wood vertical bandsaw, supposedly only 2 hp, turns at such high speed that vibration is a slight issue. Wondering if via VFD the rpm could be fine turned to reach a more harmonic speed ? And would a 2 hp capacity VFD be large enough for a 2 hp 32 inch bandsaw ?

I run a surface grinder with a VFD.
I notice that at 60Hz there is a drone or resonance.
Not a severe vibration, but when I run it at 58Hz or 62Hz
the machine is noticeably smoother.
So maybe your band saw has a similar thing going on.

--Doozer

I run my Logan 820 at 40 Hz as this is a "sweet spot" in the drive system and is most compatible with the work which I do on this lathe.

My drive package came from Dealer's or another, similar one, and included a 1 HP TEFC ABB motor and a matching TECO/Westinghouse FM-100 drive. The FM-100 comes standard with a speed pot, but I usually use the keypad to change speeds.

Normally, a Logan 820 is powered by a 1/3 HP capacitor start/induction run motor.

At first glance, the 1 HP TEFC motor might seem to be overkill, but at 40 Hz, the motor is really putting out (40/60) * 1 HP, or 2/3 HP.

Originally Posted by thermite

Have a look at the online published flat-rate refurb prices of the outfits who advertise DC Drive and VFD repair. There is precious little trouble-shooting or fault analysis time involved. Most of the fee is down to cost of known limited-life components and the labour to de-solder and replace.

WRONG

As one of those repair places of Dc drives, AC drives, Servo drives, spindle drives, VFD drives, I will guarantee you that a flat rate repair charge has NOTHING to do with wholesale replacement of "limited life components." Flat rate repair charges are a SWAG based on experience; we win some and loose some. sometimes we make a ton of money, sometimes we loose a ton of money. The charge is based on the overall average. It is a simple marketing tool. Period.

We much prefer to give a quote after evaluating a real drive, based on what IT NEEDS -- to get running again. Then, if there are potentially marginal things like batter backed ram, Dc bus caps, IGBTs, that may fail soon in our opinion (there ARE tests than can help tell this), we offer those additional preventive maintenance items as options. Then it is up to the customer to decide if he wants to spend the extra money or not. WE also sell 'refurbed' drives. This by no means mean the drive got a whole new set of dc bus capacitors - to refurb a defective drive then resell it at a refurb price seldom allows enough money to do such. And most of the time there IS a significant amount of trouble shooting and fault analysis time & effort put into making it work again to be resold. At an average of 5 drive repairs a day, I think we know the difference.