Bandsaw Modifications-crazy?

[Scott Rychnovsky]

I am still looking at getting a new bandsaw, probably a Grizzly G0514X2 19" bandsaw. I have recently been reading about the the potential of VFD motor controllers, and that has lead to the crazy idea of getting the 3 phase version of the above saw, G0514X3, which goes for the same price. My work area is wired for 220 V, so I would need some type of adaptor. I could get a VFD motor controller, such as a GS2-23P0, and rewire the bandsaw with that to take 220 V. Here is a link to the VFD:

http://web2.automationdirect.com/adc/Shopping/Catalog/AC_Drives/GS2_(115_-z-_230_-z-_460_-z-_575_VAC_V-z-Hz_Control)/GS2_Drive_Units_(115_-z-_230_-z-_460_-z-_575_VAC)/GS2-23P0

The down side is that it would add $300 to the cost of the bandsaw and it would take some work. (OK, this whole idea is probably a non-starter.)

The upside is that I would get smooth starts, automatic (programable!) smooth stops with built-in breaking, continuously adjustable RPM over a reasonable range, digital readouts for load on the motor during use, and somewhat more efficient energy consumption. None of the features is necessary, but they are very cool. This modification also makes the footbrake obsolete.

Why don't the manufactures build these VFD control boxes into most of their power tools?

Scott

[Bob Hallowell]

I would work if you bought the 3ph model But---

Grizzly already makes one but it is in a 17" model http://www.grizzly.com/products/17-Metal-Wood-Bandsaw-w-Inverter-Motor/G0640X

Bob

[Wilbur Pan]

The appropriate speed ranges for wood and metal cutting are different enough that even the Grizzly G0640X with the variable speed control requires a motor pulley change to shift from one to the other.

I think that the variable speed is useful for being able to cut various different types of metal, which is why it's readily available on metal cutting bandsaws. Variable speed is not real useful for wood cutting, as the range of useable speeds for wood cutting is so wide that being able to tweak the speed isn't necessary.

Out of the list of potential advantages for installing a VFD, the biggest one that I see is not needing a foot brake.

[Jeff Duncan]

Yup I have to agree with the others, the speed control just isn't necessary, at least I've never needed it. The power consumption, well my guess would be over your entire lifetime if you used the saw a lot, you probably still wouldn't save enough electricity to make up for the difference in cost.
And most industrial saws with 3 phase motors still use the footbrake, it's simple and it works, why change it for something electronic? With a bandsaw you generally don't need to monitor amperage. If it's underpowered for the task you'll know it, but generally if you buy a bigger machine you won't have that problem.
Hey it's your money, if you want to give it a try then go for it!
JeffD

[Peter Quinn]

Does the torque remain constant with the VFD? Will slowing down the motor significantly reduce torque? I'm not interested in in modifying my band saw but I have a new slot mortiser w/o variable speed. Most of the higher end models either come with VFD or have it available as an option as it really makes sense for boring applications given the wide range of different material and drill/cutter sizes potentially in use.

[Todd Ferrante]

To answer your specific question, the answer is simply because of the cost. On a one per machine basis, the cost vs benefit just isn't there for putting a digital speed control in every machine.

I have a digital VFD I picked up at the Cabin Fever Expo a couple of years ago. It was new in the box, but was a discontinued model. It was about $100. At the same show, I picked up a couple three phase motors ~3/4 to 1 HP for no more that $10 each. Three phase motors are easy to come by because there are so many people doing three phase to single phase machine conversions.

I have used three phase motors on multiple machines because they are smaller, lighter, and cheaper than single phase motors. I use a standard three blade twist lock electrical connector between the VFD and the motor. This way, I can use the same controller for multiple machines. The cost per machine goes down in a hurry.

There are a couple significant benefits to running with a VFD aside from getting more motor for less money. The first is true closed loop speed control. Rather than the machine "bogging down" when under load, the controller increases the current to the motor to maintain the programmed speed. The second is programmable ramp up and ramp down of the motor when turning on and off. I have a lunchbox planer with a single phase motor. When I flip the "on" switch, and the planer is plugged into the same circuit as my dust collector, the breaker will often trip. If it had a slower ramp up, this would not be a problem.

Todd F.

[Scott Rychnovsky]

I agree that I should skip the VFD controller for a new bandsaw. Variable speed just is not that important for wood. I am still impressed with them, and the idea of using one on several different machines would make the cost per machine go down. I notice lots of serious HP 3-phase motors on E-bay.

I am not sure how the torque holds up at low speeds. My impression is that you can vary the speed over a factor of two with reasonable results, but that at very low speeds it will loose torque fast. Does anyone have a better quantitative answer for this question?

Scott

[Bob Hallowell]

Scott yes most general porpuse motors will lose torque greatly as you reduced the frenquency below 30 hz, I got luckly and found a used 1 1/2 hp baldor vector duty for my lathe it has constant torque down to something like 6hz which was nice cause I could use a single pulley solution.

Bob

[Peter Quinn]

So on a slot mortiser which powers direct drive, so pulley changes are not an option, the stock set up is around 2800RPM I think. If I wanted a speed range from 400RPM to 3200RPM would a VFD be a reasonable solution, or would I need a specialized motor. Would it be a simple matter of sourcing a 3PH 3HP, or is it more complicated?

Stock motor is 3HP 220V.

[Frank Drew]

Peter,

Would you want 400 rpm for wood or will you also be using the mortiser to machine metal?

For what it's worth, my slot mortiser only had one speed and I never thought about whether speed control would be advantageous. Is your machine manually operated (plunge and table travel)?