Converting BS to variable speed?

[Perry Holbrook]

I am in need of a metal cutting band saw that will take blades under 1/2". Stumbled on a Grizzly saw that is variable speed for both metal and wood. It's over $1000 and I'm really running out of space. It has an inverter that takes single phase 220 and powers a 2hp 3 phase motor.

Since I have a lot invested in blades for my Jet 18" BS, and the Grizzly is only a 14" saw, replacing the Jet with the Grizzly is not an option.

So I am thinking of converting the Jet to VS. I found an inverter for $200 and a 3 phase motor for about $250 that should bolt right on. Was starting to look good until my local motor shop said I would probably need an inverter duty motor to run at speeds slow enough for metal cutting and that motor is $650. Now I'm within a couple hundred of a new saw.

Anybody have any thoughts?

Perry

[Joe Chritz]

I know that my dad runs a huge bandsaw off a big 3 phase motor with a VFD drive.

It works great. If you score the auction sites you should be able to get a 3 phase motor that someone is replacing fairly cheap. VFD's are still a bit expensive though.

Joe

[Sam Yerardi]

The easiest and least expensive route to converting from a wood band saw to a metal band saw as far as blade speed is to simply use pullies with multiple diameters. IMHO, we're really only talking about 2 speeds, and I can't think of any instances where a variable speed blade is really necessary for both instances. Determine the two speeds you need, and choose pullies accordingly. Your particular bandsaw might not accomodate that approach but a lot will since the drive motor is typically located external to the main housing. Granted within the metal realm there are different speeds for different materials that are necessary sometimes but generally every industrial bandsaw I have ever been around does fine for most standard materials, i.e., steel, aluminum, brass, etc. at one speed. Having designed power electronics for many years as an electrical engineer I understand why variable speed hardware is offered rather than 2-speed designs. It is because it is a bit easier to design variable speed circuitry, etc. than circuitry supporting only two speeds. It can be done, but if you're going to that much trouble, you might as well design for variable speed.

[John Holder]

you could buy a VFD for less than 300 bucks. You can run a vfd on a single phase motor. You would get better preformance from 3ph but not really worth the hassle.

[Pete Bradley]

Ferrous metal wants a really slow speed compared to wood. Most pulley setups involve a countershaft or a really big pulley. Even if you could run a single phase off a VFD, it's not clear to me that you could run the motor slow enough without leaving the start windings engaged.

$1000 for a used griz 14" seems pretty steep. Used 3PH motors are relatively inexpensive, you might well find one for less than $100 that you would be more comfortable risking. If you really need wood and metal in one machine, the cheapest approach may be to sell your wood machine and buy a wood/metal.

[jason lambert]

Just keep in mind if you cut metal you need oil and it gets oil and metal shavings over everything like you wheels, guides etc. Now when you switch to wood, put on a wood blade you will get oil onto your project you need to clean everything well and oil hides.

[Perry Holbrook]

A different pulley system would probably require a double reduction with a jack shaft . I need to go from about 3000 sfm to 300 sfm.

The Grizzly saw is New for that price.

The used 3 phase motors are not inverter rated and the frame type will require machining a new mounting plate.

Can you really use a vfd on single phase, especially at such a reduction?

As I said before, I 've got quite a bit invested in blades for the Jet, that makes replacing it and stocking all new blades pretty expensive.

Perry

[Joe Chritz]

The oil problem is a real problem to look for. I have a cheap import 14" bandsaw that I converted to metal by adding another pulley to reduce the speed to around 300 FPM. I still get a little slip because it isn't refined but I cut a fair amount of tool steel blanks for grinding knives with it.

I wouldn't want to do it on my good wood bandsaw.

Joe

[Rick Lizek]

You will still need a gear box to get it down to 200-300 from 3,000 of a wood saw.


Far cheaper to get a horizonta/vertical metal bandsaw for a few hundred bucks. That's what I have as I do a lot of metal as well. The conversion takes too long and the oil and metal chips are messy.

[M Toupin]

A different pulley system would probably require a double reduction with a jack shaft . I need to go from about 3000 sfm to 300 sfm.

At least... depending on what you want to cut, you could need a LOT slower than that.


The used 3 phase motors are not inverter rated and the frame type will require machining a new mounting plate.

The frame mount might be an issue, I wouldn't worry about the "inverter duty". It's an issue in an industrial setting, but show me ONE person who's burned up a 3ph motor in a hobby setting. Lot of folks with stories about a friend of a Friend, who had a brother, who had a girlfriend, who had a father...


Can you really use a vfd on single phase, especially at such a reduction?

Nope.

Think about the reduction issue here also. you want to go from 3000dsfpm to 300sfpm or a 10:1 reduction. With a VFD and 3ph motor you'd be taking your motor from 60hz to 6hz to get that 10:1 reduction. Now, that might burn up your motor, inverter rated or not. Not due to the electrical issue, but due to no cooling at that slow a speed.

Mike

[Rod Sheridan]

Hi, if you take a 2 HP motor and run it at 10% of rated speed, the motor is going to be 0.2 HP since the drive will run it as a constant torque machine.

Either use mechanical reduction (belts/pulley or gearbox) or purchase a small horizontal bandsaw for a few hundred dollars. That's what I did, now I don't have to worry about metal chips in the woodworking shop.

Regards, Rod.

[Jim Becker]

Perry, I do not believe you can use a VDF on a single phase motor.

[Perry Holbrook]

Hi, if you take a 2 HP motor and run it at 10% of rated speed, the motor is going to be 0.2 HP since the drive will run it as a constant torque machine.

Either use mechanical reduction (belts/pulley or gearbox) or purchase a small horizontal bandsaw for a few hundred dollars. That's what I did, now I don't have to worry about metal chips in the woodworking shop.

Regards, Rod.

I'm was just trying to duplicate the Grizzly set up with their design, seems like if it works for them, this should work.

I should have said that I already have a Jet horz/vertical saw. But frankly, it doesn't cut as square as I need in the horz mode due too blade deflection and the throat needs to be bigger in the vert mode. Plus those saws don't run blades other than 1/2".

I don't use oil on the samll saw now and probably don't need it for the kind of work I do.

Thanks for the input.

Perry

[John Holder]

Perry, I do not believe you can use a VDF on a single phase motor.


Check This Out http://www.driveswarehouse.com/Drives/AC+Drives/Phase+Converter+VFD/

[Jim Becker]

John, I could be blind, but I don't see anything at Drives Warehouse for a single phase load; only single phase input.

[Perry Holbrook]

That is the site I was looking at, but they require a 3 phase motor that should be inverter duty rated.

Perry