I have a quality 18″ Italian bandsaw which I would like to modify to allow me to cut metal. I have done a bit of Googling and found that I could obtain a variable frequency drive and a three phase motor that will allow the cutting speed to be reduced. However, the reduction needed to achieve metal cutting surface speeds is about 16:1. The consequence of this reduction is that the power will also be reduced to 1/16th, an amount that is unlikely to be sufficient to cut anything but thin sheet metal. So probably I would need to modify the existing driver and driven pulleys as well. It seems to be getting to be a major exercise.
I would appreciate any comments you have on modifying a woodwork bandsaw to cut metal, the pros and cons.
Thanks,
Bevin
Replies
A variable frequency drive allows you to maintain high torque even as you slow down the motor, but as you get down to running well below the motor's normal speed ,the driving action gets rougher and the motor can easily overheat since the cooling fan is turning too slowly to effectively cool the motor which can still be drawing full power. If you decide to go with a VFD at such low speeds you should get a 3 phase motor designed especially for VFD hook up since it will hold up better under the demands placed on it.
Instead of a VFD, I would suggest a two stage pulley drive with the pulley ratios in each stage giving you a 4 to 1 reduction, which you could achieve with step pulleys so you could also have wood cutting speeds by just switching the belt positions. This is the type of drive used on drill presses except that there would be one additional step pulley between the motor and the saw. If you used link belts, this would be a relatively simple drive to assemble and use because the belts would be self tensioning, so that the motor and intermediate pulley wouldn't have to be movable.
Serious metal cutting on a band saw, at least if you are cutting steel, is a messy process since typically a wax or oil lubricant is used, and there is also some risk that hot chips from the sawing could ignite any sawdust left in the machine.
Also, reducing the speed proportionally increases the torque on the wheels and the drive shaft, which creates a risk of doing serious damage to the wheel or shaft of a wood cutting band saw if the blade should jam for some reason. Metal cutting band saws are designed from the ground up for the application, they aren't just an ordinary wood band saw with a slower speed drive.
So, while it may be possible to use a single saw for both purposes, it isn't especially practical.
John White
Edited 7/31/2006 6:34 pm ET by JohnWW
Thanks for your reply John. Your advice makes good sense.
Yes in view of the difficulties in modification, ongoing maintenance, costs, and the less than satisfactory outcome, I will drop that plan. As you say, I would need to combine mechanical speed reduction with the VFD, plus an auxillary fan for the motor, all of which becomes a major modification. Ah well, it was worth the investigation.
My options now are to either sell my bandsaw and buy a metal bandsaw, or try and make the floor space available for a cold metal saw.
Of course the best alternative is to win the lottery and build a new workshop with attached house.
Regards,
Bevin Pettitt
You seem to have found your direction, but I thought I'd add my own experience for your and others info. Some years ago I also needed a metal cutting vertical bandsaw. I modified a Delta 14" saw to do this. Although this is an OK machine, I wouldn't call it a quality one, so I felt doing this modification wouldn't cost me anything real. I used three jack shafts to get the speed reduction. It takes a lot to get the blade speed down to the 100 ft/min. range and I didn't see any way to do it without multiple steps. Anyway, it's a tight fit to get all that new hardware in there, but I did it. The modification turned out swell. The blade speed is a bit fast, but that just means I have to use a bit less feed pressure. I can stop the blade with too much pressure although the motor doesn't stop. Obviously one or more of the belts is slipping under that condition. It doesn't bother me much so I leave it alone. As John pointed out, cutting steel is a real mess. I cut dry without any wax or pariffin but it's still a mess. The steel will gouge the table and the cutting dust will imbed into the tires. I would never advocate using a saw for both wood a steel (well, maybe to cut ironwood). Because I think this modification is one-way, that is, one cannot go back to wood, I'd never do it to a really good saw. I have other bandsaws I use for wood, so that wasn't a problem. If anyone is really interested in doing this to a bandsaw, I'll photograph the jack-shafts if that'll help.
Sapwood,
Thanks for a second opinion, it is nice to have my advice confirmed by someone with actual experience with the specific problem.
John White
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