I guess I'm wondering how much a VFD will help me out. The little grinder I'm using now is 3600 rpm I will be going with a 1800 rpm motor on my NWG. Just wanting to make an informed decision as I only get to spend it once. Thanks for the replies so far
Several people praise the VFD for its ability to dial from very slow to very fast and have any speed in between.
While that is a wonderful feature, let's not forget that entire civilizations have been built using step pulley technology. Look at any older piece of machinery that has a need for variable speed. Lathes, mills, drill presses, etc.
The overwhelming majority of newly-manufactured machinery
still uses pulley reduction, albeit sometimes even in combination with a VFD.
To me, the shining attribute of a VFD is not the "ramping" ability to have any speed between minimum to maximum, but rather the ease and quickness of changing from one speed to the next; all you have to do is twist a dial to change speed.
If you feel you want more speed options out of a sheave system, go with a 4-step instead of 3-step.
http://www.usaknifemaker.com/pulleysheave-4step-5-4-3-2-diameter-58-or-12-bore-p-868.html
Or how's this for an example of the effectiveness of "old" technology:
Many years ago I constructed a station in a corner of my finishing shop. This station was primarily used for buffing, but we also had the ability to mount grinding wheels. In addition, one of the most important attributes was the ability to connect, via threaded chuck, a flexshaft. We even used it as a turning station, much in lathe fashion, to turn large diameter wooden wheels.
So the need for variable speed was very important.
I no longer have that shop, but I still have that work station. This station uses a 1725 RPM motor, and has a 3-step sheave arrangement from the motor to a countershaft, then a 5-step arrangement from the countershaft to the final drive.
Theoretically, that's 15 possible final RPM combinations, from a measly 245 RPM to over 12,000 RPM. But I never use the top three speeds, simply due to the fact that I do care about bearing life. So I have twelve possible speed combinations from 245 to 3697 RPM.
In over 15 years, the only maintenance done to this machine has been oiling the bearings and replacing the belts. I did have to replace the final drive bearings once (that's what quickly clued me in about the top speeds).
So you have pros/cons with each method.
With the VFD, you have a direct drive system, so you have no concern over maintenance of belts, sheaves, and bearings. You also have the ability to "dial in" an exact speed, and speed changes are virtually instantaneous.
But the glaring factor is always upfront cost.
With pulleys (technically, sheaves), your speeds are limited to the amount of steps you have, and changing speeds requires relocation of the belt.
But I'm not so sure that "infinite adjustability" is all that important, and belt relocation is very quickly done if you use a twist-link belt. Also, many people hinge the motor. Whichever quick-change method you use, it takes me all of 5 seconds or less to move the belt.
Yes, using sheaves introduces mechanical wear. But if properly designed and constructed, it is of very little concern. Extra belts and bearings take up very little room on the shelf, and also cost very little, comparatively speaking. Truth be told, only those who use their equipment constantly will even have anything to worry about.
Which introduces another point- how simple is it to get the machine back into service if/when something breaks down? Are you going to be able to easily find out exactly what is wrong? And how much will the replacement part(s) cost?
Please don't take this as me having anything against VFD setups, because I don't. Matter-of-fact, I'm wanting one for a disc grinder project coming up in the near future.
But you said you wanted an informed decision, so I hope I presented both sides of the story, while avoiding all the hype.
Good Luck,
Rob
