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What exactly is a universal motor? Just like a nema 56 frame type thing?
Anybody have one of these: G0722 Milling Machine with Power Feed. Seems to be something new in the lineup.
The one big negative is the universal motor in a mill this expensive. But the again Gizzlys data is a little confused.
What exactly is a universal motor? Just like a nema 56 frame type thing?
The article on wikipedia is good. It is a brushed AC/DC motor that allows for easy speed control. The downside is that their speed isn't well regulated and drops with load.Originally Posted by Winnfield
Most machine tools use inductance motors where the speed is controlled by the line frequency (typically 1725 or 3450 rpm on 60hz in the US). Speed between the motor and the tool is controlled by a system of belts. Inductance motors are very reliable since they have no brushes to wear out and their speeds are much more stable. They are also a lot quieter due to the lack of brushes. 3 phase inductance motors can be speed controlled with a device called a VFD that changes the line frequency going to the motor.
The smaller benchtop tools talked about on this forum (like the X2, X3, G0704) typically use DC motors with SCR speed controllers. They have brushes and the noise of universal motors, but the speed controllers provide the speed stability under load of an inductance motor. They are a good option in the under 1hp range.
The 2hp universal motor used on this machine gives the manufacturer a really cheap way to get speed control, but otherwise it isn't that great. It would be nicer if the machine had cost $200 more but had come equipped with a 3 phase motor and VFD (which allows the 3 phase motor to be run off of household single phase current).
Generally the phrase is induction motor but that is nitpicking.
Throwing a three phase motor on the thing would ave bee fairly cheap, even a good AC VFD is as you say a couple of hundred and they would be using a cheaper drive anyways. Beyond the noise problem you have a maintenance problem with these machines in that brushes and commutators wear and bearings don't last due to all of that dust.
Beyond that most of these universal motors on these Chinese machines are worth crap. This can be in the significant number of motor burn ups at initialization time. The Chinese seem to have a better track record with their induction motors. Part of that could be the result of people expecting to get the rated horse power out of the unit.
In the end I suspect that the old Griz is getting real cheap here. I hate to see them go that way because it makes you wonder what other corners have been cut.
Frankly I'm not sure why Griz doesn't embrace this technology (VFD & 3 phase motors). I suspect it is a marketing problem where they need to educate their customers with respect to the positives.
I don't understand why they would use the 3 phase/VFD setup on some of their wood lathes as they do, but not the metalworking machinery.
Maybe woodworkers are more demanding? Maybe Griz expects metal worker to rebuild the machines anyways? Maybe woodworkers are better educated about the technology?
I dont mean that bit about woodworkers being better educated in a negative way, it is just an observation I've seen. That is you often see guys at auctions and such turn up their noises to machines with 3Phase motors almost as if they where pulled from a cess pool. I don't think a lot of these guys realize just how cheap and nice 3 phase inverters are these days. Often talk will turn to remotoring the machine and then it slides a bit further when DC motors are brought up.
So maybe it is market resistance. I really don't know, one thing I do know is that Griz needs to do a little more work on their marketing literature. It is sometimes lacking when it comes to documentation accuracy.
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