View Full Version : Newbie Motor selection ...

02-07-2009, 09:54 AM
I want to convert my Jet JDP-17MF 16 speed floor standing drill press to a variable speed drill press. I've done just enough research to be dangerous ...

Givens ...

All of the work is home hobbyist - not day-in-day-out. It will be metal, not wood. I would love to be able to go fast enough for 1/8 inch pilot holes, change bits and eventually slow down enough to end up with 1/2 or larger bits. The bonus round would come if I could slow down enough for up to a 1/2 inch tap without changing belts, but am willing to compromise on a belt change to do the tapping. So the drilling speed ration would be about 12:1 and the tapping ratio without a belt change would probably be 20:1.

What I think I know ...

This situation is a "constant torque" application.

I envision using a sensorless vector controller such as the SJ200-007NFU2 from www.driveswarehouse.com.

The Jet currently has a "name plate" 3/4 hp motor on it. I envision replacing it with a 1 hp 3 phase.

I also think it be best if I add a constant speed fan to what ever 3 phase motor I replace the single phase motor with.

But now it gets really sticky.

3 phase motors seem to come in three flavors - regular duty, inverter duty and vector duty. Looking at www.surpluscenter.com suggests that what appear to be regular duty motors can be purchased for reasonable prices - less than $150. However they do not seem to carry anything listed for inverter or vector duty. www.driveswarehouse.com carries inverter and vector duty motors but the price of the motor is three to four times the original price of the drill press.

So the motor options appear to be:

Wait until a reasonably prices inverter or vector duty motor comes along on ebay or craigslist ... Not real high on the list as the primary goal is holes in projects and not "a variable speed drill press".

Get a regular duty motor and a fire extinguisher from surpluscenter ...

Buy two more drill presses - which would have the additional advantage of not having to even change bits - i.e. one bit and speed per drill press - but does have the inconvenience of having to reposition the work each time - and explaining the concept to my wife ...

or ... and this is where the groups expertise comes in ... how important is an inverter or vector duty motor in this application?

Thanks for taking the time to educate me,

02-07-2009, 11:30 AM
The number of VFD's applied to non-vector motors each year probably run in the thousands, The only time I have used vector rated motors is if the present system has no motor to start with, otherwise I have always used the existing standard motor.

02-07-2009, 03:31 PM
Thanks for the response. I had been doing the research and had seen a significant number of conversions. Usually free or ebay or craigslist or ... is mentioned but the specific flavor of motor - regular, inverter or vector - was not obvious in the articles. So I was not sure if the flavor was not mentioned because is was "intuitively obvious" that it had to be inverter or vector - or the flavor just didn't really mater that much. And given the "constant torque" and speed ratio that I was hoping for I thought I would ask.

I guess the only remaining question is "how much should I compensate for torque loss at lower speeds?" Here is the - possibly flawed - thought pattern. The original motor is 3/4 hp at 1720 rpm. Even though the VFD is advertised as "constant torque" how realistic is that statement? Given that the incremental costs of a higher horse power motor and VFD is not that much, do I need to compensate for inefficiencies at lower speeds - like the envisioned 1 hp motor or even a 1.5 or 2 hp motor?

Probably over thinking this, but that is the prefered activity compared to over spending or spending twice,