VFD for drill press

[Boyan Silyavski]

I have a 2 pole 0.75kw compact frame motor which runs at 7000 rpm on my benchtop mill, I used it to replace a DC motor/controller which wouldn't give me a usable 1000rpm to 7000rpm.

Nick, how did you do that? It sound a bit sci fi. At how many Hz you run it and hows that that it still works?

[routercnc]

I mentioned to a colleague that changing belts on my drill press was a bit of a pain and he said some people had used Sturmey Archer bike hub gears instead of the pulleys and can then change to lots of speeds. They are pretty strong to take the pedalling loads. Then you just have a lever on the side of the machine to select the gear.
Or some of the fancy drill presses have a pair of cones to give a range of continuously variable speeds without even stopping the machine. Again sliding a lever selects the speed. Probably an expensive option though?

[magicniner]

Nick, how did you do that? It sound a bit sci fi. At how many Hz you run it and hows that that it still works?

Boyan,
It's a Siemens 420 (soon to be replaced with a 440) Inverter Drive with an Electro Adda 0.75kW 2 pole motor I'm not sure of the Hz it runs as I've programmed the VFD display to show RPM, I'll check the Hz at 7000rpm later today as I have an aluminium profiling job later today.
My experience so far is that these things tend to just work if you use decent quality gear, the availability of good, clear, English documentation makes programming the Siemens VFDs a 10 minute job.
I read a thread somewhere where Sir John Stevenson gave details of converting larger 3 phase motors to milling spindles with integral collet chuck and running them without issues at ridiculous speeds, 7000 rpm does what I need but I suspect I have left a substantial safety margin and that it could easily run faster,
Regards,
Nick

[Neale]

There's a lot of good info here but possibly not so useful to someone without the technical background to follow the discussion!

In short, I think that the answer to the original question is, yes, fixed pulleys with variable-speed motor is a practical proposition, but you need a VFD plus replacement 3-phase motor to do it. You can't make a simple single-phase motor into a variable speed motor just by feeding it from a VFD - unfortunately.

[Noplace]

There's a lot of good info here but possibly not so useful to someone without the technical background to follow the discussion!

In short, I think that the answer to the original question is, yes, fixed pulleys with variable-speed motor is a practical proposition, but you need a VFD plus replacement 3-phase motor to do it. You can't make a simple single-phase motor into a variable speed motor just by feeding it from a VFD - unfortunately.

lots of great information surfaced in the thread, appreciate if you can just let me know what would be the problem in using a 1ph VFD?
got my eye on this one http://www.ebay.com/itm/0-75kw-Frequ...16402#shpCntId and seems it would work, am I missing something?

[magicniner]

lots of great information surfaced in the thread, appreciate if you can just let me know what would be the problem in using a 1ph VFD?

It's 1 phase input but it's 3 phase output for use on a 3 phase motor, not a single phase motor.
You can buy a good new 1hp 3 phase motor for around £120, once you've tried a drill press with an inverter you'll never go back, jus do it ;-)

[Boyan Silyavski]

Somebody know where they sell cheapest the 500w variable speed DC motor for the small chinese mills?

[Neale]

lots of great information surfaced in the thread, appreciate if you can just let me know what would be the problem in using a 1ph VFD?
got my eye on this one http://www.ebay.com/itm/0-75kw-Frequ...16402#shpCntId and seems it would work, am I missing something?

As Magicniner has said, these VFDs take single-phase in and produce a 3-phase output that is designed to drive a 3-phase motor. Why can't you just use two of the output connections and drive a single-phase motor? Main problem (there are others) is that the motor will probably not start unaided. Single-phase motors have some clever bits in them to get them started from stationary; you often hear a click from inside the motor as they spin up to speed. This is the centrifugal switch cutting out the starter circuitry (often a capacitor bolted to the outside of the motor). This is all designed to run at a single speed. Imagine a children's swing in a playground. It swings at a steady speed, and you just need to give it a nudge at regular intervals to keep it swinging. That's the way a single-phase motor works, where the incoming alternating voltage generates a magnetic "pulse" that is synchronised with motor revs. 3-phase motors work differently - the three phases generate what looks to the motor like a rotating magnetic field at the frequency of the input voltage, and the motor follows this whatever (within reason) the speed. Obviously, it's all a bit more complicated than that, but I hope that this helps.

[Boyan Silyavski]

Boyan,
It's a Siemens 420 (soon to be replaced with a 440) Inverter Drive with an Electro Adda 0.75kW 2 pole motor I'm not sure of the Hz it runs as I've programmed the VFD display to show RPM, I'll check the Hz at 7000rpm later today as I have an aluminium profiling job later today.
My experience so far is that these things tend to just work if you use decent quality gear, the availability of good, clear, English documentation makes programming the Siemens VFDs a 10 minute job.
I read a thread somewhere where Sir John Stevenson gave details of converting larger 3 phase motors to milling spindles with integral collet chuck and running them without issues at ridiculous speeds, 7000 rpm does what I need but I suspect I have left a substantial safety margin and that it could easily run faster,
Regards,
Nick

A bit off topic. Now i need your help here. I have the micromaster 420 on my belt grinder coupled with 3kw motor, and have it programmed 0-100 hz so i reach 0-3000rpm , its 4 pole 3 phase motor. The problem is where do i make to be able to change the frequency from the operating panel? i did it once, but forgot how. Read the manual 100 times, but still can not change frequency from panel up and down button, which drives me crazy.

[magicniner]

A bit off topic. Now i need your help here.

It's not in the operator's manual, it's in the Parameter List

You need
P0003 set to 2 so that all the parameters you might want to change are accessible to you
P0700 set to 1 for command input to be BOB (panel)
You might need to select the control frequency setpoint source and a few other odds & sods but the Parameter List is where you'll find the settings described -

http://www.acpd.co.uk/sei/s/1488/f123.pdf

Regards,
Nick