Need help with Variable Speed Control for Bench Drill Motor

[chola]

Hi,

I am going to replace the motor on my mini lathe with a more powerful unit from a drill press, but would like to also add some sort of variable speed control to it.

Any suggestions? The drill press is 240volt with the motor rated at 350w.

Would the router speed control unit I've read so much about work or would I be better off looking at something else?

Any help much appreciated.

Thanks.

Colin

[NC Cams]

For low cost, consider a treadmill motor. Specifically a PMDC version with a very high pole count and a PWM style speed control. HOwever, depending on the "timing" of the armature or the skew of the laminations, you may NOT find one that is bidirectionally capable smooth and/or powerful operation.

THese offer very smooth low speed operation, wide speed range and the PWM should assure you of retaining torque at low speed. High pole count DC motors can be remarkably free of pole cogging during commutation.

Keep in mind that although you can/will affect speed via the electronics, you also greatly affect power output as you start to throttle the motor. This is why Bridgeport and Excello used a variable pitch pulley system on their mills.

By using a V/P pulley system, the motor could be kept in its peak power range all the time and speed regulated mechanically by the pully pitch change.

[Al_The_Man]

Originally Posted by chola I am going to replace the motor on my mini lathe with a more powerful unit from a drill press, but would like to also add some sort of variable speed control to it. Any suggestions? The drill press is 240volt with the motor rated at 350w. Would the router speed control unit I've read so much about work or would I be better off looking at something else?

To use a controller with the motor you mention depends on the type of motor it is, the 'router' style controllers are usually intended for universal motors, so if yours is a 1ph AC induction motor, then there are virtually no practical options open.
I would agree that it may pay to look for a DC motor rated around 90~120vdc.
But as the motor you have is just under 1/2hp, a treadmill motor may be overkill at typically 1~1.5hp.
With respect to DC controllers, you can get them as cheap as the router motor style, if you look for full wave SCR type and run off 120vac, the advantage is you do not need a power supply.
There are several that are re-labeled by different manufcturers like Baldor that just sell the controller on heatsink chassis only, which is half the price of one with enclosure, you just supply your own pot and reversing switch for just under $100.00 or $15~$25 on ebay.
Another advantage of them is they have a tach input, so if you get hold of a used DC servo motor that has a tach, you can get pretty precise speed control.
Typical style: http://cgi.ebay.com/DC-Motor-Control...QQcmdZViewItem
Al.

[chola]

Thanks guys,

A few things to think about there.


Maybe a real newbee question but how can I tell if the motor is universal or induction type?

Treadmill motors are pretty much out of the question in Australia (at least as far as I've found) as I've been searching over here (Ebay as well), and they are pretty much non existant! I also considered an electric scooter / wheelchair motor but may be overkill for what I want (hooking up 20amps through my lathe would keep me awake at night!). I also looked at some treadmill motors from the US but the freight is a killer. All sounds negative but I'm just being practical here.

The drill press in question has a 6 speed pulley / belt system, with a maximum speed of 2850rpm (my current motor is 2500 rpm but I generally never get near this speed except when polishing a part).

I guess there are plenty of lathes out there that are belt / pulley drive only anyway so I may just live with it for now.

Can you see any inherant problems with simply fitting the motor and pulleys from the drill press? There should be plenty of power seeing as the motor is rated at more than twice my current unit.

The real attraction is I can porbably get this drill press for about $30AUD - so a cheap motor and pulleys really.

Thanks again for the assistance.

Colin

[Al_The_Man]

Most drill presses come with induction motor (start capacitor on the outside), a Universal motor is AC/DC very high rpm and has brushes.
When looking at Treadmill motors, they come in all kinds of configurations, depending on what the original manuf. spent on design, I have seen everything from universal motor to various forms of DC, alot of them made very cheaply, so you have to be aware what you are buying.
Al.

[chola]

Hi Al,

The drill press I'm looking at has the 'little black box' on the outside so I presume this is the capacitor. Can anything be done with regard to variable speed on a capacitor motor?

Thanks.

Colin

[Al_The_Man]

No the 1ph induction motor does not take well to a VFD as they drop out of run at low speeds on load, you would have to go to a 3 phase motor with VFD single phase in - 3ph out.
Al.