variiable speed drill press?

[Keith Spaniel]

HI, Does anyone know why most drill presses have different pulleys to change the speeds instead of varable speed controls?

I have an older montgomery wards model that the electronics quit working.

I have seen a couple of V.S.C.drill press's but not many.

Do you think they dont make them because they are to expensive?

Or they don't last long because the control boards burn up to fast?

Thanks
.keith

[Kevin Groenke]

Cost is probably a primary consideration. A drill press is a pretty simple machine, so adding VS adds considerably to the cost. There are plenty of VS drill presses, but the less expensive machines marketed to hobbyists and woodworkers employ step pulleys to make speed adjustments. It seems that more VS drill presses employ Reeves Drives than VFD's or other speed control systems. Not sure exactly why this is, probably cost and maybe longevity. There are a few folks here who have very ingeniously converted step pulley machines to EVS with the addition of VFDs.

We recently bought a Delta 20-950 20" VS drill that I've been quite happy with (the first motor burned up but was promptly replaced by Delta)

http://www.amazon.com/DELTA-20-950-2.../dp/B000HX4S4Y

[Dustin Lorenz]

If it is a good variable speed drill press in my opinion it should have a mechanical clutch which is basically a pulley that opens up or closes on the belt (like a snowmobile) to allow the belt to be farther out or in which would also represent different diameter pulleys. This way the motor stays up at full speed or "power". To make them even better they put a digital spindle rpm readout because belt wear can change what the indicator might read at. Menards even has an off brand small bench top model with this setup. You would think they should be able to produce the mechanical style just as cheap as the different pulley setup, but what do I know. If you do have an electronic speed control and if it was variable frequencie rather then voltage it would produce better low speed "power". This style I would assume would be more expensive. I am sure the electronic ones are out there, but I think most companies go with the mechanical just like the older powermatic we have here at work, and the south bend vertical milling machine.

[Alex Shanku]

If it is a good variable speed drill press in my opinion it should have a mechanical clutch which is basically a pulley that opens up or closes on the belt (like a snowmobile) to allow the belt to be farther out or in which would also represent different diameter pulleys. This way the motor stays up at full speed or "power".

A Reeves drive

If you do have an electronic speed control and if it was variable frequencie rather then voltage it would produce better low speed "power". This style I would assume would be more expensive. I am sure the electronic ones are out there, but I think most companies go with the mechanical just like the older powermatic we have here at work, and the south bend vertical milling machine.

You cant change the applied voltage on an induction motor to vary the speed. You can, and DO, change the freq (via a VFD). This is a very common, and extremely inexpensive way of gaining true variable speed.

[Dustin Lorenz]

Some types of VFDs change frquency and voltage.

[Russ Hauser]

Years ago I bought a circa 60's Craftsman 113-24560 drill press from an estate sale. It had the standard step pulley arrangement. I didn't notice at the sale, but when I got the DP home, I found it has the optional veriable speed motor as well. I love not having to mess around with the belt and pulley changes, but rpm is guesswork.

Russ

[Matt Meiser]

Russ, problem solved. Make up a chart of dial settting vs. speed.

[Rod Sheridan]

Keith, a mechanical variable speed control is ideal for a drilling application.

As you change drive ratio, the output torque is inversely proportional to the speed, which is exactly what a drilling operation requires.

(Larger tool, lower speed, higher torque).

An electronic variable speed drive keeps torque constant (a bit of a simplification) so that as your speed drops your power drops because the torque hasn't changed.

The best of both worlds is fixed mechanical steps with a variable speed drive for the motor. (Mechanical simplicity, maximizes torque at any speed).

Regards, Rod.

[Mike Henderson]

Some types of VFDs change frquency and voltage.

Most VFDs do reduce the voltage as the frequency is reduced. The reason is to limit the current through the motor and not to reduce the speed. The speed reduction is accomplished by the frequency reduction.

As the frequency is reduced, the impedance of the motor decreases. If the voltage was held constant, excessive current would flow through the motor.

As Rod pointed out, the VFD causes the motor to produce constant torque when operated below rated frequency. Since HP is a function of torque and RPM, the power of the motor falls as it runs slower, but the torque is constant.

Mike

[Scott Hildenbrand]

I wonder.. Couldn't you add the foot pedal off an old sewing machine and make it variable speed?

[Rod Sheridan]

I wonder.. Couldn't you add the foot pedal off an old sewing machine and make it variable speed?

No, a sewing machine motor is a wound rotor motor so you can run it at reduced voltage.

A drill press has an induction motor so the speed is proportional to frequency.

You need a variable voltage/frequency drive for the induction motor. (VFD).

Regards, Rod.

[Keith Spaniel]

Thanks for your answers, but now I have another question.

1.My motor has brushes,I don't think it is a DC motor. So it must be an induction motor right?

2.The electronics are just a board about 2''x 5'' with resistors, diodes and a few more little bug looking things. Is that a frequency drive control or a speed control ?

3.So The DC motor must be the best way to go when you want to control your speed ?

Thanks for sharing your time and brain.. keith

[Mike Henderson]

Please see my comments below:

Thanks for your answers, but now I have another question.

1.My motor has brushes,I don't think it is a DC motor. So it must be an induction motor right?

If it has brushes, it's not likely to be an induction motor. Most likely it's a universal motor. You can control those with voltage changes.

2.The electronics are just a board about 2''x 5'' with resistors, diodes and a few more little bug looking things. Is that a frequency drive control or a speed control ?

Probably voltage control.

3.So The DC motor must be the best way to go when you want to control your speed ?

A DC motor was the best way for speed control until the advent of cheap electronics for doing frequency control (VFD). The advantage of an induction motor is no brushes which means less maintenance. Almost all new industrial installations of motors with speed control are now done with induction motors with frequency control.

Thanks for sharing your time and brain.. keith

[Alan Schaffter]

The biggest problem with EVS is as mentioned- loss of hp at low rpm. At low rpm I can stall my VFD-equipped Delta drillpress fairly easily. For that reason, most EVS lathes also retain mechanical speed control with step pulleys or Reeves drive.

One thing not mentioned- VFD's only work with 3 phase motors.

I also added a built-in tach and mounted the digital readout on the front panel next to the VFD run/stop switch and speed control knob.

[Dave Lehnert]

A Shopsmith is variable speed and many are still in use today from the 1950's