Mini DP - How Can I Slow It Down?

[Derek Arita]

I got this mini drill press with variable speed. Ya...it's a cheapo, but it serves the purpose in all ways, except even at the slowest speed setting, it runs too fast. I tried a cheap foot peddle, but it tripped something in the motor and the motor stopped. Fortunately, a few seconds later, when plugged back into direct power, it works again. Any thoughts on how I can slow this thing down?385226385227385228

[lowell holmes]

Put a smaller pulley on the motor?

[Cary Falk]

3 phase motor with vfd.

[glenn bradley]

Larger pulley at the arbor end may be easier. That motor pulley is already pretty small

[Adam Herman]

options:
1 replace the motor with 3 phase and VFD or universal motor with a router speed control. ( thought, universal motors are usually high RPM to begin with.

2 change your existing pulley setup

3 add another pulley to the back or side. run a belt from the small end of the motor to the big end of the new pulley, and a belt from the small end of the new pulley to the big end of the quill pulley.

[Derek Arita]

Sounds like the easiest thing to do is to change pulley sizes. If I do change the quill pulley, how do I size it to get a larger one?

[Mike Cutler]

Sounds like the easiest thing to do is to change pulley sizes. If I do change the quill pulley, how do I size it to get a larger one?

Derek
How slow do you want it to go? If that speed plate indicator is correct, your lowest RPM is 5000rpm. You're going to need an awful big pulley, relative to the size of that machine to slow it down. To slow that down you're going for the motor. You might be able to accomplish something with a router speed controller, but I'm not really sure about that. Possibility though.
Not to be a weirdo, but isn't that a jewelers drill press? I have one in the garage I was given, that has a max 4mm bit size and it's a very fast drill press also. To fast for any of my needs, but it was free.

[Derek Arita]

Mike...yes, it could be a jewelers dp. I put my hand in the shot so you could get a reference of size. Slower the better on speed. I'm using it to do some clock repair work. I have a very large DP with variable speed and it does get way down in speed. The mini dp is handier to use, but only if I can slow it down.

[Andrew Joiner]

It looks just like this one:
https://www.amazon.com/SE-97511MDP-3-Speed-Drill-Press/dp/B0040YJTTU/ref=cm_cr_arp_d_product_top?ie=UTF8

The label looks identical and the specs say: 3 Variable speeds: 0 to 5,000 per min. | 0 to 6,500 per min. | 0 to 8,500 per min.

[Curt Harms]

I recently retrofitted a larger benchtop drill press with a 3 phase motor and VFD. It works well but I need to run the VFD at least 10-12 Hz to develop useful torque. The spindle will turn at 20 rpm or less but I can stop it with my hand by grabbing the chuck. The step pulley on the motor was a non-US standard diameter 15 mm as far as I could tell so I went with a single sheave pulley. The conversion cost me just under $200 all up. Just a few things to consider.

[John Lanciani]

According to the nameplate is is variable speed within three ranges. Is the VS for the motor not working? The ranges as supplied are appropriate for the tooling and tasks that that machine is designed for.

As as far as changing the sheaves, you probably have a better chance at finding a unicorn than you do finding sheaves that will fit that machine.

[Charles Lent]

It might be possible to add a jack shaft off to the side and run two belts, one from the motor to the jack shaft pulley and a second from the jack shaft pulley to the spindle pulley. Use two different pulleys on the jack shaft. If one is two times the circumference of the other, the jack shaft pulley addition could either double the spindle speed, or cut it in half depending on how you place the belts. Look at the belt and pulley arrangement of a large drill press with say 16 speeds and you will see what is needed. Then build a smaller version of it for this drill press.

I can't see the drill press motor to know for certain what type it is, but a normal 120 VAC induction motor cannot me speed controlled effectively, because it's speed is based on the AC power frequency. even if you changed the frequency going to the motor, there is likely a centrifugal switch, start winding, and capacitor that will be switching in/out at about 20-40% of the rated motor speed. This circuit is not intended for continuous use and will burn up if you run the motor slow enough for it to engage.

If the motor has brushes, it can be slowed some with a router type speed control, but a significant. reduction in speed will reduce the internal fan's ability to keep the motor cool.

Charley



.

[Bill Space]

It looks like the label needs a little refinement. I believe they are trying to say it is a three speed drill press. I think there are three speed ranges, and each is a fixed speed.

It looks like at the highest speed, the motor pully and spindle pully are about the same size. This would indicate that the motor normally runs in the 8000+ RPM range. This would likely be a DC motor, not an AC induction motor. At this price point it is probably a permanent magnet DC motor.

To slow down a permanent magnet DC motor the only option that comes to mind is to reduce the voltage applied to the motor.

This is put speculation on my part, but I would guess that there is a rectifier in the circuit between the power cord and the motor. This rectifier converts the AC to DC which is applied to the motor. If less voltage is applied to the motor, the speed of the motor will be reduced.

If one used transformer to apply a lower AC voltage to the power plug, the top speed of the motor should drop proportionately.

Unloaded the motor should not pull too much current. You might get away with a short test using a small transformer like a door bell transformer, not sure.

Take what is said here with a grain of salt, as it is based on limited knowledge of what you seem to have.

Bill

[Art Moore]

I'd almost bet that you have a DC motor in that thing, and that the controller is not working properly. If so, your options would be (a) exchanging it if under warranty, (b) replacing the electronics with a new PWM controller, or (c) opening up the speed controller box and making sure that all the connections are good.

[Derek Arita]

Thanks for all of your responses. I'm not motor guy, so I'm trying to digest it all. The DP didn't cost much, so I don't want to put lots into it, but I will try.

[Derek Arita]

Art...PWM Controller? What's that and how would I use it?

I'd almost bet that you have a DC motor in that thing, and that the controller is not working properly. If so, your options would be (a) exchanging it if under warranty, (b) replacing the electronics with a new PWM controller, or (c) opening up the speed controller box and making sure that all the connections are good.

[Charles Taylor]

Look for a router speed control, such as this one: http://www.rockler.com/router-speed-control

(There are also cheaper ones available from the retailers that are known for, well, cheaper things.)

[Derek Arita]

Well, I think I found my answer. Inside the control box, there's a pot that serves as a fine speed adjustment. Using this pot, I was able to get the speed range down to a pretty slow speed. Granted and unfortunately, torque goes down to nothing at the very low speeds, however it does allow me to check the wobble on my centering bit and I can reposition it in the chuck to get wobble to a minimum. Once that's done, I can increase the rpm's enough to do my drilling or reaming.
I restore vintage alarm clocks and I use reamers to size the gear pivot holes. Precision is essential when reaming, so the bit itself has to be chucked up with the least amount of wobble as possible. No matter how true the chuck is, there's variance when chucking up these small reamer bits, so I check them at slow speed and reposition if needed. These reamers are made to be used by hand operated devices, that cost big bucks, however I've found that I can get equally good results by using the method I described. That's why I needed to ask the question.
Thank you for all help.