Changing the motor in Drill press

Hello

I am new to this forum and a complete novice when it comes to engineering stuff. I have been a hobby woodworker and slowly wanting to get into machining work. Been looking at lathes and mills in YouTube and getting some idea.

I own some wood working machines and i want to modify my drill press.

I want to change the motor in my drill press to a 3 phase motor and add a VFD for speed control.

Should i chose a 2 pole or 4 pole motor? I understand the speed difference,

My thoughts are, I want to remove the middle pulley in the drill press and connect the motor pulley to the spindle pulley directly and control the speed with VFD. The pulley ratio is going to be different became of the arrangement that exists already. I hope you are about to understand my rambling.

Any thoughts and advice would be much appreciated. Thanks.

Andy

Hi Andrew,

Not quite sure why you would want to do this. I have a floorstanding drilling machine, which I use for everything, wood and metal. It has a middle pulley, giving 16 speeds, just by changing the belts, so where is the gain ?

Just wondering ?

I did that some time ago with my Fobco Star machine. I always found the lowest speed of 500rpm a bit fierce with larger drills. I left the gearing alone but allowed the VFD to go up to 75Hz to broaden the range. I now rarely get out of bottom gear, just alter the VFD. I used a similar speed motor to the original. It also does away with the horrible Fobco rotary switch!

Les

Like Larry I fail to see WHY you want to do this. Belt or gear reduction gives the torque to rotate large drill bits slowly. A VFD powered motor runs the risk of overheating if run too slow. You give us no clue as to what sizes of machine or drills you are intending to use. At a guess I would say 4pole if you must, but I would save my money. Noel.

To answer the original question, Generally when choosing a motor for use with a VFD it should be 4 or 6 pole. These provide much quieter and smoother running than a 2 pole. There is no advantage in the higher basic speed of a 2 pole motor, you just need more mechanical reduction and that is lossy.
Get a four pole motor.

Robert G8RPI.

When you say the middle pulley I assume you mean that the machine has an intermediate shaft with a stepped pulley on it so you can (with some trouble) get more speeds by changing the two belts around? If that's right, I did exactly this on my VMB milling machine when I fitted a 3-phase motor and VFD. Because of the middle pulley the stepped pulleys on motor and spindle were "the same way up" and anyway the motor pulley wouldn't fit on the new motor. So I actually made a bushing to allow the intermediate pulley, which is almost the same size and the same number of stapes as the spindle, to be mounted on the motor. I use a link belt to get the necessary extra length, it has transformed the machine.

Thanks all for you input.

my machine is a floor standing Jet JDP 17 Model.
yea mechanically I can vary the speed but somehow I don’t go up there to change the pulleys for various speed. I need a step stool to do it without straining. I guess laziness is the real reason 🤣! I tend to keep the same speed for all size drill bits and have ruined some bits in the process. That’s why I wanted to control speed with VFD .

Hello JH

The current configuration is 19mm shaft and 6mm keyway single phase motor.
I have found a TEC motor of the same specs. So I guess it should be a straight swap of pulleys . I think I should be able to pull it out with a gear puller and press it into the new motor shaft. May be I will have to do some heating up and cooling done of the part to home it in. Let’s see.

There is probably a grub screw (or even two screws in the same hole) that hold the pulley on the motor shaft. Note also that 19mm and 3/4" are very close dimensionally but as regards pulley fitting might be complicating things.

Unless you are using large drills and really pushing the machine to its limits then its not worth worrying too much about the key and keyway. Just use a grub screw with a dog point (or the screw is smaller diameter than the keyway width) and let it bear on the bottom of the keway recess.

You wont regret fitting a VFD, I've just just checked on my drill on which the VFD is set up to output 4Hz to 130Hz giving a very wide speed range and totally eliminated belt changing.

Ian P

Don't go pulling on the thin flanges of a pulley with a gear puller. The all-too-common result is to pull a lump out of the flange, rendering the pulley useless. Better to heat the pulley and slide it off. Or set it in a press with plates supporting the thick body of the pulley, not the thin flanges, and press the shaft out after heating the pulley. A propane torch that fits on one of those disposable small bottles costs less than a new pulley.

And do use a key when reassembling. Driving a grubscrew into the empty keyway could damage the shaft and make it hard/impossible to get the pulley off in future.

Edited By Hopper on 09/01/2023 21:53:56

Hopper, how can a grubscrew bearing on the bottom of a keyway recess damage the shaft?

Ian P

My advice is to change the motor without disturbing the pulleys if possible. Speed control with a VFD is convenient, and it will much reduce the need for belt changes. But speed controlled motors lose turning power at low rpm, which is bad news when a large diameter drill cuts into some metals,

Belt drive is a useful when that happens because it amplifies torque when speed is reduced. Keeping belt and pulleys gets the best of both worlds. Mostly the drill is speed controlled on a middle belt setting, much reducing the need to move the belt. But if the motor struggles with a big drill, the belt can be changed down to get more torque. The belt also increases power because the motor runs faster, closer to it's comfort zone.

Dave

Most of my machines (lathe, milling machine, 2 x Meddings pillar drills, linisher, donkey saw and Elliott Progress 3A) are now running with three-phase motors and VFDs.

I converted one of the drills and the lathe to 3 phase motors because you just have so much more control.

As stated previously, you can't run the motor for extended periods at very low speeds but because I am a hobby user, the motors never get hot enough for it to be a problem. It sure saves a lot of time not having to change belts for each little thing.

I have got some feature-rich (aka more expensive) VFDs and some very low-cost ones. The Vevor VFDs (out of stock at the moment) are great low-cost VFDs when you do not need all the extra features and protections that the more expensive VFDs offer.

Edited By Jan Raap on 09/01/2023 22:31:41

By chewing up the keyway and raising burrs along the edge of the keyway that can jam the pulley in place. Grub screw bears only on one point on the end which will eventually with stopping and starting and shock loadings wear away the metal at the point of contact, allowing movement that now allows the rounded profile of the threaded screw to start chewing away at the edges of the keyway. A key spreads the load along a long flat surface with no room to move and create wear.

Driving a pulley with grubscrew in a keyway is a bodge that can end up ruining your motor spindle. Stick with the way the engineers designed the machine and use a key. It is there for a reason.

I also wanted to fit a three phase motor and VFD to my drill press, so I bought a 4 pole TEC motor which runs at the same speed as the originally fitted motor.

My drill press is an Elliot 2G, the belt goes straight from the 4 step motor pulley to the spindle pulley, so it does not have an intermediate pulley. Instead it has a high and low range gearbox built in, originally giving a speed range from 46 RPM to over 2000 with plenty of torque.

The VFD is just the icing on the cake, or would be if I ever get round to fitting it. I bought the new TEC motor, VFD and pendant control from Transwave over 15 years ago I think, and they have sat in their boxes ever since.

Maybe this is another thread started by someone that might inspire me to get yet another unfinished job completed, before it is too late.

Edited By Lathejack on 10/01/2023 00:28:05

Lot of valuable knowledge shared in the above posts. Important points are taken. When I get to doing the job, I will remember them .

I have also shortlisted the TEC motor with identical body and mounting spec to my existing motor.

have shortlisted a few VFD under £100 in Amazon.

my plan is to control the “on-off’ externally and keep the speed control on the VFD . Planing to mount the VFD in the side of the machine and a small control box at the font . So the control box will have ON OFF E-STOP, & F/R switch .

I measured the shaft of the existing motor with a digital calliper and it read about 18.90mm . So I guess it’s a 19mm shaft . I don’t know if it’s a 3/4inch shaft. It may very well be an imperial shaft .

After removing the current pully off the motor shaft and I will see if I can drive into the 19mm shaft of the new motor carefully . If there is a problem , I will order a new 19mm ID pully (May be with only 2 steps and fit that one into the new shaft.

BTW , I haven’t bought any materials yet. Just gathering knowledge and information ! It will be done soon. Sure I will post some photos!

cheers

Thank you for that clarification!

This is what i am thinking about VFD wiring . Any thoughts most welcome. Thanks

Andrew, when you get a mill in future, you may find the drill press gets used less and less. I would not recommend spending large amounts of money and time remotoring one. Spend your time and money on the mill you need and go forward. By the way, a drill press is not rigid enough for milling, if you had thoughts about that being a purpose for remotoring. Many have tried and failed with that approach (me included, when I was a young man with big ideas, lots of enthusiasm, and not much cash). just food for thought.