Drill press motor swap

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Jul 8, 2009
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I don't know about you guys, but I'm a little on the lazy side. Consequently my drill press basically ran at the same speed, no matter what I was drilling. It didn't matter whether it was a 2" hole in hardwood with a Forestener bit, or a 1/8" hole in steel - same speed.

Over the weekend I removed this guy from my drill press.

This is a perfectly serviceable 3/4HP 1725rpm motor, it served me well on the drill press for many years.

I replaced it with this.

This is a 750W brushless industrial sewing machine motor and servo controller. I've been wanting to try one of these motor/controllers for a while to possibly re-motor other tools. I thought this was a fairly easy and safe thing to experiment on. In one fell swoop I went from an OK but big and heavy, 3/4HP, single speed 1725rpm motor, to a 1HP variable speed reversible servo motor with a default speed range of 300-3000rpm. (Maximum speed range 100-4500rpm.) That servo motor is about 1/4 the weight and volume of the old motor.

This is what the front panel of the servo controller looks like.

Being intended for a sewing machine this controller is kind of specialized. It comes equipped with a receptacle that you can plug a light into. The problem was that the light's on whenever the servo controller was plugged in. A little internal re-wiring and I moved the light connection so that when the controller is switched on, the light comes on. I also changed out the original 6' power cord to a 12' cord. The original power cord on the drill press was a 10' cord and it was barely long enough to reach the outlet.

This guy comes with a Hall effect speed control that is meant to be connected to the foot pedal on the sewing machine. It had a RATHER hefty return spring that I removed. I found some info on-line about converting the Hall effect senor to a speed pot. I didn't have the parts to to that over the weekend, so for now I running of the original speed control - the parts are in the mail.

I set the drill press belts to give me 1870rpm, this was the closest belt speed range that I could get to 1725rpm. That way the rpm's displayed on the controller is sorta close to the actual speed. One thing that I have discovered is that while I can vary the speed, the display only varies in 100rpm steps. I don't know if this 100rpm step is hard coded into the controller, or if that is a drive parameter that I can change. As a controls engineer it seems kind of silly to have a 4 digit display that only displays 00 as the last 2 digits.

One foible that I may need to learn to live with is that the speed control needs to be returned to 0 before the controller will boot up, you get a Pd Er on the display. I'm guessing they're trying to tell you that you have a foot pedal error. On a sewing machine that's not a BAD thing, it's just a little inconvenient for me. But that DOES mean that you can turn the servo controller on and the light will come on, but the drill won't turn until you increase the speed.

I've only played with the drill a little bit since the upgrade so no real clue if it was worth the $110 or not. I don't doubt that that it would cost you about that much to get a new 1HP single speed AC motor. So I think going from a 3/4HP single speed motor to a 1HP variable speed motor is a good thing.

Please follow-up with the hall effect sensor to potentiometer conversion.
Servomotorkit.com sells a rotary POT switch that probably will plug right in.
I have that setup on my 7X lathe with a switch from him. He has info about what controllers his switch will and will not work on.
I was considering doing the same with my drill press too.
An excellent idea! Well done. I assume yo still have the belt changes available when you need torque at low cutting speed? As with a half inch drill or bigger into steel? You have the best if both worlds, as something I have considered, as I am also lazy with belt changes.
Very cool! I just upgraded my 1940s era Boice-Crane drill press from 1/2HP single phase motor to a 1/2HP 3 phase with VFD. I added a speed pot and start/stop switch to a front-mounted panel with a custom 3d printed cover to hold the pot, switch, e-stop and RPM display (tied to one of those cheap Hall-effect sensors available on Amazon) It has been a great improvement, but the tach isn't very stable and may need me to put some more shielding or ferrite beads on.

Well done!
I have designed a 3D printed mount for the speed pot, I'm holding off on actually printing it until the pot arrives - today or tomorrow. I want to be sure that the dimensions I found on-line are correct before I have the Plastic Pooping Robot crank out the parts.

This is the reference I found on-line for the speed control pot modifications. Servo speed control modifications This guy still needs to be turned to 0 to start the controller.

I just found this thread on hobby machinist. https://www.***************.com/threads/servo-running-rough.90139/
(When I inserted the link, it kept wiping it out, just replace the *'s in the url above with hobby plus - plus machinist and you're golden.)
This uses a slightly different schematic and different resistors, but also gives you a Run/Stop toggle switch that fools the servo into thinking you've turned the pot to 0 when you turn off the Run/Stop switch. Posts #27 & #28 show the schematic and contain a PDF that matches my "manual". I like this idea better, so I may need to order some different pots and change 3D model to suit.

I perused both pages of my "manual" last night. That's right, the manual consists of printing on both sides of a single "letter" sized piece of paper, and it's not small print either. Just not a lot of information. From what information I have been able to gather from other forums the 100rpm steps are hard-coded into the controller. (These things were designed to run industrial sewing machines, speed step settings of 100rpm would probably be "Close enough".)

I have found slight variations between the parameters but I haven't dug into it deep enough to be able to determine if the various sewing machine servo motors use the same guts, but just have different boxes. Since my servo says it used version 37 of the software, that might be a reasonable guess. It seems that some versions of these controllers have a "Belt Scale" parameter - on my controller that's probably one of the "Not Used" parameters.

Steamchick - I haven't used the drill much since I made the changes. I'm assuming that as a "servo" the controller will, within reason, attempt to maintain a speed despite the load put on the motor. That is the whole idea of a servo after all. But then again, it's probably dangerous to assume things like that with these low buck solutions. Regardless, I STILL have the option of changing belt configurations to get a lower speed - just hoping I don't ever need to use that option. I probably need to scrounge up a piece of scrap steel and try punching a 9/16" hole in it - that's my biggest drill bit. Hmmmm, wonder what my biggest hole saw is?

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Great work! I'm thinking that sewing machine motor will be especially suitable for ...

... tapping threads.


Of course, it may be even better than it seams ...

Okay, I'll stop now. These weren't that good - just so-so.
When I went through the hobby machinist thread I found out that he did the same things that I did or still want to do. He re-wired the light circuit so that the power switch on the controller also controls the light like I did. He added the Run/Stop switch to his circuit so that he could stop the motor without changing his speed setting. I can see times when that would be handy so that is the route I am going to take also. Definitely looks like I need to order some different pots, the ones I've got coming are 10K and I now need 1K. Oh well... they were less than $10 for 3 of them and I can probably use them for something in the future.

The Servo speed control modifications link that I listed above used 4 relays to switch the 2 of the motor phases and 2 of the motor sensors to reverse the motor rotation without having to use the direction button on the servo controller's panel. By using a DPDT center off toggle switch you should be able to combine switching the relays, and the Run/Stop switch function into one switch, giving you a Forward-Off-Reverse switch. I need to watch that video again to see where he put the relays, it would be nice if you could build this as a black box that plugged into the servo controller, and the motor cables then plugged into the black box. That way if your black box crapped out you could plug things directly back into the servo controller and still be able to use the motor, just not quite as easily.

Hi Don. Unfortunately, it all comes back to mathematics/physics. Motors must be limited to a maximum current - otherwise they convert all their special knowledge of how to run into smoke. When the smoke escapes they simply forget how to run. But at an OK smoke-free maximum current they produce a maximum torque. This is usually at zero rpm. But zero rpm means the job has stopped, so designers make them develop a useful torque at a useful speed. Take this torque at motor speed and use pulleys to double the spindle speed of the drill and you only get half the torque at he drill bit. OK for little holes. Also if you don't change the motor speed but gear down the spindle speed to 1/4 , the drill gets 4 times the torque. Good for that 9/16th drill into steel.
Now when converted to variable speed, the motor torque is not motor speed related but current related. Max current equals max torque. So at your previous nominal speed you have torque similar to the previous situation, but at double speed the Same torque - can be great for breaking drills? - or at 1/4 speed of the motor and spindle the Same torque.... which may be around 1/4 of the torque for that 9/16th drill bit. So you have to compensate by drilling slowly and carefully....so as not to stall the motor.
Also, but just a by-the-by, you may need additional fan cooling for the motor, because the fan is only pushing 1/16th of the air through for cooling.
The sewing main is a variable speed constant torque load, so ideally suited to this, but a drill press, lathe etc. is not.
Hence my concern....
Watch for the escaping smoke?
I've put one on a 21/2 centre plain lathe I have. They work well, only problem is they stop instantly so the chuck could come flying off. What I have done is incorporate a bicycle free wheel into the countershaft unit I made.


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Mine basically does the same thing. If I don't have a bit in the chuck it's kind of entertaining to watch the chuck open or close when the motor stops, depending on motor direction. On a working lathe swinging a heavy part, that would probably not be as entertaining - but it would probably still be exciting.

What we need to do is change the motor from a Brake to Stop function to a Coast to Stop function. On my Vevor servo, parameter number 8 is the brake setting. Its' range is 0-5 and the default setting is 1. The 2 page manual I got claims that the bigger the number, the more intense the braking. I'm going to try changing this parameter to 0 and see if it coasts to a stop. If it doesn't I'll assume that their Chinglish to English translator gave them a bad translation, and go the other direction with the parameter and see what happens.


Normally when running a variable speed fan cooled motor I try not to run the motor below 20% of its' rated speed, at least for extended lengths of time. The default minimum speed for this controller is 300rpm and the default maximum speed is 3000rpm. This servo WILL run down to 100rpm, but it sounds a little rough at that speed. Probably just because of the brushless motor design. If I run it that slow, it won't be for an extended period, and I'll watch the motor temperature, don't want to cook the windings. I personally HATE the smell of burned varnish.

Hi, the problem with mine was that it was a servo motor. There aren't any programmable parameters unlike the brushless DC motor variant. I didn't realise this and bought the wrong one basically.
Hi, the problem with mine was that it was a servo motor. There aren't any programmable parameters unlike the brushless DC motor variant. I didn't realise this and bought the wrong one basically.
Your servo controller should have configurable coast down parameters - if not, one alternative is to configure an e-stop with a relay to open the power leads to the motor/controller.
I've put one on a 21/2 centre plain lathe I have. They work well, only problem is they stop instantly so the chuck could come flying off. What I have done is incorporate a bicycle free wheel into the countershaft unit I made.
Hi Rutzen,

Thank you for the picture, I notice that you use the "Norman" tool post ! I too use one. I also notice that you are using a shim in order to adjust tool height, yours appears to be missing the height adjusting screw. I also used a split collet to secure mine to the tool post and lock it in place.

The last picture shows the adjusting screw. M6 with a brass insert in the end.


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I think the idea of the servo motor is that it is for a sewing machine and you want it to stop either needle up or needle down. I've now made a 4 tool toolpost for it but thanks for the idea on how to make a height adjust. I've been trying to find out who made the lathe, it's really well made and has a rack and pinion tailstock. I've looked through Lathes.co.uk but no luck and he can't tell me what it is either.
Hi, the problem with mine was that it was a servo motor. There aren't any programmable parameters unlike the brushless DC motor variant. I didn't realise this and bought the wrong one basically.
That's too bad.

For those that have the brushless servo version like my Vevor, last night I played with parameter 8. I changed it from the factory default of 1, to 0. I then ran the drill full speed and went immediately to 0 speed. The drill seemed to coast down to the minimum speed, then went directly to 0. I was watching the RPM indicator and when this hit the minimum speed setting the drill STOPPED. This still seemed kind of violent, but not nearly as bad as a full speed stop. I then lowered my minimum speed back to 100rpm, to make things a painless on the drill when stopping as possible.

I'll have to check the "MANUAL" to see if there is a decel parameter. I think there is, but I also think it controls the decel time from full speed to minimum speed - not full speed to 0.

I also looked at the Hobby Machinist thread again last night. On his servo the signal needed 2.4V to start the servo at minimum speed, and at 4.2V the servo was at full speed. I need to get some voltage measurements on my servo and see if the voltage values match up to his. His circuit is a simple voltage divider that gives these voltages at the 0% and 100% positions on the 1K pot. I should be able to play with the resistor values to match the voltages I need, and still be able to use the 10K pot that I have in my grubby little mitts. I'll bread-board it and see if it works.

I re-designed the mounting bracket I had originally 3D modeled to mount the speed pot. I modeled it to the correct size of the 10K pot that I have and I also added a Run/Stop switch. I also made it removable so that if in the future I decide to add a Forward/Off/Reverse function I can just un-bolt this box and build a new one.

Baby steps,
To the OP - that seems like remarkable value for money. I have come by a couple of treadmill motors (one free, one nearly so) but finding a DC controller which can work at high voltage (in my case 110 and 180v respectively) and high current, can get expensive. I happen to have an old 8A variac which I think will do me, with a 240-110 transformer after it and then a fat bridge rectifier - but it will be bulky, and if you had to buy that stuff (even 2nd hand) your all-new solution looks more attractive. Good stuff!

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