More Drill Press Mods: Adding A VFD Means No More Belt Changes

A decent drill press is an essential machine tool for almost any kind of shop, and marks a significant step up in precision compared to a hand drill. The ability to drill square, true holes is one thing, but the added power over what’s possible with a portable tool is the real game changer. If only you didn’t have to switch around those damn belts to change speeds, though.

You don’t, of course, if you go through the effort to add a variable frequency drive to your drill press like [Midwest Cyberpunk] did, along with some other cool mods. The donor tool for these mods came from — where else? — Harbor Freight. Some will quibble with that choice, but the tool was pretty cheap, and really all [Midwest] was interested in here was some decent castings and a quill with acceptable runout, since the entire power train of the tool was slated for replacement. The original motor gave way to a beefy Baldor 3-phase/240-volt motor controlled by a VFD mounted on a bracket to the left of the drill press head, allowing the stock belt and step pulley transmission to be greatly simplified.

[Midwest] also added a digital tachometer to the spindle and some RGB LEDs for zazzle. We don’t really mind the LEDs, but the lack of a safety cover on the belt drive gives us the willies. But that’s a personal choice, of course. As for performance, the mods seem to work pretty well; the advantage of a VFD is constant torque even at low spindle speeds, and that certainly seems to be the case here. Not having to play with belts to change speeds is another big plus, of course.

All in all, we like these mods and have to keep them in mind for our own drill press. We’ve seen a couple of drill press mods lately, including this extreme drill press makeover. We can only hope that this is the beginning of a trend.

29 thoughts on “More Drill Press Mods: Adding A VFD Means No More Belt Changes

      1. The name of the square hole drill is a “Watts drill”. Also try “watts brothers drill” as a search phrase to improve the results somewhat.

        The Watts drill setup has three main components: a special floating holder, the drill itself, and a guide plate. You’ll also need some way to hold the guide plate in position over the part. It’s best suited for softer, easily machined materials. The floating holders are normally found with a Morse or B&S taper to fit the drill press spindle, so you’ll need a large-ish machine with a matching taper.

        Another option that works well on a wide range of machines is a rotary broach. Those work on a similar but different principle, and plans are available from several sources to build the simple 1° inclined holder. Purchase the broach (or grind one yourself if you have the equipment), drill a starter hole, and go to town. Rotary broaches can do a lot of odd shapes, too, not just polygons.

      2. I assumed he was talking about “square” as in perpendicular to (normal to) the item being drilled.

        BTW I went another way on the VFD. I found a small expensive conveyor with a mounted DC motor with the converter\controller built on to the motor for very cheap ($10 IIRC) many years ago and simply modified the motor mount on my ancient drill press and it works well. I sold the rest of the conveyer and got my money back besides.

  1. He didn’t do a torque test before and after, that would be interesting to see how much torque you would lose if any by removing the x:y belt coupling. Overall a nice build though, didn’t know it was a simple drop in replacement :)

    1. I use a VFD with my lathe (finally an article were VFD means what I think it does!). While it does give me more flexibility with speed, I still need to change the belts for somethings, especially if I need to do low speed (e.g. large diameter) work.

      Although maybe the drill press in the article is only used for things that don’t require a big speed difference. Or maybe they do what some friends of mine do, have a drill press for high speed work, and a separate one for low speed work. This saves a lot of faffing with belts.

      1. I can confirm this. I have a BF30 “round column” drill / mill and added a VFD to the 12 speed V-belt system. It’s very useful and I’m quite happy with it, but by reducing the RPM with the VFD, you do not get more torque, while when reducing the RPM with a mechanical transmission, you do get increased torque, and this is especially needed with big face mills. So I typically use two belt settings, one for high speed and low torque, and another for low speed but high torque, and I do the rest with the VFD.

        The VFD is also great for tapping.
        I have deliberately set the VFD to have a low torque at low rpm. Then I put a tap in a drill chuck, put the tap above the hole, and slowly turn up the VFD untill it has just enough torque to start tapping. With this setup I can tap M6 blind holes and just let the tap bottom out without it breaking. Then I hit the reverse switch and get the tap out at high rpm.

    1. I don’t think you mean a literal pulley but a 1:1 DC motor powered directly by a DC motor driver can do some work. Pretty amazing torque control provided we are not talking about a 5V DC motor here either and 72VDC or so is quite off the shelf too. Great low speed high torque. Commonly used.

      1. I couldn’t find a reasonably priced VFD and motor combo, so I grabbed a DC commercial sewing machine motor complete with power supply and speed control (ran the linkage to a pedal on the floor). Vevor Canada. $120. Ended up having to machine a shaft extension but that went well. Used original pulleys and guard. Really satisfied with the results.

      2. The cheap “hobby mills” quite often have a DC motor with a variable speed control, and these motors have a horrible track record. 3 phase induction motors are relatively cheap and robust. Several of the “hobby mills” have an upgrade available with a BLDC motor, and this sure does seem worth the extra EUR150 or so.

        BLDC motors are becoming more common these days to. Washing machines tended to have universal motors, but BLDC motors are becoming more common there to, and this makes old washing machines much more interesting for salvaging the motor and motor controller.

    1. There is and it is a triangular drill bit. Forget what it’s called.
      A mortiser for wood drills a regular round hole then had a square chisel that squares up the corners in one pass

  2. I wonder if RPM feedback could be taken from the spindle and fed into the VFD, then you could get the benefits of speed control etc, but can alter the belt position on the pulleys for the torque/speed balance for the job at hand.

    1. Something like that is relatively simple to make with a microcontroller. VFD’s quite often have multiple inputs for RPM setting. Both 0 to 10V, 4 to 20mA PWM and MODBUS are common, and all of these signals are easy to generate with a microcontroller. It would probably not be good enough for rigid tapping, but plenty good adjusting RPM for cutting speed.

  3. I’ve done two lathes, my Emco Compact 8 and my ’47 Harrison L5. I sourced used 3ph motors; one VFD was used and the other from AliExpress. Both also have $9 digital tachs from AE. The 3ph motor on the Harrison replaced one almost three times its size. Both lathes run cool and quieter, and you can set the VFD to soft-start, saving on wear and tear. You still get decent torque when you show down a bit, but it does taper off. At around 8Hz I can stall both lathes by hand. The other thing to consider is that the motor fan is rated to cool the motor at its nameplate rpm, and if you run it slower for long, you’ll need to add auxiliary cooling. On both lathes it was money well spent.

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