Home Trips Motor Home
House Projects  Machine Shop
Early Computer

Drill Press Motor and Tachmeter


I decided to modify my drill press by installing the variable speed 3/4 HP sewing machine motor I discussed in Replacing My Lathe Motor.  I also plan on installing a MachTach tachometer like the one I built for the lathe.

The object of this project is my floor model Clausing drill press which I bought
new in about 1965 or 1966

My first step was to remove the stock motor and plan the mounting of the new one.  As the motor mounts to a flat plate, I have a lot of flexibility.  After positioning the motor to properly align the belt I realized I would need to add a small extension to the bottom of the cast iron mounting plate and add a new mounting hole near the top.  I will machine a new two step pulley similar to the two bottom steps of the stock pulley, to fit the 15mm motor shaft, but for now I am using the cheap 5/8 bore pulley I bushed to fit using shim stock.

The motor mounting plate provides a lot of flexibility, but did need to be extended
downward slightly.  The new tapped hole in the top center and the two in the extension
will mount the sewing motor.  I could have used an adaptor plate or board, but decided
to add the aluminum extension instead.

The motor is mounted and a link belt is installed.  I tested it by drilling a 1/2 inch hole
in some  hot rolled steel.  The only problem I had was occasional slipping of
the link belt on the motor pulley - the motor never stalled.  I need to remove a link
or two to from the belt to be able to tighten it some.  Once I have the final pulley
built and installed I plan to get the correct length of a standard belt.  They seem to
have better grip with less tension, and I do worry about this tiny motor's bearings.

For the tachometer input I decided to use magnets and a Hall effect sensor.  The optical pickup is working great on the lathe, but it is located
inside a closed cover and should stay fairly clean.  The magnetic pickup is much more tolerant of dirt and grime, and in this case, lends itself
better to the configuration of the drill press.

I mounted two magnets in the bottom rim of the quill pulley by counterboring snug fitting holes and mounting the magnets using a little
J B Weld epoxy.  The tachometer will accept up to 60 magnets, slots, or reflective strips depending on the sensor used.  The only
advantage of using a lot of points is to be able to read lower RPMs.  Two magnets keep the pulley balanced against what ever effect the
tiny magnets would have, and will let me read down to 15 RPM .  I cannot see any need to ever run slower than one revolution every
4 seconds!

The sensor which detects each passage of a magnet is a tiny little thing at less than 3/16 inch wide.

I had a small problem of an incorrect part in my tachometer kit, so completion of that is delayed a bit.  I completed all I could then set the tachometer aside.  In the meantime I am designing the mounting bracket for the sensor and the control box to hold the tach and the speed control pot.

I machined a mounting block and used JB Weld to mount the sensor.  It and the
control box cover (shown rotated 180 degrees) are placed on the drawing of the
block.  As the sensor is pretty much hidden by the epoxy, I used a marker to
indicate its centerline for easier alignment.

Clausing was kind to me and provided a 5/16 UNC hole in the perfect position to mount the sensor block.  I did drill the 9/16 dia hole
down into the center of the head casting.  This gave me a wiring route to the front of the head where the controls will be mounted with no
"close encounters of the belt kind".  The AC wiring comes up into the belt shroud from the back and enters the power box through
existing holes in the front casting.  I have a piece of thick protective rubber under the cords as they pass over the bottom flange in the rear.

  As the original power wire is almost 60 years old, with badly tarnished copper conductors, I
replaced it with new.  Instead of buying just a power cord, I got an industrial extension cord with
a 3 outlet receptacle.  I cut this cord to connect to the power switch.  I now plug the motor and
the tach power supply into this receptacle with a spare slot for the possible addition of a light, all
controlled by the main power switch.

Originally, the ON/OFF switch was mounted here.  I will mount that switch on the front of the belt cover casting, directly above.
I started to leave the power switch where it was and mount the new controls up high.  I used the drill press a few times in this configuration
and almost without fail, I would stop the motor using the power switch (as I have for decades).  Swapping the locations will make it more
natural to use it correctly, which is to turn the speed dial to 0.  The power switch is turned off only when the session is over.

That is probably the largest disadvantage of using this motor.  You cannot set a speed and just turn it on and off.  If you try to start
with a speed of over several hundred RPM motor speed, It returns an error message.  In other applications another major problem is
the way the motor reverses.  Using the two buttons on the motor controller, you enter a menu and step through several items until you
reach the number representing direction.  You manipulate it to the new direction and wait 5 seconds to exit the menu.  This is
not a problem on the drill press, as I never intend to run it backwards.

I have now mounted the boxes.  The lower box will have a labeled
overlay once I install the MachTach and the upper box will house
the power switch.  I am running the power cables through the belt
housing and feed the power box from behind for concealed wiring.

  And yes, I did clean up the nameplate and re-lacquer it.  It was really
grungy as seen in the first picture.

This is the finished Project.  The part for the tachometer came in and it took little time to
finish up.  The power switch is handy, but not so much that I hit it by mistake.  The tach
and speed control are at a good usable height.  I am pleased with the outcome!  As it is
set up now with the single level motor pulley, I can run from about 50 to about 1600 RPM.

Update of 12/5/2015  New drive

For over a year and a half
now, the drill press has been working great, with one exception.  Recently, on several occasions when the drill press was running relatively slowly, it would spontaneously speed up to what appeared to be the maximum speed for a moment, then it would resume at the set speed.
 It might do this several times during a project, or not at all.  No damage has been caused by this (except to my nerves), but if I were doing something delicate, the results could be disastrous!  (Think tapping!)  Without any documentation on the controller, and with no warranty due to my modifications, I have little chance of correcting the cause of this problem.

Dealer's Electric, the company from which I bought my Lathe and my Mill VFDs had a very good price on a package of a 1/3 HP 3 phase motor and the same model VFD I have on my other two machines.  For Black Friday they offered $10 shipping.  This is about $50 less than normal, and for well under $200 delivered, I ordered the package.  As I write this on a Saturday 12/5, it is in Prescott Valley, to be delivered on Monday.  Besides reliability there are a couple other advantages to changing:  I will no longer have to turn the speed to 0 to stop the spindle.  I can set a speed and use a switch to turn it on and off.  I will also have an easily switched reverse capability.  This will be seldom used, but is an option I will like having.  The motor frame type is identical with the original motor, so will bolt to the same mounting holes and accept the original pulley perfectly.

To mount the VFD and the new controls, I mounted a plastic junction box on the left side of the drill press head.  This box will contain all the new components to control the motor speed and direction.  The top electrical box I previously installed with the main power switch will be removed and the location will revert to the original configuration.  The box with my MachTach and the speed potentiometer will remain unchanged.

The partially machined box is test mounted on the drill press.

After finishing the machining of the control box and painting it, I installed all the components and wired them.  The box contains the master power switch and the Forward-Off-Reverse switch on the front panel, the VFD front face on the left panel, and a duplex outlet, switched by the master switch on the rear panel.  There are also a fuse, a terminal strip, and electrical cables.  I encountered one problem: the box was not quite deep enough for the VFD to mount and keep all the control wires inside the cover.  I solved this by machining a hole for the VFD in the bottom of the box.  I covered the outside of this hole with a piece of sheet metal and mounted the VFD to this metal.  This lowered the VFD by about 1/4 inch and almost cleared the wires from the inside of the cover.  Thinning the cover where the wires exited gave plenty of clearance.

Operation is slightly different from my other machines.  For this application I decided that a single twist switch for forward, off, and reverse operation would be most practical.  I will occasionally do power tapping on this machine, and this type switch is the most useful for a quick reverse of the motor at the bottom of the tapped hole.  My other two speed controlled machines have a switch to determine direction and separate start and stop push buttons.  Fortunately, the VFD is flexible enough to accept almost any control system you might desire.

The control box has been all wired including the line cord and wire connecting the motor.

The motor mounted exactly like the original one, with no modifications needed.  The rear of the control box contains a
duplex outlet for the MachTach power supply and a possible future light.

The finished installation shows the new box on the left and the original tach box on the front.
The new box contains the master power switch and the Forward-Off-Reverse switch.  The
tach box carried over from the first modification contains the MachTach and the speed control knob

Mods of 3/25/2016  Tapping Provisions

The new motor and drive have been working great, with one exception:  I have used this new setup several times for power tapping holes.  I set the spindle speed very low, allow it to tap the hole, then at the bottom of the hole I reverse the spindle to withdraw the tap.  The problem is that I don't have three hands!  I need one to hold the workpiece in place, one for the feed lever, then another to reverse the motor at the bottom of the feed.  I read recently on one of the machine tool forums of a fellow who had the same problem, and solved it by adding a foot pedal to reverse the motor.  Bingo!

Over the years I have collected 3 different electric foot pedals, so I started thinking about how to control the motor direction with one.  I decided that instead of my panel switch selecting "FORWARD, OFF, and REVERSE" I would have it select "DRILL, OFF, and TAP".   The "DRILL" position would simply be the same as the old "FORWARD" command, "OFF" would of course still be "OFF", but the "TAP" position would now route the controls through a relay which would control the direction on command of the foot pedal.  I initially was going to have the "TAP" position run forward until I pressed the pedal, which would change it to reverse.  After thinking about this, I decided to make the "TAP" position run it in reverse, letting the pedal change it to forward.  My reasoning for this was that if I should want to run the machine in reverse for any reason, the "TAP" position would do this automatically.  For tapping, as I am ready to feed the tap, I press on the pedal until I want to reverse it, then I release it.

Going through my junk boxes, I found a multi-pole relay with a 6 volt coil, my pedal switch, and a 6 volt "wall wart" type power supply.  I had previously used this power supply on my electric truck and later replaced it.  It had  wires coming from the case for both the 115 volt input and the 6 volt output.  I did replace these wires to get the length and colors I wanted for this project.  I used Velcro to mount the supply in a space barely large enough  to the left of the VFD.  I wired the relay to parallel two sets of contact for increased reliability, then made a small mount which I Velcro'd to the bottom of the case.  I added a  connector to the bottom of the box to attach the foot pedal.  It all works fine now, and the next time I decide to power tap some holes, it should be quite easy.

Here is the finished control box after adding my tapping mods.  The 6 volt power supply is just to the left of the
VFD ; The control relay is in a socket mounted to an aluminum mounting base just to the right of the VFD.  The
connector which attaches the pedal is in line with the MachTach connector and toward the rear of the box.

GO BACK TO "Machine Shop Projects"

Richard S. Mason 4/2014