Give Your Table Top Drill Press MORE POWER!

Ever felt that your drill press was grossly underpowered for your needs. I did, when I discovered that it was unable to cut with a 2" hole saw through 1/2" plywood. Having more power not only makes you feel like more of a man, but you will break fewer drill bits, and make cleaner holes of all sizes. The press I use is a Craftsman 9" model 137.219090. It supposedly has a 1/3 hp motor, but if we assume that amps are a fair gauge of power, the 1/3hp motor that I bought from Grizzly for this one is 5.3A at the same voltage, so a pretty safe bet that this is twice as powerful.

To make this project I was fortunate enough to have access to a full featured machine shop at City College of San Francisco, anyone remotely interested in machine work should seek out their local community college and take a class, before budget cuts are the end of them.

If you aren't as lucky, you can make this project just with another drill press, or without any machine tools if you use an arbor adapter, or a NEMA 48 motor.

Step 1: Gather Parts and Tools

Tools you will need:

A second drill press with vise and vee block, or metal lathe
Metric socket set up to 24mm (though 15/16 seemed to work for t
2mm Allen wrench
19/32 drill and 5/8" hand reamer (Just a 5/8" drill will do the trick in a pinch)
Gear puller, or plumbing handle puller.
A welder would be very helpful
Vernier Calipers or ruler graduated in 32nds
Medium (14") Channel Lock pliers
Angle grinder with cutoff wheel, and abrasive brush.

Parts you will need:

New Motor you may use a more powerful motor, but if it gets much heavier, you may need to counter balance the press.

New belt This should work for any NEMA 56 mount motors.

New switch (This is probably optional, but being unsure of the amp rating of the stock switch, I elected to pay the additional $4. This will also allow you to run on 220 if your shop is so equipped)

Step 2: Disassembly

My first suggestion is to take photos from every angle before taking this apart, it also helps to search the manufacturers website or other tool parts websites to see if they have an exploded view that will help in identifying parts. Here is the link for my press:

Parts diagram and replacement ordering info

The only part that technically needs to be removed in order to complete the upgrade is the motor, unfortunately, in order to lift the motor off of its mounts, you must remove the pulley guard, and in order to remove that, you must remove the idler pulley.

The drive pulley removes easily, there is a set screw in the second smallest ring, loosen that with the 2mm allen key, and pull it off.
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The idler pulley (the one above the chuck) is a bit more difficult, it is press fit on a tapered shaft, then secured with a 24mm (15/32) left hand nut.

To remove the nut place the channel locks on the smallest ring of the idler pulley with the jaws opening to your right, and turn the nut CLOCKWISE with the appropriate socket. Remove the nut completely.

The pulley must then be pulled off of the tapered spindle. To do this, I used a steering wheel puller, but would work much better to use a handle puller used for plumbing, or ideally a gear puller.
All three of these work the same way, a center screw presses down, while hooks pull up on the pulley. When you do this, the chuck will be pushed down, rather than lifting the gear up. To prevent this, raise the table up against the chuck. A few turns and the pulley should release.

To remove the pulley guard, unscrew the switch plate and remove the spade connectors to free the wires. There are four screws that hold the guard down and two clips that hold the wires in place. Remove all of them, and lift off the guard.

To remove the motor, unscrew the two hinge bolts and lift the motor up.

Step 3: Modify the Pulley

Larger motors, specifically the one I used have 5/8" shafts, and the drive pulley must be modified to accommodate the larger shaft. Fortunately this is as simple as drilling a larger hole, since there is enough excess material, and the set screw is short enough to still sink below the trough of the pulley.

You can avoid this step if you find a motor with a half inch shaft, like this one. A NEMA 48 motor will have a half inch shaft, and likely have a small enough distance from base to spindle to avoid the need to modify the pulley guard. Or you can find an adapter to reduce the shaft to 1/2".

First, remove the set screw from the pulley.

I used a lathe, and if you have access, this is much easier. Simply mount the pulley, small end out, in a three jaw chuck, making sure that it is mounted square to the headstock. The easiest way to make sure is to put a straight, 1/2" rod in the pulley, and spin the chuck by hand, watching that the end of the rod does not wobble.

Set the RPM about 300, mount a 19/32" drill in the tailstock, and drill all the way through. No cutting fluid is necessary, as cast iron is self lubricating. Then, mount a chucking reamer in the tailstock, cut the speed down to 200, and run the reamer through. If you don't have a chucking reamer, I suggest using a dead center in the tailstock to keep the reamer aligned.

If you don't have a reamer, you may use a 5/8" drill, but you will sacrifice some accuracy.

If you only have a drill press, follow these steps:

Place a 1/2" drill or straight round bar in the drill press chuck. Clamp the pulley in a drill press vise and vee block, sitting loose on the table of the press. Bring down the 1/2" guide-rod to align the pulley below it. Before releasing the guide, clamp the drill press SECURELY in place, then move the guide up and down to make sure that you are accurately centered below the chuck. Then follow directions to drill and ream as above.

Step 4: Modify the Motor Mounts

By far, the biggest challenge was to make sure that I could mount the motor accurately on the existing frame, since the new motor is so much larger.

The most logical thing to do, rather than try and bend 1/8" steel accurately was to re-use the hinge part of the mounts.

The first thing was to figure out what the distance was between the hinge mounts and the spindle. I placed the old motor on the edge of a table, and measured from the edge of the table to the side of the spindle, then subtracted .250 to bring me to the center. (see image)

I then cut off the side of the motor plate with the mounts, preparing it to be attached to the new motor flange.

There are three alignments that matter when attaching it to the new flange:
First, the distance from the hinge to the motor spindle should be as close as possible to the original measurement. Second, the top of the hinge should line up with the top of the motor body. and finally, when mounted, the spindle must be vertical.

To do this, I marked a location for the hinge on the new flange using the same method of measuring as above, and clamped it in place with a vise grip. I then mounted it on the press with the pulley guard set in place, and eyballed the minor adjustments.

Removing it from the press, but with the clamp still in place, weld the two pieces together. It is a good idea to weld two spots and then double check alignment before completing the weld.

If you don't have the ability to weld, drill two holes for 1/4" machine screws and tighten well.

The final adjustment was to weld or bolt on a piece of scrap steel to extend the baseplate on the right side, so that the adjustment bumper will hit.

Step 5: Reassembly

The drill goes back together in reverse order:

First the motor, and mounting bolts.
Then the pulley guard
Then the pulleys and new belt. Make sure that the set screw is aligned with the keyway in the motor shaft.
Finally the wiring. If you are replacing the switch, the model mentioned pops right in to the existing opening with no adjustment.

Currently, you cannot close the cover, since the pulley is farther out.

See