Introduction: Motor Made New McGyver Style
This drill press fell over onto a concrete floor. The motor bearing mounts shattered. They were a cheap cast alloy integral to the end caps of the motor. A new motor is too expensive for this inexpensive drill press, but the tool is also too good simply to junk. I decided to rebuild the end caps of the motor with new mounts for the armature bearings, but tolerances are close and the bearing mounts need to be centered and sturdy.
- Black iron pipe
- 1/8" x 1/2" strap iron
- 1/4" x 20 hex nuts
- 3/16" steel rod
- Aluminum sheet
- JB Weld
- Metal lathe (or a half-round file)
- Digital caliper
- MIG welder
- Tin snips
Step 1: Spider Mount
The first step was to cut short lengths of black steel pipe (about 5/8" long each) and make the internal diameter a little larger so the pipe sections slide onto the motor bearings mounted on the motor armature. (I had the luxury of access to a metal lathe. Not much material needed to be removed. If plenty of time and patience were available, careful work with a half-round file would do the job, too.)
Then I made four arms of 1/8" x 1/2" steel bar and welded them to the sections of black pipe. See the black marks in the graphic for the location of the welds. The arms are each about 1 1/4" long.
Step 2: Centering the Armature in the Stator
The graphic represents a form very much like the motor armature. Notice the two black marks. I wrapped the circumference of the armature with two turns of black plastic electrical tape where the black lines are. Two turns was just about right. The armature was still loose enough in the stator to go in and out as needed, but tight enough to hold the armature centered inside the stator.
Step 3: Fitting the Spider
With the armature inside the motor, slip the black pipe sections on the front and the rear bearing of the motor. File away any remaining jagged edges from the old bearing supports inside the end caps. Slide the end caps of motor into place.
I rested nuts for 1/4" bolts on the spider arms and welded them into place. (I had made two pieces of sheet metal shaped like a "C" to cover the opening and protect the enamelled copper coils inside from hot molten steel falling on them and shorting the windings.)
Wait until the welds cool. Take the motor apart and remove the electrical tape from the armature. Remove the sheet metal pieces protecting the windings from hot steel globules.
Assemble the motor again. Spin the armature slowly by hand. Hopefully, the armature spins smoothly without rubbing on the stator. If that is not the case, sight through the end of the motor to determine how and where the armature is off center. Shim or file the 1/4" nuts to move the armature toward center and check by spinning the armature.
Step 4: Secure the Spider Mounts
See the text boxes in the photo. I cut 3/16" rod to lengths about 5/8" long and welded them over the nuts already welded to the spider arms. These rods keep the spider from moving inward into the motor with vibration.
I made a rudimentary grease seal for sheet aluminum and welded it in place with two 3/16" rods. These also keep the armature from dropping out of the motor in time with vibration. (The armature will be in the vertical position in use.)
I found the welded nuts and the short pieces of rod could not be as precisely placed as I had hoped, nor did they stay in place as well as I expected. There was a need to secure them. When the armature spins freely, mix some JB Weld and place it so it secures the nuts to the end caps of the motor. Wait 24 hours for it to harden before you put power to the motor.
Step 5: Congratulations and What Could Go Wrong
It was a very happy experience when my motor worked again with almost no cash outlay. But, I had a couple of problems along the way.
When the motor first ran smoothly, I noticed it was running backwards. On a capacitor motor like this one, the fix for that would normally be to reverse the connections to the starting windings. But, I had not disturbed the starting windings. Then I realized I might have inserted the armature from the wrong end of the motor frame. Taking the armature out of the motor and inserting it from the other end reversed the direction of its rotation. Problem solved.
At one point, I put power to the motor. It growled and the armature froze. I was part of a second slow to shutting off power and there was a blue spark. After that the motor ran more slowly and it got hot quickly. A check with an Ohmmeter revealed a weak electrical path from the coils to the frame of the motor. That usually means the motor needs to be rewound. I did a visual inspection and found the armature snagged a fine wire in the starting winding while I was sliding the armature into the stator, scraped the enamel off of it, and pushed it too close to the stator where it was able to short. I moved the bare portion of the fine wire out of the way and insulated it. Then the motor worked fine again.
Other damage: A small bit of the pulley on the motor broke off, but that is not a real problem. Also, the plastic cooling fan blade on the armature shattered. I made a new fan blade from sheet metal and fastened it into place with a small hose clamp. (I placed the screw part of the clamp to counter any imbalance due to the partially broken pulley.)
The photo shows that one of the bakelite knobs on the drill press broke and I had to make a replacement.
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