Dale's Homemade Robots

This drill was purchased from Harbor Freight on sale for $16.99. It's item # 04285-4CXA. I bought 6.

Specs: 3/8 inch, 14.4 volt, 0-550 RPM reversable with variable torque settings. The motor is size 550.

The disection begins...

The chuck is screwed onto a threaded shaft and locked in place with a 5mm left hand thread screw. Remove the screw by turning CLOCKWISE. The screw is installed tightly but is made of soft steel. A good #2 phillips screw driver is required to avoid striping the slots. After removing the locking screw the chuck can be unscrewed by turning counter clockwise.

Remove the torque adjuster by removing 2 small screws.

Now remove the rest of the torque limiter parts.

Also remove the 16 metal balls in 8 holes.

With the torque limiter removed the internal toothed gear will spin freely and not transfer any torque.

This is a chuck end view of the internal tooth gear which must be locked to the case. Note the 8 raised points on the edge. These match the positions of the 8 holes in the case.

Place the gear train back in the case and turn it until the 8 raised points exactly center with the 8 holes. Use a sharpe pen to mark the position.

Remove the gear assembly.

Drop in a 1.5od x 1.25id O-Ring (1/8 inch thick).

Put the gear assembly back in and align with your mark.

Be sure to replace the round metal plate.

Put the motor back on. Due to the extra thickness of the O-Ring you will need to tighten each of the 3 screws a little in sequence to torque down the case and push the O-Ring into the 8 holes.

The case will be flush when screws are tightend fully.

On the left we see the effect of the 8 raised points forcing the O-Ring into the holes and locking the gear assembly to the case. These holes can be threaded with a 5mm x 0.8 tap to facilitate mounting if desired. If you don't want metric threads you can use a 10-32 tap but the fit will be a little loose.

Update July 2006: It has been reported that this O-Ring hack will fail under very heavy loads such as driving axe weapons doubling as self righting mechanisms. The bright side is the gears cannot be stripped. I assumed this hack would only be used on drive wheels where the torque is reasonable. If you need all the torque the motor can provide and accept the risk of gearbox destruction, I suggest tapping the holes and using screws to lock the torque limiter.