This week I have another new replacement part to share with you for the N Gauge Minitrix 9F.  I’ve already made replacement parts for this locomotive such as the eccentric rod crank pin which you can read about here and the cross head, which you can read about here.

The Minitrix 9F has always been a good runner but, apart from the eccentric crank pin and cross head, it suffers from wear in the plastic gear after lots of running.

The worm gear on the motor shaft is metal and drives a plastic gear, this in turn drives two metal gears which drive the metal gears between and on the axles.  The first gear is made from plastic, I believe, because it’s a double gear and it’s cheaper to make it in plastic than metal.  A double gear means it has a large and small diameter gear moulded into one piece as illustrated below.

Because the original gear is plastic and is driven by and drives metal gears, over time it wears down and looks like this.

Sometimes a slight wear can be overcome by slipping a pack under the rear of the motor, tilting it forwards, causing the worm gear to push down onto the plastic gear but eventually it will wear out.

You can see the larger gear, which is driven by the worm gear, has lost its points and the bottom left side has worn more than the rest.  This may be because the side rods jammed, stopping the gear, but the worm gear carried on turning, chewing the plastic.

The new 3D printed part, as shown below, is printed in Shapeways Fine Detail Plastic.  This is a hard material and long-lasting which has been proven with the O Scale gears I made a few years ago.  You can read more about those here.

The plastic gear spins on a metal axle which fits into the new gear without enlarging the hole.

Fitted back into the chassis before the motor is re-fitted, the new gear can be seen in the top of the tower.  At this stage the gear can easily be tested because the worm gear is not stopping all the gears from turning.  Running the wheels along the work bench turns all the gears, including the new one.

With the motor re-fitted, along with the weights and shell, the locomotive can be tested on power and it runs nice and smoothly.

The gear is available here.

Next week I’ll have another new replacement part to share with you.