Back Gear

Last Updated: 14 March 2009
There's really not much story to tell here, but for completeness I'll go over what I did with the back gear.  The back gear is merely a reduction geartrain that permits slow head speeds and very high torque.  The pulley cone in the headstock is separate from the headstock spindle, with a large bearing surface between the two so that they can rotate at different speeds.

In normal running, the motor drives the countershaft which, via the flat belt, drives the pulley cone in the headstock, which is mechanically linked (via the bull gear pin) to the headstock spindle.

In back gear mode, the bull gear pin is disengaged, which allows the spindle and the pulley cone to rotate at different rates.  The back gear shaft is then engaged, which transmits power from the pulley cone, through 2 reduction gears, then into the headstock spindle at the rear.

This figure shows the basic functionality I've just described.  The only thing not visible is the headstock spindle, which runs through the center of the pulley cone.

This mechanism worked fine, but I dismantled it anyway for cleaning and inspection.

The back gear has a plug at the center of the shaft which is supposed to be lubricated annually using Teflon grease.  Upon disassembly I found there to be a light coat of old oil inside, but no grease.  There was also oil residue coating everything.  I have a theory that the black/brown residue that's left behind when oil dries up has a tendency to protect metal parts from damage if they are operated in a state of low-lubrication for awhile.

Removing the back gear assembly is straightforward.  First, remove the set screws located beneath the castings in the headstock.  This photo shows the rear one, and there's another one at the front of the shaft.

At the front of the assembly there's a big bushing that must be driven out (after the set screw is removed).  Note: the slotted screw shown in this photo is NOT the set screw for the bushing!  That particular screw holds down a shield that fits over the top of the headstock there.  The set screw for the front bushing is located beneath the casting.

To drive out the bushing I placed a flat-blade screwdriver tip in the position shown in the photo and gently tapped with a light hammer.  The bushing doesn't fit real tight in there - in fact, if there weren't an oil residue film on the bushing it would slide right out without the need for a hammer.

The bushing is slotted, and I used a flat blade screwdriver to twist it out the last 1/2 inch or so because at that point it wasn't possible to keep driving it out with the screwdriver from the back side.

On reassembly, I discovered there's a way to adjust the holding power of the back gear shaft.  As you tighten the set screw that retains this large bushing it causes the bushing to squeeze the back gear shaft (since the bushing is slotted).  That way you can adjust how much torque it takes to pull the back gear lever into position for using the back gear.

Once the front bushing has been removed, the spindle for the back gear can be pulled out, as shown in the photo.  I had to pull hard and twist at the same time, but it slid out without any trouble.


I soaked the back gear, screws, and bushing in degreaser ovenight.  The spindle I cleaned with some extra-fine steel wool to remove the aforementioned residue, then greased everything up with Teflon grease and set it aside.

I also went back and cleaned up the bores in the iron headstock casting so that the bushings for this slide in and out by hand.

Shown in this photo is the fully assembled back gear and the Teflon grease I'm using.  Got the grease from McMaster-Carr.  You may notice that when this photo was taken the back gear shaft is backward!  The correct orientation places the larger gear at the same end as the hand lever.  It becomes obvious which way it goes when you try to reassemble it on the headstock.