Repairing the backgear on my Atlas Lathe

When I purchased my lathe in May of 2011, I was warned that there was a problem with the backgear. I was also encouraged by predictions that it probably would not be hard to set right.
Here is a picture of my headstock showing the backgear and almost all of the relevant moving parts:

Some parts have been removed for cleaning and repair, but everything relevant to the backgear is in clear view here. The backgear is the pair of gears on the shaft to the rear. This assembly can be moved in and out of engagement by the use of a lever (not visible) on the right. When engaged, the backgear reduces all speeds by a factor of approximately 6.0.

How it is supposed to work

There are 3 parts on the spindle that get involved with the backgear:

When the backgear is not engaged, a belt drives the pulley cluster, which is rigidly coupled to both the bull gear and the small gear. The small gear is just along for the ride.

The bull gear can be disengaged from the pulley cluster. This is done by pulling a pin to the right. After this is done, the backgear can be pivoted into engagement. Engaging the backgear without retracting the pin will lock up the spindle, and probably break things if power is applied.

With the backgear properly engaged, the belt drives the pulley cluster and small gear, which are not coupled to the spindle, they just revolve freely. The small gear drives the big backgear, and the little backgear drives the bull gear, which is fixed to the spindle and away we go.

How mine is screwed up

There are two problems, both of which, in my analysis trace to an error made when parts were reassembled on the spindle. My analysis is simply that the pulley cluster is mounted too far to the right. If it was moved left it would permanently engage the small gear (trapping it against a collar), and it would be far enough away from the bull gear that the pin, when retracted would not mate with it.

More information


Have any comments? Questions? Drop me a line!

Tom's home page / tom@mmto.org