Most lathes reverse the motor ,not the gearing to reverse the spindle. If you are new to lathes, be aware that your chuck is screwed on and selecting reverse brings the danger of it unscrewing as soon as reverse is selected. A spinning chuck bouncing off the bed of the lathe and onto your toes is not something to look forward to. Reverse is usually only used in the very slow speeds. It would be a good idea to get hold of a manual for the lathe before you have an accident. "lathes UK" have a list of useful manuals and parts lists for sale on their website.

If we are talking about reversing the lead screw then the reversing system is quite simple.

The double gear drive on the lever pivot about the shaft that shows two gears, there are three positions fwd, neutral and reverse. In its current position the headstock shaft drives through the left gear and then to the right and down the gear train. In the opposite direction the left hand gear becomes redundant and drive is direct from the right hand gear.

Edited By Bob Brown 1 on 18/04/2020 16:16:59

Ah!! Sam's comment has prompted me to wonder if the OP is indeed thinking that the back-gear lever is for reversing the spindle. This would indeed lock thing up until the lever by the chuck , not shown in the photo, is operated.

It seems as though the ‘back gear’ needs explanation to the OP. It is for selecting a lower range of spindle speeds – whether in forwards or reverse – not for changing rotational direction of the spindle.

Edited By not done it yet on 18/04/2020 19:34:31

Maybe a bit more info about how you are selecting reverse would help us. If it is the red lever then a picture end on like Bob's would help us as perhaps your lathe has the wrong gears on this cluster.

To select reverse of the direction of the spindle and chuck you have to have a motor that does reverse and a correctly worked switch.

To select back gear you first move the lever on the front of the headstock to the left, then move the layshaft lever on the left of the headstock upwards and may need to slightly move the chuck and belt to get things into mesh, then test it by moving the belt by hand, then find the oil points for both the layshaft and the pulley block and oil them and the groove that is on the front of the bull wheel (biggest gear) and finally you are ready to go.

Sounds like the tumbler gears are not engaging properly*, on my model C the lead screw turns the same way as the spindle with the lever in the up position (when using it for carriage feed the carriage moves towards the headstock) and 'backwards' with the lever in the down position.

* and possibly there is something else wrong if it is locking up/

AFAIK the C doesn't have a power cross feed in any of it's versions. But yes, surely reverse feed of the lead screw would cut a LH thread?

Have a look at Bob Brown's pics above the top pic the LS will turn the opposite way to the the spindle, in the bottom it will turn the same way. The only way this could be otherwise would be if both tumblers are not engaging in the 'down' position but the single tumbler was still engaging with the spindle fully and the top change gear. It's easy enough to check by turning the chuck by hand and watching the gears move.

If you're still stuck tomorrow let me know I'll post a couple of short videos of how my Model C change gear work.

First pic is forward second is reverse. In the first pic the left hand tumbler gear is not engaged with either the spindle gear or the on on the lower idler gear, they are connected by the RH tumbler. The odd number of gears mean the Layshaft will turning the same direction as the spindle, the second pic the RH tumbler engages with the lower idler gear but to the spindle only via the RH tumbler giving an even number of gears and reversing the direction of the layshaft. Your lathe has an additional gear in there which would reverse the direction (as well as changing the thread pitch) but it shouldn't affect the working if the tumbler gears.

Take pics of the tumbler gears in the 3 positions of the lever and post them. We may then be able to tell you what is going on.

This could be misleading as the Model C has a different mechanism for engaging and driving the back gears. The drive pin is replaced by a sliding bull wheel gear with dogs/pins that engage with the spindle pulleys. This is operated by the lever on the front of the headstock and the mechanism is quite hard to see clearly as it is buried up in the business end of the headstock casting.

But yes you are right, engaging the back gear without releasing the pin would lock the spindle (and Boxford used to recommend it as a way to lock the spindle for chuck removal though it is advised against these days).

I think the OP has stated that the problem is with screw cutting up thread and implied that the back gear 'trick' is not what is happening.

Edited By Sam Spoons on 19/04/2020 10:19:43