Monday, April 7, 2014

Lathe: Shimming Carriage Gibs

The gibs on the carriage went out of adjustment again, bringing the project I was working on to a temporary end. Highly annoying. Instead of just adjusting them, I took the time to shim them.

The mini lathe's carriage gibs are held in place and adjusted by opposing screws. Two of them push the gib away from the carriage, while three of them tighten the gib to the carriage. In theory, by balancing the screws against each other you can adjust the gib/carriage/bed clearance. In reality it's a crappy system. It's hard to adjust, puts a lot of stress on the gib, and bends the two ends of the big toward to the bed, making it even hard to adjust properly.

To switch to shims remove the small locking screws and leave the socket head cap screws. Starting with the back of the carriage, slide a shim between the gib and carriage, tighten down the three screws and see what it does. If the carriage won't move it's too tight, if there is any movement it's too loose. On mine the back gib ended up with a 0.035" shim. Once that's done, repeat on the front. When testing for movement, make sure there is there isn't any play between the carriage and the bed's prism.

Once the shims are in place, apply blue tread locker to the screws, tighten everything down, and lube the ways.

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