Modern Taig Coupling

Having developed a method for fitting the 4 tubes that make up the original stepper motor coupling, sometimes it still takes a while to get the coupling togther. Looking at it recently I thought "Why can't I simply replace the nut?" and so I picked up some of the19mm oldham couplings along with the correct tap and drill to thread them out. ...split...

One of the common problems with the old coupling was the ocasional fault that resulted in the tues being split. I would not have expected this to happen since the motors should stall first, but having seen the results ... The acetal plate of the oldham coupling has a much higher breaking strain, but is a little close to the design limit when using the 1.8Nm motors. However I'm actually looking to run 3Nm motors and I'm happy that the 19mm coupling will be more reliable than leaving the older coupling. I can machine the old coupling out to take the 8mm shaft, but this requires removing the bolt before machining, and filling a slight flat on the stepper motor shaft as the bolt thread just impinges on the 8mm hole. Machining out the 19mm hub is more reliable, and the resulting stack fits nicely wthin the motor mount. The set screw will be required to clamp the hub once the preload on the bearing has been set.

While I do not anticipate a problem using the 19mm coupling, another option would be to switch to the 25mm hubs, but this requires more space between motor and leadscrew than the basic configuration will allow. The previous solutions have involved cutting back the end of the leadscrew to allow more space, but I think that it makes more sense simply to provide a spacer between the motor and clamp plate of the mount. I've not yet worked out just how thick the spacer would need to be, but I only anticipate a few millimetres.

Update ...

On closer inspection of the data I've discovered that the closed hub spacing is 4mm shorter than the through hub ones we normally use with the rotary tables. I've got a batch on order from Huco which I'm hopeful they will get out today so I can play with them tomorrow. Looking at the hubs I've got this will fit perfectly, and with the clamp version we will not have the problem of damage to the leadscrew thread due to the set screws.