RapidChange Automatic Tool Changer / Cross Threading?

RapidChange Automatic Tool Changer. I get asked about cross threading. it inherently does not cross thread but I thought I would explain why.

Requirements
The RapidChange Automatic Tool Changer system works as well as your CNC machine. Your machine will need to be repeatable. In other words, missed steps will cause misalignment. If you have closed looped steppers you will not have this problem.

For tool changes, you should have a highly repeatable process, which is independent of how precise it is. Endstops for example are not precise, but they are extremely repeatable if you approach them at the same vector. That’s why homing works in 2 iterations.

Dual gantry systems are very good at getting out of square, causing the misalignment that you may not have seen yet. This can happen for multiple reasons, the most important ones being open loop steppers running too fast or accelerating too fast. But it happens for a more practical reason as well: a lot of (frequently used) cheap TB6600 drivers out there are unreliable and will just miss steps during normal operations, which will cause this misalignment in an hour or less.

There’s also a simple solution: add an optional homing cycle before using your tool changer (before every change). Or even better: g53 g0 x0y0 and then $H home x,y. If the g0 fails and runs into an endstop, it’s out of square and will alarm; normally it will just home without a change. Closed loop users won’t need it, it’s only required for open loop systems. That will render cross threading virtually impossible in most cases. Also, the CNC system itself should arguably alarm if a homing cycle doesn’t return to zero, because it’s an indication of a bigger problem.

For more information please visit us at
rapidchangeatc.com