Cross Threading?


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.

Cross Threading: 

ACTUALLY cross threading the hardened steel of the spindle would require EXTREME torque, far beyond the 14 foot pounds that our system delivers. The only potential problem is for the nut to become stuck at the start of the threading process. The ONLY way this could possibly happen would be through GROSS MISALIGNMENT where the spindle shaft is NOT perpendicular to the magazine.

After thousands of tool changes I have found that the only time it fails is when I force it to. The precision and repeatability of CNC and the RapidChange ATC Magazine, inherently prevent this from occurring!

Manual tool changes are a hassle for many reasons, mainly because it’s difficult to start the threading process by hand. Precisely holding the nut relative to the spindle shaft is not that easy when you’re trying to do it quickly. We just end up fumbling around until they line up and we can finally thread the nut. Then we grab our wrenches and finish tightening it.

This brought to mind the fear of cross threading when I tested the first prototype and I will admit, it was a tense moment. I was almost waiting for it to happen, when suddenly it smoothly loaded the tool and I jumped for joy. Then it became obvious as I remembered that a CNC is a precision machine. It will return to the same location in X Y and Z and in the same orientation vertically every single time without fail. This is why we use computer numerical controls on machines in the first place. When the clamping nut is in the same location and orientation every single time, why wouldn’t the nut thread perfectly?

The RapidChange ATC Magazine holds the clamping nut precisely in the same location and orientation after being unloaded every time due to the design of our RapidChange Socket (which by the way is NOT a hexagon, this geometry does not work when unloading the tool).

Every time a tool is loaded, if the spindle and nut are always precisely aligned and oriented, this makes it far more repeatable and accurate than changing tools by hand,

not to mention much faster.

Happy tool changes!

Updated on October 20, 2023

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