Broaching Internal Splines on CNC Mill

A client reached out to us for help on Broaching Internal Splines on their CNC Mill.

“Thanks again for all of your help organizing our custom broach tool for our spline work.  We received everything the other day and have it installed in the machine and ready to go. 

I have a question about programming this specific project.  I’ve read through the website and paperwork that we received but can’t seem to find this specific topic addressed. 

In the examples discussing this for a mill, there is only one instance of broach work being illustrated – for example, one instance at 12 o’clock for a keyway.  So moving into the cut and retracting are obviously going to be in that Y axis direction. 

However, for my situation I’ll need to rotate about the Z axis to cut another two splines and then repeat a number of times after that.  Therefore my movements into and out of the cut will not be directly on X or Y. 

So, my question is: what is the usual approach for this situation?  I’ve come up with a couple different solutions myself but wanted to see what the common or “normal” way of doing this is.  One thing I’ve realized in the world of machining is there’s many ways of arriving to the same solution!  Just some are easier than others, and right now my solutions are a bit time consuming. 

I know doing spline work in a lathe would be straightforward by indexing the C axis, but this part is not suitable for the lathe. 

Thanks, looking forward to your feedback.”

Our response:

“I’d recommend using G68 (work coordinate rotation). This should be the easiest way to get around the programming issues. You could create a subprogram which is programmed at 12 o’clock. Then use G68 to rotate the work coordinate before you call the sub program back up for the remaining splines. G68 rotates the work coordinate. G69 cancels it.

See this website for more details: https://www.cnccookbook.com/g68-g69-rotate-coordinate-cnc-g-code/

For more information on programming your CNC Mill

Broaching Internal Splines
Indexable Spline Broaching Systems

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