Spindle and axis warmup routine

[aussiemike]

Does anyone run a warmup routine on their CNC router? I m still building my Avid Pro and see that they have such a function in their Mach4. The supplier of my spindle said to warm up the spindle before the days first use and others have noted it s good practice to run each axis throughout their range of length and speed. Seems like some simple g-code would do the trick. Any thoughts?

 

[tmtoronto]

Did they happen to give the reasons for the warm up? For my small router I can see one benefit being to ensure all systems are working properly, and perhaps catching issues not indicated by software faults, like something physically blocking an axis' travel. From what I understand for more professional/industrial use cases, where extremely tight tolerances are required, the warm up routine will ensure all parts of spindle and CNC are properly lubricated and have warmed up sufficiently so as to minimize/eliminate issues related to thermal expansion. I remember having seen many videos from different manufacturers that have examples of simple code to use.

 

[aussiemike]

You hit the nail on the head. Thermal expansion and lubrication. Spindles are precision equipment designed to be in tolerance at operating temperatures. If you go straight into levelling a slab first thing on a winter morning, the spindle will have a shorter life. As for the axis warmup, gets the linear bearing grease and motors up to temperature under no load. Also an opportunity to hear any odd sounds to investigate before any damage is done. It was metaphorically described as stretching and warming up before the workout. I found some g-code that takes the spindle through a series of increases over five minutes. It maxed at 10K so probably a mill. I can adjust it to suit my 30K spindle and it won t be difficult to add some code to do a few laps around the track.

 

[zombieengineer]

@aussiemike - is your setup for business or a "weekend machinist"?

I suspect the issue is the balls in the spindle bearings heat up first before the bearing race catches up (difference in mass) - as a result the balls are under a much higher preload until the temperature evens out and the bearing race has expanded to match the slightly increased ball diameter. The scale of the bearing (e.g. diameter) has a big impact, double the diameter of the bearing and it takes 4 times as long for the temperatures to stabilize (square of size - more mass x thicker layer for heat to transfer through).

I doubt that a "weekend machinist" would need to do an extensive warmup routine (other than a pre-start check to make sure everything is functioning, jog each axis back and forth) as the items such as the spindle are rarely loaded anywhere near the design rating (unless you are leveling a slab as you mentioned - Avid CNC provides some details of what full load looks like on their 4HP spindle page: pushing a 1 " wide bit with a 4 mm depth of cut in hardwood at 10 meters/min). Lightly loaded machine means lower temperature rise and therefore less stress while the temperature stabilizes. If in doubt - stick a mains power meter on your VFD drive supply cord and see what the actual power draw is compared to the spindle nameplate rating.

In a production environment the G-code would be optimized to fully utilize the machine capabilities (constant high spindle loads), combined with a larger machine means a warm-up is recommended if the machine has cooled down.

Disclaimer: My background is a chemical engineer, not a mechanical engineer - take my advice with a pinch of salt. The issues of heat soaking of equipment does come up in my work in the form of heat up of furnaces to prevent the refractory lining cracking.