I’ve been trying to troubleshoot an operational inconsistency in my ATC system for some time now…
During a tool change the actual release of the tool relative to the timing of the spindle’s subsequent upward retraction on the z-axis seems delayed. This leads to the tool fork being pulled up by the tool and snapping back down with a jarring thud. The fork retains the tool but I can never trust that a step hasn’t been missed in the process. When the thud is enough to be felt ion the table I re-zero the system and restart the cut program from where it left off.
The vertical yank on the fork and snap/thud symptoms are variable.
I’ve tried fine-tuning the tool rack coordinates many times to little sustained avail.
Through all my testing it seems to get more noticeable after having made some passes.
In testing for vertical play in the z-axis with motor powered I’ve come up short.
PRO4896/NEMA34, CNC Depot HK30C, CNC Depot tool forks, linear magazine rack at the rear of the machine.
Retuning tool rack coordinates a bit lower on the z-axis
Minimizing air line length to reduce friction-induced delay
Decreasing the z-axis retract speed after tool release (from 60 to 40 ipm)
Rebuilding/double-checking z-axis internals (Oldham coupler, ball screw, brake, etc)
I’ve considered a dwell command between the tool release and z retraction commands but this would only be a band-aid.
It’s defeating to not trust something designed to be repeatable.
Any insight or ideas are welcome.
I think you’ve nailed it.
The drawbar requires 90-110 psi but within that range there seems to be a big difference in timing performance. On top of that the spindle caser pressure requires 30-110 psi and it’s detrimentally parasitic over time. Seems my air system gets a bit anemic.
I’ve added independent regulation to the case pressure and dropped it to 40psi.
Also rebuilt the compressor’s aging pressure switch and increased it’s cut-in/cut-out range by 10-15 psi.
Your wisdom and experience are much appreciated!
Yep, differing pressures will effect drawbar timing.
Also temperature of your shop.
Then there is the heat of the tool holder if it’s left in the spindle to cool. The drawbar will have to come from behind and knock the tool holder out. As @djdelorie and I have learned, maintenance of the taper is crucial to this process.
So, follow the industry standard and give either a 0.0625" to 0.125" of play in the tool holder clamps OR just accept the wear on the tool holder clamps. You will replace them about every 12 months for a medium duty shop.
My carousel has the play required. I also have two pressure sensors, one on the main line for “system pressure” and one on the drawbar for release and capture monitoring.
Funny aside, when I was using a custom protocol I could measure the pressure falling on the drawbar and time the seating action to that.
Then I had to switch to ModBus which means you are always around twice the polling rate behind. Newfangled would never license me the headers to compile as a motion controller so now I am happy I built in the play but sad because it could be very, very different.
As part of my “done with the machine” procedure, I put away whatever tool is in the ATC before parking the spindle near the machine home. There have been a few times when a long job heats up the spindle, and after cooling it’s very difficult to remove the tool.
I’ve had the tools “stick” or maybe kind of pop out rather than be just “released” from the spindle as well. Since I’m doing doing actual ATC, just quick tool changes, it’s not really a deal for me. That said, it can be a hell of a surprise sometimes to have the tool shoved into your hand rather than simply released.
Every time it’s happened, I’ve noted that the tool holder is either warmer or colder than I expected. A warm spindle with a short toolpath sometimes ejects hard, but more commonly a cooling spindle that’s been idle seems to be the culprit. I wonder if it’s just an issue of the mass of the tool holder cooling more slowly than the innards of the spindle, and the temperature differential and tight tolerances ultimately are the cause.
But, now that I type that I suspect that big expensive fancy machines don’t have this issue.
What I’m really saying is… I have no idea, I just don’t wanna drop a tool holder when the spindle barfs it into my hand.
Actually, it’s the taper. All spindle in the ISO30 will exhibit the same behavior.
That steep of a taper is great at keeping the tool from slipping but it can be difficult to release after the holder and the holder collet sleeve heat and cool together.
It is recommended (please do verify, I am just some random guy on the interwebs) to use just a tiny amount of Permatex Nickel Anti-Seize. Tiny dab and rub it on just the taper, not the pull stud. Then wipe it off. The trace amounts will keep it from sticking. Doesn’t take much.
Also, it will attract dust and swarf and hold it much better so leave the vacuum on during tool changes.
This is the exact advice Alex gives on this issue. We started using a tiny amount on all our tools and it solved our issues. I believe that is the exact one he recommended.
Our tool changer is in an enclosure and one other thing that helped was heating it when the shop was cold. We use a radiant heater appropriate for a dusty environment set to 70 or so with a switch on the control box to turn it on and off. The enclosure also keeps the dust off of the tapers. We still blow off the taper with air automatically during a tool change.
All of these remarks make complete sense with regards to the patterns of behavior I’ve noticed. I will incorporate the additional Permatex Nickel Anti-Seize step as well.
Your collective insights are much appreciated!