When a Spindle Won't Let Go

Tool spindles can be finicky, and sometimes fail to release a tool properly. Here's one example, and a discussion of what could be causing the trouble. January 27, 2008

Our spindle isn't opening up completely to allow it to release or accept tool holders. I checked the air pressure and tried it in manual mode and I got it to release the tool holder that was in, but now it doesn't want to grab any other tool holders. This was a replacement spindle that was installed approximately 4 months ago. Since the installation it had worked fine until this point. I am hoping this is something minor that I may be overlooking (I can't afford to be down another 3 days waiting on another replacement spindle). Any suggestions?

Forum Responses
(CNC Forum)
From contributor A:
I experienced the same problem occasionally with my HSD spindle. Usually the operators leave a tool in the spindle for a long time and the cone sticks to the inner opening of the spindle. Another problem I experienced was exactly what you describe. It usually means some basic cleaning is required of the release switch. Also check the connection to your spindle as the plug may be loose.

You also have to check where the controller thinks the tool is. Sometimes depending on the sequence of removing or inserting the tool, the control may think the tool is not in the correct place. On our Biesse Rovers, if the machine, for example, stops in the middle of performing a tool change, it registers that a tool change occurred but the tool is still physically in the HSD spindle.

From contributor M:
Contributor A makes good points. You can clean your collets, lube the draw bar, check air pressure and air dryness. If none of that helps, check the i/o's via the control. Your machine manufacturer should be able to help you with these. A series of steps have to be completed for a successful tool change and you will be able to see where the failure is here. Another thing to look at (probably last) is the cylinder on the top that actuates the drawbar. I replaced one of those once.

From contributor B:
There is a lot of information missing here. The more you can give, the more direct we can make the suggestions. You said the first tool holder would not come out. How did you manage to get it out? My guess is that it was stuck, as others have said, and you were able to pry it down and break it free while holding the green release button. If that is the case, then your system probably still sees a tool installed even though there isn't, as suggested above. If you can enter a "no tool" command, do that next. That would be a T0 on my system. That will tell the computer there is no tool in the spindle. If this doesn't work, then tell us more about how you freed the stuck tool holder, and what exactly happens when you try to pick up a tool.

From the original questioner:
The tool holder wasn't stuck. I have had that problem before. The draw bar was actually pushing the tool holder down slightly, but not enough to release the retention knob. The tool holder I got out, I did by prying out similar to when it would get stuck.

After talking to Thermwood, we came up with two options that could be causing the problem:
1. Problem with the air cylinder.
2. The spindle shaft that I put in recently had a problem with the part that grabs the retention knob.

They are sending me both parts to try, but I think the problem is with the spindle shaft part. I took the air cylinder out and it seems to be working fine. As far as the tool holders getting stuck in the way you guys mentioned, I started cleaning the holders periodically with scotchbrite and haven't had a problem in a long while. Thanks.