Troubleshooting a Sticky Tool Holder

CNC pros try to find the source of a tool-changing problem. March 25, 2007

My tool holder is getting stuck in the spindle. It only happens after a relatively heavy cut and if I try to use the tool changer, it will sometimes pull through the forks and then crash into the next tool I want to pick up. Any ideas why this might be happening? What might I do to fix this problem?

Forum Responses
(CNC Forum)
From contributor T:
You should check to see if any of the sensors for the tool changer are getting covered with dust. This may be why it only happens after heavy cuts.

From the original questioner:
I don't think it has any sensors that are involved in tool changes like that. The tool holder is also very hard to remove by hand in the situation I have. In the worst of cases I have to use a rubber mallet to tap the holder loose.

From contributor J:
What type of tool holder are you using? Our machine has HSK holders. This happens sometimes to ours. Usually a sign that the draw bar needs adjusted or washer springs in spindle are going bad.

From the original questioner:
Our spindle is an HSD ES 919. It uses an ISO 30 toolholder.

From contributor R:
Maybe you have some wear or a burr inside the tool holder. Have you tried switching out that tool holder immediately after this happens, and making the same cut to see if a different tool holder does the same thing?

From contributor M:
What brand and model machine? What style of tool changer (fixed, magazine, etc.)? Do you have any issues with water in your pneumatics? Have you in the past? What do the cones look like... rusty, nicked, carbon buildup? What is the condition of the tool changer? Try to give us a feel for all the subtle little things going on.

From contributor B:
This topic has been discussed numerous times. Check the archives for some really good threads on the subject.

Bottom line here is tool holder maintenance. Our HSD ES915 and ES919 ISO 30 holders gave us this problem on a regular basis before we started rubbing down the holders with Scotchbrite 2 to 3 times a week. It only takes about 2 minutes to do the whole rack.

Also, turn the spindle on very slow speed and wrap the Scotchbrite around the end of a 3/4" x 6" dowel. This will clean the inside of the taper. There are actually tools made for this, but I've found the Scotchbrite works just fine. Don't use your finger! Use a fine texture pad rather than a coarse texture.

Sticking still happens a few times a year, though, so we keep a large forked auto repair tool (something to do with bearings or tie rods I think). The forks are very thin and far enough apart to slip between the collar on the tool holder and the spindle neck. A gentle downward press on the fork handle pops the tool holder free.

If the problem takes a while to solve, you could reprogram your tool unload sequence to move backwards out of the forks before rising. It's an inefficient solution but will protect your rack forks until you solve the problem.

From contributor C:
As for the removal tool, try a Porter Cable 3 HP router wrench (or similar). They are stamped and either will fit or can easily be ground a bit to fit.

We found that adding a tool removal code to our post (T10 on our Fanuc) so that at the end of each program the tool goes back to the rack seems to keep the tool from sticking and probably cools it a bit. If you are running a one tool program and want to turn it off, just delete it from the code.

ScotchBrite is a good practice. We use a little lacquer thinner as a lube and to cut the pitch from hot wood. Also, make sure the hardware on the tool changer is tight. Ours was loose and caused similar problems.

Any thoughts on the HSK 63 tool holders? Are they better than the ISO 30? On our new machine, we can choose which one we want. I like the idea of having the same tool holders on all our machines. Is that a worthy criteria to stay with the 30's? Any thoughts?

From contributor B:
I was thinking that if I ever changed out my HSD ISO30 spindle, I would go to HSK to be rid of the sticking issue once and for all. Then I mentioned this to Paul from CNT Motion (I have a CNT 900 router) during IWF and was surprised to learn that the same type of issue can occur with the HSK holders.

So, I guess the answer is do a bit more research on the overall advantages of both holding systems to make your decision. It sounds like the sticking issue isn't going to be the one that sends you one way or the other.

From contributor M:
Great points by all! HSK holders are very nice holders. The spindle to holder fit is much more precise, rigid and balanced. However, they too are just as subject to sticking if not properly maintained. I often recommend people begin a daily regimen of cleaning the cones with denatured alcohol and clean clothes. Instead of Scotchbrite, I recommend using a bronze bristled brush monthly or as deposits are noticed. Normally if you adhere to the daily cleaning with alcohol and cloth, the brush may never come into play. Also, clean the spindle of the electrospindle in the same manner (never blow compressed air into an electrospindle)! There are also spindle taper cleaners available through Travelers, MSC, Enco, etc.

From contributor E:
We have found that the tool holder sticking problem is eliminated when we use a liquid cooled HSK 63 spindle on the DMS CNC routers. The spindle stays at a constant temperature, whereas a fan cooled motor is at the mercy of the ambient air.

From contributor K:
I would not say that a liquid cooled HSK will eliminate the problem because we have 3 of them and 4 air cooled ISOs. One of the HSKs went bad in just over one year and some of the ISOs have lasted over 7 years. I would have to say that proper maintenance is key but does not mean this won't still happen. The springs will still wear and the draw bar will stick.

From the original questioner:
Thank you to all who responded. I still have not resolved this issue but I have found the conversation most interesting and I am glad to know I am not alone on this one.

From contributor B:
One more thing you can do is put a very light coating of anti-seize compound in the spindle taper. If this does not solve the problem then you most likely have a problem with the draw bar/tang retention system.