Occasional misalignment of spindle dogs with SMTC - cause?

Hi all. I've got a 2010 Super Mini Mill 2 with a side mount tool changer (they only made it for that model a few years). Lately I've been getting some hard bangs at tool changes. It seems to happen randomly and with different tool holders (so I don't think it's an issue with a particular holder). It can be fine for 10 tool changes, and then BANG!

Today it happened and right as the tool was about to be fully inserted into the spindle I think I noticed the spindle dogs rotate slightly. The dogs then seemed to momentarily catch the side of the tool holder dog recess and then there's a bang as the tool gets fully pulled in. On inspection after it happened I noticed a burnish mark on the tool holder (it was a new holder, so the mark just happened), and a tiny metal chip on the dog. Some close up shots of the spindle dogs show that there is also burnishing and rounding of the edges. See pics below.

I just had a Haas tech in the other day for something and he checked the angular position of the spindle dogs. I re-checked it today, hitting estop right before the tool changer goes up to the spindle, and it looked like the dogs where correctly positioned. So, it seems to be a sporadic thing.

Just wondering if anyone has any ideas about what could be going on here? Is this likely a bad spindle encoder or perhaps a bad belt? Something else? I haven't serviced the spindle myself but would give it a go if this was something a basic shop guy like myself could manage. FWIW this machine is still relatively new to me and it sees only relatively light use for prototype work. Thanks for any input.

Have you tried M19 before doing a toolchange?

Booze Daily said:

Have you tried M19 before doing a toolchange?

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I tried sending a few M19 calls and the spindle orients correctly every time. If you try to rotate the spindle while running the M19 it resists fairly strongly.


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I had a broken spring behind the plunger in the tool changer arm causing something like that a while back although it would also toss a holder in the chip pan now and again.

I once had a different brand machine that developed a worn key in motor/spindle coupler; just enough to occasionally miss alignment. WAG!

kustomizer said:

I had a broken spring behind the plunger in the tool changer arm causing something like that a while back although it would also toss a holder in the chip pan now and again.

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Got it. I checked the tool changer arm and both spring mechanisms appear to be fine. Again, I think I've seen the spindle dogs rotate slightly when this happens so I tend to think it's an issue in the spindle or electronics somehow.

Perhaps the encoder drive belt is bad? I would think something of the like, electronic stuff normally works or not.

kustomizer said:

Perhaps the encoder drive belt is bad? I would think something of the like, electronic stuff normally works or not.

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I had the same thought. I checked the encoder, belt and pulleys - they all look fine. Tension is good. So, not sure that's it.
I've just done a full maintenances on the changer arm - locking pins and catch mechanisms - to see if that helps. First number of tool changes have been ok so I'm going to keep running it to see how it goes. If it continues to fail randomly I wonder if that points to a faulty encoder.

miks said:

I had the same thought. I checked the encoder, belt and pulleys - they all look fine. Tension is good. So, not sure that's it.
I've just done a full maintenances on the changer arm - locking pins and catch mechanisms - to see if that helps. First number of tool changes have been ok so I'm going to keep running it to see how it goes. If it continues to fail randomly I wonder if that points to a faulty encoder.

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My experiance with encoders on Haas machines is that the control will throw an alarm if there is a problem, I am not sure where else to point you, sorry

kustomizer said:

My experiance with encoders on Haas machines is that the control will throw an alarm if there is a problem, I am not sure where else to point you, sorry

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Thanks. Well, I ran a few programs today. First 20 or 30 tool changes went fine but then I did see a tool get hung up on the spindle dogs for a moment. Then it was fine again until I finished. I don’t know what else to do but change the encoder. Hard to troubleshoot because I can’t repeat the problem predictably. I’m getting no alarms but not sure what else to do.


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Keep us posted if you would.

kustomizer said:

Keep us posted if you would.

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Ran a few programs today - probably 70-80 tool changes all told and no issues. Dunno. The local HFO suggested a few days ago putting some drops of light hydraulic oil (DTE 24) in the tool changer and spindle air lines to keep those mechanisms (solenoids etc) free. I did so. Not sure if that’s helping. Anyway, I’ll keep going. Time will tell.


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