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Hexagon Wrist Failure After Less Than Four Years - Is This Normal?

A bit over three and a half years ago we bought our first continuous-scanning-capable CMM, a Global S Blue 9.12.8 with a HP-S-X1 scanning head (I believe that's just Hexagon's rebranding of the Leitz LSPX line) and Hexagon's 7.5 degree indexable auto wrist, the HH-AS8-T7.5. What the machine has allowed us to do has been amazing, and on the whole we're very happy with the system.

We've never crashed it badly (as in, nothing big enough to make any visible dents on either the scanning probe or the wrist), though I did put too much torque on the scanning head trying to set up a star probe at one point and had to replace that.

Over the course of the last week or so we've had repeated instances of the wrist not seating - sometimes it will try multiple times and then succeed, other times it will not succeed and then just give up. This morning I had to power cycle the entire system to get it to work after it gave up. From what I've seen this behavior points to a failure of the wrist that will require a replacement.

We use the machine frequently over two shifts, five days a week, but beyond the regular use I don't think we do anything that should be particularly hard on it. I see pictures in Hexagon's marketing literature of these heads waving around huge laser scanners that must weigh a good bit more than the scanning head we have on it. Is this seemingly-short lifespan normal? Did we just get a bad egg? Is there something in our use or programming that could be causing more than typical wear? My boss is not very happy at the thought of having to replace these so frequently. Any ideas would be appreciated.
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  • "We've never crashed it badly (as in, nothing big enough to make any visible dents on either the scanning probe or the wrist), though I did put too much torque on the scanning head trying to set up a star probe at one point and had to replace that."

    visible damage isn't the ONLY indicator of problems. repeated forcible unseating of the pivot does internal damage. I've not seen the inside of any head newer than a PH9, but the 'lock' of the PH9 is a flat plate that one of the servo pulls to 'force' the locking indents into position to secure it into that rotate. Now, on the PH9, if you repeatedly forced it to unseat, especially at a specific angle, then the plate would get warped at that indent inside the head, and you would start getting seating errors. On the PH9, there is a set screw that you can tighten in order to get more 'power' on the locking plate and that could get you along for quite some time before you had to RBE the head. That set screw is long gone since it allowed people to get more life out of the head. I have no idea if that plate locking mechanism is still in play in the newer heads.

    Also, there is a life span of rotations. If your programs are constantly changing angles more than they should (as in, using the same angle in multiple places in the program instead of all at once) you are wearing the head out faster than you should be.
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  • "We've never crashed it badly (as in, nothing big enough to make any visible dents on either the scanning probe or the wrist), though I did put too much torque on the scanning head trying to set up a star probe at one point and had to replace that."

    visible damage isn't the ONLY indicator of problems. repeated forcible unseating of the pivot does internal damage. I've not seen the inside of any head newer than a PH9, but the 'lock' of the PH9 is a flat plate that one of the servo pulls to 'force' the locking indents into position to secure it into that rotate. Now, on the PH9, if you repeatedly forced it to unseat, especially at a specific angle, then the plate would get warped at that indent inside the head, and you would start getting seating errors. On the PH9, there is a set screw that you can tighten in order to get more 'power' on the locking plate and that could get you along for quite some time before you had to RBE the head. That set screw is long gone since it allowed people to get more life out of the head. I have no idea if that plate locking mechanism is still in play in the newer heads.

    Also, there is a life span of rotations. If your programs are constantly changing angles more than they should (as in, using the same angle in multiple places in the program instead of all at once) you are wearing the head out faster than you should be.
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