Wear in work holding tools 1

[Ramkiyengar]

Fretting is a wear phenomena when two steel parts for example a holder and spindle mouth, rub against one another. Fretting is caused by imperfect mating between
toolholder taper and spindle, creating vibration and heat which develops the fretting. A cermet coating of tungsten carbide can reduce fretting. I would like to know how others have reduced fretting in work holders.

 

[ornerynorsk]

My experience has been that most fretting is caused by cutting forces being applied to the tool, and thus the toolholder, are inducing elastic stretch into the retention mechanism, be it a stud or drawbar. The coating of a toolholder will not cure this particular issue. I have seen far less fretting on older manual machines in which the drawbar must be tightened manually into the threaded body of the holder than on toolchanger machines which rely on a pull stud. Having said that, I would much rather wear out the toolholder than the spindle receptacle, so any anti-wear treatment would be better suited to the spindle versus the toolholders.

Modern CNC machines with toolchangers have their drawbar tension checked during a proper calibration cycle, but I've still worn out many toolholders over the years. I remember running an old Cincinatti Simplex horizontal boring mill many, many years ago, with 50 taper spindle and about 25 or 30 HP and a manually tightened drawbar to retain the toolholder. I could remove over 300 cubic inches of HY100 in 20 minutes during a roughing pass with no ill effect after dozens of such passes. I highly doubt the same could be accomplished on a CNC center. I still had to rotate 9 inserts on the shell mill and shovel chips after each pass, but the toolholder held up fine.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.