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More Milling Machine Woes

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Twizseven:
Making 6 off imperial adaptors for EMG-12 end mill grinding machine.  These are 20mm diameter silver steel. Turned, sized, drilled and reamed  them all.  Drilled and tapped 5mm holes in 3 off them.  Started to drill 4th with a 6mm stub drill.  Stopped mill to change to 4.2mm tapping drill.  Hit start on mill, motor appeared to start but drill chuck not rotating.  Chuck would turn by hand.

Off with motor to check.  >:( The 19mm keyed spindle had snapped flush with the end of the motor casing.  :'( Absolutely perfect flat, clean break.  Bugger thinks I.  There was 2mm of stub sticking out of gearbox.  How to remove? :noidea:

Myford 3 jaw chuck done up tight as possible on the stub, two screwdrivers to lever it.  came up 1/2 mm.  Repeat, Repeat, repeat ad infinitum.  Eventually the stub is out. :cartwheel:

Now need new motor. :Mad:

Colin

Jo:
 :toilet_claw:

:headscratch: Which milling machine was it that failed?

Jo

Vixen:
Hello Colin,

Sorry to hear this, Drive motors don't come cheep. :ThumbsDown: :ThumbsDown:

I had a similar shaft failure on a stepper motor a few years ago. That particular failure was caused by a grossly over tightened toothed drive belt creating an excessive side load which eventually led to a fatigue failure of the shaft, right next to the bearing.

Mike

Twizseven:
Jo,

It was the Chester Super Lux.  New motor s going to be about £200.

Might have to start looking for a proper machine.

Only problem........  "Get rid of this one before you replace it"

Trouble is I would have to, as not enough space to fit another in.  Might be a problem as what I would like to get is a tad larger.

Bridgeport with 36" table.  Need to check heights and sizes to see if can get through garage doors and power requirements.

Mike,

No idea why it failed.  My engineer mate, Tom, reckons the spindle was very soft and had a very sharp transition from motor spindle to the 19mm shaft. (which was where it failed).

There was no load on it as it started up.  The gearbox is still as free as  before.

Motor wise have two choices:

Exact replacement from Chester - will wire up immediately.

Motor from TEC.  Same size , power etc. but electrical connections not in same position so the existing flexy and power connections might all have to be replaced.

Simplicity is pushing me to Chester option and hope they did not have the same type of cheese used to make the motor shaft.

Colin

Allen Smithee:
If the shaft was too *soft* you wouldn't see a clean break - you'd see a sort of spiral staircase-shaped bit of torn metal. A clean break is a brittle failure, tending to suggest a hard material through which a crack propagates along the crystal structure of the metal. Look at the surface of the part carefully with some magnification - try to see if the clean break has two zones. One zone might be slightly duller than the other, suggesting an initial crack propagated as a fatigue crack until the remaining cross-section couldn't take the stress and so snapped clean. This would be a fatigue failure.

If it IS a fatigue failure then it suggests there is a cyclic sideways (ie not axial) load which grew a crack that was initially due to another cause (like an abrupt section change or a machining defect). The most common source of the cyclic load would be an axial misalignment in the shaft connection or an overtensioned belt/chain drive. If either of these situations exist I would recommend correctingthem before fitting a replacement - otherwise the new one will suffer the same fault.

€0.0007 supplied,

AS

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