Author Topic: More Milling Machine Woes  (Read 1749 times)

Offline Twizseven

  • Full Member
  • ****
  • Posts: 275
More Milling Machine Woes
« on: March 04, 2019, 06:34:01 PM »
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

Offline Jo

  • Administrator
  • Full Member
  • *****
  • Posts: 12555
  • Hampshire, england.
Re: More Milling Machine Woes
« Reply #1 on: March 04, 2019, 07:14:27 PM »
 :toilet_claw:

:headscratch: Which milling machine was it that failed?

Jo
Usus est optimum magister

Online Vixen

  • Full Member
  • ****
  • Posts: 1228
  • Hampshire UK
Re: More Milling Machine Woes
« Reply #2 on: March 04, 2019, 07:47:14 PM »
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
It is the journey that matters, not the destination

Offline Twizseven

  • Full Member
  • ****
  • Posts: 275
Re: More Milling Machine Woes
« Reply #3 on: March 04, 2019, 10:42:10 PM »
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

Offline Allen Smithee

  • Full Member
  • ****
  • Posts: 923
  • Mordor, Middle Earth
Re: More Milling Machine Woes
« Reply #4 on: March 04, 2019, 11:28:08 PM »
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
Quidquid latine dictum sit altum sonatur

Online Vixen

  • Full Member
  • ****
  • Posts: 1228
  • Hampshire UK
Re: More Milling Machine Woes
« Reply #5 on: March 04, 2019, 11:34:39 PM »
Hello Colin,

If you have decided to replace the Chester with a real Bridgeport in the near future, then going for a replacement Chester motor will be the easiest repair, leading to an easier sale. New buyers prefer standard machines and may shy away from modified or 'fixed' machines.

If you decide to keep the Chester for a while longer, then a higher priced motor, from a respected manufacturer may be a wiser choice than more Chester Cheese

Not much fun having to make these unscheduled decisions, You know it's going to hurt, whichever way you turn.

Good luck

Mike
It is the journey that matters, not the destination

Offline Jasonb

  • Full Member
  • *****
  • Posts: 6533
  • Surrey, UK
Re: More Milling Machine Woes
« Reply #6 on: March 05, 2019, 07:46:54 AM »
If you are going to keep it for a while and opt for a different motor may be worth thinking 3 phase and VFD to give a bit more variation in speeds than the 6 gear ratios allow. That has always been my intention should one of my DC brushless variable speed machines give up the ghost.

Offline Jo

  • Administrator
  • Full Member
  • *****
  • Posts: 12555
  • Hampshire, england.
Re: More Milling Machine Woes
« Reply #7 on: March 05, 2019, 07:55:09 AM »
I would look at this as an opportunity to get rid of it and see if Tom can find you a nice Aciera F3  :LickLips:

Jo
Usus est optimum magister

Offline Twizseven

  • Full Member
  • ****
  • Posts: 275
Re: More Milling Machine Woes
« Reply #8 on: March 05, 2019, 06:02:34 PM »
I think I might treat this as an "opportunity" :)

Colin

Offline Twizseven

  • Full Member
  • ****
  • Posts: 275
Re: More Milling Machine Woes
« Reply #9 on: March 28, 2019, 09:47:56 PM »
Put a new Chester motor on and it is quieter and now works.  BUT.... An opportunity has occurred.  Done a deal but due to work cannot take ownership till mid April.  Will definately need to retire.

Watch this space.   :whoohoo:

Colin

Offline b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 13601
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: More Milling Machine Woes
« Reply #10 on: March 28, 2019, 11:53:57 PM »
Hmmmmm....sounds interesting.  ;)

Bill

Offline Jo

  • Administrator
  • Full Member
  • *****
  • Posts: 12555
  • Hampshire, england.
Re: More Milling Machine Woes
« Reply #11 on: March 29, 2019, 08:39:21 AM »
Sounds promising

Done a deal but due to work cannot take ownership till mid April.  Will definately need to retire.

I hope you have started advertising that old milling machine so you have the required space, you wouldn't want to get in trouble  :stickpoke:

Jo
Usus est optimum magister

Online Vixen

  • Full Member
  • ****
  • Posts: 1228
  • Hampshire UK
Re: More Milling Machine Woes
« Reply #12 on: March 29, 2019, 09:02:41 AM »
I think I might treat this as an "opportunity" :)

Colin

Colin

Did you have the "opportunity" to pick up something really nice?

Mike
It is the journey that matters, not the destination

Offline Twizseven

  • Full Member
  • ****
  • Posts: 275
Re: More Milling Machine Woes
« Reply #13 on: March 29, 2019, 09:41:21 AM »
Jo, Mike, Bill

The best bit is the Chester and my old Excel surface grinder are going in part exchange.  The other half said something had to go  :( but to be realistic I needed it to go to make space as the new machine has a somewhat larger work envelope than the Chester.  its a 2011 machine but appears never to have been used (well maybe a vice had been bolted to the table and then removed.  Still got its protection grease on in places.

I need move the Caterham 7 somewhere else out of the way, disconnect grinder and Chester and get them on pallet trucks, sort some shelves which may have to move, paint the floor, rejig some of my 3-phase outlets.  Trouble is I am working away most of next week and part of week after.  This retirement idea seams to be gaining favour.

Colin

Online Vixen

  • Full Member
  • ****
  • Posts: 1228
  • Hampshire UK
Re: More Milling Machine Woes
« Reply #14 on: March 29, 2019, 10:46:30 AM »
Staffordshire is a bit too far from the South Coast, otherwise I would have offered to lend a hand for the musical chairs

Mike
It is the journey that matters, not the destination