Model Engine Maker

General Category => Chatterbox => Topic started by: Twizseven on March 04, 2019, 06:34:01 PM

Title: More Milling Machine Woes
Post by: Twizseven 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
Title: Re: More Milling Machine Woes
Post by: Jo on March 04, 2019, 07:14:27 PM
 :toilet_claw:

:headscratch: Which milling machine was it that failed?

Jo
Title: Re: More Milling Machine Woes
Post by: Vixen 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
Title: Re: More Milling Machine Woes
Post by: Twizseven 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
Title: Re: More Milling Machine Woes
Post by: Allen Smithee 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.

Ä0.0007 supplied,

AS
Title: Re: More Milling Machine Woes
Post by: Vixen 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
Title: Re: More Milling Machine Woes
Post by: Jasonb 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.
Title: Re: More Milling Machine Woes
Post by: Jo 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
Title: Re: More Milling Machine Woes
Post by: Twizseven on March 05, 2019, 06:02:34 PM
I think I might treat this as an "opportunity" :)

Colin
Title: Re: More Milling Machine Woes
Post by: Twizseven 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
Title: Re: More Milling Machine Woes
Post by: b.lindsey on March 28, 2019, 11:53:57 PM
Hmmmmm....sounds interesting.  ;)

Bill
Title: Re: More Milling Machine Woes
Post by: Jo 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
Title: Re: More Milling Machine Woes
Post by: Vixen 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
Title: Re: More Milling Machine Woes
Post by: Twizseven 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
Title: Re: More Milling Machine Woes
Post by: Vixen 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
Title: Re: More Milling Machine Woes
Post by: b.lindsey on March 29, 2019, 12:11:54 PM
Colin retirement is definitely the way to go!!  Highly recommended :)

Bill
Title: Re: More Milling Machine Woes
Post by: Twizseven on March 29, 2019, 01:13:04 PM
Mike,

Thank you for the offer but yes I think a bit too far.

Its certainly going to be a case of musical machines.

Mill out and onto pallet truck

Grinder out and onto pallet truck

Move BCA jig borer to where the mill used to be

Hope there is space left for the new mill.  Hopefully the machine movers will have skates and rollers.  Need to get  it over the pit.

Move Myford S7 to where the grinder used to be.

I have a horrible feeling that my four wall mounted engineers wooden chests are all going to have to come down and be relocated (God knows where)(wife will, say get rid off).

Raise 3 shelves

Lister D stationary engine may also have to move.

Is it all worth it I ask myself.

Colin
Title: Re: More Milling Machine Woes
Post by: bent on March 29, 2019, 08:46:18 PM
Quote
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.

Err, backwards I think.  Take a piece of chalkboard chalk, and torque it along its axis to snap it - it breaks in a spiral/helix shape, which is the mark of brittle materials (glass works here too).  Take a piece of soft copper wire, lead wire, or some dough and twist it similarly, and it shears at 90 degrees to the axis, which is indicative of ductile failure.  Beachmarks for fatigue, I agree.  Sorry to be persnickety, but it can be important to know what torsional fractures look like and what to do if you want your stuff to behave differently.
Title: Re: More Milling Machine Woes
Post by: sco on March 29, 2019, 09:32:15 PM
Is it all worth it I ask myself.

Oh boy don't I know that feeling!  Spent the last month or so insulating the floor and walls of my workshop which has involved lifting and moving every piece of machinery, all the storage, shelves, junk etc. multiple times and still not finished.  Should be all done in a month or so but starting to flag....

Simon.
Title: Re: More Milling Machine Woes
Post by: Twizseven on March 29, 2019, 10:15:41 PM
Mill is all disconnected and bits taken off and cleaned.  Ready to be lifted when mate with Large engine crane appears.  Surface grinder disconnected and cleaned but not a cat in hells chance of moving it without the crane.  Got it high enough to put some rebar  underneath but cannot roll it.  Needs the larger ally rollers.  Lifted shelves an 1 1/2".  Thank goodness I used Unistrut and only had to remove shelf contents, loosen bolts in zebs and push/lever them up a bit.  If I can move the machines before Sunday I might be able to paint the floor before working away Monday/Tuesday.  There is so much stuff stored between the machines I'm not sure where its all going to go to.

Colin
Title: Re: More Milling Machine Woes
Post by: Twizseven on March 30, 2019, 07:33:06 PM
Crane only just managed to pick up grinder.  Both machines on pallet trucks and first coat of floor paint down.  Second coat will go on in morning.

Just remembered that I do not have neutrals on my 3 phase supplies.  Thatís a bit of a b....r as new machine needs a neutral.  Looks as though I need to get a minor rewire sorted quickly.

Colin
Title: Re: More Milling Machine Woes
Post by: Twizseven on April 09, 2019, 07:40:31 PM
Rewire done, put in new cable rather than trying to thread a neutral all the way round workshop through ceiling etc.  Walls touched up.

Space is made (hopefully enough).

Machine movers coming sometime between 6:30 and 7:30 in morning.

Picture 1 - old machine
Picture 2 - painted space

Picture 3 - appears tomorrow

Colin