Last catastrophe of Old Year!

martinHi All,

It was all going so well....

Making a series of small brass caps for oil cans on my new to me S7; cutting 4BA thread using the mandrel handle, getting ready to radius the end before reversing the part to finish it.

Missus brings me a cuppa and tells me about a 'phone call, was a bit distracted and switched on lathe with handle still in spindle. Horrendousl vibration as out of balance and something flew off and hit me on the forehead as I was reaching for the stop button so missed it which allowed it to ramp up to full speed.

Somehow handle came loose and smacked into the alloy end casing before I could hit stop button.

Handle bent and broken but easily repairable, end casing badly damaged, cracked in several places but still sort of in one piece.

My nerves badly shaken but unhurt so ok! Really upset me as I am usually careful amount the handle.

Now on lookout for another end casing....

Could have been worse I suppose?

The spring loaded ones are relatively safe because you need your hand on it for it to work

There are chuck keys too

http://www.mini-lathe.com/m4/C4/ck02.jpg

(Glad you're ok btw, roll on 2017)

Edited By Ady1 on 30/12/2016 14:04:15

Ady

I think Martin means the spindle mandrel handle, which remains firmly fixed in the spindle while it wreaks havoc.

Martin, see messages

Hello Martin,

​I've just read your story and was very glad to hear you got away without damage to yourself, other than perhaps some unscheduled washing..

When I worked in industry there were always safety posters for various things, a very graphic one showed the effects of a chuck key being flung out off the lathe. it had embedded itself in the timber wall behind the machine;. imagination filled in the blanks.

I have a form of 'panic' bar across the whole bench in my workshop, lean on it to kill all the machines; lathe, mill or bench drill, they are all protected by it with a twist to release stop button. It has been useful with drill grabs and a bottoming in a blind hole on the lathe on one occasion.

If the casting has broken cleanly, you might consider rebuilding it with epoxy resin with the parts held in register using lumps of putty to bed them down on.

Best wishes Brian.

That sounds like a very astute idea, I don't think i'd possess the know-how to make that. But 3 phase inverter fed, "coast to start" set up motors are a very underrated safety feature, that unfortunately can't be done on single phase,

but basically, the motor climbs up from it's slowest speed to start, all the way up to wherever you've set it, this means that the power going through it at the start is so small that it cannot gather the momentum needed to throw the chuck key at you, it simply rotates half way round at the point where the key falls out. It's no substitute for common sense but it is far more forgiving that having full power thrown at you. At which point the key is a deadly projectile.

You're only ever in real trouble when the motor has the go behind it to twist your arms, clothes, etc.. you can't react quickly enough to that. Which is why a panic button/kill switch is a very good idea. It just always has to be in a place where you can reach it!

I personally don't use the spring chuck keys because I never had them when I worked on bigger lathes and it just irritates me slightly.

Michael W

Edited By Michael-w on 30/12/2016 14:48:41

Michael W,

My set up is coast to start but when I missed the stop button because something hit me, small chip I think, it had time to ramp up to full speed.

The end casing is repairable but I do not feel like looking at it every day and reminding me!

What I can't workout is how the handle hit the casing as there was good clearance, unless the vibration opened the casing and the first whack shut it agin by which time the handle had bent in enough to keep belting the casing.

Yes, it sounds like you had an unlucky sequence of events. I wonder if you could refabricate this casing out of plate steel ??

Michael W

Edited By Michael-w on 30/12/2016 14:58:36

David A Tuff

When I started my apprenticeship with a medium sized electric motor manufacturer fifty years ago, Health and Safety was virtually unknown but if you were caught leaving a chuck key in a lathe it was immediate suspension without pay for the day.

I'm sure though that this was to protect the machinery not the workers..

I only once saw this rule disregarded when a chuck key was propelled through the toolroom partition wall into the assembly shop next door. Luckily no one was hurt but it could have been carnage!

David T.

.

It certainly could, Martin !!

Very glad you lived to tell the tale.

Thanks for having the courage to share the story: People need to hear of a 'true life' event occasionally [otherwise they drift into believing it's all 'elfin safety' myths].

MichaelG.

You were destined to survive - how else would you have been able to tell us about it?

Glad it wasn't too serious.

Neil

(Who has never left a mandrel handle in place and started the lathe )

Glad you did not cop for more Martin. I have a golden rule when using the mandrel - I ALWAYS turn the power of on the wall socket before fitting it up the spout. It works well for me as more often than not I forget the mandrel is in place and am genuinly taken by surprise when the lathe will not start......doh!.......... Rik

We could learn from this. Make the mandrel handle part of a lock out switch. Ie the mandrel handle has to be "in the rack" to allow power to be used (although I guess some of you will use power for the DRO) !!
BobH
Ps, I hope the cup of tea survived

I was once being shown round a nearby engineering museum, when I spotted a chuck key left in a chuck. Great was the embarrassment thereof! My minilathe chuck guard is interlocked with the start circuitry, which I have been grateful for now and then.

Geoff

Martin,

Its all been said above, however, as you have a VFD fitted why were you not screwcutting with that? No need for a mandrel handle.

Good idea! Will do that and have already made a large Yellow sign to hang over the ON switch that just says:

"MANDREL OUT!"

a - Still getting used to the machine generally and have not yet tried using the VFD for screwcutting.

b - Tiny 4BA internal thread only 3/16" deep with parts 10 to do the handle is really easy.

c - I like using the handle as I did not have one before getting this lathe.

I have been meaning to make a safety system using a bathroom string pull switch wired into the latch circuit for the NVR relay and the string stretched across the length of the lathe bed above the front shear. The idea being that in a panic I might not think about where the off switch is but flailing arms and even head if I suddenly pass out with a heart attack would fall onto the string.

Although most mandrel handles jam into the bore on my Hobbymat which has no back gear so needs a handle I clamp a ring onto the outside of the back end of the spindle. The handle has an aligning rod that is a loose fit in the bore and 3 short pins that engage holes in the aforementioned ring. A light spring would push this away when not actually being used though with this lathe the switch is too difficult to operate accidentally.

I'm pleased it was only your pride and hardware that was damaged and not yourself.

As one who is about to get a mandrel handle I will definitely take on-board the safety suggestion above. I definitely like the "interlock" idea for two reasons. Not only does it minimise the likelihood of switching the lathe on with the handle in place, it also means there is a definite storage place for the handle rather than amongst the other bits and pieces in cabinet below..

Edited By Brian Oldford on 30/12/2016 18:00:56

on a similar vain , when I was at work , I started a cement mixer and the handle failed to disengage , I moved sharpish and shouted a warning . It rotated several times before coming off and shot over the yard . It was a big heavy thing , it would certainly do some damage if it hit anyone , luckily it missed but it was a brown trouser moment

phil

Fortunately I have a Colchester Mascot which has a foot brake stop switch!