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Dangerous Practices

4Jaw Chuck workholding

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John Stevenson15/09/2010 23:52:34
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5068 forum posts
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As regards parting of using the tailstock.
 
Just after dinner today I started with 5 bars of 2" steel about 7" long stuck them in the chuck with about 5" protruding, centred, drilled and reamed to 15mm.
Supported with the centre and parted a slice off at 10mm wide, all the way thru, moved up and repeated until I had 10.
 
Put these on a mandrel, skimmed the OD up and transferred to the gear hobber, whilst it was cutting went back and cut another 10 off, repeat, rinse and repeat until by the time I went for my tea I had fifty completed gears.
 
What's all the fuss about ?
 
John S.
Rob Manley15/09/2010 23:59:30
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71 forum posts
14 photos
 where's your risk assesment John? 
John Stevenson16/09/2010 00:30:21
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5068 forum posts
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Carried out prior to the job and determined that the only risk affecting this was if they weren't at the hardeners at 7:30 sharp tomorrow I was at risk of not getting paid.
 
That's enough for me.
 
John S.
Lawrie Alush-Jaggs16/09/2010 14:11:13
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118 forum posts
32 photos
Poor old Crewmech.  Three pages of replies and we haven't heard back from him.
We did all this nonsense to death in Scribe a line last year.
Lawrie
chris stephens16/09/2010 14:24:57
1049 forum posts
1 photos
Ah yes, Lawrie,  but here we have virtually unlimited space compared to the magazine and it is sooo much quicker to respond. 
chriStephens 
Bob16/09/2010 20:01:25
51 forum posts
1 photos
Hi All
 
May be I am missing something, but I can't see why the steam chest could not be held conventionally in the 4 Jaw to turn the bosses and end faces?  In Photo 28 the steam chest is shown gripped conventionally so the chuck must have the capacity to accommodate the width of the steam chest. As to settling the casting back against the body of the chuck then in Photo 31 there is nothing to be gained over just gripping the work in the jaws as at this stage the rear face is still a rough casting. My concern would be gripping the machined surfaces with those nasty chuck jaws. I would pack a piece of shim between the work and the finished faces just to be on the safe side. If the concern was that the top and bottom faces were only gripped close to the chuck then use some parallel steel packers between the chuck jaws and these faces about half way up the chuck jaws. (I always find these tricky to balance in place while setting the work up).
 
The chuck jaws on any half-way tidy 4 Jaw should hold work parallel to the axis of the lathe without reference to the chuck face. Most of us rely on this with the 3 jaw without stopping to question the fact. The mechanism of the 4 Jaw is not much different regarding the arrangement of sliding surfaces to ensure the jaws move parallel to the face of the chuck.
 
As for the unconventional use of the diagonal grip in the 4 jaw this will grip work very tightly, but I would worry about the stresses imposed on the chuck body by this sort of (ab)use. I would avoid doing it with my best 4 jaw.
 
Bob
John Olsen17/09/2010 00:42:27
1294 forum posts
108 photos
1 articles
Hi Bob,
You can sometimes use the infamous double sided sellotape to hold the packing together while you get organised. Once the pressure from the jaws come on, the tape is of course no longer relevant. I always have a roll or two in the workshop, as well as cheap Chinese box tape, which is incredibly useful for boatbuilding.
 
regards
John
John Olsen17/09/2010 09:26:13
1294 forum posts
108 photos
1 articles
Well, Having finally found my latest copy half way across the garden...there is a storm on and the <censored> postie has not put it in the box properly...the magazine has managed to wick itself half full of water through the tiniest hole in one corner, so I still can't read it until it is dry. So it has been taken apart and is drying on towels. However I have managed to look at the offending photograph, and my conclusion is that it is all a windup. The job is not going to fall out like that, the chuck is not going to be damaged, so what is the fuss about?
 
There is one little wrinkle that Harold could try, he mentions the fun of getting a drill to start on the inside face of the far end of the  steam chest. If you make up a little centre punch the same diameter as the valve rod, out of a bit of silver steel, you can put a little dot in guided by the hole at the gland end. You do this before opening that hole out to take the gland, but after it has been drilled and maybe reamed to the rod size. So your little punch has a guide and will make a nice little dot that the drill should start on OK.  After you have made a few engines like this you will have a collection of these punches in all the common sizes.
 
They tell me a four facet drill will start more reliably on a face like that, but I only have a  few of those drills, mostly not the sizes I would need.
 
regards
John
Richard Parsons17/09/2010 09:58:31
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645 forum posts
33 photos
 
Some folk tend to be like the ‘Gnomes’ of ‘Elfin Safety’ who spend all their time thinking about what might happen. Their ideas are based on the need for absolute safety. They know the formula “Ph+ Pn = 1” which says that the probability of an event happening plus the probability of it not happening is 1. Because of this they are always thinking what might possibly (no matter how remote) could happen and forbid it.
These days you must (in their eyes) have paper qualifications to do any thing. I wonder how they would have dealt with Henry Blogg G.C. BEM plus 3 RNLI  Gold and 4 Silver medals. Henry as coxswain of the Cromer Lifeboat launched on service 387 times and saved 873 lives. The Gnomes would not, these days, let him paddle on the beach, let alone let him launch in a lifeboat. 873 lives saved is not a bad catch for a man who had no papers and who was once said to have said “When the shout goes out we go out” and to some pumped up ‘little tow-rag’ “Cromer men do not turn back”.   

I used to have 3 notices on my shed door these said “Keep out – this means you!”, “No Admittance – for any reason” and finally “KYBNOOTH” Painted iin 6" high letters in red –Keep your (basic Anglo-Saxon).Nose Out Of This Hut-. It still did not stop em! nothing does!  The only thing is to try to keep 'under their radar'.

Edited By Richard Parsons on 17/09/2010 10:02:00

Ian S C17/09/2010 13:00:17
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7468 forum posts
230 photos
John, for those little center punches, old chain saw files are what I use, you can get them from 1/8"/3mm to 1/4"/6mm in steps of 1/16", very handy files new or used. Ian S C
JasonB17/09/2010 16:35:52
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25215 forum posts
3105 photos
1 articles
Or long series center drill will do the same thing, you can get them upto 6" long.
 
Jason
Stub Mandrel17/09/2010 21:44:51
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4318 forum posts
291 photos
1 articles
I've just deleted a huge, long , boring post
 
Suffice to say I'm fed up of the 'elf and safety' moaning.
 
We all have a responsibility to eachother to ffer advice taht is soundm, and to bear in mind that what is written here or ME will be seen as teh advice of the experienced and followed  
 by those who are less experienced or less competenet to realise where things are going wrong.
 
I am someone who for many reasons feels they are competent to work with mains electricity. The weekend before last I spent several minutes immobilised one the floor after touching wires I thought I had isolated*.
 
We can all be blase, but remember the really unluck ones aren't here to brag...
 
Neil
 
*my wife thought it was hilarious - she said I can't have been that badly affected as I was swearing so much.
 
 
Chris Trice20/09/2010 01:22:09
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1376 forum posts
10 photos
For what it's worth, I part off with tailstock support all the time but never all the way through. I part off near the chuck but leave a sufficiently stiff core of metal so I can stop the lathe, remove the tail centre and then hacksaw through the final bit. You then just face off as normal. Never had a piece come adrift yet even in the occasional jam up. In fact I'd argue that being wary of a particular technique makes you less likely to have a mishap because you take things carefully. It's non-thinking overconfidence that causes accidents.
 
As far as holding material in a four jaw diagonally is concerned, it's a measured risk assessment. It depends entirely on the degree of cutting force and the direction it comes from versus the amount of grip the chuck is applying as to whether the piece will shift. Enough force in the right direction will always ovecome a friction grip but how likely is it that those forces will reach that figure? A heavy milling cut will pull an end mill out of a taper collet if the gripping force is not sufficient but no one insists the same cutters must be threaded and fitted in a non-slip Autolock chuck. Nothing in life is 100% risk free but as long as common sense and balanced reasoning used, where's the problem? Keep the grip firm and the cutting forces light and you're unlikely to have any problems. 
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