Dangerous Practices

[Nicholas FarrParticipant @nicholasfarr14254]

Still no explination why one believes its a dangerous practice then.

Regards Nick.

[HasBeanParticipant @hasbean]

I’ve just received this issue this morning and having looked at the photos I’m afaraid I can’t see the problem. I’ve seen this method of workholding advocated many times in various books and publications and have used it myself (I must add I have no machining background as such).
If anything there would appear to be greater jaw to work surface contact than if placed otherwise, so as long as the jaws are tight against the work what’s the problem?.
It’s all well and good to say it’s ‘dodgy’, ‘dangerous’ or ‘bad practice’ but can someone please explain why?

 

Paul

[J A Harvey-SmithParticipant @jaharvey-smith]

I can’t speak for the originator of this thread or anyone else, but there is one potential failure mode with the method shown in figs 30-32 that does not apply to the more conventional setup of fig 29.

 

For the benefit of those unable to see the figs in question, in fig 29 we see what might as well be a rectangular work piece held in a four jaw chuck  with each jaw bearing on a flat surface about half way along each side.  With the chuck tightened by a normal person, not a gorilla, there is just about no normal event that could cause the work to shift in the chuck – you should be able to machine this piece with confidence.

 

Figs 29-31 show a rectangular work piece held diagonally in a 4 jaw chuck such that the work piece is pinched between the sides of two pairs of jaws, close to either end of the work.  Even with the chuck tightened by gorilla, application of sufficient side force would shift the work piece in the chuck.

 

This method has its uses and in some cases can only be avoided by using a bigger chuck/lathe!

 

[Anonymous]

Here’s my two pence worth, and a quick stir of the pot!

 

I don’t think I’d part off completely using tailstock support. However, I do use tailstock support when partially parting off at a distance from the chuck. I’ve added a photo (my first upload!) to illustrate this. For reference the item is cast iron, 3.5″ inches diameter, and is on a stub mandrel. I think the speed was about 350rpm.

 

The use of double sided tape, or wax, or resin, are well established techniques within professional machining for grinding, milling and, less commonly, turning. Of course the item is less firmly held than with clamps, but it is often the only way to hold some items. I have an item in my current work related design that will almost need the use of double sided tape. It is a plastic sheet 4mm thick, and 300mm by 400mm, that needs to be mostly milled away to a thickness of 1mm, leaving a series of 3mm projections. Doubled sided tape would seem to be an ideal way of holding it down and ensuring a consistent 1mm base thickness over the area.

 

It’s telling that neither of the two posters who have objected to the said workholding have actually give any reasons as to why it is dangerous. I suppose that the item could fly out of the 4 jaw chuck, as it may only be held by friction with the chuck jaws. But this is not much different to milling a part parallel to the vice jaws.

 

I’m cynical enough to think that the fact both of them would have been rusticated/sacked for doing this says more about the intransigence of both unions and management of the time rather than possible dangers. In the ‘good old days’ you would probably have been sacked for changing a light bulb too; ’cause that’s an electricians job, and that’s a different union.

Regards,

 

Andrew

[Rob ManleyParticipant @robmanley79788]

You sir need to clean your lathe before taking photographs – it gives the impression that people actually do stuff instead of moaning

 In the age of the risk assessment and ‘who can i sue’ it is going to become increasingly common as the ex-industrialist (because let’s face it, children from school have no experience now) becomes the normal geographic within our hobby and demands ‘best practice only’ to be published without criticism. 

We have to face it, people in our hobby are limited by materials, equipment, space, and sometimes experience.  We are not taking massive cuts, swarf hitting the wall across the room etc. but can sometimes take hours boring a hole, taking minute cuts that would make a professional machinist blush because that’s what our machines can handle.  

 A good friend of mine started in this hobby with a single book by LBSC.  It contained phrases such as ‘chuck it in the lathe’ and other rather non-descript instructions.  Now, what do you do? Throw the job at the machine? probably not.  Common sense prevails and after placing the job in the chuck with plenty sticking out  you move onto the next sparse instruction only to find that you have too much sticking out and the job chatters or worse, you have a prang and bend the bar.  So, you move the work piece closer to the jaws and continue trial and error style.  How exactly did these people survive with so little precise, distinct instructions?  Maybe they didn’t.  Maybe that’s why 90% of people at exhibitions have white hair?

 Photographs within articles say more than words ever could, but should not be taken as ‘the way to do it’ instead should be seen as the way the author has done then due to his circumstances and equipment.  

 A quick warning about double sided tape.  My windowsill is my graveyard of projects.  Where prangs, mistakes etc. go to reside for the rest of their lives.  On that sill are two disks which were held together and the diameter machined.  They are still stuck together after 6 years.  Tis good stuff. 

 

Wear safety glasses, fit an easily removable – non frustrating machine guard if swarf is airborne, enjoy and make stuff. If it goes wrong, try and try again. 

 

(couldn’t post from word using the button as I get a forbidden massage?) 

[NJHParticipant @njh]

Given that 10V / 10H series is aimed at beginners this thread is very useful. Harold does emphasise in his “Top tip” that this is an unconventional set up and the care that needs to be employed when using it. The very strong position of the first post ( whether you agree with it or not) has prompted a very thorough look at the method and the overall view is clearly that it is a useful technique when used carefully. Surely this sort of exploration of pros and cons is just what the inexperienced machinist needs?  Safety must always be paramount but working safely requires an appreciation of the risks. It is better not to discover these risks by accident ! 

Regards

Norman

Edited By NJH on 15/09/2010 12:59:30

[Anonymous]

Hey! The lathe is clean; I’ve added another photo to illustrate a dirty machine. The pile of aluminium swarf is over 4″ deep. I knew the small shovel I made in ‘O’ level metal would eventually come in useful for something!

 

Hmmm, for some reason the system has decided that the emotions area is forbidden. Ah well, I’ll just have to stick with plain English.

 

Regards,

 

Andrew

[chris stephensParticipant @chrisstephens63393]

The trouble with time-served machinists is that they are taught to follow instructions and not question the whys and wherefores. The claim that some machining practise is bad but unable to say why, smacks of this outmoded teaching method. I seem to recall that after WW11 the excuse that “I was just following orders” is no longer an excuse and we must think for ourselves.

We, as largely self taught Amateurs, are free to make our own rules based on what actually works. The ends truly do justify the means, well they do in my Engineerium!

 

Note to self, must put up a sign over the door that starts “abandon hope all ye who enter here.” to warn off visitors.

chriStephens

PS Andrew, the emoticons are still there , but you have to go to the top of the page, each time, to get them. 

[StovepipeParticipant @stovepipe]

As an article I read many years ago said, “Think what would happen if the tool slipped, and be guided accordingly”.  Common sense would appear not be allowed in many cases.  I would suggest that the vast majority of lathe users would apply a measure of savvy, would not necessarily follow literally an example in the magazine. Having just pricked my finger on a piece of thin wire, I won’t do that again, and I don’t need an “Elfin safety adviser” or someone of that ilk to tell me what to do.

 

Just seen Chris Stephens post – should notice read “any safety advisers enter these premises at their own (high) risk “

 

Dennis

Edited By Stovepipe on 15/09/2010 13:37:08

[Tony Pratt 1Participant @tonypratt1]

As a time served Toolmaker I totally disagree that machinists just follow instructions and don’t question anything. When you are training apprentices this perhaps would be the case for safety’s sake but any decent machinist has to be aware of the whys and wherefores of each and every job he undertakes in order to make it in the most efficient and safe manner and hopefully not scrap too much!

I actually said to my 18 yr old son on Monday that I could only show him the basic lathe techniques and it would be up to him to build on it.

 

Tony

 

 

[Nicholas FarrParticipant @nicholasfarr14254]

“Even with the chuck tightened by gorilla, application of sufficient side force would shift the work piece in the chuck.” by J A Harvey-Smith.

 

Didn’t read in the text; plough into it and get this bit done and out of the way. I think if you were to apply the amout of force required to shift the set up in the photos, you shouldn’t even be using a lathe. The use of the tailstock centre support is mentioned and shown. This is said for “added security” which makes it even less likely to shift sideways even if your cut was a bit to heavy.

      Still not covenced that it is a dangerous practice.

Regards Nick.

                  

[David Clark 13Participant @davidclark13]

Hi There

I have the small book about building the Stuart 10.

This is the updated version by Andrew Smith.

This shows the same operation on the side of the steamchest as Harold has done.

The only real difference is that Andrew used the 3 jaw chuck.

regards David

 

[WALLACEParticipant @wallace]

 

More likely scenario is Harold would be on the phone to Stuarts for a new casting if it had come loose ! That’s usually my benchmark for doddgy practices – learnt by bitter experiance –  the longer time it took to machine / expensive / irreplaceable the item is, the more clamps I put on it to make sure it doesn’t move.

 

Then add an extra one, just in case. 

 

W.

Edited By WALLACE on 15/09/2010 20:45:43

[Sean CaveParticipant @seancave62792]

Gentlemen,

 

I hadn’t received my copy of Model Engineer when I read the above somewhat heated discussion. When it arrived I hurriedly turned to Harold Hall’s article to see what horrors were depicted therein. I have to say I was rather disappointed. The method of workholding illustrated is, I feel, quite a normal one for the model engineer who is often confronted with having to deal with awkward castings with his somewhat limited equipment. it is a method I have used successfully many times myself.

 

Such a practice would naturally not be used in production, since tasks are allotted to machines designed to deal with them. As for supporting work in the tailstock whilst parting off is taking place, I have often found it handy to prevent the piece parted off from falling down into the coolant tray. I have never suffered any misfortune as a result.

 

Can anybody tell me what all the fuss is about?

 

Sean Cave

[chris stephensParticipant @chrisstephens63393]

Hi Sean,

In answer to your last sentence, could it be the OP has no imagination or alternatively it could be he has too much. 

Anyway the outcome is that it clearly worked for Mr Hall, so it can’t be all that bad!

chriStephens 

[VersabossParticipant @versaboss]

Well that ME issue finally arrived here also today, and I did the same as Mr. Cave above. We have a saying here ‘I laugh a hole in my belly!’ 

I wonder that nobody mentioned that in this operation maybe half a mm or if you prefer a 1/32″ of that butter-soft Stuart cast iron is removed, and this possibly in 2 or 3 passes. Even if a 3-year old would have tightened the chuck, it would be sufficient for that.

I often have to face both ends of some 60 x 60 x 150 mm steel lumps, sticking almost full length out of the (4-jaw) chuck, and up to now none of them went ballistic! (no tailstock support possible).

Greetings, Hansrudolf

[John Stevenson 1Participant @johnstevenson1]

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 ManleyParticipant @robmanley79788]

where’s your risk assesment John? 

[John Stevenson 1Participant @johnstevenson1]

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-JaggsParticipant @lawriealush-jaggs50843]

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 stephensParticipant @chrisstephens63393]

Ah yes, Lawrie,  but here we have virtually unlimited space compared to the magazine and it is sooo much quicker to respond. 

chriStephens 

[BobParticipant @bob17059]

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 OlsenParticipant @johnolsen79199]

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 OlsenParticipant @johnolsen79199]

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 ParsonsParticipant @richardparsons61721]

 

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 “P_h+ P_n = 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

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