Major flaw in the world of engineering

[JAParticipant @ja]

Just a comment: Before you do any cutting make sure the work is absolutely firm in the chuck (or whatever is holding it) and the cutting tool likewise. Doing so may still mean you could mess up the job but not doing so will mess up big time.

I use a face plate on the lathe far more than a 3 jaw self centering chuck. A Keats plate is also a really useful work holder. In addition to these a good set of collet chucks is invaluable.

JA

[JasonBModerator @jasonb]

Mike, if you want an accuracy of say 0.001" and know your 3-jaw can do 0.0005" or better then what is the point of spending time clocking it in a 4-jaw when the 3-jaw will do?

I just looked up my 3-jaw maker says repeatability better than 0.02mm that is 0.0008" and I have clocked it at less than 0.0005". They also make better ones as mine is just "standard precision" but I wonder if as Howard says they are not seen much as mine costs about £500 and the better ones £1500 for a 125mm 3-jaw so not likely to be seen much in the home workshop, luckily mine was NOS and cost £100.

Industry these days seems happy to CNC a part on one end of a bar and then transfer to the second spindle opposite the first to machine the second side using 3-jaw chucks and get the concentricity they need. Though they may be using machined in-situe top jaws or just high quality chucks

[Mike PooleParticipant @mikepoole82104]

I accept the points Martin and Jason make but if concentricity is critical you will need a quick confirmation check with a clock as you never know when a swarf chip is undermining your expected accuracy. I was taught that a 3 jaw is an everyday general purpose work holder and the accuracy and repeatability should always be questioned. Of course for many jobs concentricity is not critical and a decent chuck in good condition will be entirely satisfactory. For the few moments required to just position an indicator and spin the job to check that all is well could save a job from a random burr, dirt or swarf particle upsetting things. Changing chucks and collets or machining soft jaws takes time so only doing it when the job demands it will save time and effort. The case was made by the late Commander Barker for machining the backplate register for the chuck body undersize to allow the chuck to be adjusted to run true and the bolts tightened, a poor man’s Griptru. When you consider the construction of a scroll chuck it is miraculous that they are as accurate as they are.

Mike

Edited By Mike Poole on 23/04/2023 20:42:29

[Clive Brown 1Participant @clivebrown1]

Posted by Mike Poole on 23/04/2023 18:52:36:

. The case was made by the late Commander Barker for machining the backplate register for the chuck body undersize to allow the chuck to be adjusted to run true and the bolts tightened, a poor man’s Griptru.

Mik

I think it was Prof. Chaddock who wrote in his Quorn series that when this was first suggested, the editor of ME refused to print it.

[Andy StopfordParticipant @andystopford50521]

Paul, you might like to watch this video for general information about chucks:

and definitely watch this one:

[paul mcquaidParticipant @paulmcquaid48093]

Thanks mate I will.

It makes it a lot easier to understand seeing the work being done as opposed to reading about it. which with some authors can make it sound quite daunting…

[BazyleParticipant @bazyle]

Posted by paul mcquaid on 23/04/2023 10:10:14:

It's just a shame that not everybody knows the things that make engineers roll their eyes up at eh?

Not just engineers. Everybody and every thing when we were just apes. Then mankind learned to talk which not only enabled us to transfer each bit of discovered knowledge but revolutionises the way we think by enabling us to create our internal monologue. The transfer of knowledge took a leap forward when we invented BOOKS and actually read them, a skill that seems to have been lost recently.

(There was an interesting program on the BBC a couple of years ago that explained that people born deaf and dumb who are not taught sign language have difficulty in progressing mentally beyond a 5yr old because without speech they cannot develop an internal monologue, which develops in children only when they learn to speak)

[Chris CrewParticipant @chriscrew66644]

If you apply common sense and logic in the workshop you will find that you know more and have skills that you never knew you had and you will find that fitting a backplate, especially one that is part finished and threaded, is a very simple task. As I have said before, if a method works for you then you must have done something right no matter what any other's opinion may be. Don't be afraid to try anything because you will not make a mistake, you will just learn a lesson and we all must have scrap-boxes full of 'lessons', I certainly have. Remember, the man who never made a mistake never made anything.

Edited By Chris Crew on 24/04/2023 09:08:36

[Mike HurleyParticipant @mikehurley60381]

+1 for that Chris

[roy entwistleParticipant @royentwistle24699]

My dad used to say that " experience is built on mountains of scrap. "

Roy

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