Lathe Accuracy

[Michael GilliganParticipant @michaelgilligan61133]

Posted by not done it yet on 10/12/2016 18:02:56:

There is no such thing as "VAT free" from Machinemart. It is a fallacy. It is simply a sale period with that particular reduction on the normal retail price as shown normally. The only legit way of buying from a VAT registered company is with VAT added ( or buying VAT exempt items – like books or children's clothing, etc.).

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Quite … But it is fairly common for companies to advertise "VAT free" to describe "you, the VAT-paying customer will only pay an amount equal to the nett list price … we will work out the sums."

Is it really worth making a fuss ?

MichaelG.

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Edit: "fairly common" usage has included this, for Skoda

http://www.rainworthskoda.co.uk/news/0-finance–0-vat–offer-extended#.WExL_bTfWhA

Edited By Michael Gilligan on 10/12/2016 18:44:37

[MWParticipant @mw27036]

MPosted by Neil Wyatt on 10/12/2016 18:10:07:

Posted by John Stevenson on 30/01/2015 17:52:45:

The accuracy isn't in the machine.

It's in the bloke on the handles.

Going back to the beginning of the thread, i have to agree with John on this!

Indeed, and even if you remove it one step on cnc, it's still the guy pushing the buttons whos making the calls and mistakes do happen even in highly automated factories, I should know because I worked for them, customer and general public only sees the preface of the mischief underneath!

Michael W

[HopperParticipant @hopper]

Posted by Neil Wyatt on 10/12/2016 18:10:07:

Posted by John Stevenson on 30/01/2015 17:52:45:

The accuracy isn't in the machine.

It's in the bloke on the handles.

Going back to the beginning of the thread, i have to agree with John on this!

As they say, it is the nut that holds the cross slide handle that is most critical.

[David ColwillParticipant @davidcolwill19261]

Posted by Neil Wyatt on 10/12/2016 18:10:07:

Posted by John Stevenson on 30/01/2015 17:52:45:

The accuracy isn't in the machine.

It's in the bloke on the handles.

Going back to the beginning of the thread, i have to agree with John on this!

This explains why nothing I make ever fits!

On a more serious note I think most beginners don't know how accurate their lathes are and therefore get caught out. The more experienced / methodical know when they are working close to the limits of their machine and take steps or workarounds to deal with the situation.

There is much to be said for doing basic accuracy checks every 6 months or so just so that you know what's what.

The fact that a machine isn't ultra precision needn't be anything to worry about (not in my world anyway).

Checking the accuracy of your machines. Sounds like a good idea for an article.

David

[Roger Provins 2Participant @rogerprovins2]

I've seen extraordinarily good work turned out from old far from accurate lathes. I've also seen very good lathes that have never done any serious work at all, aside from turning out test bars.

Roger

[AjohnwParticipant @ajohnw51620]

Posted by Neil Wyatt on 10/12/2016 18:10:07:

Posted by John Stevenson on 30/01/2015 17:52:45:

The accuracy isn't in the machine.

It's in the bloke on the handles.

Going back to the beginning of the thread, i have to agree with John on this!

I don't agree entirely as I would put it a different way. It's more a case of getting down to the inherent accuracy of the machine when needed and if that isn't acceptable doing something about it. That may mean hand work of some sort. Getting there means taking reliable measurements too. Also usually some thought about the best way to make something.

The taig / peatol I had did turn very round parallel work – until I asked too much if it and then it turned a couple of thou taper over about 4" as the head had warped. Cured by turning it to size in sections. Maybe not everybody's idea of how to cure a problem like that but in that case it was MY best option. It finished up correct to less than a couple of tenths. Ok for a mandrel.

John

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[Howard LewisParticipant @howardlewis46836]

Whilst I agree with John about the nut holding the Handwheels, even an accurate machine will not produce accurate work if it is not properly set up, and aligned. Which is why Myford devote space in their Operator Manuals on levelling.

If the bed is twisted, and/or the gibs slack, on a "good" machine, it will not produce work of the accuracy of which it is really capable. Remember the folk who have improved the performance of fairly mediocre machines by attention to detail.

And, if you want the ultimate in accuracy, it will cost . The sort of machine that we mostly use for hobby work, will probably produce work that meets our requirements. If you want micron accuracy and repeatability, you are not looking for a hobby machine, but a professional toolroom machine, properly set up. and used in a temperature controlled environment.

Did we buy the machine to produce work for what we require, or to pursue theoretical figures?

(My car is claimed to be capable of 100mph+, but because of where it is driven, it rarely reaches 70 mph; so does the claim really matter?)

I have a box of slips, but do not try to work to 100ths of a thou, (1, because I don't need to – and 2, lacking a controlled environment, cannot measure to that level of accuracy anyway)

And how accurate and repeatable are our measuring instruments? Does my 0 -1 " micrometer match the internal mic for accuracy? Letting them both "soak" in the same environment as the slips for 24 hours, with minimal hand contact, may provide a fair indication.

Most of us produce one offs, rather than large volume, so we make one part to fit the corresponding one. For things like piston/bore fits, you can always lap if the fit is that important.

Sorry to rant on, but lets think in practical terms.

Howard

[Steven HalkerstonParticipant @stevenhalkerston22077]

Posted by Howard Lewis on 11/12/2016 21:35:00:

(Snip) And, if you want the ultimate in accuracy, it will cost . The sort of machine that we mostly use for hobby work, will probably produce work that meets our requirements. If you want micron accuracy and repeatability, you are not looking for a hobby machine, but a professional toolroom machine, properly set up. and used in a temperature controlled environment.

Yes indeed and that is pretty a basic thought process for even an undergrad Engineer, I think I may have mentioned somewhere that even for the particular job I'm working on at the moment I have had to take temps into account to ensure dimensions are correct (20deg C?) and to ensure that when I come to fit a deep groove roller bearing to what is in this instance a pulley, it will be a good fit for it's life and also be removable/replaceable as the current plastic units, even at £50 a pop are just disposable items for the want of a £4 bearing.

Did we buy the machine to produce work for what we require, or to pursue theoretical figures?

In my case quite simply as a hobby jobbing tool to fill in time after being retired due to multiple health issues, it is a pleasant surprise nonetheless to see that even that which is often considered a cheaply made that turns out poor results – check out some of the horror stories on you tube. However if a machine has a fundamental flaw such as a twist of a cracked bedplate then no matter how good an operator is they will be unlikely to consistently overcome that kind of issue, the machine then becomes ready for spare parts.

(My car is claimed to be capable of 100mph+, but because of where it is driven, it rarely reaches 70 mph; so does the claim really matter?)

Equally my modded vehicle is capable of speeds in excess of 150mph, that is a completely academic figure though but does tend to indicate underlying acceleration and mid range performance, braking ans suspension demands so on and so forth and yes, I do track the car so although it will never see it's top speed utilised, it is put under a fair bit of pressure from time to time. Equally though my wife and I will fill the boot, throw the hood and take it across Europe without a thought. Would I machine up anything critical to the car's suspension, braking system or basic engine operation – unlikely – I need warranted equipment that is designed ground up using the correct materials and processes of manufacture. With Engineering my background I probably could do so but for insurance purposes and my own piece of mind. I'll take the warranted parts thank you.

I have a box of slips, but do not try to work to 100ths of a thou, (1, because I don't need to – and 2, lacking a controlled environment, cannot measure to that level of accuracy anyway)

And how accurate and repeatable are our measuring instruments? Does my 0 -1 " micrometer match the internal mic for accuracy? Letting them both "soak" in the same environment as the slips for 24 hours, with minimal hand contact, may provide a fair indication.

Most of us produce one offs, rather than large volume, so we make one part to fit the corresponding one. For things like piston/bore fits, you can always lap if the fit is that important.

Sorry to rant on, but lets think in practical terms.

Howard

It seems I must be the one to apologise for coming on and just making what I thought were a few innocent comments about being relatively happy about a lathe I purchased that has taken me back some 30 years to my apprenticeship and young craftsman days I had no idea that it would get some folks so heated.

I'll keep twiddling the hand wheels on the Clarke and doing measuring in a correct and proper fashion and hopefully it will keep turning out the one of parts that I and friends may need.

As an aside, during my career whilst 'on the tools' I did work hand in hand with some of what were possibly the country's best machinists to produce and replicate parts that would see temps in excess of 560deg C and pressures of over 160 bar, some parts that would be of considerable mass that would also be subjected to high rotational speeds therefore centripetal forces, thankfully none of those components failed in service to my knowledge, had they, I would have known as my name – and the machinist's were traceable back to utilising non OEM parts. Just saying. p.s. I definitely would not have used the Clarke for these jobs LOL.

I thank you all for the encouraging comments BTW but not wishing to stir up rants, especially as a newbie to the forum I shall respectfully bow out of this discussion. Regards.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Steven Halkerston on 11/12/2016 22:14:15:

BTW but not wishing to stir up rants, especially as a newbie to the forum I shall respectfully bow out of this discussion. Regards.

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But, Steven … This forum is powered by rants … They are its very life-blood !!

MichaelG.

[Steven HalkerstonParticipant @stevenhalkerston22077]

Nice to hear, no stranger to many forums I know rants are often funny and By C….. I’ve had many myself.

I just don’t want to create bad feelings on a very simple subject.

i.e. been there far too many times where an innocent thread ends up getting like shit in a stick.

You know where I’m coming from. Car forums are are amongst the worst out there.

My ethos is to both learn and teach where possible without any agro, that I can do well but do we need it.

I talk about machining on a twopence halfpenny lathe whilst we live in a really bad world.

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