What to get: Imperial or metric

Hi MichaelG, over the years I've found my Spells never work, however you seem to have interpreted the correct word

I didn't say it was! Perhaps I should be clearer; in general fractions mean work to 'rule' dimensions.and you can generally assume someone using a rule will be accurate to within 1/64"

Naturally if you are faced with fractions smaller than 1/32", you need to take extra care but you will generally find dimensions less than this are typically the nominal sizes of materials or fixings or for adjustment (e.g. set valve so open 1/64" at TDC or leave a clearance of about this amount) generally not dimensions to be cut to - although there are exceptions few people would be expected to work to 1/128" with a rule.

Neil

Nick

MichaelG.

I suggest you revise your maths!

Russell.

If this was integer arithmetic, the mean of 1 and 2 would be 1. I've been caught out by this type of thing when using integers to reduce memory requirements in code for processors. Even wierder is for example 2 * 99/100, which comes out as 0. Why? It obeys BODMAS, so it does the divide first, which comes out as zero because it rounds down to the nearest whole number, then multiply anything by zero and you get zero. I'd much rather have 2 as the answer (real answer in floating point is 1.98), but you have to be careful how you write it

Edited By duncan webster on 28/08/2016 16:32:31

Base 10 metric is very simple but...and a BIG but!

As I grew up in an Imperial world my natural instinct is to convert metric to imperial and then

make a judgement. I have no feel for metric, which only time provides, and I haven't that much left!

I hope 'not done it yet' explains because he's set me wondering too!

I guess he may have been thinking about rounding when he wrote " The simple maths principle". In that case 1.5 would round up to 2.

After repeatedly being caught out by BODMAS as a programmer I started to use brackets galore. Colleagues good at maths were always annoyed by unnecessary brackets but it reduced the embarrassing numeric accidents I kept having!

Dave

Another thought, sometimes it's useful to calculate the geometric mean. On the dangerous assumption I got the sums right, the geometric mean of 1+2 is 1.414 (-ish)

So depending how you do it, the mean of 1+2 could be 1, 1.414, 1.5 or 2

I think it was muzzer in another thread who warned against over thinking things...

Dave

Edited By SillyOldDuffer on 28/08/2016 17:22:50

Edit It was a dangerous assumption that I'd get the sums right: the square root of 3 is 1.732, not 1.414.  Serves me right for trying to be a smarty pants.

Edited By SillyOldDuffer on 28/08/2016 17:26:40

So... use Reverse Polish Notation

Different processors & languages use different standards for rounding - it creates havoc for Java as it has to run the same code in many environments, there's a long page on the paedia of wiki.

Neil

+1 I'm still using a Hewlett Packard RPN calculator from the 1980s and have Reverse Polish calculator apps installed on my smartphone and tablet.

Russell

At one company where I worked we convinced one of the secretaries that Reverse Polish was so advanced that it wasn't even in the Kama Sutra.

Back to engineering; given the number of errors that have been posted in this thread when converting from imperial to metric, or vice versa, I'm amazed that anybody manages to make anything at all in any sort of unit.

Andrew

I follow my grandfather's advice on that: converting gives you another chance to f^#k up, learn to work in both. So although my machines are metric(as you would expect when they were bought new in the 21st century), on the rare occasions imperial jobs come up, I push the button on the digital caliper, and get an inch micrometer out of the drawer.

.

I do ...

I'm quite happy with dimensions like 20mm +/- 0.005"

MichaelG.

Thanks guys,

the thread took an interesting direction! I did my apprenticeship in imperial, am now 60 and wanting to set up my little workshop as I step back a little from work. I can handle the maths no problem for conversions etc. I'm thinking of metric and looking at the Warco lathes and mill.

Looking at the previous posts, will these suffer from the leadscrew discussions mentioned earlier?

thanks for the replies, they have been very helpful. I have only a benchtop lathe at the moment.

The lathe I am thinking of is the GH1330 or similar and the mill is the HV.

thanks all.

Gareth

Warco offer this machine with DRO fitted. If you went with that option that would make the discussion simply one of are you going to cut more threads using TPI or metric pitch and if you know get the one with the leads crew that matches your needs.

Martin

In my opinion the only thing that really matters is screw cutting and beginners tend to use taps and dies anyhow. You are probably going to be working from drawings in both systems along the way.

Larger threads are going to generally be specials or Whitworth form and you are most likely to be cutting both the internal and external threads so you can choose whatever suits your equipment anyhow. Changewheel lathes can generally be persuaded to cut any pitch you like with a bit of fiddling. Gearbox lathes are perhaps a little more restrictive but that may be just me. The only real constraint is if you spend your time making replacement parts for old motor cars and bikes as has already been mentioned.

Regarding Lathes, all digital calipers and mics work in either system. So to turn diameters set your caliper/mic to the mm or inch size required and hit zero. Switch to the units the lathe works in and turn down to size. Mill's are generally going to end up with DRO's which work in either system. Much more important to buy the best lathe you can afford/fit in your workshop.

regards Martin