BA ME or Metric?

[alan2000]

Thanks for all your reply’s, I was away from the pc all day today, so this is the first chance to log on.
I was surprised to find that imperial measurements still had such a firm hold on model engineering ( at least in this country) after all the metric system has been in use in industry for so many years now.
I am building my first engine and so far, have spent about £80 on taps and I will probably spend twice that before it is finished.
It’s not really about the cost, but more the system; I find it easy to think in metric, even though I was brought up with imperial.
I read the Stuart plans and convert to metric use the lathe in metric and check the size in metric.
I was surprised to find the Stuart plans still using imperial (surely they could produce both) I spend more time with a conversion book than I do with any other tool.
Just try to ask a 14 year old to measure 13/32 or 11/16 and they think you are joking.

Alan

[Deleted]

Just ask my 14 year old to do ANYTHING and he thinks you are joking ! Do you want to swap kids ? ;D

[Smifffy]

...I'm with you here Alan. This English stuff is just far to confusing. My drawings are all in English, but I soon convert that to something more useable :-)

[havoc]

....... until somebody brings in their old left handed, imperial, clockwork flooglehorn for repair

I tried to imagine what that looks like but failed miserably

Not a big problem I think, we have been using metric since the french revolution. So even if it is older than that I guess we can safely assume that it won't be any of the current imperial threads either.

[Jo]

I must be honest I struggle to measure 13/32" or 11/16" with out converting it to decimal. Once it is decimal it matters not if the underlying units are based on the length of someone's thumb or the length of the path travelled by light in a vacuum during a time interval of 1/299792458 of a second. But I know which one I find easier to visualise.....

Jo

[Tel]

havoc said:

....... until somebody brings in their old left handed, imperial, clockwork flooglehorn for repair

I tried to imagine what that looks like but failed miserably

That's understandable mate - no doubt you are more familiar with the right handed, metric version. ;D

[ChrisCrosskey]

I feel your pain :-).... I keep a pad in my workshop which is the shopping list for the next time I order from whereever turns out to be the sensible place to order from next, and there's always taps adn dies on it.....

You've got two choices with drills, either buy a set, or buy the "right drills".

for a Stuart I'd have thought either a metric set from 1-6mm in 0.1mm steps will cover all the BA threads for tapping and clearance, or a set from 1/16-1/14 in 64ths plus a number set from 1-60.... or a full 115-drill imperial kit (1/16-1/2, 1-60, A-Z), I got given a Chronos one for Christmas and it's not too bad, unlike the monstrosity it replaced that cost about 35 quid but the drills might have well been TiN coated cheese for all the good they were....

If you are going to be building more Stuart stuff (or similar sized things) then you will be using the same BA etc threads over and over again so buying Dormers from somewhere like Farnell or RS might make sense. If you are buying individual drills buy good ones... when you have a set if you find one drill getting a lot of use buy good ones when you have to replace it...


I'd stick with the threads as listed but it isn't too hard to find equivalence tables for drills and I'd also invest in a copy opf Tubal Cains Workshop Handbook as it has a lot to say about tapping drill sizes, for starters in soft metals drill a bit oversize, there isn't a thread out there that uses 100% flank engagement so there's no point tapping 100% depth threads, drop it to 75-80% and there's no real loss in strength but you won't shear off anythign like as many taps, and the smaller BA's are always a struggle, especially for a beginner.... I would go with the suggestion of getting the Carbon Steel ones from Tracy Tools to start off with. THey are pretty good quality and used carefully will last a long time, if you break one it won't hurt as much to replace......

Part of the reason that there is still so much use of BA, ME etc fasteners in the hobby isn't just atavistic conservatism, it's just that there's more likely to be the "correct" size in th esmaller sizes. Metric standard series only offers 1.2, 1.6, 2, 2.5 and 3, and they're all coarse.... there's a dozen or more small imperial and BA screw forms in that size range so one of them is more likely to be a good match for the application......

If it were me I'd recommend buying the Tubal Cain book, look up what he suggests for the tapping sizes you need and buy two of each plus the clearance ones you need and 2-tap sets for the BA and ME's that you need for this project from Tracy Tools. Invest in a 115 set from Chronos or a 1-6 set as soon as possible and then repeat as neccessary for each project until one day you find that you don't need any tools for the next project (this is at some mythical point int the future BTW, few of us ever reach this particular Nirvana, I certainly haven't)

Chris C