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unc / unf to metric

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Clive Farrar15/10/2011 18:35:35
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I have just bought the set of bottle engine castings from Forrest Classics.
 
I knew it was from the USA but it never even crossed my mind about the threads.
 
All the screws etc are supplied but I do not think i have the taps to match.
 
Not checked my stock yet as I can not get in the gargage.
 
So 5-40 3-48 2-56 1-72 uk source of taps at a reasonable prince of convert to metric
 
discuss!!!
 
Regards Clive
JasonB15/10/2011 19:14:26
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This is a little table I made up when working on American designs. For UNC/UNF just choose metric fine or coarse to get the closest to the tpi
 

 

Its not quite complete and the fractions should really be on a separate line but it does for me.
Tracy tools, tapdie.com should have reasonably priced tools

Jason

Edited By JasonB on 15/10/2011 19:18:29

JasonB15/10/2011 19:47:20
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Just tarted it up a bit
 

JohnF15/10/2011 22:14:24
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For good reasonabley priced minature UNF try Brownells.com in the USA they are a gunsmiths supply house--I use them quite a bit.
 
In fact I will be placing an order soon so could tag on anything you want if you contact me direct.
John
Terryd16/10/2011 06:51:25
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Hi Clive,
 
I would suggest that if you decide (perhaps for authenticity) to use the original American thread sizes Tracy Tools is about the best bet. Their carbon steel taps are perfectly adequate for most model engineering. Most of Brownells taps appear to be out of stock.
 
However I prefer to convert to metric as Jason suggests . Effectively you then only need two sets of taps - metric fine and metric coarse. No messing about with 7 or 8 different thread systems with all the expense and frustration that entails. Since my workshop burnt down claiming most of my tools, I have gone entirely metric and have not regretted it.
 
Just an opinion,
 
Terry
JasonB16/10/2011 07:22:03
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The only thing about converting to metric threads is that you are OK with fasteners but if you are threading the ends of rods etc then you need to change the rod Dia, hole it goes through and so on.
 
And there is also the fact Metric nuts and bolt/screw heads are quite flat and look wrong on say a Hit & Miss or steam engine.
 
For both these reasons I prefer to convert to BA. I've just machined all the fixings for a 1/2" scale Domestic stovepipe from hex stock and Metric would look well different and you could not even get the larger dia heads in in some places.
 
J
Gone Away16/10/2011 17:52:35
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Apart from the 2-56, those are quite oddball sizes even in North America. You'd be a little pushed taps/dies even here - it would take some digging at least (odd number threads (1, 3, 5 etc are essentially non-preferred).
 
I'd take the advice given - change them to metric. I'd probably even do that from here (Canada) where UN threads are the standard.
Gone Away16/10/2011 18:30:33
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BTW, there's a decent thread substitution table (British/US/Metric) at:
 
Clive Farrar16/10/2011 19:17:39
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Thanks guys the thread tables are neater than the ones i had found and have been printed off to go in the garage.
 
Unless i have them in my current collection which i doubt then it will be metric as i will only need to source a 1.6 mm. Tracy ?
 
 
I do have BA but i think they only go down to a 10.
 
Regards Clive
David Clark 117/10/2011 12:03:53
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Hi there
I hyave a series to publish on the bottle engine in ME.
regards David

Edited By David Clark 1 on 17/10/2011 12:04:07

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