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Which screw thread system to use?

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Dan14/11/2009 07:48:46
5 forum posts
Hello all,
I'm finally approaching a point where I may find time to actually do some building. I have castings for a 3 1/2 gauge Virgina and the ME beam engine gathering dust atm.
 
At present I have no inventory of hex head screws so will need to build up stock, and need to decide on one system to go with.
 
As far as cost and availability is concerned which would be the better system to go with: BA, UN, or metric? Tap and die cost and availability would also have to factor in.
 
 
BTW, an up to date comprehensive article on this subject would be interesting for M.E.
JasonB14/11/2009 08:32:28
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25215 forum posts
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1 articles
UN are mostly found on models where the design originates from America, you will find it difficult to obtain in the UK taps, dies & fixings in teh smaller sizes such as 8-32, 5-40, etc
 
The BA range has smaller increments than metric and you will not need to start substituting material sizes. eg a 5BA thread will often be used on 1/8" stock but if you change to the nearest metric M3 the stock will also have to be altered to 3mm as well as any other parts, holes etc.
 
I also find the turned BA nuts look a lot better on a perood engine than the flatter metric ones.
 
If you were more into IC engines then I would say go metric but as most loco, traction engine and stationary engine drawings use BA I would stick with that.
 
You can always mix and match for example I am building a V twin ic engine that is drawn with UNC size threads as the design is American, but I am using metric threads but some are being cut onto imperial stock as its easier to obtain 5/52nd steel from the ME suppliers than 4mm.
 
Jason
Circlip14/11/2009 08:51:27
1723 forum posts
Most of the screw sizes can be changed for Metric, and if you make your own bolts and nuts, the BA flat size Hex material can be used.
 
   HOWEVER, when it comes to adjustable items, Valve rods etc., it could be prefferable to use BA threads.
 
  Regards  Ian
David Clark 114/11/2009 09:25:35
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3357 forum posts
112 photos
10 articles
Hi Jason
Article on threads or article on Beam Engine?
 
No, don't answer that.
Both will be covered in the new year.
regards David
 
IanT14/11/2009 10:15:38
2147 forum posts
222 photos
For me it will depend on what work I'm undertaking.
 
Clearly if I'm restoring my (older) workshop equipment or 'pre-owned' models - i use the original screw sizes - which means a lot of imperial and BA threading. So my need for this tackle has not gone away - and I tend to watch out for BSW, BSF taps and dies at car-boots etc - and buy them if in good condition and the price is right.
 
For new build models (and I'm into Gauge 3 - 2 1/2" scenic gauge) I still use BA screw sizes (which is a metric thread anyway) together with the normal ME sizes (32 and 40 tpi). It seems to me that these threads are ideal for modelling purposes and I have no need for metric threads in their place. I do however buy metric drill sizes to use with them.
 
When I am building new pieces of workshop equipment (where I need more strength/robustness) I am standardised on Metric threading - typically M4-M12 - in 'even' sizes, normally coarse. It's much cheaper these days and you can get nuts, bolts, studding at most hardware stores - whereas you can no longer get imperial hardware.
 
For the record - most of my machinery is Imperial in nature - but I measure and cut in mm - as I find this convenient - and I simply convert everything before I start work. But when I'm thinking about much larger dimensions (laying carpets, garden work etc) then I'm still thinking in terms of yards and feet. I can convert to Metric easily - but that's not what I start with when I'm thinking how wide is that room, how long is that fence etc.
mgj14/11/2009 10:20:27
1017 forum posts
14 photos
Personally I prefer metric, because of availability. If you need them there are plenty of 1/2mm sizes. Perhaps a lot depends on the scale you are working in. If I need a special I can make one. (Maybe too I'm influenced by the fact that my local fastener people stock mainly metric and are open on a Saturday morning?)
 
Steam fittings - you are going to need a set of taps and dies for the ME series, which are imperial sizes, 55 degree thread form. I also like the ME series for adjustable stuff because being so fine, I find it quite easy to adjust accurately.
 
I don't think you can buy ME nuts and bolts can you? I think they are more for fittings.
JasonB14/11/2009 10:35:16
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25215 forum posts
3105 photos
1 articles
Some Steam fittings are available with metric FINE threads mostly used in Europe so it would be possible to go all metric.
 
Not seen ME nuts and bolts either
 
BA is probably more use in the smaller scales than the bigger locos and traction engines, though they can still need small stuff. I've just made a couple of Split Pins 0.52mm dia to fit 1/16" pins.
 
Jason
 
PS David, it was not me asking about the articles

Edited By JasonB on 14/11/2009 10:36:13

Edited By JasonB on 14/11/2009 10:37:48

Dan15/11/2009 06:50:12
5 forum posts
Wow what a great range of replies in such a short period of time. Very interesting to read!
 
hmmm......I leaning in the direction of dropping any idea of a standardised system for my model work. I think I'll stick with the original BA as the designs were done up with, particularly where I need hex head, and then for flat head and grub screws mix and match with imperial, as Jason suggested. They're models solely for myself so no need to stick with one system. The "dilemma", if you can call it that, is I'm in Western Canada where the metric system has been slow to infiltrate and BA has always been rare, therefore I have a vast assortment of top quality imperial taps and dies down to 0-80 as well as all imaginable hardware to match.....except hex head. Compared to BA there doesn't appear to be much available for small hex head in metric or imperial in the tiny sizes so I think I'll stay well away from that notion. As with Jason I also prefer the appearance of turned BA anyway.
 
So........if anyone happens to be unloading their inventory of BA hardware I may know of a buyer
 
Mr. Clark: I look forward to the upcoming articles  ( I take both ME and MEW) One aspect of the different systems that I've wondered about is long term useage. Questions such as; Is BA being phased out? How much longer is BA going to be readily available?
chris stephens15/11/2009 17:34:25
1049 forum posts
1 photos
Hi guys,
Did I read somewhere, that there is a new British Standard for BA threads, indicating that they are still considered "current".
chriStephens
Ian S C16/11/2009 01:15:18
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7468 forum posts
230 photos
In Canada you'll proberbly have most available UNF and UNC,I use both of those here in NZ quite a bit,although I also use BSF and Whitworth an sometimes metric,the latter being the standard here.

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