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Post by Roger on Jan 1, 2014 14:28:15 GMT
But the thread is not the bit you see. It's the screw heads and nuts. True, but presumably the heads are not scale on the BA sizes then? It's an interesting topic and I really have no idea as to whether model engineers hex heads are different to the standard ones for a given size. I suspect that they are, and if that's the case, they have to be made specially anyway. It's unlikely that off the shelf industrial fasteners are going to look the part if I'm being honest, and that's probably true of imperial ones too.
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Post by alanstepney on Jan 1, 2014 16:50:08 GMT
There is a British Standard for BA, and that includes the head dimensions.
The "size smaller" heads we used to get were made by simply using the correct hex bar (to suit the head dimensions) for the size one above that of the threaded part.
As materials went over to metric, suppliers used the closest metric hex bar to the head size they actually wanted.
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bhk
Part of the e-furniture
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Post by bhk on Jan 1, 2014 19:58:08 GMT
Now that's handy. I wonder if anyone makes them in other than stainless steel, I don't think those would look right on a model unless they were painted over of course. Here's another supplier of the same but at much cheaper prices by the look of it. www.pts-uk.com/Products/Hexagons_Hexagon_Head_Set_ScrewsWow that is cheep!!!! Will have to mail order from the UK I think!
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abby
Statesman
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Post by abby on Jan 1, 2014 20:19:29 GMT
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Post by Roger on Jan 1, 2014 21:09:53 GMT
That looks like a very competent company, thanks for that.
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44767
Statesman
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Post by 44767 on Jan 1, 2014 22:53:03 GMT
This is an interesting issue. Just when every new model should be designed using metric (even if it is a model of a 19th century locomotive) there is exactly this issue of fasteners. As you know I am designing the BR standard class 3 tank in 5" gauge. Right from the start I decided to detail the drawings in metric and use metric material where appropriate. Also because a) BA is a metric based system, b) it is readily available to model engineers and c) it has appropriate head sizes, I chose to use these fasteners in my design. Of course if the builder wishes to use another system he is welcome to. For much the same reason I will use the ME system for the pipework as it is the "standard" thread system used for this application in working models. Most commercially available boiler fittings use this thread system- much the same as today we still use BSP threads for pipework when building machinery and installing plant.
Striplar, generally I agree with you but, as has been said, it's the lack of appropriate head sizes that is the problem. Having said that I wonder what they use on the continent when building their scale models.
Happy New Year!
Mike
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44767
Statesman
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Post by 44767 on Jan 1, 2014 23:23:44 GMT
I have just seen your link abby. Do they manufacture exactly what you require to order or is there a list of all screws available? I'm thinking that if they can go down to M1 hex nuts they should be able to do everything I need. It's just the range of hex bar they can use that would determine the size used.
As an aside re the head sizes on BA hex-head screws, normally the nuts and screws for a particular size thread were different sizes across the flats (I think the nuts were made from the next size up hex-bar). This is so one doesn't need two sets of spanners to do up a nut and bolt and why my set of BA spanners has even numbers, e.g. 6BA and 8BA, on each end of the same spanner and not 6BA and 7BA.
Mike
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abby
Statesman
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Post by abby on Jan 2, 2014 0:22:56 GMT
Mike , they have a very large stock and will manufacture any turned small part or screw on their Swiss autos, unfortunately small imperial sized steel hex bar is no longer manufactured unless ordered by the tonne . As one would expect milled steel hex is more expensive.
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44767
Statesman
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Post by 44767 on Jan 2, 2014 0:33:35 GMT
Presumably, since they're done on Swiss autos, the thread is milled with a hob rather than cut with a die. Since then they can drive tooling timed to the spindle they should be able to turn the flats onto the screw. There is a method I learned at Tech for doing this. Bar stock size then shouldn't be an issue.
I'll do a simple model on Solid Works of the principle and see if I can animate it and post it here.
Mike
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44767
Statesman
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Post by 44767 on Jan 2, 2014 3:47:07 GMT
As promised, the animation of turning flatsThis is a simulation of a production method for turning flats onto a workpiece. The workpiece is the round bar on the right and the cutter is represented on the left. The cutter must be timed to the workpiece through gears and turns two times for every time the workpiece revolves one turn. The cutter would be on a slide which is wound in towards the workpiece until the desired size is achieved. You will notice that two flats are produced at 180 degrees to the other from the single point tool. Therefore by having two cutters at 180 degrees to each other, four flats would be produced and by having three equi-spaced cutters, a hexagon could be turned. This could be used for creating spanner flats on a shaft or even the head of a bolt. It would be used on automatic machines and means that second operation work is not required for machining the flats.
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Post by alanstepney on Jan 2, 2014 7:30:45 GMT
You dont need to invent something to turn flats (or hex, square etc). It was done long ago.
Back when everything was made on Capstan lathes there was a nice box that fitted in the turret that would give you square, hex or octagonal heads or bar, once it was set up. I only saw one once, it was making (roughly) 2" hex headed bolts. My abiding memory is the noise!
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44767
Statesman
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Post by 44767 on Jan 2, 2014 8:34:06 GMT
You dont need to invent something to turn flats (or hex, square etc). It was done long ago As I said, I learned about this while studying but had never seen it done. It was hard to understand how it worked at the time but I have always kept it in mind and so now I thought I'd just see how the geometry worked. It looks quite simple really. I'm sure it is used still on autos etc. and it would get around the hex-bar size issue. In fact one could use round bar. Mike
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Post by Roger on Jan 2, 2014 9:16:44 GMT
I guess I'm just obstinate and don't like being dictated to by out of date conventions and availability. I only have a few imperial and BA taps/dies and resent buying them when there are perfectly good metric ones that do that same job. I'll either make my own screws since there aren't that many, or get some made and sell what I don't need. I can use the CNC mill to make heads of any size easily enough on a piece of rod so I don't have to source several different hex sizes. It's an interesting subject though, and I wonder what the uptake would be if metric hex screws were readily available.
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Post by RGR 60130 on Jan 2, 2014 10:31:08 GMT
I don't see imperial threads going out of use any time soon, certainly not until the metric range is expanded to replace the others. I still find UNC and even BSW used to anchor studs into castings because the coarsest metric threads are inferior for the task (the other end of the stud may well carry a metric nut). Tapered NPT fittings are used the world over on instrument and tubing fittings - just look at a Parker or Swagelok catalogue to see what I mean. It seems to me that the ISO metric system was started but never completed?
Reg
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44767
Statesman
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Post by 44767 on Jan 2, 2014 10:34:07 GMT
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Post by Roger on Jan 2, 2014 11:07:57 GMT
I don't see imperial threads going out of use any time soon, certainly not until the metric range is expanded to replace the others. I still find UNC and even BSW used to anchor studs into castings because the coarsest metric threads are inferior for the task (the other end of the stud may well carry a metric nut). Tapered NPT fittings are used the world over on instrument and tubing fittings - just look at a Parker or Swagelok catalogue to see what I mean. It seems to me that the ISO metric system was started but never completed? Reg I agree entirely, it's a painfully slow process, but one that will eventually see some threads abandoned. BSF and BSW have largely been abandoned, at least in the UK, but they will continue as a niche just like most older thread forms for decades. I don't have a problem with any of that, but I wouldn't expect to find anything but Metric sizes on anything new after thirty years of metrication! Still, that's human nature and inertia for you. One blessing is that there's no more proliferation of new 'standard' threads, international standards agencies have put a stop to that. I'm not sure how incomplete the metric system is to be honest. I don't know if there are any tapered threads defined for example. The metric system does allow for custom sizes that use standard metric thread forms on non standard diameters but of course that's not much use for making a stud for cast iron. I guess the argument is that Metric Coarse threads are good enough even for that purpose even if they don't give the same ultimate strength as a coarser thread form. I'm sure it would help is the US came good on its commitment to go metric, but that seems further away than ever, given the dire state of their economy. Mind you, even there, there's a creeping acknowledgement that production for the rest of the world has to be metric and I guess that domestic units will inevitable end up with the same build. It's going to be a might slow process though.
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abby
Statesman
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Post by abby on Jan 2, 2014 11:11:21 GMT
I will stick my neck out and say that most of us have and use imperial threading gear , the reason being that the majority of MEs that I have met seem to be retired or near that age. For most of us our tools were an extension of work (often "borrowed" from )and so tended to be mostly imperial or UNC/F with metric coming much later. Pesonally I have not bought imperial sized threading gear for many years but I have hundreds of imperial taps dies and chasers , many in r/h and l/h versions. I have only a couple each of the smaller metric sizes which I have purchased much more recently. Newcomers or youngsters will no doubt tend to go metric but with the amount of imperial tooling still available I don't see it being replaced soon. Alan , I don't think Mike was trying to reinvent the wheel most of us have an engineering background and are well aware of the methods for turning squares and hexagons , and for drilling same , even if we do not use such methods. Many of the members will have no engineering background and will probably find such a simple diagramatic explanation very interesting.
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44767
Statesman
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Post by 44767 on Jan 2, 2014 11:11:30 GMT
Striplar, your dreams have been answered! here's a taste of what's on this siteI've just been trawling the net for you! Mike
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Post by Roger on Jan 2, 2014 11:21:36 GMT
Just to throw in a bit of an open question. Presumably model engineering bolts with hex heads would just be the next size down from the standard one? ie M4 is 7mm AF so that would become 6mm AF? Just looking at a miniature spanner set, the sizes are 3mm / 3.2mm / 3.5mm / 4mm / 4.5mm / 5mm and 5.5mm
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Post by Roger on Jan 2, 2014 11:25:32 GMT
Striplar, your dreams have been answered! here's a taste of what's on this siteI've just been trawling the net for you! Mike Brilliant! Thanks Mike, they're dear but then it's only to be expected. This is what they say... 'Our metric sizes are UNM (Unified National Miniature Thread Series) which is the standard for use in model making, instruments, miniature mechanisms and watchmaking.' It looks like a bit more research is required to see what those definitions are. A nice chart would be a great find!
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