Lisa
Statesman
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Post by Lisa on Oct 30, 2015 15:30:28 GMT
So I'm having to restock/refit parts of my workshop as I get back into model engineering, and in the process I've left myself wondering about BA threads. Back before my dad sold off a large chunk of the tools, we had been in the process of switching to an entirely (or mostly) metric workshop; metal stocks, drills, taps, dies, etc. Of course it never would have been entirely metric, as most (older at least) designs are drawn in imperial, and most fittings are ME threads; but new machine tools are metric, as are most metal sizes. Thus things like axles are 20mm instead of 3/4", use a M5 tap instead of 3/16" and so on, with imperial dimensions used only where necessary.
This brings me to where I am now, and particularly in replacing smaller taps and dies.
The smallest tap/die I currently have is 3mm, below that I need to buy new as the old sets got sold off (or were claimed by my brother, and thus either lost or broken by now). So I'm wondering if I should get new BA taps/dies, or switch to the metric equivalents.
Going all metric would simplify some things such as identifying a thread, and the idea of a "standard" thread type feels somewhat more organised to me. Anytime a BA (or other) thread is specified on a drawing, I'd just use the nearest metric equivalent, as there's metric thread at 0.2mm (or less) intervals in the smallest sizes, down to 1mm; equivalents to 0-14BA, plus some in between. But, smaller metric fasteners are not necessarily easy to get hold of, so I'd likely end up having to make a lot of nuts and bolts myself.
On the other hand if I stick with BA for small threads then fasteners are easier to get hold of, compared to the smaller metric sizes. Plus there's no need to deviate from the design. But there'd also likely be a crossover point, either in the case of a project having larger threads in metric, and smaller in BA; or in having both metric and BA tools and fasteners on hand, and choosing one or the other depending on the project.
I've been dithering on what to do for a while, but I'm going to need to buy one or the other (or both) soon, so I thought I'd share my indecision with you all.
Basically this is my chance to go all metric, if I want to, which I'm not sure if I do.
Any thoughts?
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Post by Doug on Oct 30, 2015 15:51:33 GMT
It is reallty a matter of personal choice their really is no right or wrong. I myself am a mordernist with model engineering and i like to use all and any new tech i can get my hands on (CNC 3D printing etc etc) however i have a full set of BA taps dies and a full set of ME 32 and 40's plus some odd Brass sizes. i dont have any Whit, AF or any other imperial dies etc everything else is metric. Roger is building his speedy fully metric mine is fully BA & ME etc. i have no issues with either method however i would not like to see or would never mix the two myself (small metric and BA) i cant see small metric being any cheaper or easier to get hold of than BA so no advantage either way as far as i can see. so as i said its down to personal preferance. sorry its no help at all
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Post by Deleted on Oct 30, 2015 16:26:39 GMT
As Doug has stated it's really down to personal choice...myself I'm all BA/ME, not just because it's traditional but also the amount of available ME items that use these threads. Another point which is very important to me is scale, now I'm not up to date on metric bolts etc except in far larger sizes which i use a lot in my other hobby of classic cars but as far as I'm aware you can't get metric hex bolts with smaller sized heads on them?. I stand to be corrected if I have this wrong, either way I'll stick with BA/ME as it gives the scaled look that's important to me.
Pete
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Post by goldstar31 on Oct 30, 2015 16:35:17 GMT
My thoughts- for what they are worth- are that BA threads are Metric threads.
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Post by rogsteam1959 on Oct 30, 2015 17:34:18 GMT
Metric bolts and nuts don't look good on models imo. The hex is a bit too big. And if you have to buy models screws and nuts it very expensive. For my MoK I'll buy all in BA. It's my opinion, not a recommendation. Cheers Michael
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Post by Roger on Oct 30, 2015 18:29:01 GMT
Personally I don't see any need for BA threads or ME threads for that matter. About the only exception might be to allow for standard injectors to be fitted. There are perfectly sensible Metric threads close enough to be substituted without any difficulty or significant redesign. Obviously if you have all the taps and dies as well as stocks of fixings then there's no reason to change. If you're starting from a clean sheet though, it's a different matter. Both standard BA and Metric hex bolts have heads that are too large, so you have to source either with reduced heads or make them yourself. Knupfer (no connection) in Germany sell everything you could possibly need down to the smallest sizes with reduced heads and the quality is excellent in my opinion. For the larger sizes, you may have to switch to one of the Metric Fine series threads, of which there are many, but you don't appear to need those. Here's a chart I made up so I could quickly see what thread would be the most sensible to substitute on my build. They do go smaller than M1.2 but that's as small as I wanted to go. Thread charts by Roger Froud, on Flickr I also freely substitute 6mm for 1/4", 5mm for 3/16", 3mm for 1/8" etc when it comes to selecting stock materials and adjust the design to suit. Most of the sizes specified are just the closest Imperial dimensions to the scaled ones, unless you recalculate the exact size from the works drawings, you won't know if 1/4" or 6mm is closest anyway.
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Post by chris vine on Oct 30, 2015 19:00:47 GMT
One thing I have noticed is that most BA nuts and bolts are made of super free machining and quite weak mild steel.
If you go for metric you will have a huge range of materials to choose from. For myself I am still BA ME, but it is mainly inertia!
Chris.
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Post by Roger on Oct 30, 2015 19:09:43 GMT
One thing I have noticed is that most BA nuts and bolts are made of super free machining and quite weak mild steel. If you go for metric you will have a huge range of materials to choose from. For myself I am still BA ME, but it is mainly inertia! Chris. The same is true for Metric Model Engineering fasteners with reduced heads, they are usually soft. It does open up the possibility of using high tensile cap screws, grub screws etc in Metric sizes, but they are of limited interest. In general, the strength of the bolt comes from its large size relative to scale though, so the fact that they aren't very strong doesn't matter. It's the same whether you go Metric or Imperial. With regard to inertia, nothing much will change all the time that people think you can't get the bolts. I said as much to Macc Models, but whether they will begin to stock Metric Fasteners remains to be seen.
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Post by andyhigham on Oct 30, 2015 19:31:08 GMT
When I built Manny Gardner, I used BA except for bolts and nuts in the smokebox where I used metric stainless steel and the bolts holding the cylinders to the frames where I used high tensile metric. Incidently, a useful feature of metric threads, subtract the pitch from the nominal size to get the tapping drill. eg M6 x 1 the tapping drill is 5mm, M4 x 0.7 the tapping drill is 3.3mm A useful addition to any workshop is a set of metric drills 1mm to 6mm in 0.1 steps (4 thou in dinoasaur measurement), a fraction of the price of imperial drills and will cover most small imperial sizes
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Post by vulcanbomber on Oct 30, 2015 20:39:50 GMT
When I built Manny Gardner, I used BA except for bolts and nuts in the smokebox where I used metric stainless steel and the bolts holding the cylinders to the frames where I used high tensile metric. Incidently, a useful feature of metric threads, subtract the pitch from the nominal size to get the tapping drill. eg M6 x 1 the tapping drill is 5mm, M4 x 0.7 the tapping drill is 3.3mm A useful addition to any workshop is a set of metric drills 1mm to 6mm in 0.1 steps (4 thou in dinoasaur measurement), a fraction of the price of imperial drills and will cover most small imperial sizes Rules true for any 60 degree thread... So it applies to UNC and UNF threads as well.
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mbrown
Elder Statesman
Posts: 1,719
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Post by mbrown on Oct 30, 2015 21:09:29 GMT
Although I am a confirmed Imperial person (can't "think" in metric...) I note that Polly Models in the UK has a good range of small metric screws and nuts in brass and steel with various heads.
Malcolm
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Post by mutley on Oct 30, 2015 21:40:15 GMT
Go metric, I swapped all the BSF threads for metric and will stick with metric except for boiler fittings which are BSP or ME.
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steam4ian
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One good turn deserves another
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Post by steam4ian on Oct 30, 2015 22:43:32 GMT
Lisa
Since you are building a Blowfly stick with Metric. I don't recall any fastener on a Blowfly smaller that 1/8" or 3mm.
Ian
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Post by andyhigham on Oct 30, 2015 22:44:39 GMT
A commercially bought M3 bolt is probably stronger than a ME supplied 4BA bolt. My next model will have commercially bought metric high tensile fastenings (1000 for the price of 10 ME supplied BA equivalent). Any heads that look too big can be reduced without too much drama
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Post by andyhigham on Oct 30, 2015 22:50:53 GMT
Mushroom head allen screws are dead useful. A blob of silicone sealant in the hex and a lick of paint and they look like rivets, dig the silicone out with a scriber and you can dismantle
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Lisa
Statesman
Posts: 806
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Post by Lisa on Oct 31, 2015 5:04:38 GMT
Go metric, I swapped all the BSF threads for metric and will stick with metric except for boiler fittings which are BSP or ME. This is what I'm leaning towards, metric for everything except boiler fittings, simply because I don't think it's worth losing the interchangeability with commercial fittings. Roger, that is an extraordinarily useful chart, and Knupfer seem to have a good range, so thanks. Not quite as easy as the overnight delivery I can get with BA fasteners locally; but I'd imagine that the more of us that use metric, the easier it will be to get a hold of.
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peteh
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Post by peteh on Oct 31, 2015 8:17:56 GMT
I would also add in another factor COULD be local stockists. If building a Blowfly I assume you are in Australia so metric is possibly easier to source. But there again it's not as though BA is readily available 'down the street' for most of us anyway
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Post by andyhigham on Oct 31, 2015 9:11:09 GMT
I thik I should have said button head allen screws not mushroom head. Blame it on "Black sheep ale"
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Lisa
Statesman
Posts: 806
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Post by Lisa on Oct 31, 2015 10:22:03 GMT
I would also add in another factor COULD be local stockists. If building a Blowfly I assume you are in Australia so metric is possibly easier to source. But there again it's not as though BA is readily available 'down the street' for most of us anyway I can get BA taps/dies/nuts/bolts fairly easily locally from Hobby Mechanics (plus EJ Winter, and various other ME suppliers) who can also do next-day delivery if I need 'em quick. Metric on the other hand I've so far only found suppliers of small hex-headed bolts in Germany (Knupfer and Modellbauershop), the UK (Polly), and (ironically for metric) the USA (Scale Hardware). Plenty of places sell cheese head and countersunk though, I can buy them 10 minutes walk from home from jaycar electronics; but even on a simple freelance narrow gauge loco they wouldn't look right, and even then I wouldn't want to restrict myself to what I'm building now, but allow for future/other projects as well. Still, that's more places stocking/selling small metric fasteners than I knew about a few days ago, thanks to various comments here.
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Post by fostergp6nhp on Nov 2, 2015 20:26:17 GMT
My 5" WD Alco is commercial metric fixings just for ease with an engineering suppliers just down the road, but the 4" scale road loco will be UNF/UNC just like my other 4" road engine.
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