American 5-40 thread – BA or metric equivalent please?

[Stuart chugg 1Participant @stuartchugg1]

I have, for my first project. an PM research mill engine machined kit which uses 5-40 cap screws for assembly.

I would like to fit studs and nuts in place of the cap screws so the finished result would look more prototypical.

I would like to know if there is a B A or metric thread equivalent as the castings are already tapped 5 – 40.

I ask because I am finding it difficult to source the 5-40 screws in the uk.

Thank you.

Stuart

[Stuart chugg 1Participant @stuartchugg1]

[JasonBModerator @jasonb]

You may be in luck with 5-40 as you can sometimes get a 5BA screw into the threaded hole, really depends on what size tapping drill was used and how many turns of thread there are. Failing that running a 5BA tap will just ease the thread enough for you to use your prefered fixings.

There are several sources here for 5-40 but the heads are often oversize for teh right look, a supplier I use is Modelfixings.

J

PS Welcome to the forum

[John ReeseParticipant @johnreese12848]

The 1/8 -40 model engineer thread is almost identical to 5-40.

[duncan webster 1Participant @duncanwebster1]

5BA is 43.1 tpi, so 14 thread pitches of 5BA is the same length (more or less) as 13 pitches of 5-40. This means that after 7 pitches, the crest of one thread will meet up with the crest of the other. %BA is also bigger OD (only by 1 thou). Putting 5BA bolts in 5-40 holes doesn't sound at all right to me. You can't get 1/8 * 40 nuts and bolts, so you'd have to make them, in which case you might as well make 5-40.

You can buy 5-40 nuts on e-bay, but the postage from US is silly. What you need is a relative over there to buy them for you and then send them across. A more radical solution is to drill them all out and fit M3 helicoils, but that might be a bit OTT

[Anonymous]

UNC taps and dies are readily available in the UK, so it would be simple enough to make ones own 5-40 UNC studs and nuts.

Andrew

[JasonBModerator @jasonb]

Duncan, having made quite a few US sourced models it is possible to do what I said and fit BA to UNC provided the criteria I mentioned allow it eg the hole was drilled with a large tapping drill and number of turns of thread is not too high. Though I mostly throw the supplied UNC fittings into a box never to be used again

Unless the OP buys from one of the specialist ME suppliers in the states who do small hex then the nut hex will look horibly wrong as they tend to come up even larger than stock metric nuts. These people do nice fixings that look right and will fit into the space available which stock nuts may not

Andrews is the best option assuming the OP has the machines which he may not as its a machined kit rather than raw castings

[Neil WyattModerator @neilwyatt]

Sorry to hijack – but for a model engine like Kittiwake, what are the most appropriate style of fittings for things like the crankcase?

[JasonBModerator @jasonb]

They would have used BA or the smaller Whitworth sizes (1/8" x 40 W fits quite well into 5-40UNC). Cheese heads were quite common or the slightly rounded topped Fillaster versions for holding smaller items. Studs and nuts are also still appropriate and what I would go for to join the main two halves of the case together

[Ian S CParticipant @iansc]

I use quite a few 1/8 40/BSW in my models (because I'v got quite a few 1/8 BSW screws and nuts), a lot of my bolts are round head, but a few thou off the side and top and the are near enough to a cheese head that fits in a 3/16" counterbore, or just looks tidy. Ian S C

[mechman48Participant @mechman48]

Have just similar quandary yesterday, my S10V calls for 5/16" x 26 tpi for the gland nut in the bottom cover, having checked my charts for nearest – 5/16" x 24 tpi UNF… & not having any in my 'old' tap collection I decided to use 5/16" x 32 ME taps, a finer thread but I don't see that it will adversely affect anything… horses for courses when needs must.

George.

[duncan webster 1Participant @duncanwebster1]

Jason, you might well be able to get 5ba screws down a 5-40 hole, you can get 3/8" whit bolts down M10 nuts quite easily. That doesn't mean it's a good idea

[Stuart chugg 1Participant @stuartchugg1]

Thanks to all who contributed to my question.

I tried the 5ba suggestion with a screw I had and it worked a treat.

[JasonBModerator @jasonb]

Good to know it worked out for you. It's not the ideal way and I would not want to use it where my life depended on it but on a small model like this with little loading it should get you out of trouble .

Keep us posted on progress and post a picture or two of teh finished engine when you get to that stage.

J

[Neil WyattModerator @neilwyatt]

Posted by JasonB on 15/06/2016 09:24:21:

They would have used BA or the smaller Whitworth sizes (1/8" x 40 W fits quite well into 5-40UNC). Cheese heads were quite common or the slightly rounded topped Fillaster versions for holding smaller items. Studs and nuts are also still appropriate and what I would go for to join the main two halves of the case together

Thanks Jason. I'm not sure whether to go for period or contemporary – In some ways I fancy using cap heads where they would be used on a modern engine, ETW was no Luddite.

Neil

[JasonBModerator @jasonb]

I won't black ball you if you do. I have done it myself on some of the aero engines that I have carved from solid rather than use slot heads like the original cast engine was 70yrs ago. Just don't start using them on period steam engines

[MWParticipant @mw27036]

Posted by duncan webster on 16/06/2016 11:31:57:

Jason, you might well be able to get 5ba screws down a 5-40 hole, you can get 3/8" whit bolts down M10 nuts quite easily. That doesn't mean it's a good idea

Oh i've tried it and it's not. It will only go so far… if i were the OP i'd heed duncan's warning as the pitch doesn't have to change alot to make a difference. 

Michael W

Edited By Michael Walters on 17/06/2016 21:53:32

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Walters on 17/06/2016 21:50:15:

Posted by duncan webster on 16/06/2016 11:31:57:

Jason, you might well be able to get 5ba screws down a 5-40 hole, you can get 3/8" whit bolts down M10 nuts quite easily. That doesn't mean it's a good idea

Oh i've tried it and it's not. It will only go so far… if i were the OP i'd heed duncan's warning as the pitch doesn't have to change alot to make a difference.

.

Given that Stuart's intention is to use studs … I suppose the mis-matched thread might be considered a reasonable way of 'locking' them into the casting.

In any other circumstances … I agee with Duncan !!

That said: I note that the deed is already done.

MichaelG.

[JasonBModerator @jasonb]

Also if anyone wants 1/8 x 40 nuts, contary to whats been said they ARE available here for example. Before someone says it there is usually enough slack to get the 55degree and 60degree threads to work in practice particularly in the smaller sizes even if the theory says otherwise.

[duncan webster 1Participant @duncanwebster1]

Posted by JasonB on 18/06/2016 10:19:11:

Also if anyone wants 1/8 x 40 nuts, contary to whats been said they ARE available here for example. Before someone says it there is usually enough slack to get the 55degree and 60degree threads to work in practice particularly in the smaller sizes even if the theory says otherwise.

I wouldn't worry about the different thread angle, the pitch isright, so a much better solution.

[steamdaveParticipant @steamdave]

Posted by JasonB on 18/06/2016 10:19:11:

Also if anyone wants 1/8 x 40 nuts, contrary to what's been said they ARE available here for example…

… And they are a good company to deal with.

Dave
The Emerald Isle

[Author]

Posts