Soldering nuts

[Andy J]

Need to solder some 6BA blind nuts onto what is I think are zinc plate fixtures. Could be steel plate but they certainly came from Flair originally and I suspect he used the same metal across all his kits.

 

The query I have is should I use brass of steel nuts to avoid any metal compatibility issues?

[Mike T]

I'd just abrade back to bright metal the area you want to solder to.  I'd abrade the blind nuts as well, unless they are tin plated.

[Geoff S]

I'd use brass nuts because they're easier to solder.  Coming from an electrical background I used to use 6BA and 4BA threads a lot but if I were soldering nuts to a plate as blind nuts I definitely use a metric thread - 3mm to replace 6BA and 4mm to replace 4BA unless there was a good reason not to. 

 

Obviously, as Mike T writes, clean both plate and nuts for a sound joint.

[Martin McIntosh]

You cannot solder to galvanised steel so would probably need an abrasive wheel or something. Same applies to zinc plated push rods. On steel, always use a mild, none corrosive plumbers flux (Wickes) since the stuff in multicore is not really strong enough.

[Andy J]

Stuck with using BA as the model has most of the blind nuts fitted already. Its just the odd one or two that appear to have come off.

[Andy J]

What is the best technique to use to ensure the nut aligns up with the plate hole? Assume I simply tin the nut first and then clamp it to the plate with a spare screw and apply a little more solder.

[Don Fry]

Flair stuff just need abrasive cleaning and non corrosive flux. They used a grade of tin plate. Centre with a wooden peg. I assume the plate is off the plane?

[Martin Harris - Moderator]

2 hours ago, Geoff S said:

I'd use brass nuts because they're easier to solder.  Coming from an electrical background I used to use 6BA and 4BA threads a lot but if I were soldering nuts to a plate as blind nuts I definitely use a metric thread - 3mm to replace 6BA and 4mm to replace 4BA unless there was a good reason not to. 

 

Obviously, as Mike T writes, clean both plate and nuts for a sound joint.

Point of order - BA is a metric thread!

[Geoff S]

7 minutes ago, Martin Harris - Moderator said:

Point of order - BA is a metric thread!

 

Yes, I know but not in modern terms. My grandfather's watch repair bench had containers with BA nuts and bolts up to at least 20BA.  It was a used a lot in, if not started for, clocks and watches.  He started his repair business in 1878 and I remember watching him work right up to 1945, (the year he died) when I was 5 and he was (I think) 84.

[Engine Doctor]

BA is metric pitch but the thread form is I believe different , they screw in so far and get stiff. 

Re abrading steel for soldering dont use wet n dry paper or emery cloth as they leave carbon particles that hamper the solder from flowing. Use glass paper for cleaning / abrading. Tin both parts before soldering. Another trick I was taught in metal work classes is to wipe the cleaned steel with a strong copper sulphate solution. This leaves a thin layer of copper on the metal . Copper and lead have an affinity for oneanother so solder will flow easily when up to temp. We even used the copper sulphate as a flux . 

[Geoff S]

2 hours ago, Andy J said:

What is the best technique to use to ensure the nut aligns up with the plate hole? Assume I simply tin the nut first and then clamp it to the plate with a spare screw and apply a little more solder.

 

Yes. Drill the hole, then, after all the cleaning, hold the nut in place with a suitable machine screw/bolt with Vaseline on the thread (you don't want to solder the whole thing) and solder in place.  I've done it often with fibre glass printed circuit board for various jobs

[Andy J]

12 hours ago, Engine Doctor said:

Re abrading steel for soldering dont use wet n dry paper or emery cloth as they leave carbon particles that hamper the solder from flowing. Use glass paper for cleaning / abrading. 

Thanks ED for the tip of using the correct type of abrasive paper. Perhaps that is why I have had difficulty in soldering pushrods in the past.  Sure I have some Copper Sulphate in the back of the cupboard but it may have got thrown out long ago.

[kc]

BA threads are based on the Thury ( Swiss ) system which is metric but not quite the same as ISO threads which we call metric and write as M4, M6 etc.  See Geo Thomas book The Model Engineers Workshop Manual for more details including a table of both ISO and BA comparing dimensions.   Basically ISO  and BA are not interchangeable but some sizes are near enough to seem as though they are!

 

EKP Supplies make & sell BA nuts etc in steel and brass.

 

It might be easier to tap the metal with a metric or BA thread.   Tracy Tools sell individual taps and dies and they are not too expensive if a just a taper tap can be used - a 6BA tap is £1.50   M3.5 is £2

 

Older electrical fittings can be a source of BA threaded bolts  - light switches were held on by long BA bolts  but now are metric.  

 

[Martin Harris - Moderator]

I didn't mean to suggest that BA and metric were interchangeable - just being a little pedantic in it not being widely recognised as originating from a metric thread form.  It has a much lower flank angle for better holding power than the 60 degrees adopted by mainstream metric threads.  The starting point, 0BA is the same diameter and pitch as M6 Coarse but then follows a geometric formula by decreasing by a factor of 0.9 for each increment. I suppose technically it is wrong to just refer to an M whatever thread without quoting its pitch as there can be many variations...

[kc]

Looks like you have read Geo Thomas great book too Martin.    It nearly diverted me into model engineering instead of aeromodelling, but I saw sense and chose planes!   Aeromodelling gets us outdoors with friends.

I think Mr Thomas would have advocated Metricexit as well as Brexit!  

[Martin Harris - Moderator]

Not read it but I still visualise distances in imperial despite being introduced to the S.I. around the age of 11 - which was several years ago…

[Outrunner]

3 hours ago, Martin Harris - Moderator said:

I didn't mean to suggest that BA and metric were interchangeable - just being a little pedantic in it not being widely recognised as originating from a metric thread form.  It has a much lower flank angle for better holding power than the 60 degrees adopted by mainstream metric threads.  The starting point, 0BA is the same diameter and pitch as M6 Coarse but then follows a geometric formula by decreasing by a factor of 0.9 for each increment. I suppose technically it is wrong to just refer to an M whatever thread without quoting its pitch as there can be many variations...

 

The BA threads are 47.5° angle as opposed to 60° ISO metric.

 

The convention when quoting metric threads is if no pitch is mentioned then it is metric coarse, if it's a fine pitch then you quote the pitch too as there can be many metric fine pitches for a given diameter.

[PatMc]

20 hours ago, Engine Doctor said:

Re abrading steel for soldering dont use wet n dry paper or emery cloth as they leave carbon particles that hamper the solder from flowing. Use glass paper for cleaning / abrading.  

I must have got a lot  of fake wet 'n dry paper & emery cloth over the past 6 or 7 decades, my soldering joints have never been any problem.  😉

Edited July 19, 2023 by PatMc

[Martin McIntosh]

Always use a file on push rods if you want to make a proper job. I was a professional solderer as part of my jobs most of my working life.

By the way, if soldering up piano wire u/c`s also use a file; it makes the job so much easier.

[Andy J]

Used a file to clean the plate surface as recommended, whilst some of the 60/40 (leaded) solder took, it was not a 100% coverage.  Also tried tinning an old steel 6BA nut which was also cleaned with a file but once again the solder failed to flow. So will have to look at using a plumbers flux as well as purchasing some new brass nuts.

[Don Fry]

Andy, you haven’t mentioned, what solder are you using? I would be using a 60/ 40 mix Pb/Sn, with a non reactive flux, Bakers flux in my case, ( still using what my dad won off the CEGB 60 years ago).

Soldering is a knack, easy when you have it. 
Do you have anyone you know can show you. It’s not an intellectual process.