Villiers HT Lead threads on armature plate.

[chiefy]

Hi everyone does anyone know what the thread size is where the HT lead screws into the armature back plate,I have a back plate that needs the thread cleaning out to make good again I would say the thread is 1/2"" and I suspect it is UNF but I am not sure I would like reassurance before I run a tap down. Regards Keith.

[Woodsman]

Hi Keith,

I believe you are right - see this link.
http://villiersservices.co.uk/index.php?main_page=product_info&cPath=8_18_61&products_id=535

That would be 1/2" diameter  and 20 tpi.  
Do you have a thread gauge? They come in very handy and only cost a few quid for the cheap Silverline set. You could also try:
http://www.baconsdozen.co.uk or

[chiefy]

HI Paul .Thanks for that lead to Villiers services they say 1/2" UNF I will now run a tap through the plate, I do have a thread gauge Which measures Whitworth £ Metric threads (sods law) I will look out for a UNF one. Best Regards Keith.

[Darryl Ovens]

So long as your thread pitch gauge covers (imperial) Threads Per Inch TPI and (metric) pitch in mm per thread then you can measure any thread by using a threading table to tell you the pitch of that diameter thread.  For instance "standard" 1/2" UNF is 20 TPI so just use the 20 TPI guage on the "Whitworth" range. (1/2" BSF is 16 TPI).

[chiefy]

Hi Darryl,Thanks for that I did not know this are the thread angles the same for UNF & Whitworth, it looks like you have saved me from buying another thread gague,thats a good start to the day, I am now off to drive a 7 1/4" loco (school holidays).Best Regards Keith.

[Woodsman]

Hi Keith,
Darryl is dead right - pitch is the same but thread angle is 60 deg (as per ISO metric)
You can find thread charts about half way down this page

http://www.baconsdozen.co.uk/tools/conversion%20charts.htm

[chiefy]

Greetings Paul,Thanks for that super,Best Regards Keith.

[Woodsman]

Forgot to add; the thing to take away from this discussion is that because the diameter and pitch are the same - with slight difference in thread profile (different angle and flattened top to UNC) it is possible, with a decent spanner and some effort to run a UNC nut down a BSW bolt. Not good.

More info here:

http://www.anemo.eu/blog/what-is-the-difference-between-bsfbsw-and-unfunc/

[Darryl Ovens]

Hi Paul and Keith,

Good point about the fit,  Where I served my apprenticeship (Fitter Turner), they were a bit hot on not mixing the 60 deg UNC with 55 deg Whitworth.   We were doing the refits on Naval vessels, (mostly Whitby and Leander Frigates).  They were steam turbine and were superheated and quite high pressure.  So the strength of fasteners was often very important.
If you compare the tables you will see that most of the UNC and Whitworth sizes happen to be the same pitch, (over 1/4" through to 2", the only exception is 1/2"), and the difference between 55 deg and 60 deg is near impossible to see by eye unless you have ideal conditions.  The best give away on male treads is the nice big radius at the top of the Whitworth thread or a corresponding flat on UNC, but even that is hard to judge on commercial grade bolts, especially the smaller sizes and the clearance is such on commercial grades that they screw together quite happily and you usually can't "feel" any difference, often head size/markings is your only clue.  
The problem is that the different angle means the thread only touches at either the OD or near the core (minor dia) of the thread, depending on which way around the mismatch is.  So all the stress is concentrated there instead of spreading it over the face of the thread, and to take the load, the thread deforms till it is touching over a greater area.  This deformation means you are already part way to stripping the thread!
I guess any application where safety is a concern and a consequence will be hot on not mixing the fastener threads.  
UNC (and metric) generally have "UNC" (or "M") on the head amongst the other markings and are usually higher tensile than mild steel plus the head A/F (Across Flats), size is usually fractional inch (or whole mm).
Whitworth generally has a blank head, is only mild steel (especially early ones), and the head size is bigger and a weird non round figure size, hence the special Whitworth spanners.

Cheers
Darryl

[chiefy]

Hi Paul,The web site you mention infers that production UNC threads are rounded to a degree and not flattened as they would be if cut in the lathe very interesting,we could not interchange nuts at 1/2" as Whitworth thread is 12 tpi and unc is 20tpi ,but i can see it would be possible at like for like dia and tpi but it sounds a bit brutal Best Regards Keith.

[chiefy]

Hi Darryl, As i said to Paul I can see that it would be possible to mix the threads on like for like diameters but sounds very iffy to me, I did put a Whitworth 20 tpi gague up to 1/2" UNC in a darkish area with a light behind and a magnifying glass to view with and I could see that it was letting light through not a perfect match on a 3/8" whit bolt it did match, a lot of the stuff us guys play with seems to be whit,Very interesting stuff this has turned out to be, great. Best Regards Keith.

[Darryl Ovens]

Just a small point; that 1/2" "UNC" bolt you have must be "UNF", if it's pitch is 20 TPI.   1/2" UNC is 13 TPI, only one tooth per inch difference (from Whit at 12 TPI), but that will stop it screwing on after 1 or 2 turns depending on the clearance.

[chiefy]

Hi Darryl, you are right it is UNF that was just another senior moment, as my Dad used to say by the time it gets to friday we are singing Happy Birthday trying to remember our own Name!!!. Best regards Keith.

[Darryl Ovens]

Ha ha, yes I know that feeling,  If someone asks me my birthdate I have to stop and think, And as for age .  .  well somebody keeps changing that, if I wasn't born on a round figure I wouldn't have a hope.  Peoples names are another issue. . .

[Woodsman]

First giffer. Are you any good with names?
Second giffer. Not bad.
First giffer. Excellent - whats mine ?

I've put my vacuum cleaner on ebay - it was just gathering dust.

[chiefy]

Hi Darryl, Birthdays are a constant niggle for me my wife died 6+ yrs ago and she looked after all family birthdays,I have everything on a calender, my kids ,sons and daughters in law grandkids, but i have given up buying presents i just give them money and a card i never realised what a stressful job it is running a domestic household i definitely was not cut out for this job. Best Regards Keith.

[chiefy]

Hi Paul, Thanks for making me laugh, I can tell you a true story,when i was a young boy just after the war my mother said to me you will have to take your dads snap tin to his work he has forgot it, my dad worked for a company who made textile machinery when i got to his work he was in the office talking with this guy who was wanting some change gears for a carding engine, i was told to sit in the corner and wait,after a while they agreed on the gears the guy wanted and the guy says how much will it cost my father was busy working it out on a piece of paper he looked up and said £18.19.6d the guy said good we will take that with pleasure my father looked at him for a moment and replied if you are having pleasure with us it will be plus 10%, ive never forgot that i dare not have laughed at that time but i often smile when ever i hear someone say i will have that with pleasure.Best Regards Keith.

[Woodsman]

I've also deleted all my German contacts from my mobile 'phone.
Now it's Hans free!!

[chiefy]

Hi Paul,In 1958 or 59 i took my father and uncle in a ancient ford van to look at some pigs they wanted to buy when we were on our way home father says pull into this pub and we will have a drink this was at horbury bridge, the Bingley arms which is sited between the river and the canal my uncle and father climbed onto a buffet at the bar and ordered 2 pints of dark mild and something non alchoholic for the lad he is driving( i got ginger beer) outside it was very warm and it looked like it was going to rain, they each took a drink and looked at each other,just then the landlord sidled up to the bar and says it looks like rain my uncle replied hi and it f_ _ _ ing tastes like it is it out of the river or the canal. oh dear time to go.

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