By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Forum House Ad Zone

metric taps

All Topics | Latest Posts

Search for:  in Thread Title in  
<< First < Prev 1 2 3 4 Next > Last >>
Tel24/11/2011 00:26:05
avatar
157 forum posts
28 photos
 And there, gentle reader, is the simple and practical answer!
Terryd24/11/2011 03:45:00
avatar
1946 forum posts
179 photos
Posted by Robin Woodward on 23/11/2011 20:36:11:
Hi All,
 
.......................... On a lot of the imported machines I have come across over the past twenty years I have found 1/4-20 UNC bolts with 10mm A/F heads on, I am sure knowing the USA that their SAE standard would definitely not call for a Metric head. To which standard these bolts were made is unknown to me, but none the less they are in the market place, further more when I replaced them with a standard UNC bolt the improvement in fit was very noticeable...................................
 
Rob
 
Hi Rob,
 
It is interesting to note that MG and Morris cars used metric threads with Whitworth heads until around 1955. Perhaps this was because most mechanics would not have metric spanners in those days? So much for standardisation - perhaps it didn't matter when there was less international trade.
 
Regards
 
T
David Paterson 424/11/2011 04:09:14
83 forum posts
8 photos
Terry,
 
I was shy about throwing this in - my first car as a young officer cadet at Duntroon was a '54 TF.the distributor and some of the engine bolts were this mix of metric and BSW. The doco at the time attributed it to a French influence of all things and the system was referred to as 'Nuffields mad metric'
 
Incidentally - the car also lead to many other interesting engineering questions - Why do the English drink warm beer? They keep it in Lucas fridges.
 
Dave
 
 
 
JasonB24/11/2011 07:32:26
avatar
25215 forum posts
3105 photos
1 articles
Just an update, I was not quite correct in what I said. Infact there was no visible damage to the bolt, on returning to the workshop I unwound the remains of the female thread from the bolt which looked as good as new (well as good as a poor quality one)
 

I should also add that contary to what some said the undersize bolt was a sloppy fit in the thread. Also although there were some markings on the bolt head there were no grade marks so I didn't cheat and knowingly use a 10.8 grade bolt.
 
 
 
J
Andrew Johnston24/11/2011 19:39:46
avatar
7061 forum posts
719 photos
Just when you thought it was safe to come out from behind the settee........I thought I'd try and reproduce Jason's results. Here's a picture:
 

I drilled a couple of holes in a piece of steel plate from the scrap bin. No idea what the material is, but probably hot rolled low carbon steel. Thickness measured as 7.98mm. I drilled the holes with a 7.1mm drill straight off, no pilot hole. I forgot to measure the first hole, but the second measured 7.18mm before tapping. The holes were tapped with a Dormer spiral flute tap; because it was the first M8 tap I found in the drawer.
 
First I tried a SHCS. I did it up as tight as I could with a hex wrench, followed by a Mole wrench. I ended up gripping the head in the vice and belting the plate with a hammer. Hence the damage at the bottom right of plate in the picture. Eventually the screw started to extrude material from the plate and the threads in the plate started to strip. It also damaged the crest of the threads on the bolt. The bolt grade was 12.9.
 
Then I tried a stainless steel bolt, says A4-70 on the head, from RS in the second hole. Using a large adjustable spanner the bolt failed. The thread in the plate looks fine.
 
So, a score draw. I expect everybody will have their own views, so I'm not going to draw any public conclusions.
 
Regards,
 
Andrew
JasonB24/11/2011 19:56:50
avatar
25215 forum posts
3105 photos
1 articles
Andrew, could you let us know what the two fixings measure over the thread crests? would be interested to know.
 
J
Terryd24/11/2011 21:32:00
avatar
1946 forum posts
179 photos
Posted by Andrew Johnston on 24/11/2011 19:39:46:
Just when you thought it was safe to come out from behind the settee........

 
................So, a score draw. I expect everybody will have their own views, so I'm not going to draw any public conclusions.
 
Regards,
 
Andrew
 
 
Thanks Andrew,
 
that will do for my models. Perhaps if I ever work for NASA or the NPL I may need different standards?
 
T
Versaboss24/11/2011 22:53:38
512 forum posts
77 photos

Well, I also did an experiment. But before you should know the following: I do, more or less regularly, work for customers. I always use the 'standard' tapping diameters for metric threads, that is dia - pitch. Found in all the tables I have, and also written on a large plate on my Fehlmann drill (on which the tapping is done, under power). I have (mandatory) to check the threads with thread gauges. Yes, I have some taps which cut oversize threads! .

So I took a scrap of Aluminium, 20 mm thick, and bored 2 holes, 6.8 and 7.1 mm. I did not measure them, but due to the drills I used they are spot on. Tapping both M8, and checking with the gauge. Lo and behold, both are perfect! But, and this is a big but for me, looking down into the hole the lager shows distinctive truncated thread. From former (bad) experience I know that my customer would not be pleased with them!!! .

Conclusion: for my own purposes, and in the more difficult materials, I would also drill a gnat's whisker larger next time.

Greetings, Hansrudolf



Andrew Johnston24/11/2011 23:25:30
avatar
7061 forum posts
719 photos
Posted by JasonB on 24/11/2011 19:56:50:
Andrew, could you let us know what the two fixings measure over the thread crests? would be interested to know.
 
J
 
For the SHCS I can't find a new one in my box; M8 is not a size I tend to use. The 'used' one measures 7.85mm across the (damaged) crests. A new M8 stainless screw measures 7.9mm at the start of the thread, 7.87mm in the middle and 7.75mm just under the hex head. Both threads are rolled.
 
The broken portion of the stainless steel screw measures about the same as the new part; 7.9mm at the start, 7.85mm in the middle and 7.75mm under the head.
 
As an aside the SHCS is very consistent both axially and radially. The stainless steel screw not only varies axially the readings vary by 0.05mm or more radially.
 
Regards,
 
Andrew
DMB25/11/2011 00:14:21
1585 forum posts
1 photos
Re Terry D `s post today @ 0345. Could it be that back in 1955 and earlier, Metric threaded bolts were made from Imperial sized Hex. bar as this was probably all that was cheaply available but since industry has gone over to Metric, metric sized Hex. bar is now the el cheapo stuff to use, even for Imperial/USA threaded bolts?
For sometime now, it has been necessary to use Metric spanners on certain BA sized Hex. Hd. screws, as Metric Hex bar is all thats available.
 
 
DMB25/11/2011 00:17:40
1585 forum posts
1 photos
Woops! forgot the time - my prev. post here should have read TD`s post of the 24th @ 0345.
Stub Mandrel25/11/2011 19:18:45
avatar
4318 forum posts
291 photos
1 articles
Lots of interesting stuff here. A couple of observations:
 
I use Tubal Cain's drill sizes as a starting point but sometimes go one, or for larger threads two, sizes smaller as sometimes the amount of thread looks really shallow using his sizes (ebven with new drills). These sizes ARE much kinder on taps but beginners really should remember to use cutting oil on the tap as well.
 
I had an interesting one the other day - 12 BA machine screw and standard nut overtightened - the head of the screw sheared off and I was tightening from the nut side i.e. the thread engagement in the nut was strong enough to more or less pull the head off the screw!
 
I contemplated this and realised that the core area is less than the cross section of the full length of engaged thread, and that as long as the threads can deform slightly under load the whole length will share the load.
 
Neil
 
Now the real question - should the lock nut go on top or underneath?
 

Tel25/11/2011 19:56:33
avatar
157 forum posts
28 photos
 and how many angels can sit on the head of a pin?
Michael Gilligan25/11/2011 22:03:25
avatar
23121 forum posts
1360 photos

I have just found this very handy reference:
http://www.numberfactory.com/

The < Nuts,Screws,Bolts > calculator is especially good.

MichaelG.
Andrew Johnston25/11/2011 22:09:16
avatar
7061 forum posts
719 photos
Posted by Tel on 25/11/2011 19:56:33:
and how many angels can sit on the head of a pin?
 
That's a trick question. The answer, of course, is none, as they've all drunk too much Fosters.
 
Posted by Stub Mandrel on 25/11/2011 19:18:45:
 
Now the real question - should the lock nut go on top or underneath?
 
 
Aaaaah, the old ones are the best ones. I say let's think laterally and put it in the middle.
 
Regards,
 
Andrew
 
PS: The locknut goes on top.
JasonB26/11/2011 07:26:21
avatar
25215 forum posts
3105 photos
1 articles
As we are talking metric threads lets just go for a Nyloc nut
 
J
Ian S C26/11/2011 10:09:36
avatar
7468 forum posts
230 photos
Or you could use a Pal nut, theres no mistaking where that goes. If you don't know them, theres a bit of research for you. Ian S C
Nicholas Farr26/11/2011 10:58:49
avatar
3988 forum posts
1799 photos
Posted by Robin Woodward on 26/11/2011 10:30:51:
Hi All,
snip
Being ex-aircraft industry myself it is either lock wired or castellated nut and split pin as far as I am concerned, why fit two nuts when you can fit one, you have to think of the weight may be that's why the beam engine as a source of power for flying did not catch on, too much weight due to all those locknuts.
snip
 
Rob
 
I suppose it depends on the application. In my experience in industrial vibrating screens and conveyors, locking wire or castellated nut and split pins, just snap. I was always under the impression that these methods were used to retain nuts/set screws in their locations, should they become loose for some reason or other, e.g. you do not want a loose set screw working its way out of a hole inside a gearbox and getting mangled up with the gear teeth. Nylocs seldom vibrate loose in my experience.
 
Regards Nick.

Edited By Nicholas Farr on 26/11/2011 11:00:10

Nicholas Farr26/11/2011 11:52:03
avatar
3988 forum posts
1799 photos
Hi all, further to the question about tapping drill sizes, below is a couple of quotes from a Presto Engineers Cutting Tools booklet.
 
Tap Drill Size
"Use the correct tap drill size, ensure that the hole is round and true. Those tap drill sizes given in pages 23 t0 27 generally afford a thread depth o 75% or more - which we recommend for short hole tapping. For long thread lengths, fine pitches and small diameters a reduced amount of thread depth is sometimes desirable."
 
Hand Taps
"For hand tapping, the conventional set of 3 taps with straight flutes is recommended. It is essential that the tap is presented squarely to the work and that the taps are correctly aligned. When these taps are used in a machine it is not usually necessary to use the taper tap."
 
Nowhere in this booklet do they give different tapping drill sizes for machine or hand tapping. The tables fall within the max/min minor dia's of the respective nut standards Metric BS3643; Unified BS1580; Whitworth BS84; BA BS3643
 
The sizes given in pages 23 -27 for the Metric taps are the same as those in the Zues booklet and other booklets that I have and I have never had any real problem with them and will continue to use them in general terms, but please note that I'm not trying to convince others not to use Tubal Cain's references or any any one else's ideas for that matter. You must draw you own conclusions from the information above.
 
Regards Nick.
 

Edited By Nicholas Farr on 26/11/2011 12:01:10

Chris Trice26/11/2011 15:32:34
avatar
1376 forum posts
10 photos
There's no right or wrong figure that must be obeyed. The point was simply that for a neglible loss of thread engagement, there is a huge reduction in the risk of breaking the tap. Tubal Cain argues that in the vast majority of cases likely to be encountered by the model engineer, the benefits of driling a few points larger massively outweigh the disadvantages. It could be argued that 80% engagement is even better but even the Zeus tables draw a line. It's just a question of where the builder wants to draw it. The figures TC uses to illustrate the principles and prove the maths are based on the specs of what metric nuts and bolts should be and as mentioned earlier on, allows for a slight increase in bearing surface due to extrusion effect. As with all these things, the builder should work with whatever figures they feel comfortable about given the materials and quality of tools they have to work with.
 
For the record, here is a direct quote by TC from "The Model Engineer's Handbook" :
 
"The majority of published tapping drill tables are intended for use with tapping machines or adaptors. These have slipping clutches and/or automatic reversal to cope with overload or bottoming of the tap. The tables are designed to accept the higher thread engagement found in 'production' workshops and are not suitable for hand tapping."
 
From the same page:
 
"The other type of failure - shear across the thread, or stripping - is unaffected by any reduction of thread engagement until at least 50% of the thread has been removed; even then the screw would still be stronger in shear than in tension."
<< First < Prev 1 2 3 4 Next > Last >>

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Sign up to our Newsletter

Sign up to our newsletter and get a free digital issue.

You can unsubscribe at anytime. View our privacy policy at www.mortons.co.uk/privacy

Latest Forum Posts
Support Our Partners
cowells
Sarik
MERIDIENNE EXHIBITIONS LTD
Shopping Partners
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest

 

Donate

donate