M8 tapping drill

[Iain DownsParticipant @iaindowns78295]

I'm sorry. Really. I'm ever so sorry.

I promise I will never ever ask a question again….

Iain

[Mark CParticipant @markc]

Oh, OK I accept. Just need to see if everyone else will?

Mark

PS. I was going to measure some scabby studding in the morning and add to the last drawing for Michael as well…

Edited By Mark C on 15/10/2016 23:16:44

[JasonBModerator @jasonb]

It would be interesting top compare the FEA of the 7.1mm hole with scabby studding in it. I have a bit that measures 7.67mm have you got a scabbier bit?

The studding is also likely to be made from old fridges so that should probably be entered into the equasion too

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 16/10/2016 07:29:34:

… I have a bit that measures 7.67mm …

.

What does the thread-form look like on that, Jason

Truncated, or full-but-undersize, or something between ?

MichaelG.

[JasonBModerator @jasonb]

I'll take a pic, back in a few mins.

[JasonBModerator @jasonb]

It's an interesting point Michael, a fully formed but undersize male thread will have thinner crests in contact with the female thread than one that has been cut from undersize material so I would expect the fully formed male thread to fail first.

Anyway this is the stud I mentioned early on when I first enquired whether people who worked out percentage engagement bothered to measure the male thread.

M8 commercial studding, seems to have fully formed crests, rough almost torn surface and should we deduct the thickness of the plating

I also mentioned on about page two that I had seen undersize studding on which the crests looked more like an ACME form, I can't take a pic of that as it is now surrounded in 1/2 cubic meter of concrete holding up a clients tennis court post but here is a fine example of a rolled M10 thread with an OD of 9.32mm Proportionally that would be 7.46mm if M8

J

 

Edited By JasonB on 16/10/2016 08:20:40

[Roderick JenkinsParticipant @roderickjenkins93242]

Of course, I make my own studs using a split die where I can carefully control the thread diameter. I don't just pop down to B&Q

Rod

Edit:. According to the ISO standard shown (much!) earlier in the thread (!) , my sums suggest that the od of m8 is 7.73

 

 

Edited By Roderick Jenkins on 16/10/2016 09:19:10

Edited By Roderick Jenkins on 16/10/2016 09:19:58

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 16/10/2016 08:12:42:

M8 commercial studding, seems to have fully formed crests, rough almost torn surface and should we deduct the thickness of the plating

.

This ^^^ may be the new 'international standard'

It probably fits 5/16" 20 tpi Nuts equally well badly

MichaelG.

[JasonBModerator @jasonb]

Rod, depending on tollerance of thread your 7.73 would be just below minimum, max would be 7.92.

Have a go with the calculator MarkC linked to here, just select M8 x 1.25 and leave the rest as is then calculate.

[Raymond AndersonParticipant @raymondanderson34407]

Further to Jason's measurements of some "scabby " M8 studding, I went and measured a piece of M8 threaded rod that came off a job I was at, It is just plain threaded rod [ galvanized ] that is used for hanging cable trays ect, it measures 7.76mm then took the measurement of a piece of M8 10.9 threaded rod [ self colour ] that I use for clamping studs on the LUX MM and it measures 7.88mm . So that gives a range from 7.67 up to 7.88. quite a range.

Also measured some M16 10.9 threaded rod [ also for clamping studs on the K &T ] and it is 15.87mm and a M16 10.9bolt measures 15. 89mm so not much variation on those 2.

edited for changing a £  to a  & sign.

Edited By Raymond Anderson on 16/10/2016 11:12:22

[Mark CParticipant @markc]

I was having trouble thinking of the best way to get the contact faces to work in the FEA but I think I have a solution. The solver is busy with the problem as I type….

Mark

[Flying FiferParticipant @flyingfifer]

6 days & 11 pages of posts later, has the OP drilled & tapped the b????y hole yet ? Hope it wasn`t for an urgent job the customer would be a wee bit p//d off by now.

Alan

[Mark CParticipant @markc]

Alan, yes he has – he even posted the pictures but we have moved on since then!

Mark

[Mark CParticipant @markc]

Ok Jason, it took a while to configure for the new geometry and make the simulation work but I managed to get it to run and here is the result using mild steel female thread and low tensile (175 MPa yield) stud. Everything else is the same so you are seeing a true comparison as far as the FEA is concerned.

Mark

[JasonBModerator @jasonb]

Thanks Mark, compared with the first ones you posted its easy to see the stresses are much much higher on the small percentage of metal that is in contact

[Mark CParticipant @markc]

Yes, and I have also got this for Michael…

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 17/10/2016 20:24:09:

Thanks Mark, compared with the first ones you posted its easy to see the stresses are much much higher on the small percentage of metal that is in contact

.

… and, incidentally, it shows one of the reasons why threadlocking compounds can be so successful.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Mark C on 17/10/2016 20:26:44:

Yes, and I have also got this for Michael…

.

Excellent job … Thanks Mark

MichaelG.

[Mark CParticipant @markc]

As a point of interest (if you are interested in this sort of thing) it was necessary to create the thread geometry on a fixed reference plane set normal to the helix feature and then create feature axis fort both parts. They then had coincident mates created between the axis and to align the pressure faces the feature sketches were used with a fixed point on one sketch made coincident with the flank of the female thread. This allows me to "easily" reconfigure the assembled thread at whatever geometric conditions I chose…….

Mark

[Author]

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