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Model Engineering in UK - Model engineering, metal crafts in UK 

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Oh god. This group *is* active Suzy 01-08-2008
Posted by Tom on January 18, 2008, 7:17 am
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 Tony Jeffree wrote:

> wrote:
>
>
>>Look up any respected tapping table, and they will quote 5mm for M6x1.
>
>
> I guess that may be true for some limited definition of "any respected
> tapping table". However, the smallest diameter recommended in Tubal
> Cain's book is 5.1mm (for 85% engagement).
>
> Regards,
> Tony
>
Depends on whether you place an individual's opinion over either, a well
established reference source i.e MH, or a manufacturer like Dormer.
Somehow I know where my preference lies.

Tom

Posted by Tony Jeffree on January 18, 2008, 9:06 am
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 wrote:

>Tony Jeffree wrote:
>
>> wrote:
>>
>>
>>>Look up any respected tapping table, and they will quote 5mm for M6x1.
>>
>>
>> I guess that may be true for some limited definition of "any respected
>> tapping table". However, the smallest diameter recommended in Tubal
>> Cain's book is 5.1mm (for 85% engagement).
>>
>> Regards,
>> Tony
> >
>Depends on whether you place an individual's opinion over either, a well
>established reference source i.e MH, or a manufacturer like Dormer.
>Somehow I know where my preference lies.
>
>Tom

Actually, he quotes this as the British Standard preferred size, not
as his personal opinion. So the "well established reference source" in
this case is a British Standard.

Regards,
Tony

Posted by Tom on January 18, 2008, 3:07 pm
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Tony Jeffree wrote:

> wrote:
>
>
>>Tony Jeffree wrote:
>>
>>
>>>wrote:
>>>
>>>
>>>
>>>>Look up any respected tapping table, and they will quote 5mm for M6x1.
>>>
>>>
>>>I guess that may be true for some limited definition of "any respected
>>>tapping table". However, the smallest diameter recommended in Tubal
>>>Cain's book is 5.1mm (for 85% engagement).
>>>
>>>Regards,
>>>Tony
>>>
>>
>>Depends on whether you place an individual's opinion over either, a well
>>established reference source i.e MH, or a manufacturer like Dormer.
>>Somehow I know where my preference lies.
>>
>>Tom
>
>
> Actually, he quotes this as the British Standard preferred size, not
> as his personal opinion. So the "well established reference source" in
> this case is a British Standard.
>
> Regards,
> Tony
>
Whereas MH as regards:
British Standard Tapping Drill Sizes for ISO Metric Coarse Pitch
Series Threads [Supplement No. 1 (I967) to BS 1157: 1965)
        
Quotes 6 x 1 @ 5mm with 81.5% as the recommended and 5.1 as the
alternative @ 73.4%. % as the theoretical.

Interesting. :-)

Tom

Posted by Tom on January 18, 2008, 7:05 am
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Austin Shackles wrote:
> enlightened us thusly:
>
>
>>LOL So you know people who scorn Machinery's Handbook? Who believe maker's
>>like Dormer don't know what they're talking even though they make the taps?
>>You're never heard of arriving at the tapping size for metric threads by
>>subtracting the pitch from the diameter?
>>Your daytime occupation is?
>
>
> pitch-diameter is a useful rule of thumb but taking one from the air, M6x1
> is normally reckoned to want 4.8mm drill, and the rule-of-thumb gets you
> 5mm, which is a fair bit less thread on one that size.
>
> It really all depends on material and what the job's doing. if it's low
> load stuff in steel, 50% thread is going to be fine. If you're talking soft
> material with hard screws, then you want as much thread as you can
> reasonably get, and decent grade of correct-size and fully-threaded bolts to
> boot.
>
Really?
Can you cite a source that recommends 4.8mm? Without going to far from my desk
MH & Dormer both quote 5mm which gives 81.5% Why would you need greater
engagement?

Tom

Posted by Austin Shackles on January 18, 2008, 8:48 am
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enlightened us thusly:

>Austin Shackles wrote:
>> enlightened us thusly:
>>
>>
>>>LOL So you know people who scorn Machinery's Handbook? Who believe maker's
>>>like Dormer don't know what they're talking even though they make the taps?
>>>You're never heard of arriving at the tapping size for metric threads by
>>>subtracting the pitch from the diameter?
>>>Your daytime occupation is?
>>
>>
>> pitch-diameter is a useful rule of thumb but taking one from the air, M6x1
>> is normally reckoned to want 4.8mm drill, and the rule-of-thumb gets you
>> 5mm, which is a fair bit less thread on one that size.
>>
>> It really all depends on material and what the job's doing. if it's low
>> load stuff in steel, 50% thread is going to be fine. If you're talking soft
>> material with hard screws, then you want as much thread as you can
>> reasonably get, and decent grade of correct-size and fully-threaded bolts to
>> boot.
>>
>Really?
>Can you cite a source that recommends 4.8mm? Without going to far from my desk
>MH & Dormer both quote 5mm which gives 81.5% Why would you need greater
engagement?

I think it was a table on the back of a steel rule. Hardly a guaranteed
source, I admit. Presumably it represents 100% engagement, assuming Dormer
et al have it right.

and yes, probably unnecessary. There is, though, the point someone made
about inferior or worn screws - if I'm making a threaded boss for example
with an M6 hole in it, then I don't know what quality or condition the screw
used will be. If I drill with a 4.8 the chances are the hole is 4.9
anyway... and the tap seems to cope (in mild steel).

Tapping M5 into the head of a stainless A4 bolt is a bit more questionable.
Luckily, I don't have to do that often.
--
Austin Shackles. www.ddol-las.net my opinions are just that
Travel The Galaxy! Meet Fascinating Life Forms...
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