Oh god. This group *is* active

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Oh god. This group *is* active Suzy 01-08-2008
Posted by Tony Jeffree on January 8, 2008, 5:37 pm
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 On Tue, 08 Jan 2008 20:49:02 +0000, Mark Rand

>>3.5 mm is what I would use for steel - 65% thread engagement, which is
>>fine. For Al or other softer materials I might use 3.4 mm - 80% thread
>>engagement.
>
>58% surely.

Nope...80%...and his name's not Shirley <G>

Regards,
Tony

Posted by Mark Rand on January 8, 2008, 7:15 pm
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>On Tue, 08 Jan 2008 20:49:02 +0000, Mark Rand
>
>>>3.5 mm is what I would use for steel - 65% thread engagement, which is
>>>fine. For Al or other softer materials I might use 3.4 mm - 80% thread
>>>engagement.
>>
>>58% surely.
>
>Nope...80%...and his name's not Shirley <G>
>
>Regards,
>Tony


Core diameter for M4x0.7 is 3.141mm...

3.5mm looks like 58% to me :-)

Mark Rand
RTFM

Posted by Suzy on January 8, 2008, 10:10 pm
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> wrote:
>
>>On Tue, 08 Jan 2008 20:49:02 +0000, Mark Rand
>>
>>>>3.5 mm is what I would use for steel - 65% thread engagement, which is
>>>>fine. For Al or other softer materials I might use 3.4 mm - 80% thread
>>>>engagement.
>>>
>>>58% surely.
>>
>>Nope...80%...and his name's not Shirley <G>
>>
>>Regards,
>>Tony
>
>
> Core diameter for M4x0.7 is 3.141mm...
>
> 3.5mm looks like 58% to me :-)
>
> Mark Rand
> RTFM

Not for the depth of thread, Mark!



Posted by Tom on January 8, 2008, 11:15 pm
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Suzy wrote:

>
>>wrote:
>>
>>
>>>On Tue, 08 Jan 2008 20:49:02 +0000, Mark Rand
>>>
>>>
>>>>>3.5 mm is what I would use for steel - 65% thread engagement, which is
>>>>>fine. For Al or other softer materials I might use 3.4 mm - 80% thread
>>>>>engagement.
>>>>
>>>>58% surely.
>>>
>>>Nope...80%...and his name's not Shirley <G>
>>>
>>>Regards,
>>>Tony
>>
>>
>>Core diameter for M4x0.7 is 3.141mm...
>>
>>3.5mm looks like 58% to me :-)
>>
>>Mark Rand
>>RTFM
>
>
> Not for the depth of thread, Mark!
>
>
Have to agree with Mark.
With a tapping hole size of 3.3mm, theoretical thread depth is 81.5%
So with a tapping hole size of 3.5mm giving a thread depth of .25mm as against
.35 of the 3.3mm hole. %= .25/.35 x 81.5 = 58.21%

Tom

Posted by Tony Jeffree on January 8, 2008, 7:05 am
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>I know 3.3 mm is the preferred drilling for a 4 mm tap, but in practice is
>3.5 mm OK? My supplier only stocks "standard" taps (no starters or
>bottomers)
>
3.3 is on the tight side for M4 - Tubal Cain's book lists BSI
recommended sizes as 3.5mm for 65% thread engagement and 3.4mm for 80%
thread engagement, so 3.3mm sounds like somewhere around 95%. That
would be fine for tapping in soft butter, but would be a recipe for
broken taps in anything sticky (Al) or hard.

As Lester observes, drills often don't cut to size, so that may save
you, but I would choose 3.4 or 3.5 depending on the material.

Regards,
Tony


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