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Posted by David Littlewood on January 18, 2008, 7:11 am
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>>>
>> Not by people whose views I respect.
>> You assume that 100% thread engagement involves full contact at root
>>and crest. This is a very bad idea, and not in accordance with the
>>standards. If you actually look at the thread geometry (which varies
>>according to whether you are looking at ISO metric, BSW, BA etc, but
>>the same general principle applies to all) you will see that the
>>correct calculation is more complex than the simplistic one above.
>> I don't really see how I can explain it further, without diagrams -
>>and frankly, I don't see why I should, I've given you the reference,
>>check it for yourself. I put forward these thoughts to add to the
>>debate, if you don't like them you can have a full refund of what you
>>paid for them.
>> David
>>
>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?
Well, I suggest you read what Machinery's Handbook actually *says*
before getting too dogmatic. I quote from my 25th edition, page 1815:
"Tapping troubles are sometimes caused by tap drills that are too small
in diameter. The tap drill should not be smaller than is necessary to
give the required strength to the thread as even a very small decrease
in the diameter of the drill will increase the torque required and the
possibility of broken taps. Tests have shown that any increase in the
percentage of full thread over 60% does not significantly increase the
strength of the thread. Often, a 55 to 60% thread is satisfactory,
although 75% threads are commonly used to provide a measure of
safety...... In general, when the engagement length is more than 1.5
times the nominal diameter a 50 or 55% thread is satisfactory."
Interestingly, they later quote (page 1827) the BS recommendations
(which typically give 81.5% engagement for the "recommended" and 70% for
the "alternative" sizes ) without referring back to this advice, which
is of course not consistent with the BS numbers.
And of course, far be it from me to wonder if a manufacturer of taps may
not be entirely bothered if you break rather more taps than you need
to...
>Your daytime occupation is?
>
Irrelevant.
David
--
David Littlewood
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Posted by Tom on January 18, 2008, 7:51 am
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David Littlewood wrote:
>
>>>>
>>> Not by people whose views I respect.
>>> You assume that 100% thread engagement involves full contact at root
>>> and crest. This is a very bad idea, and not in accordance with the
>>> standards. If you actually look at the thread geometry (which varies
>>> according to whether you are looking at ISO metric, BSW, BA etc, but
>>> the same general principle applies to all) you will see that the
>>> correct calculation is more complex than the simplistic one above.
>>> I don't really see how I can explain it further, without diagrams -
>>> and frankly, I don't see why I should, I've given you the reference,
>>> check it for yourself. I put forward these thoughts to add to the
>>> debate, if you don't like them you can have a full refund of what
>>> you paid for them.
>>> David
>>>
>> 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?
>
>
> Well, I suggest you read what Machinery's Handbook actually *says*
> before getting too dogmatic. I quote from my 25th edition, page 1815:
>
> "Tapping troubles are sometimes caused by tap drills that are too small
> in diameter. The tap drill should not be smaller than is necessary to
> give the required strength to the thread as even a very small decrease
> in the diameter of the drill will increase the torque required and the
> possibility of broken taps. Tests have shown that any increase in the
> percentage of full thread over 60% does not significantly increase the
> strength of the thread. Often, a 55 to 60% thread is satisfactory,
> although 75% threads are commonly used to provide a measure of
> safety...... In general, when the engagement length is more than 1.5
> times the nominal diameter a 50 or 55% thread is satisfactory."
>
So?
LOL For all your quoting I notice your not keen to quote MH's tapping size
for the thread in question.
> Interestingly, they later quote (page 1827) the BS recommendations
> (which typically give 81.5% engagement for the "recommended" and 70% for
> the "alternative" sizes ) without referring back to this advice, which
> is of course not consistent with the BS numbers.
>
Why should the BS standard adhere to some advice in a US publication?
>
> And of course, far be it from me to wonder if a manufacturer of taps may
> not be entirely bothered if you break rather more taps than you need to...
>
>> Your daytime occupation is?
>>
> Irrelevant.
>
As for not using a tap maker's chart because they're in the business of
making taps, ergo they quote incorrect tapping sizes as they prefer that
you break them, obviously you're not in an occupation that requires quality
to sell.
>
> David
>
>
Tom
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Posted by David Littlewood on January 18, 2008, 8:20 am
Please log in for more thread options >David Littlewood wrote:
>
>>
>>>>>
>>>> Not by people whose views I respect.
>>>> You assume that 100% thread engagement involves full contact at
>>>>root and crest. This is a very bad idea, and not in accordance
>>>>with the standards. If you actually look at the thread geometry
>>>>(which varies according to whether you are looking at ISO metric,
>>>>BSW, BA etc, but the same general principle applies to all) you
>>>>will see that the correct calculation is more complex than the simplistic
one above.
>>>> I don't really see how I can explain it further, without diagrams
>>>>- and frankly, I don't see why I should, I've given you the
>>>>reference, check it for yourself. I put forward these thoughts to
>>>>add to the debate, if you don't like them you can have a full
>>>>refund of what you paid for them.
>>>> David
>>>>
>>> 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?
>> Well, I suggest you read what Machinery's Handbook actually *says*
>>before getting too dogmatic. I quote from my 25th edition, page 1815:
>> "Tapping troubles are sometimes caused by tap drills that are too
>>small in diameter. The tap drill should not be smaller than is
>>necessary to give the required strength to the thread as even a very
>>small decrease in the diameter of the drill will increase the torque
>>required and the possibility of broken taps. Tests have shown that
>>any increase in the percentage of full thread over 60% does not
>>significantly increase the strength of the thread. Often, a 55 to 60%
>>thread is satisfactory, although 75% threads are commonly used to
>>provide a measure of safety...... In general, when the engagement
>>length is more than 1.5 times the nominal diameter a 50 or 55% thread is
satisfactory."
>>
>So?
>LOL For all your quoting I notice your not keen to quote MH's tapping size
>for the thread in question.
As I said below, they quote the BS table, which as you well know gives
3.3 (recommended) and 3.4 (alternative). What I am pointing out is that
their actual advice is in conflict with the BS table they print. What
part of that do you find difficult to understand? And *I* notice you
don't actually respond to the point they make.
>> Interestingly, they later quote (page 1827) the BS recommendations
>>(which typically give 81.5% engagement for the "recommended" and 70%
>>for the "alternative" sizes ) without referring back to this advice,
>>which is of course not consistent with the BS numbers.
>>
>Why should the BS standard adhere to some advice in a US publication?
Ask the people who write them. As I said elsewhere, I suspect that the
BS figures are aimed at industrial production, with torque control.
>>
>> And of course, far be it from me to wonder if a manufacturer of taps
>>may not be entirely bothered if you break rather more taps than you
>>need to...
>>
>>> Your daytime occupation is?
>>>
>> Irrelevant.
>>
>As for not using a tap maker's chart because they're in the business of
>making taps, ergo they quote incorrect tapping sizes as they prefer that
>you break them, obviously you're not in an occupation that requires quality
>to sell.
I always know when someone descends to ad hominem attacks that they have
run out of arguments. Since none of your above remarks is even remotely
helpful or responsive to the points I have raised, there is clearly no
point in us continuing.
David
--
David Littlewood
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Posted by Mark Rand on January 18, 2008, 7:30 am
Please log in for more thread options On Fri, 18 Jan 2008 00:42:51 +0000, David Littlewood
>>On Thu, 17 Jan 2008 01:51:39 +0000, David Littlewood
>
>[Some stuff snipped]
>>
>>>
>>>Personally, I go for about 65%, unless the above factors suggest
>>>otherwise, and use stub drills kept mostly for this purpose.
>>
>>Then stop recommending 50.8%.
>>
>I didn't *recommend* it, I simply showed some calculations -not mine,
>but those of a very highly respected engineer. Neither he (pretty
>authoritative) nor I (relatively insignificant) recommended 50%, just
>showed it was perfectly viable.
But you are. You are telling people to use 3.5mm which is incorrect for an
M4x0.7 thread.
>>
>>>
>>>Going back to your suggested 3.3mm, this will give over 90% thread
>>>engagement; tapping torque will be through the roof, and tap breakage
>>>(even in Al) a real risk - unless the drill lets you off the hook by
>>>drilling oversize. 3.5mm will give you 65% thread engagement, which will
>>>be way more than enough unless you are only engaging a couple of threads
>>>(in which case you should probably be using a bush or some other
>>>method).
Have you actually looked at a tapping drill table form M4x0.7? Can you provide
a cite for _any_ one that recommends 3.5? 3.3mm is the correct tapping drill
for the thread and is what the taps are designed for.
>>
>>3.3mm is the bloody recommended tapping drill size for an M4 Coarse thread!
>>
>Not by people whose views I respect.
Ask them again...
Mark Rand
RTFM
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Posted by David Littlewood on January 18, 2008, 8:08 am
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[snip]
>>>
>>>Then stop recommending 50.8%.
>>>
>>I didn't *recommend* it, I simply showed some calculations -not mine,
>>but those of a very highly respected engineer. Neither he (pretty
>>authoritative) nor I (relatively insignificant) recommended 50%, just
>>showed it was perfectly viable.
>
>But you are. You are telling people to use 3.5mm which is incorrect for an
>M4x0.7 thread.
>
Only by your definition of "incorrect", which seems top be "does the job
with a fraction of the risk of breaking the tap".
>>>>
>>>>Going back to your suggested 3.3mm, this will give over 90% thread
>>>>engagement; tapping torque will be through the roof, and tap breakage
>>>>(even in Al) a real risk - unless the drill lets you off the hook by
>>>>drilling oversize. 3.5mm will give you 65% thread engagement, which will
>>>>be way more than enough unless you are only engaging a couple of threads
>>>>(in which case you should probably be using a bush or some other
>>>>method).
>
>Have you actually looked at a tapping drill table form M4x0.7? Can you provide
>a cite for _any_ one that recommends 3.5? 3.3mm is the correct tapping drill
>for the thread and is what the taps are designed for.
>
I already did. As I said in my earlier reply to another dogmatic
follower of BS/manufacturers' tables: has it occurred to you that tap
manufacturers probably care rather less than most people if you break
more taps?
I suspect that the BS tables are designed to suite industrial
manufacturing, where torque control is standard and significantly
reduces the risks of breakage. In the home workshop, where torque
control is virtually unknown, and you probably don't have a gross of
replacement taps on the shelf, but do have time to drill holes in stages
to get them the right size, things are different.
>>>
>>>3.3mm is the bloody recommended tapping drill size for an M4 Coarse thread!
>>>
>>Not by people whose views I respect.
>
>
>Ask them again...
>
Right, got a ouija board?
Look, this debate is getting stupid. You don't have to agree with me,
but you (and the others who also keep on parroting the BS
recommendations) might at least have the courtesy to read the references
I have quoted and say why you disagree with them. My views are much less
important than theirs, which are (in the case of TC) extremely well
supported by diagrams etc. All *I* can say is that I have followed these
recommendations for years and *never* had a stripped thread.
Also, remember that you learn most when people disagree with you,
provided you actually debate, not simply repeat your own views without
listening. Either you learn something you didn't know, or you go back
and validate your own assumptions, and understand them better. I
personally don't care whether you agree with me or not, you are free to
use whatever drill size you want, and if it works for you, good. I
simply pass on these thoughts to try to add to the understanding of the
OP and others who may not be so experienced.
David
--
David Littlewood
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