paul
Member
Posts: 8
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Post by paul on Jul 12, 2007 22:39:35 GMT
Why is it that the two most recent (decent quality) metric HSS taps I've bought both have a thin 'neck' between the cutting portion and the shank? They seem to function well but there's visible twist at this neck point when 'the going gets tough'.
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ace
Statesman
Posts: 528
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Post by ace on Jul 12, 2007 22:46:28 GMT
Hi Paul
As per my thread, the BA set I purchased all have the reduced shank just after the thread and they nearly all broke off here and in the same place, just after the thread. I'm not sure of the make on these as there is no name on them just the size and tapping drill required. they came in a great wooden box which is proving to be more useful than the taps that where in it.
ACE
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SteveW
Elder Statesman
Posts: 1,399
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Post by SteveW on Jul 12, 2007 22:47:24 GMT
Paul,
I'd guess it's a built in weak link. These things will take a lot more grunt before they break but they still break if you over do it. If they do it'll be at this waist and leave (hopefully) enough sticking out to grab hold of and allow removal. But I might be wrong
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Post by mmaidnz on Jul 12, 2007 23:29:43 GMT
Paul,I maybe talking through my hat here,but I thought that the "neck"part was to facilitate tapping deeper holes.The shank could bind on the thread in a deep hole. I doubt manufacturers would design in a "weak" point.That would be like admitting your product is rubbish  |
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Post by alanstepney on Jul 13, 2007 19:00:40 GMT
I believe that Steve W is correct.
Remember that the tap and die makers main market is industry, where power tapping is the norm. It doesnt take much to break one when you are working close to the maximum possible speed, and extracting the broken part needs to be quick and simple, to save time (=costs).
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Post by havoc on Jul 13, 2007 20:39:55 GMT
So they will trow away the piece. Be serious, working an hour to recover a piece is more expensive than making one extra (which they do anyway if they are smart) and count the cost of a new tap. This is fine and dandy for us who don't count their time but in industry labour is more expensive than tools. Been there, done that, total waste of time...
These days when you drop an electronic component, you don't even look down but take a new one. Cheaper that way. Same for metal work. If you work that close to the limits then you know some pieces will break. This is calculated into the price. Let the machine work: trow away the piece and get on with the next one. The people are there to let the machine work, not to do anything themselves because that costs more. get over it, this is a hobby with different rules than real life.
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Post by chris vine on Jul 13, 2007 22:12:00 GMT
Hi Havoc,
Thow it away? I think it depends on what you are making and tapping holes in as to whether it is cheaper to bin it or spend a few minutes extracting the tap.
Parts in the Aerospace industry could be worth many thousands of pounds!!
chris.
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simonwass
Part of the e-furniture
Cecil Pagets 2-6-2 of 1908. Engine number 2299. Would make a fascinating model....
Posts: 472
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Post by simonwass on Jul 13, 2007 23:29:51 GMT
A good tip I was told, always drill your tapping hole 1 size larger especially if tapping a blind hole. In our sizes we are never putting any real strain on the part so a 60% ish engagement should be enough, the charts are 75% I believe?
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Post by havoc on Jul 14, 2007 7:59:52 GMT
And they have to be so accurate and trustworthy they work them so hard the tools break? My take is that if the pieces are that expensive then they don't work the tools to the limit. That might explain part of the expense. It takes longer to make them.
It is the cheap mass produced stuff that is worked with the tools at the limit of the possible cutting rates.
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Post by chameleonrob on Jul 14, 2007 8:02:11 GMT
A good tip I was told, always drill your tapping hole 1 size larger especially if tapping a blind hole. In our sizes we are never putting any real strain on the part so a 60% ish engagement should be enough, the charts are 75% I believe? bear in mind that depending on the material there will be some plastic deformation as well as cutting. if you drill and tap a hole in aluminum with 60% thread engagement you may well find that you have closer to 90%. the same will apply to varying degrees to other materials, although I wouldn't count on it with iron. rob |
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Post by AndrewP on Jul 14, 2007 8:54:09 GMT
The charts in my 'bible' , Tubal Cain's Model Engineer's Handbook, are all for 65% engagement which I have always thought a sloppy fit, I haven't the courage to deviate from it though ;D
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