Author Topic: Why is this??  (Read 1864 times)

Offline vcutajar

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Why is this??
« on: December 30, 2014, 12:35:06 PM »
I would like to ask a question which has been nagging me for quite a while.

Today I was tapping an 8mm fine (1mm) hole in the base of the Corliss and that is when I remembered this question.

Why is it that metric fine tap sets always come with two taps whilst metric course sets always have three taps?

Is it because the metric fine sets need to cut less material?  This is just a guess.

Regards

Vince

Offline Bluechip

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Re: Why is this??
« Reply #1 on: December 30, 2014, 02:27:31 PM »
I have Metric Fine with 3 taps per set. [ Guhring IIRC ?? ]

These are the usual sort: taper-second-plug ... are yours serial taps?

Dave
 

Offline vcutajar

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Re: Why is this??
« Reply #2 on: December 30, 2014, 02:50:31 PM »
Dave

I had to google serial tap to know what they are and still I can't say what mine are.  All I can say is that all the metric fine tap sets I have have been bought from two different local suppliers.

Vince

Offline Bluechip

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Re: Why is this??
« Reply #3 on: December 30, 2014, 03:24:56 PM »
Serial taps usually have rings on the shanks ... comme ca ...

http://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Taps/Serial-Taps---Metric-BSW-BSF

These are 3 per set ..

I can't see why they should be 2 per set ?? If you think 8mm x 1mm is roughly 5/16" x 26 TPI the Imp. would be 3 per set, even 5/16" x 40 TPI would be too so I don't think it's to give them an easier time cutting. Depth of Cut on 40 TPI is quite small ...

However when I was a small pup B.S. Conduit taps were often 2 per set IIRC.

Dunno Vince ... ask for a refund ....  ;D

Dave


Offline arnoldb

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Re: Why is this??
« Reply #4 on: December 30, 2014, 03:55:48 PM »
Hi Vince - you're right about the "less material to remove" for the metric fine taps.

My favourite brand uses true serial taps - they cut sequentially more for each tap, and the last one is both a final and bottoming tap in one.  For this brand, the standard metric taps are three to a set, and the metric fine ones two to a set.  If a hole is tapped with only the first two taps for the three tap sets, or the first tap for the metric fine sets, even if tapped through-hole a normal screw won't fit - the last tap has to be used to get the hole to size.  I nearly had a fit the first time I bought a metric fine set, as I happened to check the taps and there was one "missing"; the salesman had some explaining to do  :LittleDevil:

My second-choice brand's taps aren't serial - even though there's three taps to a set for normal metric.  On a thin workpiece with a through-hole, once the hole is tapped with the first tap, a screw will already screw in properly, and the other taps are only needed for blind or deeper holes.

For most material the second brand works well, but for more difficult stuff, the serial taps make life a lot easier.  In fact, tapping something like 304 stainless with the serial taps feels the same as tapping mild steel with the non-serial ones - even though you have to make a pass or two more.  The thread quality is also a lot better - materials that will show "tearing" in the threads with the non-serial taps are left with a very smooth thread finish for the serial ones.

So I guess it's not only how much material is removed per pass, but also depends on the material used and the quality of finish the taps will give that plays a role.

Kind regards, Arnold
Building an engine takes Patience, Planning, Preparation and Machining.
Procrastination is nearly the same, but it precludes machining.
Thus, an engine will only be built once the procrastination stops and the machining begins!

Offline Tjark

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Re: Why is this??
« Reply #5 on: December 30, 2014, 06:08:08 PM »
Vince I got a big set off machine taps.
All of them are one piece taps, also the fine treaded taps.
Never had troubles with tapping thread.
Even the M1.6 in steel is no problem if you use sharp taps.
I got a lot off those taps made by Linig, Emug and Volkel.

     Tjark.