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Thread: Taping a hole metric / whit
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2nd Oct 2021, 05:37 PM #1Intermediate Member
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Taping a hole metric / whit
20211002_155216.jpg
I am lost for understanding what to pick for tapping a hole that is 1/2 inch 20 tpi. My set seems to serve bother system. But then it seems to be only metric. The second tap from the right seems to be the right one 1/2 NF20. But how could a tap serve both metric and whitworth system. I guess that it is M14x 2.0 pitch.
How to read it correctly?
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2nd Oct 2021, 06:01 PM #2
Hi Dave,
The lettering on the case seems very confusing ! It might be that the set contains both metric and imperial taps.
The clue would be to read the size engraved on the tap itself. Often both the tap size and the tapping drill size are engraved.
1/2" inch by 20 TPI would be a Whitworth or UNF thread, 13 mm would be the closest metric thread but it isn't a standard size.
HTH.Best Regards:
Baron J.
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2nd Oct 2021, 06:51 PM #3Senior Member
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I have a metric set and a separate UN set exactly the same (45 piece each from H&F), and they use the same case to carry each set.
If it's a metric tap set, then the metric tap sizes will be the ones to guide your selection, otherwise use the UN sizes.
Andrew.
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2nd Oct 2021, 11:44 PM #4
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3rd Oct 2021, 12:33 AM #5Best Regards:
Baron J.
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3rd Oct 2021, 01:24 AM #6Senior Member
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Beg to differ Baron. UNF and UNC are 60º as are metric threads.
Pete
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3rd Oct 2021, 05:39 AM #7
Hi Pete,
Thankyou for your post correcting my error !
Yes I should have checked that I was looking at the right line of the table I was referencing. The table ran off the right side of the screen and of course when I scrolled it across I read the wrong line.
I do apologise for my mistake, I consider my wrist slapped.Best Regards:
Baron J.
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3rd Oct 2021, 08:22 AM #8
Hi davewok
Its easy to get confused but once you understand how the system works it becomes easier.
I fancy I spotted an N printed on the shank of the tap at the edge.
That will probably read NF( National Fine ) - some taps it may read UNF - Unified National Fine. the coarse threads are usually in UNC Unified national Coarse
https://www.aimsindustrial.com.au/as...Size-Chart.pdf
The card covers many types of threads - Imperial and Metric. You will find what you seek in there. It also recommends best tapping drill diameters.
You might like to save the chart as its a very handy. Often the Sutton card card is a giveaway at machine tooling outlets and bolt shops,sometimes bearing shops.
A thread pitch gauge -if your tap set doesn't have one.- is a handy tool.
https://www.totaltools.com.au/thread...gauge-set-2-pc
Grahame
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3rd Oct 2021, 08:57 AM #9Most Valued Member
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Following on from what Grahame said, I'd suggest you print out a thread tapping drill chart. (Unfortunately the Sutton one looks like it would not be very printer friendly with all that blue background but there are heaps out there to chose from) and stick it up in your workshop somewhere. Also a decimal/imperial/metric conversion chart.
Some metric threads require a tapping drill that will not be a whole or whole + 1/2 size ie the suggested size might be 5.2mm. You can quite often get close with an imperial drill. Which is where the decimal/imperial/metric conversion chart will come in very handy.
If you have access to a laminator, then laminating the charts will make them more workshop proof.
regards
peter
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3rd Oct 2021, 10:30 AM #10Most Valued Member
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Here's a metric tapping drill chart I made because I struggled to read the tiny text in the Black Book.
The green columns are for the commonly recommended thread engagements and have the same figures you'll find in most tapping charts. But as bollie7 said, you often won't have the exact drill size. So I created columns for other thread engagement percentages. This allows you to see whether a drill bit in your set will give an acceptable thread engagement.
I can't recall exactly, but I believe the 70% and 60% figures are based upon three threads engaged. If the female thread is deeper than three threads you can use a lower engagement figure (i.e. a larger tapping drill) and still have adequate strength. For tapping difficult materials like SS and titanium I recommend using a lower engagement figure anyway.Chris
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3rd Oct 2021, 10:45 AM #11Golden Member
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I'm with mahgnia on this one - at the time I purchased a tap and die set I could have had either a metric fine/coarse set or a UNC/UNF set - both sets used the same plastic case marked with both UNC/UNF and Metric fine/coarse, my set has only metric taps and dies.
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3rd Oct 2021, 10:58 AM #12
The method I use to find a drill size for tapping is; I use a nut of the thread I want to cut and poke a drill through the hole in the nut. I bought a set of metric drills that are 0.5mm steps apart and choose a drill that way. I never seem to pick a drill that is tight in the hole in the nut so I go for the looser one, drill the hole then cut the thread. I figure that a loose drill in the hole will give me deep threads in the project. I also figure that this method works with any tapping job, WW or UNC, UNF and Metric
Just do it!
Kind regards Rod
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3rd Oct 2021, 05:19 PM #13Intermediate Member
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my set was from machinery warehouse. I think that the same box is used for Whitworth and metric. The lettering on the taps only say metric. The whole set should be metric. I would not think that I want to deal with imperial systems when located in Australia.
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3rd Oct 2021, 05:22 PM #14Intermediate Member
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It is frustrating that I want to tap a hole to fit a nozzle. it seems plumbing fixtures are commonly used with imperial system.
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3rd Oct 2021, 06:43 PM #15Most Valued Member
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Are you sure you want ½” x 20 tpi? That’s ½” UNF. Most plumbing fittings in Oz are BSP. And I hope I’m not preaching to the choir, but for ½” BSP, the ½” relates to the size of the pipe, not the thread on the fitting. The thread is about 21mm. Apologies if you already knew that.
Chris
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