Tap Drill diameter in thread.xls for DIN/ISO internal straight thread?

[bshbsh]

Hello everyone,

I have very little to do with pipe threads so I'm not very familiar with them, and don't understand the "Tap Drill" data column in the thread.xls file. I tried to look up thread specifications and they are different than in the thread.xls file.

As far as I understand, this is the diameter of the ground hole for tapping the thread. Tap Drill in other thread types (e.g. ISO metric thread) corresponds to this as well. But the data for the ISO228/DIN2999 is wildly different.

Could someone explain it to me or point to the right direction? Thanks.

[mcgyvr]

Which sheet are you referring to? BSP Pipe Threads sheet? BSP Taper?

The BSP taper doesn't seem to match any common tap drill charts.. But its a taper so it will need to be reamed.. 

[WHolzwarth]

I've looked at ISO Pipe Threads in Thread.xls and the Tap Drill column at the very right (Column U).

The contents of this column doesn't make sense to me, but it looks like they are not used. If you make a drawing and dimension a hole, then you'll find the values of Column K.

Look at Wikipedia:

https://en.wikipedia.org/wiki/British_Standard_Whitworth

In the Whitworth table you can find the Tap Drill sizes listed in ISO Pipe Threads sheet.

There seems to be some mismatch between ISO Pipe Threads and BSP Pipe Threads in Thread.xls.

You can calculate and compare some data here:

http://www.amesweb.info/Screws/British-Standard-Pipe-Parallel-Thread-BSPP.aspx

[bshbsh]

It's not accessible to me right now so I'm not sure, but I think the sheets are called "ISO Pipe Threads" and "DIN Pipe threads" or something. ISO228 and DIN 2999, particularly the internal (hole) parallel threads, like G1/4".

I have hole notes in the form of "<hole diameter> x <hole depth>, <thread custom description> x <thread depth>". for ISO metric threads the tap drill data matches the drill hole diameter, but for the mentioned pipe threads it is completely wrong. IIRC, for the G1/4 the tap drill is 6.35 in the table (which is exactly 1/4 of an inch), but the actual hole drill is about 11.8mm or so.

But as said, I'm completely clueless about these, I might misinterpreting the table. 🙂

[bshbsh]

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@WHolzwarth wrote:

The contents of this column doesn't make sense to me, but it looks like they are not used. If you make a drawing and dimension a hole, then you'll find the values of Column K.

Look at Wikipedia:

https://en.wikipedia.org/wiki/British_Standard_Whitworth

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That column can be used if you use custom hole notes.

And here's the table with the right tap drills for Rp/G holes as per ISO7/DIN2999 and ISO228:

https://en.wikipedia.org/wiki/British_Standard_Pipe#Pipe_thread_sizes

8.8mm for G1/8", 11.8mm for G1/4", etc.

Unless these sheets aren't for ISO228 and DIN2999. But they have to be because there are separate sheets for tapered pipe threads.

I'm confused as hell.