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Drill & Tapping Holes vs. Bore and Threading Question
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Posted by: jempc

05/04/2005, 21:47:11

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I have been working in a machine shop for the past year and we bore holes and thread them. I cant find any info on this, all I can find is info on drilling and tapping. Any help on this would help. We make parts with NPT, BSP and ACME threads.

Thanks
Jay







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Re: Drill & Tapping Holes vs. Bore and Threading
Re: Drill & Tapping Holes vs. Bore and Threading -- jempc Post Reply Top of thread Forum
Posted by: randykimball
Barney
05/18/2005, 23:07:01

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OK, enough already.... wink...
You can refer to the "Machinery's Handbook" for information on thread cutting.
But.. here is the simplistic jest of it all:

If you have a large hole or threaded shaft of somewhere around 1.5" or larger it begins to become more reasonable to bore or turn and thread with a threading tool. In the current technology this is often done on a CNC mill or lathe. On the CNC mill the process can be done with thread cutting cycles that calculate the circular motion of the cutter with the pitch. On a CNC lathe the pitch is calculated with the rotation of the work. There is much technology in this area and most machines now come with built in programs to handle the process. All are based on the root diameter or the maximum diameter of the thread and pitch to result in the correct pitch diameter and thread form when using the correct shaped threading tool or cutter. A thread gage should be used to do the quality control and the thread gages must have a quality control system of their own.

In smaller diameter threads it is often more reasonable to drill and tap or turn and chase with a die or die chaser. More often it is now popular to roll the thread form. This is when a hole or shaft of near pitch diameter is threaded using a thread roll tap or roller that coins the thread into the work causing the thread to be formed by upseting the material from the bottom of the vee to the thread crest. This form of thread making also provides a work hardened thread which can increase the strength of the thread. The threads are usually tested for quality control with thread plug or ring gages and they too, require a quality control system to be in place.

The choice to bore or turn and single tool or thread mill the thread, or to drill or turn and tap or chase with a die is a choice made completely by the case to case situation based on which is more effecient in that situation.

.... unless the engineer has noted that it is required that the thread be cut by a certain process. This is done because of and according to the requirements and properties that effect fractures and cracks at the thread points or material stresses induced. This is the reason the "J" thread form (for example)was developed. The "J" form of thread addresses the radii at the root and crest of the thread form, and addresses the allowable tearing and fracturing induced during the cutting process. Therefore the "J" thread tool was one of the first to have a complete thread form on the cutter to control the total thread form and require the pitch of the tool match the thread being formed. It was developed for the aircraft inductry to do away with the feather at the peak of the thread and the cracks at the root of the thread, because these can cause fractures or thread jambs.

happy threading,
-randy-





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Re: Drill & Tapping Holes vs. Bore and Threading
Re: Drill & Tapping Holes vs. Bore and Threading -- jempc Post Reply Top of thread Forum
Posted by: devitg

05/06/2005, 19:26:54

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Boring or drill , does not make the difference.
You can even use a holesaw, lasercutting , peircing , emmbos.
The material and its thick make the difference.
The fact is the diameter to be "Holed"

Some NPT or BSP need to be tapholed , mainly when threading high pressure cilynders head , such the used for Oxigen , Nitrogen or Natural Gas.







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Re: Drill & Tapping Holes vs. Bore and Threading
Re: Drill & Tapping Holes vs. Bore and Threading -- jempc Post Reply Top of thread Forum
Posted by: jason123

05/06/2005, 16:22:20

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Boring and tapping is generally a larger form of drilling and tapping, for a 3" BSP female thread you would bore out and tap at 3" BSP. For a 1/4" BSP you'd drill and tap, hope this helps






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Re: Drill & Tapping Holes vs. Bore and Threading
Re: Re: Drill & Tapping Holes vs. Bore and Threading -- jason123 Post Reply Top of thread Forum
Posted by: yesharsha

05/17/2005, 12:18:39

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i agree with you...
also in case of boring, if i am not wrong, they use spade shaped tools, for easier and quicker material removal...
Well, I am familiar with the various types of taps, can you further help me, how a bored hole with be threaded ?
and correct me if i am wrong, about how a hole will be bored.






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