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Anonymous Poster

# How to Calculate Thread Depth

11/18/2009 12:19 AM

what is the formula for calculating threading deep?

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Anonymous Poster
#1

### Re: Thread

11/18/2009 3:57 AM

which thread? which depth?

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Anonymous Poster
#2

### Re: Thread

11/18/2009 7:15 AM

What a dumb question !

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#3

### Re: Thread

11/18/2009 7:16 AM

I always just go all the way to the bottom.

Seriously, if you're using a 60° tool, just go to 0.65 x the pitch. That's roughly one-tenth the pitch past the minor diameter surface.

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#4
In reply to #3

### Re: Thread

11/18/2009 12:50 PM

Do you mean how deep should your threads be to prevent stripping?

2 1/2 x the diameter is the ultra safe depth, but some say 1 1/2 times is enough

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Anonymous Poster
#5

### Re: How to Calculate Thread Depth

11/18/2009 10:45 PM

It all depends on the material (its mechanical properties), the bolt pre-stress Vs the thread strip strength.

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#6

### Re: How to Calculate Thread Depth

11/19/2009 1:31 AM

GA from me too Lab.

But as this 1.5 or 2.5 decision is based in a feeling for the materials, allow me to add;

To work out the 'holding strength' exactly you need the tensile strength of the threads root diameter (root area x tensile of the screws material) compared to the effective area of the thread engaged in the base material times that materials compressive strength.

The effective area of the thread is roughly 80% of thread OD less root dia.

When you divide this thread effective area into the area the material said you need to equal the screws root strength, you get how many threads are required.

That number of threads required times the pitch gives the depth required.

IF the question means "how do you decide the tapping hole diameter" this varies with the thread system - so look it up in a book or chart.

If you are asking this about a metric series thread - subtract the thread pitch from the screw OD. In theory the tapping hole is 95%, but in practice a screw thread is under-size and drill will drill sufficiently oversize to just use the 100% number.

You can do the same 'simple subtraction' with Imperial 60° threads by first converting OD and pitch to metric.

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Anonymous Poster
#7

### Re: How to Calculate Thread Depth

11/19/2009 11:54 AM
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#8

### Re: How to Calculate Thread Depth

11/19/2009 2:13 PM

Is it a metric or imperial thread? If it's metric you take the pitch away from the diameter

Example If you want to calculate an M20 x2 thread ,the core sive is 20-2= 18 mm.

Hope this helped THis works for all 60 degree threads

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#9

### Re: How to Calculate Thread Depth

11/20/2009 9:59 AM

Seems as though that I remember that regardless of thread diameter, three fully engaged threads is all that is required, if the materials are the same.

Don't remember where I got such a notion, but it's there stuck in my brain.

Cheers!

Anonymous Poster
#10
In reply to #9

### Re: How to Calculate Thread Depth

11/20/2009 11:28 AM

It is not that only three threads are sufficient, the load on the threads are maximum in this zone. Then it tapers off. However if there are only 3 threads engaged, the load on these three will cross the yield limit and make them fail.

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#11
In reply to #9

### Re: How to Calculate Thread Depth

11/20/2009 9:52 PM

Hi Lyn, from buttress and square perhaps (lead screws and clamps)?
It depends on the thread system's depth to root diameter ratio.
But 3 would not do for the usual 'coarse'; Whitworth, UNC, Metric (C), ANC and definitely not the 'fine' series BA, UNF, BSF Metric fine or Bicycle, Microscope, to illustrate the range of thread depth to root ratios out there.

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Anonymous Poster
#12

### Re: How to Calculate Thread Depth

12/05/2009 4:11 AM

I think your other guest has the wrong end of the stick, although what he says is true. From a toolmakers point of view, there is a difference between thread depth and thread engagment. With regards to engagment, our rule of thumb on "v" threads is min twice thread OD, more if space allows. on tools that are regulary stripped for servicing this is important as your threads will hold up longer. There is plenty of litreature with regards to thread depth, ie half the difference between theoratical OD an ID. Check the specific standards for your thread. Take note of what effects Root and Crown rads make, as well as the type of fit required, also wether you are imachining iternal or external threads. When things become nasty, for example cutting very large threads or gringing thread gauges, thread depth is measured over rolers or wires that engage the thread flanks as this gives a true reflection of where you stand geometricaly with your threading. hope this helps.

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#13

### Re: How to Calculate Thread Depth

05/22/2011 8:19 PM

Simple answer, for Unified threads, is 0.6134 x pitch. Pitch being 1/threads-per-inch.

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#14

### Re: How to Calculate Thread Depth

01/02/2017 1:26 PM

For m=18*1.5 how much the thread height will be?

Anonymous Poster #1
#15

### Re: How to Calculate Thread Depth

08/25/2017 12:06 AM

hello all
which formula can i used to get the height of thread as per noted in root area formula?
exm;
in BS ISO 898-1
A=PI/4 [d2 +d3/2)2
d2=basic pitch diam =D-0.75
d3=minor diameter =d1-H/6
d1=basic minor diam =D-1.25H
H=The height of the triangle on which the thread is based=0.866025p
so where 0.866025 come from????
thanks

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