DRILL / TAP SIZING

[jspangler]

Hi

Just wondering if anyone had a simple formula for finding out which drill size to use with a given tap size ( metric and standard).

 

Thanks

 

John

[Charles Davis]

I don't think anything like that exists.

 

You need to use a drill chart.

 

There is an OP file included with Mastercam that includes spot drill, drill, and tap ops for common drill sizes.

 

Toolpaths, Operations, Right click, Get from library, Select, tap.op9, taps.op9, or tap_in.op9.

 

Try it, it's great.

[Karl@CP PISTONS]

There is a formula which will tell

you what size hole to drill given

what thread percentage and major diameter...

E-mail me if you need it ([email protected]) I will have to look for it.

[Michael Reynolds]

Hi John!

 

Actually, there is a formula. OD-P

 

Or, if you have a 3/8-24 ID thread,

it would be .375-(1/24). (Pitch is

1/Number of threads).

 

For Metric threads it's the same.

 

A simple example is for a 3/8-16 thread -

3/8-1/16=5/16.

 

Here's a link to my web page, which has an

automatic calculator (botom of the page,

"Mike's handy dandy calculator")

 

http://mpt.corning-cc.edu/~reynolds/Machining_Formulas.htm

 

Hope this helps!!!

 

Mike R.

[JAMMAN]

Actually, for metric you do a straight subtract IE

M6 X 1 would take a 5MM drill, M8 X 1.25 would take a 6.75MM drill. I have used Mikes english formula for years and it works great.

[ROB]

FORMULA FOR FINDING SIZE OF DRILL ON ANY TAP

MM OR STD.

EXAMPLE FOR STD TAPS:

(1/2-13 TAP)

1/2=.500

1/13=.076

(RESULT)

.500-.076=.424 OR 27/64 DRILL

 

EXAMPLE FOR MM TAPS:

(14X2.0 TAP)

EASIEST IS TO CONVERT TO DECIMAL

14/25.4=.551

2/25.4=.078

(RESULT)

.551-.078=.473 OR 15/32 DRILL

[jspangler]

Thanks. Access to this forum has made my life easier once again....

[Karl@CP PISTONS]

The unsimple fomulae for those interested is

(Thread O.D.)-((.01299*Thread Percentage)/Threads per Inch)= Hole Size

 

or for metric threads

 

(Thread O.D.) - ((Thread Percentage* Pitch)/76.98)= Hole Size

 

Karl

[Guest]

It is fairly common knowledge that the percentage of thread engagement above 60% does not significantly increase the strength of the thread. Therefore, when I calculate thread hole size I always use a formula that allows me to specify the desired percentage of thread. You can use the following formulas to calculate tap hole size based on a desired percentage of thread:

 

American Unified Thread:

 

Hole size = Basic Major Diameter – ((1.08253 * desired percent of thread)/Number of threads per inch)

 

America National Thread:

 

Hole size = Basic Major Diameter –((1.29904 * desired percent of thread)/Number of threads per inch)

 

ISO Metric Thread (all dimensions in MM):

 

Hole size = Basic Major Diameter – (1.08253 * Pitch * desired percent of thread)

 

Desired percent of thread is expressed as a decimal. 75% would equal .75

 

I hope this helps.

 

[ 04-17-2002, 11:56 AM: Message edited by: Marc_Lindsey ]

[Chips Ahoy]

.61343 x TPI = single depth of thread for O.D. standard thread per side.

.54127 x TPI = single depth of thread for I.D. standard thread per side.