11/16-18 thread tap drill size

[fen2art]

Ok so my copy of Machinerys handbook doesn't have this one and my brain doesn't want to do the calcs (or would like confirmation of my numbers)...anyone know the tap drill size for 11/16-18 threads?

TIA

Phil

 

[Barry Weeks]

Early Ford tie rod ends? I always have used the same tap drill as 11/16-16, 5/8". You can buy DOM tubing from Speedway or others with a 5/8 ID and a 7/8" OD that is about ready to cut to length and tap. For a heavier tie rod or draglink, get 7/8" OD x 1/2" ID, and drill the ends to 5/8".

 

[whiskeykid]

I found this same question on another forum awhile back. Here's the answer:

Calculating a tap drill size-

.975 divided by the pitch(18 in your case) yields the double depth of the thread,which for an 18 pitch would be .054"

Subtract the double depth (.054) from the major diameter(11/16 or .6875" in your case) and the result would be the tap hole size which here would be .633".

Assuming deflection/spindle runout etc in this case a 5/8" (.625") drill would be the ticket.
__________________

 

[fen2art]

Thanks

WK Thanks for the formula and confirmation.

Barry W. also some curent Jeep tie rod ends.

fen2art

 

[precisionmetal]

In a pinch, I've always used OD minus the pitch. Never let me down yet.

 

[whiskeykid]

So... OD minus the pitch is 0.6875-0.18? Is that how you figure it out, by dividing the pitch by 100 and subtracting it from the OD?

 

[Limy Sami]

No, convert pitch of TPI in to thou, ie 18tpi =1/18 = 0.0555 therefore .6875 - .0555 = .632, say 5/8 . for general purpose on that dia .007 is niether here nor there.

 

[yanshi]

My reply is late, but maybe I can provide some value on how to calculate tap drill size, which will be usefu for others. the size is 0.632", how do I get it? (11/16-1/18)=0.632", For United Inch thread, the rule is subtracting 1/thread per inch from the diameter. For example, 1-8 UN, 1- 1/8= 7/8″, 7/8″ is the tap drill size! 1/4-20 UN, 1/5″ is the tap drill size, (1/4-1/20=1/5″ )some knowledge of thread taps,this article has the detail introducing the formula.

 

[LKeithR]

Early Ford tie rod ends? I always have used the same tap drill as 11/16-16, 5/8". You can buy DOM tubing from Speedway or others with a 5/8 ID and a 7/8" OD that is about ready to cut to length and tap. For a heavier tie rod or draglink, get 7/8" OD x 1/2" ID, and drill the ends to 5/8".

At one time we did a lot of automotive specialty stuff. For Hot Rods and lighter service we used a 7/8" x .156" wall tube and reamed it to 5/8".
For heavier vehicles like Jeeps we went to a 1" OD tube for a lot more strength...

 

[Red James]

Another way to easily calculate the tap drill is to look on a chart for another size tap WITH THE SAME PITCH, like 5/16-18, and note the difference of MAJOR - TAP DRILL, then subtract the difference from the major dia you want to tap.

 

[Delta Iron Works]

Bore = size - (dd x %)
X= .6875 - (.073-.75)
X= .6875 - (.055)
X= .633
5/8 drill or bore to size

 

[michiganbuck]

Here is a handy calculator

UN imperial screw thread calculator
You may need to copy paste the above link

just punch in .687 and 18 tpi
Comes out .605 to .620 minor diameter.

39/64=.609
5/8 = .625

 

[3t3d]

Bore size = OD - pitch For cutting taps
Bore size = OD - 1/2pitch For forming taps

 

[eKretz]

Necro-Gents... This thread has been resurrected from 2008. So yes, the gentleman from China is a smidge late. (Literally the understatement of the decade?)