I have a 1/2-13 tap ground special with a .4715/.465 pitch dia.,need help figuring drill size?
I have a 1/2-13 tap ground special with a .4715/.465 pitch dia.,need help figuring drill size?
Or in medieval terms 27/64". for standard 1/2" UNC 13tpi.
BUT oops..
It may be smaller. What is with the regrind?
Super X3. 3600rpm. Sheridan 6"x24" Lathe + more. Three ways to fix things: The right way, the other way, and maybe your way, which is possibly a faster wrong way.
Here is my bushman's method for calculating tap drill sizes.
Find the decimal equivalent of 1/lead(pitch) in this case 1/13 = 0.0769"
Subtract this from the OD; 0.5" - 0.0769" = 0.4231"
Take the next fractional drill size up from this which is 7/16" = 0.4375" and you will get somewhere between a 65% and 75% thread; okay for most purposes.
0.4715" - 0.0769" = 0.3946" so you could choose between 25/64" or 13/32".
But all this is not necessary; the tap was ground down by about 1/32" so simply go down 1/32" from the standard tap drill size.
An open mind is a virtue...so long as all the common sense has not leaked out.
Pitch diameter on a standard 1/2-13 tap is .450, so your tap is oversize. Correct?
yes tap is oversize
Sounds like an allowance for galvanized bolts.:withstupi
Super X3. 3600rpm. Sheridan 6"x24" Lathe + more. Three ways to fix things: The right way, the other way, and maybe your way, which is possibly a faster wrong way.
At least it should be a nice fit in a 'clearance' hole.
1/2"-13 2B Pitch Diameter is pitch diameter of 0.450 to 0.4565, or an average of 0.45325 with a tap drill size of 0.4219
So if your pitch diameter is .4715 to .465, or an average of 0.46825, wouldn't it make sense to have a tap drill size of +.015" larger @ 0.4369"?
yes ,thats what i thougth ,drilling it .015 to .020 larger . I have 1200 parts to tap wanted to be sure since i don't have go or no go gage.
Hey Pop, For that many parts why dont you just take the time to make you a go and no go gauge.
Drilling oversize by the amout the tap is oversize is the solution. What material are you using? If it's soft like aluminum it's not as critical as if it's stainless steel or something even tougher. Also there's something called "First piece inspection". Self explanatory. With as many pieces as you are making you always allow for scrap.