The size of drill?

[saw]

Hi, I need to know, how big must I drill for threading a 5-40 tapp?
I found this:
  TAP    Decimal Drill Size
4-40     .0860
4-48     .0935
5-40     .0980

Do you think that this is right? 

[Jasonb]

that may be a bit on teh tight side, for most things you don't need such a full thread engagement, try a #43 drill which is 0.089"

Jason

[saw]

Thanks Jasonb   
Where can I find a tabel for all of those drills and tabs. I am use to mm so this is hard for me.

[mklotz]

Diameter of numbered screws = 0.060 + 0.013*N where N is the screw number.  Thus for a #5...

Diameter = 0.060 + 0.013*5 = 0.125

Tap drill size for 77% depth of thread = major diameter - 1/tpi = 0.125 - 1/40 = 0.1"

For other percentages of depth of thread

Tap drill size = major diameter - 0.013*dot/tpi

where dot = depth of thread expressed as percentage.

[saw]

Thank you, but I am not sure that I am a wize man for that 
However I found this page http://www.csgnetwork.com/drillsizeconvert.html så I know a bit what it is.
It's so hard to try to do somthing from a US-plan, you have inc, you have your fanny number(#40) iver you're plan is diffrent. It's like learning a new language, but I am stupid enough so I continue. I can always learn somthing new, or just change som words with some new friends. 

[ieezitin]

Saw

When I am not sure I Use the .9742 ratio. It’s not dead balls on like shown on all the charts, but a few 10ths of a thou don’t bother me that much.  It certainly works.

Divide .9742 by the thread pitch. Next subtract your answer from the tap diameter this will give you the tap pilot drill size.

Example. ¼-20 bolt.

Divide  .9742 by the pitch 20 and you get .0487 Now subtract .0487 from the diameter of the tap .250 You get .20129 this is your drill size. Remember stainless, cast, aluminum are percentage slightly different, so apply as necessary.   This will always get you in the ball park.

Hope this helps.   Anthony.

[mklotz]

.9742/0.013 = 75%

so that is the rule I showed but adjusted for 75% depth of thread rather than the 77% one gets using "1" in place of "0.9742"

[andyf]

i Saw,

Here's another table, showing the metric tap drill size as 2.65mm for 5-40 UNC: http://mdmetric.com/tech/thddat9.htm#uc

That just leaves you with the problem of finding a 2.65mm drill.

Andy

[kvom]

My drill index box has the tap/body drill sizes for most common imperial threads written on the box lid.  Very useful. 

[saw]

Thanks folks no I think I kan manage it. 

[Jasonb]

Just read your post again and I gave the size for 4-40,the first on your list of 3, was a bit early in the morning.

This site has a lot of thread sizes and the tapping drills are in metric

http://www.gewinde-normen.de/en/index.html

J

[Lew_Merrick_PE]

Thanks Jasonb
Where can I find a tabel for all of those drills and tabs. I am use to mm so this is hard for me.

Benni,  Take a look at the document titled Pilot Hole Considerations posted at http://www.scribd.com/Lew%20Merrick.  It will probably tell you more than you ever wanted to know on the subject.  There is also a document titled UN Thread Data Chart that covers the Unified National (American standard inch-based) screw threads in fair detail.