Looking for a good reliable Acme thread drill/tap chart

[ltlvt]

Well so far I have downloaded about a Gazillion charts and none of them give me the drill size for a 5/8" -10 TPI Acme thread. All of them want me to use a 5/8 x 8 tpi.
I am at the point of drilling and tapping the cross hole for the cross-slide nut. Thanks in advance. I'm thinking I saw somewhere that the drill size was .531 to .535. I just don't want to trash all the hard work and head scratching I have done to get me this far.

 

[mmcmdl]

Internal and External Thread Dimensions - Dependable Acme Threaded Products Inc

The dimensions listed below can be used to determine the diameter along with the thread pitch.

www.dependableacme.com

ACME Threads: Dimensions, Charts & Formulas

The Ulitmate ACME Thread Resource: Basic Dimensions, Classes, Tolerances, Formulas, Charts, and Explanations

www.machiningdoctor.com

 

[woodchucker]

machinery's handbook. Loaded with info.

 

[T Bredehoft]

See Woodchucker above... That's the most complete...

 

[WobblyHand]

From my 17th edition Machinery's Handbook for 5/8"-8 General Purpose Acme internal threads it says:

Major diameter 0.6450" - 0.6650" Classes 2G, 3G & 4G
Minor diameter 0.5000" - 0.5062" Classes 2G, 3G & 4G

I don't know if an ACME tap cuts on the minor diameter. If it doesn't the drill has to be greater than 0.5000".
Next drill size up is 12.80mm (0.5039") or 13mm (0.5118"), then comes 33/64" at 0.5156".

Hope that helps.

Edit: I guess it doesn't help. My bad. I need to look up 5/8-10. Should be able to calculate it, although there's some fudge factors mentioned in the Handbook.

 

[ChazzC]

Since you're looking for 5/8-10 and most sources for "Acme Thread Tap Drill Size" only have 5/8-8, you'll have to do some calculating; here's the formula with an example for any size, any TPI:

https://newmantools.com/tech/acmetapdrill.htm

 

[WobblyHand]

Since you're looking for 5/8-10 and most sources for "Acme Thread Tap Drill Size" only have 5/8-8, you'll have to do some calculating; here's the formula with an example for any size, any TPI:

https://newmantools.com/tech/acmetapdrill.htm

Using that as a guide, I get 0.625 - 1/TPI + 0.005 = 0.625 - 0.100 + 0.005 = 0.530"

I still think the Machinery's Handbook is the reference, but haven't gone through the math yet. I'll look at it in a bit. Their formula is a little more complicated.

 

[Asm109]

Can you measure the root diameter of your tap and drill a hole a scosh bigger than that?

 

[ltlvt]

Can you measure the root diameter of your tap and drill a hole a scosh bigger than that?

I don't have any thread measuring wires.

 

[Chipper5783]

Wires are for if you are measuring the pitch diameter of a V type thread. Acme threads have a flat top, flat bottom. In your case the major diameter is 0.625”. Use a narrow measuring tool (blade mike, or probably the narrow jaws of most any calipers) measure from the crest to a valley, subtract that from the major diameter = thread depth relative to the center line. Then take major diameter - 2x the thread depth, there is your minor diameter. The tap drill is a “scosh” larger than the minor diameter.