16ga.com ~ View topic

Joined: 09 Feb 2015 Posts: 909

I'm not a machinist. Can anyone give me a answ,ere. Thanks Bill

Joined: 04 Sep 2024 Posts: 7 Location: Pennsylvania

According to my chart 10-24 gets a #20 for steel and a #25 for aluminum, brass etc.

Joined: 09 Dec 2012 Posts: 839

Every chart I reference says #25. Except for this one, which lists the nbr 20 for only 50% of the thread. When I worked in machine shops, I never heard of cutting a 50% thread

https://littlemachineshop.com/reference/tapdrill.php?srsltid=AfmBOorxspZ-sTW_6g8Xrmem9YQzV0qczILS0A0zy4q1T1-oNFFS0ROA

Do a google search on

10-24 tap drill size

it will return lots of results, such as:

https://www.lincolnmachine.com/tap_drill_chart.html

https://boltdepot.com/Fastener-Information/US-Tap-Drill-Size?srsltid=AfmBOoofELPvWKi0u7MwYaB9eK-h-l4sqwGv5frAOFz6Q1vzpRCw552I

https://www.victornet.com/reference/Tap_Drill.html

https://www.americanfastener.com/tap-and-drill-size-chart/

and so on

here is a reasonable discussion regarding it.

for all practical purposes, strength of the tapped threads, etc, you want 75%, which is pretty much industry practice, often times, a lesser percentage is used to increase production speed as you can machine tap faster with a lesser percentage.

https://www.gwstoolgroup.com/tapping-tip-dont-let-percent-of-thread-derail-your-part/

DO NOT FORGET to not go the whole way without breaking the chip. that means a turn or two, back the tap up a turn and continue the pattern. if you don't you get one continuous chip per cutting edge and it can tangle up, jam and cause the tap to break. always always use cutting oil, any oil will work, just use it

If you are working on a project and you have some buggered threads but don't have a tap, you can take a bolt and using a file or a dremel, etc cut flutes in the end of the bolt in the same manner as a tap.

I have fixed lots of buggered threads this way, cleaned out dirty ones, etc

Joined: 09 Dec 2012 Posts: 839

also if you have a way to support the tap handle, there will be less chance of breakage or getting the hole tapped crooked.

here is a good video showing one method

https://www.youtube.com/watch?v=oRv6UXpVwrE

Member Joined: 06 Oct 2007 Posts: 2504 Location: West MI

All great info so far. Will add...

If you are working on a project and you have some buggered threads but don't have a tap, you can take a bolt and using a file or a dremel, etc cut flutes in the end of the bolt in the same manner as a tap.

if using this method, don't use a grade 2 or 5 (common zinc plated stuff on hardware store shelves that isn't what they used to be) or below. Use Socket Head Cap OR Grade 8 (or above) screws/bolts, they are far and away harder/tougher than the lower grades. 1 turn in 1/2 turn out w/oil, babysteps.

Joined: 09 Feb 2015 Posts: 909

Joined: 09 Aug 2007 Posts: 503 Location: WI

For 10-24 use a #25 drill (0.1495) or a 3.8mm