hi guys ,
was wondering what % thread engagement do you all drill when working on soft metals such as aluminium and ferrous metal such as stainless steel etc. Usually on tap drill size chart , the recommended drill size is based on 75% thread engagement , but I’ve read online , some people uses as little as 50% for hard materials. any recommended range to look out for when tapping hard materials as well as soft materials?
thanks
bryan
Hi @bryanang,
I do a lot of work with 316 stainless steel and I always go for 70% thread engagement.
But sometimes if I need to go 3 to 4 times the diameter of the tap deep I drop it down to either 60 - 65% thread engagement.
Hope this helps
I found that if you are working with materials that don’t work harden (aluminum, 300 series stainless, brass etc) if you form tap you will have an easier time. It will produce stronger threads, longer tool life and you won’t have the chip problems in blind holes. Just keep in mind that it requires a larger tap drill. For cut taps on harder to cut materials if tool breakage is a problem go with 60% thread engagement. I have never had a problem with tread strength.