Machinist's Minute: Do you need to drill out cracks?

It won't matter for cast iron!

[ajwunde]

Mechanical engineer here. A drilled hole will have a much lower stress concentration factor (K) than a sharp edge of a crack. Whether or not this factor change is enough to prevent continued cracking is dependent on material, conditions, loading of the part, and radius of the hole. In general it is a pretty safe bet that a small drilled hole is better than a crack.

[bryanfox]

When i was getting my a and p license we were taught to do this in every material when making a repair. Its cool to hear another perspective. That you for the history lesson.

[petergriffin]

Whoever gets to be an apprentice under this man is truly blessed. As a milwright of 10 years, I'd take an apprenticeship under this guy in the drop of a hat. Where is this shop located? Michigan by chance?

[jmfarms]

I have never repaired steel cracks by drilling at the end of the cracks. Mainly because the crack runs further than what is usually seen with the eyes. I usually grind out the crack and taper the groove several inches from where the crack appears to end.
I have actually rewelded cracks that were repaired by someone else who drilled at what they thought was the end of the crack. But they didn't drill far enough and the crack just continued on the other side of where they drilled.

[CJ-ntcs]

When it comes to aerospace manufacturing radius's are extremely critical.

[garrisoncase]

Dang it Howee you tell the top secret stuff!

[lorenzoghinelli]

That trick is also used by aereo-mechanics to repair broken plexiglass windows on small aircraft.

[davetunbridge]

You have to remember when you drill a hole you are basically tearing the material leaving stress fractures all around the hole. To prevent further cracking you need to ream the hole and cold hole work it, split sleeve that is expanded minutely to create concentric rings around it bit like dropping a stone in a pond. The rings prevent the crack from spreading. Did this a lot on aircraft.

[johnsjunkyard]

I often wondered about the validity of drilling stop holes in steel parts and just how important it was. Not bad practice but is it really necessary... It makes much more sense in cast iron though, (and even wrought iron I'd guess).

[steven]

Or drill out when you are welding aluminum

[northmanlogging]

Drilling cracks is a classic example of well this is what I learned so I do it regardless of why, and never question grampa...

Its why I call things like this "grampa tales" grampappy did it like this, and daddy did it like this and I"m too stupid to question what or why, so how dare you question me!
me... Grampappy died before I was born, and dad wasn't around.... so I question EVERYTHING

[readplanet]

When I was in college, the cast iron drilling method was what I was taught also. Good videos. Have A Productive Day! 🛠️🗜️🧰