Originally Posted by
sweeks
A few years ago I noticed cracks propagating out from the stress relief hole. Rather than make a hole large enough to include the cracks, I drilled "crack-stop" holes at the ends of the cracks. There has been no further progression of the cracks. It's not pretty, but it works. I don't understand why the manufacturers don't make the holes bigger to start with... it's surely not "rocket science"!
Nicely done. I especially like the fact that you've chamfered the holes and left them with a good finish to minimize stress risers.
If may be of interest to some that in auto racing, when weight reducing holes or holes for rivets are drilled in small parts, chamfering is indicated. One technique to reduce stress risers in that hole is to put a ball bearing larger than the hole on a solid surface, then put the hole in the part on top of the bearing, and put another bearing on top of that. Then you whack the top bearing with a hammer! Hones are sometimes used to smooth the chamfer, too.