So I’ve come up with another plan. Correct me if this is a bad idea, but what I hope to do is to drill out the hole completely and then re-thread it. I’m going to get a bit the size of the replacement eye bolt, drill it out completely (threads and all) and then re-tap with a bigger square bottom tap. Then I’ll buy a replacement eyebolt rated it for some ridiculous high weight and use it instead of the eyebolt I purchased.
Note that you can find a tap chart anywhere on the web by searching the key phrase ” tap size chart”. I use this one from http://www.shender4.com/. Here is an excerpt:
Here are the specifics:
My new keel eyebolt is 1/2 inch. It is a 13 thread. This is highlighted in yellow on the chart. The orange highlight of 27/64 is the matching drill that you can buy with it from the well-known Catalina parts supply company . Am I reading this wrong, or since this is an iron core, should the drill size sold be 29/64, not 27/64?
It doesn’t matter for my keel. Given that the existing hole is 1/2 inch size my new drill size for iron should be slightly bigger. I picked 33/64 , which is highlighted in pink. I will also need a tap sized for a 33/64 hole with a 9/16-12 thread.
A tools/parts supply website, mcMaster-Carr sells taps and has a great website to help you find out which one you need. The problem is, taps don’t come in the sizes I just calculated. I can’t get a 9/16-12 sized for 33/64, but I can get a 9/16-18 with a 33/64 hole. The chart says the hole should be 17/32 for iron. Does making the hole 1/64 less matter? Seems like they wouldn’t put it in the chart if it didn’t matter.
Assuming that will work, now I need a 9/16 eye bolt with a 18 thread. Let’s head back to McMaster-carr, they also sell eyebolts in all sizes.
Working my way through the different options I found a 9/16 – 18 Zinc plated steel eyebolt (with shoulder) rated for up to 5,000 lbs. That should handle my little 550 pound keel. (Note that it can still lift 1,000 lbs even when the lift angle is 45 degress) Note also that the shank length is 1 5/8. The eyebolt that I bought has a shank length of only 1″.
So now all I have left is to drill a new hole and tap new threads.
One other thing. The site says “All taps are for use on most metals and plastics. Also known as hand taps, use them with a tap wrench”. I don’t have a tap wrench. They sell a tap wrench for a tap this size (over 1/2″) for $44. All this for a one time use. Can these be used with a socket or wrench? The welder used a metric socket on his tap, but the socket stripped out before he finished, so that’s a strike against it. Any alternatives?
On more other thing. Once I get the drill bit , is it going to be possible to drill into the iron? Do I need a special drill? How hard is this going to be? I didn’t post the drill bit search result, but they have those too ($22 each). Should I get two? Will a single one do the job?
What do you think?