Keel bolt #3 - Next steps
I gave more thoughts to the idea of banging down remainings of the keel bolt and decided to try something else. After all - smashing rusted iron into oak might lead to more problems. And I can always resolve to this once I exhaust all other, more civilised, methods.
So - the problem looks like on below simulation:
Simplified model of keel bolts accessible from the main cabin. There are more of them but this year I intend to replace 4 main bolts.
Two front bolts are removed. Remaining bolts, including one which got stucked, go through thick layer of deadwood (oak). It is this wood which most probably caused bolts to rust entirely, yielding failure at removal.
I imagine that remaining part of bolt #3 looks like thin iron rod surrounded by brittle iron-oxide which expanded into oak around, thus sitting very tight.
The plan is to drill out the core (iron) with thin drill and then re-drill the whole sandwich with appropriate sized drill bit.
Challenges:
get the pilot hole straight through iron core, without it wandering into oak
get appropriate sized drill bits to go through circa 85cm sandwich
For the first problem I intend to use steel pipe as a guide.
I’ve found very nice, thick-walled stainless pipe of external diameter matching exactly nominal hole diameter: 3/4 inch. Internal pipe’s diameter is 14,5mm so I need 14mm drill bit which will slide into the pipe and use it as guidance for first few centimeters of drilling. After that it should be less tricky.
Second problem can be addressed in 2 ways: either get a small bit and weld it to a pipe or rod of appropriate diameter or try to find ready bit which is long enough. The second way is obviously better - the drill will be straight and equally strong along the whole body. The last thing I want is a broken drill of hardened steel sitting in this hole if welded joint fails.
Kell advised to check Flinks Järn. Indeed they have long drills but unfortunately they sell stuff only to companies, not private persons like me. Too bad.
Luckily my local hardware shops: Roslags Järn and Swedol have metal drills (Milwaukee and Bosch) of appropriate diameter for pilot hole. Length is little too short - 600mm - but… “beggars can’t be chosers” so I bought these tools.
I’m not worried that battery-drill will not be up to the job: this thing has more torque than my sledgehammer or my old electric drill.
I will start with 14mm bit guided in a pipe. If that will be too hard I will go smaller - 12mm bit - with some nylon or teflon bushings to keep it centered in the pipe. Hopefully this will make a lengthy pilot hole for next step: 18mm drill. The remaining part of keel bolt, as drills will not reach all the way to iron ballast, will have to be banged down with heavy hammer or sledgehammer with concrete drill. And of course lots of heat!
Now: the problem is that my boat, being built in Sweden in 50’s, has most metal fastenings made in ANSI standard, not metric. Hence - the awkward 19mm diameter hole and bolts threaded 5/8 UNC. Metric drills do not cover this dimension, instead there is 18 and 20mm step. I figure that after drilling 18mm pilot hole I can smash down remaining 1mm of iron-oxide while driving new keel bolt into the hole.
In case that does not work I can re-drill the hole into 20mm diameter but that will also require drilling in cast iron, getting new thicker bolt, different nut size and thread on this bolt.
Not perfect - I’ll need another set of tools to remove it in 10 years, for inspection or replacement. Well, that is a backup solution for now.
Another way is to use this steel pipe to clean the oxide debris to required diameter. Either I will just hammer down the pipe, having sharpened bottom edge, or I will form this edge into circular saw, harden it with quenching and attach handle on top to spin the pipe as a hand drill.
Should that not work - I will use concrete drill (they come in 1m size or longer) with pneumatic sledge hammer. Last resort, brutal but my sledgehammer is gathering dust so some exercise would be perfect.
These are the ideas for now. They need to wait until after Christmas so maybe I will figure out yet another way, like - pouring phosphoric acid into this damn hole???
Good thread on WoddenBoatForum about different ways: http://forum.woodenboat.com/showthread.php?138318-Removing-iron-Keel-bolts/page2
Anyway - don’t wait with checking or replacing old bolts. Definitely not for 60 years. Removal of healthy bolts is easy and well worth the effort. Otherwise you get yourself into my situation.
Thanks to previous owners of Meritaten…