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So I have a Burnham 11 section cast iron sectional boiler thats a bolt has snapped of for the rear sight glass. Currently being held by one bolt which will probaly also snap off. (We are replacing the sight glass and sight glass gaskets. Any tips or hints on drilling out and retapping the threads. Never done it before, Seems it could be one of those real easy things or a long day. Thanks guys.
Be sure to use a center punch on the snapped off portion of the bolt. Be sure that you are as close to center as possible. EZ out the snapped off bolt. Am not familiar with the sight glass bolts on a Burnham, but , one thing that you dont want to do is drill too deep. It may breech the boiler. Again I am not familiar with the configuration, so this may or may not be a concern. DO NOT break off the EZ out. If it feels like it is going to snap, STOP. Remove EZ out and drill hole to the next larger size and re-tap hole to that size. Take your time and good luck. Oh, and use cutting oil to make tapping easier.
If your talkin' bout removing a bolt... left hand drills and screw extractors { easy outs } do sometimes work. Striaght holes well centered are the ticket. Another way many of us use is to weld a grade 8 or better bolt to whats left. The bigger bolt the better. You said it was C.I., heat it up cherry hot around 1/3 of the loser bolt. Slight impact action and she's comin' out...
Good Luck........ stay safe out there bros..
AND MERRY CHRISTMAS
I would skip the EZ-outs altogether. They always break, and if you do break one off, you had better have a dremel tool with some tungsten carbide cutters. If you have enough bolt to grab onto with some vise-grips, heat the bolt up, hit it with a hammer a few times and back it out while it's hot. If you don't have enough, grind the bolt flush with the flange, use a center punch, drill it out and re-tap it. Use cobalt drill bits. You can make a bottom tap out of a regular tap if you need to by just grinding the leading 1/2" of the tap off.
Good luck! Make sure you know what you're doing. Have patience and look it over thoroughly before deciding on the best course of action. Number one priority should be trying to preserve the bolt stud sticking out so you can use that.