Reply to "Snapped bolt in block - how deep can this be drilled?"

...Now Your going to hear from a Professional Machinist; if You Care to Listen! DO NOT use a 'EZ-Out'(Very Very HARD!)if and when it Snaps off, Your NightMare has Just Begun! As well as making a good living Machining Parts for, Assembling, and Calibrating in; 'Power Transmission' Gearboxes, from 500 HP up to 17,000 HP; a very small part of My work has been to fix the blunders of other 'Mechanics' who have tried and failed to remove a 'Broken Bolt'. I.E. FIRST Remove the Hardened EZ-Out AND then the Broken Bolt! There is Only ONE way to Remove a EZ-Out! Clamp the 'Part' down on the Milling Table, find the 'Dead Center' and Mill the EZ-Out, Out, with a 'Carbide End Mill'! The Carbide Endmill can be used only once! Because as It 'Cuts'(actually Wares away)the Very Hard Steel, the Carbide Mill itself Desintigrates!

NOW! Your Bolt problem stems from the use of a Bolt that was Too long; when screwed in it 'Bottomed Out' Before Clamping, so then more force was used, snapping off the Bolt where the shoulder meets the threads!

To remove the Bolt: This will be difficult because You will have to use a 'Hand-Held' Drill motor. The Bolt is a 5/16-18. The 'Tap Drill' for it is an 'F' drill, Decimal=.257" If You do not have an F drill, You may use a 1/4". This is the largest drill You will use and NOT harm the Threads. Yes! Get the Top of the Broken Bolt as Flat as You can (a 1/4" end Mill in a drill Motor will do the job enough to get a centerpunch centered). You won't need Carbide Because the Bolt is Soft. Then, Start with a 1/8" Drill and drill all the way through! Will be 1-1/2" to as deep as 2.0". Be sure to use Oil to keep the Drill Bit from Burning up!! Move up to slightly larger drills, and finish with the 'F' drill. Now Your at the 'Root' Diameter of the 5/16-18 Thread, and the 'Old' Bolt Threads are all that remain. All You do now is use a 'T' Handle Tap Wrench with a 5/16-18 TAP. Now Try to 'Retap' the threads! You'll most likely get it in a couple of turns and then the Tap will JAM!! This IS What we want! Now Unscrew the Tap and 'if 'it's' Cooperating', the Old Threads will come out with the Tap being unscrewed! May take a few times of tapping in and out! WD-40 Helps! When All of the Debris is removed; use some oil and clean-up the threads by running the Tap Down-in a couple more times. This should leave You a Clean Bore with Fine Original threads! If the Remaining Threads are too 'Buggered-Up' to be of use...Your last resort would be; to drill and tap for the 'Next Larger' Bolt! That would be a 3/8-16, TapDrill 5/16". Ofcourse; 'That' Hole in the 'Mounted Part' will have to be drilled to match 3/8". Good-Luck with it!!

Marlin