Re: Corroded Bolts in Aluminum
oh my...corroded bolts, huh? Yea, these can be quite the hassle. Getting enough heat on them, til they glow red, is the best method. There are times though, that they break, reguardless. If you end up breaking them, then it's good to have some sort of centering jig, that fits snugly over the bolt and a small center hole to get the drill bit perfectly centered. It's too easy to get off center and have a drill bit walk on you. Gawd...I hate that.
I'm an amateur machinist but have learned the basics to avoid that.
Use a punch if at all possible, then you need a machinist's centering drill bit , they are designed for vertical mills. They always move the centerline of the drill bit towards the shank by design. Look like this,
http://www.drillspot.com/products/454957/Keo_30251_Spotting_Centering_Drill
You can't actually drill hole with it but it gives a 1/8" start. This bit will not wander around if properly started (punch). If used in a drill press or vert mill it will always follow the centerline of the spindle. So a steady hand(2 hands) is good. Trying to drill deeper than the shank width of the drill results in snapping the tip off in the metal, thats kinda bad.
Drills wander because the drill shaft is slim and bends under load, a center drill shaft is magnitudes thicker than the cutting tip.
Clean machining is all about rigidity.
Getting snapped bolts out is a snap with a low power welder.
If building up a weld in alum special care is needed to protect the alum, its simple with cast iron blocks.
Alum will distort or just melt if too aggresive an approach is used, let cool between welds, tap with hammer, remove slag and keep going. Most guys just grab the weld with locking pliers and many times the bolt is already loose from the heat anyway.
Steel bolts into alum blocks is ez, the corrosion is the elec resistence which the weld heat burns into ash, the bolt can often be removed by hand, no tool required. I use a mig, I talked to one guy who said he does half a doz engine blocks in 30 minutes and gets em all.
Says the ez outs are best if the bolt is already loose because torque is reduced as the ez out has to be smaller than the bolt dia anyway.