A quick project using A2 tool steel-lessons learned

Janderso

Jeff Anderson
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Hi gang,
One of the guys at work asked if I could help repair one of his 3 jaw pullers. The job includes sourcing better quality steel (A2 tool steel) and duplicating 4 pieces and drilling 8 holes, de-burr etc. then a home hardening/tempering effort.
I was drilling the 3rd hole, all was going swimmingly, when all of a sudden the drill bit stopped drilling.
I must have created too much heat.
These are good quality drill bits says I,
I grabbed another bit, slowed down, used more cutting fluid and finished the remaining holes without any more issues.
Inspecting the damaged drill bit, it looks and feels like material was welded on to the bit. There was some pretty blue coloring as well.
I'll let you know how the rest of the operation goes.
I really don't have the time for this but, I just couldn't say no when an opportunity to work with something new came along.
 
Are you using a coated drill? Cobalt? Carbide? If your problem isn't heat alone, it may be cementing/fouling. Your untreated A2 is martensitic, and your drill bit is probably austinitic steel. Both your base steel and probably your bit are chromium-molybdenum alloys. When the bit gets too hot, right at the point of action martensite converts to austinite, and fusion welding/galling can occur. What I'm trying to say is heat control, pecking, and irrigating may be called for. Choosing a bit that is dissimilar from your base metal would also prevent this. Probably a good candidate for solid carbide drills, because cobalt steel is too similar to A2, minus the cobalt. Carbide gives you heat resistance and dissimilarity. That's worth two cents and not a penny more. Just more factors to consider while you're winding down for the evening.
 
The rule with work hardening steels is to keep the drill cutting real chips, never stop feeding and let it rub, not even for half a second. Be ready at the beginning of the cut to make the whole cut non stop if possible. If you do need to stop for some reason like the drill going dull, make the transition from cutting to backing out as early and instantaneously as possible. When you start cutting again, do it all at once, no sneaking up on the drill pressure. I have had really good luck with those techniques, after ruining work earlier by not being assertive enough. Coolant or plenty of a really good cutting oil helps a lot. Show that steel who's boss!
 
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The rule with work hardening steels is to keep the drill cutting real chips, never stop feeding and let it rub, not even for half a second. Be ready at the beginning of the cut to make the whole cut non stop if possible. If you do need to stop for some reason like the drill going dull, make the transition from cutting to backing out as early and instantaneously as possible. When you start cutting again, do it all at once, no sneaking up on the drill pressure. I have had really good luck with those techniques, after ruining work earlier by not being assertive enough. Coolant or plenty of a really good cutting oil helps a lot. Show that steel who's boss!
All good advice, Bob.
 
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