How large a bit before needing to predrill?

Jake2465

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About what size would it become necessary or at least advisable to predrill with a smaller bit? I have a little project that needs a 5/16" hole shot through about .750" aluminum plate. I would like to just pop one of my HSS screw machine bits in the collet and do the entire hole with it and forgo the predrill.
 
I'm curious to see the answers. I almost always predrill. Less work for the final drill.
R
 
I'm curious to see the answers. I almost always predrill. Less work for the final drill.
R

I am curious to see the answers, too :eek 2:. I almost never predrill, lol.
 
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On a BP, I have drilled 3/4" with out pre drilling.
 
I have found over the years that predrilling, especially in steel, makes the larger bits last longer.
Mark
 
In aluminum I never pre drill and Have drilled 2" holes. In soft metals and plastic pre drilling or step drilling can lead to bits grabbing.
 
I don't know about you guys but I don't predrill unless I go above 1/2" but that's when I hold the drill in a drill chuck. On my lathe, I use morse taper drills and can go up to almost an inch without predrilling. Drilling a hole with the main drill is always more accurate for me and prevents any grabbing.

Jake, a 5/16" hole in aluminum without predrilling is no problem - just spot it and drill it.
 
I will go along with mikey on this one since it is aluminum and a 5/16 bit. I predrill most holes in steel and above 1/4-5/16 in aluminum. It's more of a habit than anything.
Have a good day
Ray
 
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