Drill Drift

Awl --
How does a drill drift in x,y, with drill depth?
I would like to drill four 5/16 holes through a series of 1/4" alum plates
(actually wide 6061 or 6063 bar), where the holes must line up later (within
.001-.005), and wonder how deep I can stack these plates and stay out of
The hole is a clearance hole for 5/16 threads, but a semi-tight clearance
I am hoping 8 plates would be OK, with a "regular" drill, either 118 or 135
If not 8 plates, about how many?
How does drift vary with speed, feed, pecks, drill point geometry, etc?
Best drill? I will of course spot the hole.
On a fadal, altho I have considered a P-pushing fixture on a drill press or
BP to do this, as well.
On the fadal, I suppose I could come back with a long 5/16 em, which would
increase the clearance a bit, but would improve alignment. But I'm hoping
to not have to do this.
Reply to
Proctologically Violated©®
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PV, I'd use a 5/16 parabolic flute, split point drill. I wouldn't think you would have problems. I drill a 5/32 hole in a 10.00" long alum piece 5.20" deep from both ends using a parabolic flute drill. The worst mismatch is around .010 I would guess.
I use a Titex drill for this, none of those Costco Worksmith drills!
Best, Steve
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Your drift is going to be mostly a factor of the quality of your drill bits and the tightness of your drill spindle. An import special drill bit in a $69 Harbor Freight 5 speed drill press is going to be all over the map. Same operation in a high speed CNC spindle with stub length drill might be 10x tighter tolerance.
Proctologically Violated©® wrote:
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have you considered one of those insert type drills ? they had them at my last place and they went nice and fast into tool steel, and dead accurate too. when the insert wore, replace and keep on going. highly recommeneded.
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You need to be using a quality drill with a good point and relief, but I have found the most important point is starting each hole with a center drill. If a jobber length drill drifts off even a couple of thousandths, you are no longer in line with the spindle and will be forcing the error to multiply as you drill.
I have drilled 5/16" holes through aluminum castings as much as three inches with no more than .002 drift.
Of course, having your spindle perfectly square with the work piece is usually very important as well, depending on the required accuracy with the outside edges of the work piece.
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That was a very interesting read. Since I just fix the machines and you program and run them, you send in the tuition check. I'll just thank Kirk for the lesson ;)
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