|
Posted by Proctologically Violated©® on July 5, 2009, 10:24 am
Please log in for more thread options
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
trouble.
The hole is a clearance hole for 5/16 threads, but a semi-tight clearance
hole.
I am hoping 8 plates would be OK, with a "regular" drill, either 118 or 135
deg.
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.
--
Mr. PV'd
Mae West (yer fav CongressShill) to the Gangster (yer fav Lobbyist):
Hey, Big Boy, is that a wad (of cash) in yer pocket, or are you just
glad to see me??
Experiment on Homo Sapiens -- CEOs, Lawyers, and Politicians, in
particular.
Spare the animals.
Click here every day to feed an animal that needs you today.
www.theanimalrescuesite.com/
|
|
Posted by Garlicdude on July 5, 2009, 10:39 am
Please log in for more thread options Proctologically Violated©® wrote:
> 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
> trouble.
> The hole is a clearance hole for 5/16 threads, but a semi-tight clearance
> hole.
>
> I am hoping 8 plates would be OK, with a "regular" drill, either 118 or 135
> deg.
> 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.
>
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
--
Regards,
Steve Saling
aka The Garlic Dude ©
Gilroy, CA
The Garlic Capital of The World
http://tinyurl.com/2avg58
|
|
Posted by Proctologically Violated©® on July 5, 2009, 11:13 am
Please log in for more thread options
> Proctologically Violated©® wrote:
>> 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 trouble.
>> The hole is a clearance hole for 5/16 threads, but a semi-tight clearance
>> hole.
>>
>> I am hoping 8 plates would be OK, with a "regular" drill, either 118 or
>> 135 deg.
>> 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.
>>
>
>
> 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!
Don't worry -- the only thing parabolic on those Costco drills is their
wobble.
--
Mr. PV'd
Mae West (yer fav CongressShill) to the Gangster (yer fav Lobbyist):
Hey, Big Boy, is that a wad (of cash) in yer pocket, or are you just
glad to see me??
Experiment on Homo Sapiens -- CEOs, Lawyers, and Politicians, in
particular.
Spare the animals.
Click here every day to feed an animal that needs you today.
www.theanimalrescuesite.com/
>
> Best,
> Steve
>
> --
>
>
> Regards,
> Steve Saling
> aka The Garlic Dude ©
> Gilroy, CA
> The Garlic Capital of The World
>
> http://tinyurl.com/2avg58
|
|
Posted by RoyJ on July 5, 2009, 12:54 pm
Please log in for more thread options 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:
> 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
> trouble.
> The hole is a clearance hole for 5/16 threads, but a semi-tight clearance
> hole.
>
> I am hoping 8 plates would be OK, with a "regular" drill, either 118 or 135
> deg.
> 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.
>
|
|
Posted by Kirk Gordon on July 5, 2009, 9:02 pm
Please log in for more thread options Proctologically Violated©® wrote:
> 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
> trouble.
> The hole is a clearance hole for 5/16 threads, but a semi-tight clearance
> hole.
>
> I am hoping 8 plates would be OK, with a "regular" drill, either 118 or 135
> deg.
> 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.
<putting on my teacher's hat and firing up the verbositizer...>
Drills drift with depth when the axial thrust is large enough to:
A. Cause the drill to flex
B. Defy correction by the balance between the opposed radial forces
from the cutting edges.
C. Both of the above
Try this for a test. Put a small jobbers length drill (1/8 diameter
or less) in a drill press. One of your Costco specials will work just
fine. Start it cutting on something sorta tough, probably not aluminum.
After it gets started, gradually feed it harder and harder, and watch
it carefully. As the feed pressure increases, the drill will flex,
taking on the shape of a vertical jump rope. If you could freeze it in
that state and examine it carefully, you'd see that the jump rope curve
extends all the way to the point of the drill. This means that the
point is no longer pointing along the same centerline as your drill
press spindle. It's now pointed into the work at an angle, which is
determined by the severity of the jump rope effect.
For a while, a drill in this state will scrape and claw and drill an
oversize, bell-mouthed hole. After a few revs, though, being that it's
a drill, it'll figure out how to start drilling like it (sorta) should -
exept that it's still pointed into the work at an angle. So, it'll
drill at an angle. Often, it'll drill at an angle that continues to
increase as it goes deeper into the work. That's because, once it finds
a way to start drilling, the jump-rope effect gets compounded by the new
angle of attack. Things just get worse and worse. I've seen small
drills cut sideways by as much as a whole diameter, when drilling only a
few diameters deep, even though they were held in decent spindles, and
didn't have any serious runout problems till they were flexed by
excessive infeed pressure.
Normally, a good grind on the drill will keep the radial forces
balanced, and will try to correct for most of the above. But the
possible correction is limited, and is easily overwhelmed by infeed
pressure and drill flexibility.
There are two possible solutions. One, use a drill with a properly
split point. This will have cutting edges that go almost all the way to
center, and will have very little chissel point. It's the chisel that
requires a lot of axial thrust, since it's just squishing and squeezing
metal out of its way, and can't really cut like a real cutting edge.
Cutting edges themselves need torque; but very little infeed force,
unless they're really dull. Get rid of the chisel, and you get rid of
the thrust problem. You can feed faster with a split point, and still
not flex the drill. Which means you'll have an easier time drilling
straight holes instead of crooked or curved ones.
Second solution should be obvious. Use carbide. It's much more
rigid, and won't flex like HSS. Simple.
Apply both of the above solutions at once, and you should get
straight holes easy.
With regard to stacking plates, there can be some problems. When
you start drilling a hole, you've got the point of the drill, center
only, pushing on the work. It's the center that does the most pushing,
even on split point drills. As the drill goes deeper, you're using both
the point and the cutting edges, creating maximum push. Whatever force
it takes to drill well will try to deflect the workpiece, unless the
work itself is very rigid or very well supported.
Suppose, just for the sake of argument, that the aluminum plates
you're drilling are able to flex a little bit - maybe just .005" when
the drill is pushing to the max. So you start drilling, with a nicely
chosen feedrate of, say, .010 per rev. And the work deflects a bit, and
then resists, and drill goes fine - right up until the point breaks
through the other side of the plate. Then, all of a sudden, the biggest
part of all the pushing force is gone, and all that's left in the plate
are the drill's cutting edges, which don't push all that hard. In fact,
they can actually pull at the work instead of pushing it, just because
of the way they're shaped. So, at the instant the point breaks through,
your plate goes instantly from being deflected .005 away from the drill
to being back at flat and normal, or maybe even being pulled toward the
drill a little bit. What started out as a nice neat .010 per rev
feedrate suddenly becomes .015 per rev, or more. Bad news. The drill
bites too hard, probably pulls the plate even farther toward the
spindle, which increases the feedrate even more, and so on, until you
either break the drill, or decide to turn down your feedrates so they're
way less than optimal during most of the cut, just to be tolerable when
the drill breaks through.
Now, take all of that and stack the plates 4 or 6 deep, so the total
possible deflection is much bigger, and the drill has to do 4 or 6
breakthroughs during every cycle. It gets real messy in a big hurry.
If you want to test this, just go back to the drill press you used
earlier, put a decent size drill in the chuck, and drill through a test
plate. When you get to where the drill is just about to break through,
you'll probably instinctively back off the feed pressure and grab
tighter with the hand that's holding the work. That's because you know
that the work is going to jump, and buck, and try to screw itself right
up the drill bit, if you're not real careful. Same thing happens in a
CNC machine, even if the clamping and smooth infeed help reduce it a bit.
So, you'll need to support your plates underneath. Don't bridge
them across blocks or parallels, but support them everywhere with a
sacrificial plate underneath. That prevents downward deflection. Then,
find a good way to clamp everywhere over the tops of the plates, so they
can't bow upward when the drill's edges tug at them. A sacrificial
plate on top, with pre-drilled holes, works best, as long as it's
substantial and rigid enough to truly hold the plates down and keep them
flat.
If you support the plates properly, and pin them down adequately,
then drilling a stack of plates shouldn't be any different than drilling
through a thick piece of solid. If you don't contain them well, and use
the right kind of drill, you're gonna need a lot of drills, and probably
some good drugs or alchohol to get you through the day.
<verbositizer to idle, teacher's hat back on the hatrack...>
KG
|
| Similar Threads | Posted | | Drill Sharpeners | July 2, 2009, 10:21 pm |
| Re: Everybody else can drill the holes .... | September 4, 2009, 4:13 pm |
| Re: Everybody else can drill the holes .... | September 4, 2009, 4:35 pm |
| Anyone need Drill chucks? | January 22, 2010, 7:20 am |
| Drill chucks | January 22, 2010, 8:38 pm |
| Re: Drill speeds & feeds | April 24, 2006, 5:41 pm |
| Drill speeder for CNC lathe | May 26, 2006, 8:07 pm |
| what is the difference between VMC and drill tap center????? | June 2, 2006, 1:01 pm |
| Drill chuck thread | August 3, 2006, 7:05 am |
| Spot drill redux | September 3, 2008, 9:43 pm |
|
|
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap
>
> 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
> trouble.
> The hole is a clearance hole for 5/16 threads, but a semi-tight clearance
> hole.
>
> I am hoping 8 plates would be OK, with a "regular" drill, either 118 or 135
> deg.
> 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.
>