Deep Drilling, Straight, Long Reach, Aluminum

I need to drill some holes in 6061 aluminum. No problem. I have drilled a lot of holes in 6061 aluminum.
The need to be deep holes. I've technically drilled deep holes in
aluminum. Just maybe not this deep. Deep relative to drill diameter.
They need to be pretty straight.
This is for a 1/4" pivot/hinge pin. The hole can be large and sloppy (moderately). 5/16 might be to much, but an H or I drill might be tolerable. I might even be able to get away with a J drill. The goal is that there is enough room for the pin to be on center within a few thousandths somewhere in the open space of the hole.
On tiny (1/8 and under) deep holes (relative to the drill diameter) I've just bought carbide drills from Precise Bits. Stubby little carbide drills do drill pretty straight. This isn't like that.
I have to reach past almost two inches of obstruction on one side that prevents the chuck from being lowered beyond that point and then drill through 2 inches of metal for the pivot hole.
I did it with the prototype by spot drilling with an over extended spot drill, drilling a little over half way with a jobber drill, flipping the part (same issue on the other side), and repeating that process. The holes were pretty close, and I sort of wallowed out the little bit of ridge (not to bad) by forcing a drill through the hole off the mill by hand. (Cordless drill).
It was really sketchy, but it just barely fell within spec. Now I need to make 51 pieces like this. I can see it going badly after I get a little tired from making these parts for a few days. The drilling is done as a 3rd and 4th setup after machining on two other faces of the work piece. I have to do the drilling (I think) as two setups because the other side is two such pivot bosses that need to be drilled, and they are 2.005 inches apart. Drilling them from one side would be over 4.25 inches of reach not counting break through. That's just to much for me to have any confidence in meeting my admittedly rather sloppy spec.
I have been looking at parabolic drills, but other than not needing to peck as often due to their ability to clear chips I don't see any benefit for drilling "pretty straight" holes. Only thing I can see that would help with staying "pretty straight" is spot drilling for a good start and a carbide drill to follow.
Of course mounting has its issues as well. The part has an "ear" that is 1.5 (apx) x 2 x .05 that can be clamped in the vise. It does have one saving grace. There is a square perpendicular boss on the back of the part than can register for height and squareness (perpendicularity) on the top of the vise jaw. Once I have a process that works "good enough" I should be able to repeat from part to part fairly quickly.
http://yumabassman.com/forums-new/gallery/2_12_10_19_4_34_56.jpeg
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Some companies make deep hole drills see http://www.guhring.com
Note, a gun drill is the traditional method of drilling deep, straight holes but they are probably not what you want to use for your operation.
A solid carbide to start the hole and drill say 3/4 or 1 inch as a guide and than a long fluted drill to finish.
--
cheers,

John B.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 12 Oct 2019 16:36:42 -0700, Bob La Londe wrote:

...

...

...

...

...

I'd look at making a jig or fixture with drill jig bushings (like at <https://www.carrlane.com/en-us/product/drill-jig-bushings and <https://www.travers.com/drill-dig-bushings/c/299572/>) arranged in pairs, one guide near the edge of the part to constrain the shank of the bit, and another to constrain the tip of the bit. Some bushings taper slightly.
--
jiw

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"Bob La Londe" wrote in message

Besides mumbling something about drill bushings and a fixture to hold them and the workpiece, my real suggestion is to ask if there is any possibility you can talk the customer into milling out most of the material in the 2" portion? Make the one long ear into two short ears like on the other side. If this is just a slightly sloppy hinge pin hole, does it really need to be solid for that length? Being solid won't improve the alignment since that is set by the 2" width, not material in the middle.
--
Regards,
Carl Ijames
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 10/13/2019 8:49 AM, Carl wrote:















That is a perfectly valid option, and one I had considered. The problem really is that I sent the customer a prototype (2 actually linked together) that worked. Now its kind of hard for me to go back whining that its to hard. LOL.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Oct 13, 2019, Bob La Londe wrote

Is there any way to fixture this to a lathe faceplate, such that the desired drill centerline is on the lathe rotation axis? Spinning work, stationary drill, drill is compelled to follow the rotation axis. Start with a spotting drill (with long solid shaft), follow with parabolic drill. Use lots of coolant.
Failing that, make a fixture on the lathe to ensure that the drill bushings are colinear.
Joe Gwinn
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload


My old, worn lathe disproves that theory. Drill bits held in the tailstock most certainly can wobble, and the hole can drift off axis, as clearly shown by reversing a drilled bushing blank in the collet, inserting the drill bit in the hole and turning the spindle. I have to straighten the pilot hole with a boring bar and then drill to final size.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Oct 13, 2019, Jim Wilkins wrote

One can almost clamp the tailstock to calm the wiggle. The lateral offset may be off center as well. But these rears cause tapered holes. If the chuck jaws are off, and the workpiece is held at an angle to the rotation axis, you will get crooked holes. The classic way to test this is to center drill a piece of stock held in the chuck, and also turn the outside of the bar without disturbing the chuck, Inside and outside should be concentric, although there may be some taper, not necessarily parallel.
More generally, think of it this way. If one is drilling on a mill, the hole will be made wherever the drill is located when the quill is moved downward.
on or very close to the rotation axis, the drill bit will promptly snap right off.
Joe Gwinn
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload


One can almost clamp the tailstock to calm the wiggle. The lateral offset may be off center as well. But these rears cause tapered holes. If the chuck jaws are off, and the workpiece is held at an angle to the rotation axis, you will get crooked holes. The classic way to test this is to center drill a piece of stock held in the chuck, and also turn the outside of the bar without disturbing the chuck, Inside and outside should be concentric, although there may be some taper, not necessarily parallel.
More generally, think of it this way. If one is drilling on a mill, the hole will be made wherever the drill is located when the quill is moved downward. If one is drilling a rotating workpiece in a lathe, if the drill bit
on or very close to the rotation axis, the drill bit will promptly snap right off.
Joe Gwinn
======================Have you ever seen a drill bit walk in a circle around the intended hole location?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Oct 13, 2019, Jim Wilkins wrote


Yep, if one is slightly off center, but not so much that the drill bit snaps off immediately. This will yield a tapered hole on center. But the drill will nonetheless follow the rotation axis. If the starting dimple is on the rotation axis, the hole will not be tapered. This is the basic principle of the gun drill.
One way to get the dimple on axis even on a loose lathe is to hold a spotting drill in a boring-bar toolholder on the compound, with cutting edge of the tip on the side towards the operator, and move carriage such that the drill slightly off center to the operator side. The drill will now cut an accurately centered albeit slightly oversize dimple. Adjust tailstock so that a pointed rod held in its chuck is centered on the dimple, and then replace the rod with a pilot drill bit, and proceed.
use a pilot drill that provides ample clearance for the solid core of the endmill bit. Note that reground endmill bits will be undersize. Or, one can use a reamer. A piloted reamer is a standard way to ensure that the holes are co-linear despite the gap between separately-drilled sections.
Joe Gwinn
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 14 Oct 2019 09:40:35 -0400, Joseph Gwinn


The dominant characteristic of a gun drill is that it tries very hard to follow a straight line, regardless of where that line is pointed. It has no tendency to follow, or return to, the axis of rotation of a workpiece. The start of the hole is all-important, and is usually accomplished by careful alignment of the workpiece and a drill bushing, or by boring a starting hole equal to the gun drill's diameter.
--
Ned Simmons

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Oct 14, 2019, Ned Simmons wrote


I see the source of confusion. I should have mentioned that the term "gun drill" has come to mean two very different approaches to achieve very long and slender holes that are straight, as for a rifle barrel.
The traditional approach was to rotate the barrel in a lathe and use a long straight drill held stationary in the tailstock. Often, the lathe was purpose-built. This method is modernized and still widely used: .<
https://www.youtube.com/watch?v=B_SmN3xjgxQ

The other method is the rotating D-Bit on a perhaps hollow rod, where the workpiece is stationary and only the drill rotates - this is what you describe above, and others have explained.
The rotating workpiece approach was first, and people did use the D-bits as
got good enough for use on stationary workpieces as well. This is widely used for such things as coolant passages in heatsinks.
Joe Gwinn
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 15 Oct 2019 21:46:56 -0400, Joseph Gwinn



That video is of a BTA drill, despite the text on the page. The voice-over describes it as such. The tooling is is similar to a gun drill only in that the tool is guided on pads that follow the cutting edge(s). In a gun drill high pressure oil is pumped to the cutting edge thru the hollow drill shank and the oil and chips exit the hole thru a groove in the shank. A BTA drill turns that inside out -- the chips and oil are evacuated thru the drill shank.
What I described as gun drilling applies whether the workpiece is stationary or counter-rotating (I was not talking about D-bits). While the D-bit is likely the precursor to the gun drill, the difference between them is considerable.
The most accurate gun drilling on cylindrical workpieces is typically done on machines with a high-speed drill spindle and a slowly counter-rotating work drive.
In any case, none of the tools we're talking about -- gun drills, BTA drills, D-bits, or twist drills -- will self-correct to follow the axis of a workpiece, whether the work is rotating or not.
--
Ned Simmons

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Oct 15, 2019, Ned Simmons wrote


approaches

and you are talking about where we are.
Going back to the original question, if one sets things up correctly, with rotating work as stationary drill (of reasonable stiffness), the drill prefers to follow the rotation axis. As with everything, if one does not get the details reasonably correct, it will fail one way or another. There were many discussions of this on metalworking sites ten years ago. Joe Gwinn
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 16 Oct 2019 09:16:40 -0400, Joseph Gwinn




True, but that's a more modest claim than your contention: "Yep, if one is slightly off center, but not so much that the drill bit snaps off immediately. This will yield a tapered hole on center. But the drill will nonetheless follow the rotation axis."
--
Ned Simmons

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:



What Ned says is true. And gun drills have a much different point geometry than a D bit. A gun drill point is ground such that the bottom of the hole is shaped like the letter W. This helps to guide the drill. As do the pads ground on the tip of the drill. D bits work similar to gun drills because the drill is same diameter as the hole, at least for a way, say 5/8 inch long on a 5/16 drill size. So if there is a good diameter to start the D bit will tend to make a very straight and accurate hole. There is a method of gun drilling with modern gun drill bits that rotates the workpiece as well as the drill. This method makes the hole the closest to the axis of rotation. But as in regular gundrilling the drill must be guided accurately or the hole will not coincide with the axis of rotation. Eric
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 10/16/2019 8:23 AM, snipped-for-privacy@whidbey.com wrote:



I'm glad you guys kept going on and on arguing about what is and was or will be a gun drill or the source of what we call gun drills today. It was in my mind when I was playing around on Fleabay. I have a separate PayPal account I use to sell a few things on Ebay, and I pretty much spend anything that comes in to that account on Ebay for misc toys to play with. I bought a few things today including a new old stock F size gun drill short enough to fit in the envelope of the mill I want to use it on, and long enough to do the job. It was actually cheaper than the solid carbide drills I ordered the other day. Ah'reckon one-er-ta-udder o' demm day're tings should oughta do-da-trick.
I'm planning to throw a piece of stock in the mill and drill - er make - a bunch of holes using three different methods to see which one consistently gives me the straightest hole in a reasonable amount of time. If the carbide drills are "straight enough" they will be the fastest, so I have high hopes for them.
Typically I drill the clearance holes for 1/4 inch hinge pins with an F drill. The only reason the allowance for these was so large was because the customer recognized that it might be difficult to drill straight enough... and he is integrating the parts with an assembly where he isn't certain about fit up. That's ok though. I already figured out an alternative for him that will work if his Rube Goldberg machine doesn't.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:



Modern gundrills rely on high pressure oil not only for chip evacuation but also to support the hollow drill shank. You may have trouble using the gundrill to remove all the material because of these reasons. But if used as a reamer there should be no problems. Eric
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 17/10/2019 17:00, snipped-for-privacy@whidbey.com wrote:



I wondered about this when I considered using a gun drill for a job and wondered if a electric fuel injection pump would be up to the job, I have never tried it in the end but it's still in the back of my mind as an option.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:



A gear pump would work. Fuel pump not so much. Gundrills use large hydraulic pumps and good filters so that the oil pumped down the drill is debris free. They reall operate at high pressures and volumes. When a drill breaks or a drill breaks through the part the amount of oil that comes out in just seconds is huge. I have seen this more than once. Kinda like a hydraulic hose breaking on a piece of heavy equipment, but worse. Eric
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.