# Need tips on drilling a long thin through hole



## tjb (Dec 7, 2019)

I need to drill two holes in a piece of 5/8" aluminum that measures 2" x 4 1/8".  The holes need to be 3/16" and go through the 4 1/8" length.  They need to be very accurate, so I plan on doing the operation on my mill.

I have found several bits to choose from but don't know what parameters to select (material, point angle, etc.).

I've never tried to drill a hole that deep and narrow, and life would be difficult if the bit breaks off in the hole.  Any tips to help avoid a catastrophe?  Drill speed/feed rate/etc.?

Thanks in advance.

Regards,
Terry


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## Z2V (Dec 7, 2019)

Could you drill from both ends and meet in the middle?


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## tjb (Dec 7, 2019)

Z2V said:


> Could you drill from both ends and meet in the middle?


Thought about it.  Would rather avoid it because that would introduce a potential misalignment.  I see that as a worst case scenario solution that I hope I can avoid.

Thanks


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## mmcmdl (Dec 7, 2019)

Guhring parabolic drill would work nicely .


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## tjb (Dec 7, 2019)

mmcmdl said:


> Guhring parabolic drill would work nicely .


Any one in particular?  MSC Direct lists 12 of them.  They range from about $15 to $476 with all kinds of different parameters.

Thanks


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## Bob Korves (Dec 7, 2019)

Good luck, TJB.  I would not want to try that one if the drill must stay closely accurate to the center line.  Someone who does gun barrel boring might have the best advice...


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## mmcmdl (Dec 7, 2019)

Yes , they are expensive . If you have their big book they explain what performs best for special applications . I don't have the book in here at work . They make deep hole drills for aluminum though , one of my past jobs required drilling 12" deep thru aluminum for a drone antenna ( SP ) . I pecked it on a cnc lathe with no problem .


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## tjb (Dec 7, 2019)

Bob Korves said:


> Good luck, TJB.  I would not want to try that one if the drill must stay closely accurate to the center line.  Someone who does gun barrel boring might have the best advice...


Thanks, Bob.

Hopefully one of our riflemen will offer some advice.

Regards,
Terry


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## tjb (Dec 7, 2019)

mmcmdl said:


> Yes , they are expensive . If you have their big book they explain what performs best for special applications . I don't have the book in here at work . They make deep hole drills for aluminum though , one of my past jobs required drilling 12" deep thru aluminum for a drone antenna ( SP ) . I pecked it on a cnc lathe with no problem .


Wonder if I could improve my odds of success by starting with a 64th under screw machine or jobber bit.  Then following with the extended length?

Anyone?

Thanks,
Terry


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## mmcmdl (Dec 7, 2019)

When you state " needs to be very accurate " , regarding diameter , true position , parallelism ? All of the above ?


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## tjb (Dec 7, 2019)

mmcmdl said:


> When you state " needs to be very accurate " , regarding diameter , true position , parallelism ? All of the above ?


The holes will need to match up to holes in a larger piece of steel.  I will drill those holes as well.  I would consider true position to be the most important consideration with parallelism being a close second.  If I match the two pieces from the sides I START the holes, that could account for a slight bit off on parallelism.  Can't miss it by much, admittedly, but it should work.

Regards,
Terry


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## mmcmdl (Dec 7, 2019)

tjb said:


> If I match the two pieces from the sides I START the holes, that could account for a slight bit off on parallelism



Exactly . If you did need it to be close to perfect , you could drill over size then bore for a bushing from both ends . That's if you didn't need that .1875 diameter the full length of the part .


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## tjb (Dec 7, 2019)

mmcmdl said:


> Exactly . If you did need it to be close to perfect , you could drill over size then bore for a bushing from both ends . That's if you didn't need that .1875 diameter the full length of the part .


I think I'm at least theoretically on the right track.  Does that help narrow down my choices for a bit?  I'm no expert in making that kind of selection.  And I do need the .1875 for the entire length.

Regards,
Terry


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## Cooter Brown (Dec 7, 2019)

Gun drills are made for drilling very long holes.....


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## Mitch Alsup (Dec 7, 2019)

I found up to 0.002" of run-out when drilling 13/64'ths through 0.5" of 6061.

If you need than more accurate than that, you need something other than a conventional drill.


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## RJSakowski (Dec 7, 2019)

I would drill from both ends with an undersize drill.  If there is a slight mismatch where the two holes meet, drilling the second hole tend to follow the first hole resulting in a slightly larger diameter at the intersection.  Following with a larger drill will blend the two holes.  Depending on the mismatch, I might step up to my final diameter with multiple drill sizes.


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## mmcmdl (Dec 7, 2019)

Looking thru the toolbox in here at work i'm finding solid carbide boring bars a lot smaller then what you need that would easily reach over the 2 1/16" depth to get half way thru . You would still have the mismatch where they meet though unless you were dead nuts on positioning and machine tram . One of the options for going deeper that we used quite a lot were to grind the shanks down on out micro bars and sleeve them for extra length . PITA but the gubmint paid for the R & D and all tooling .


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## tjb (Dec 7, 2019)

I think I'm going buy an extended length bit and try two or three passes at drilling straight through on a similarly sized sacrificial piece of aluminum.  I'm guessing I can get by with a thou or two of run out.  If not, I'll go to a Plan B.

That gets me back to my original question:  Any advice on drill bits?  I like Guhring, but what material/tip angle/etc.?  And any suggestions on speed and feed rate?

Regards,
Terry


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## mmcmdl (Dec 7, 2019)

Most Guhrings are 130 degree points high helix with a thick web . They make 120 degree also if I remember correctly . For aluminum , no coating . High polish .


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## mikey (Dec 7, 2019)

Terry, you are looking to drill something with a depth to diameter ratio of about 22:1. You need a gun drill if the hole has to be that deep and accurate. A twist drill, parabolic or otherwise, will not drill accurately at that depth. That is, hole alignment all the way through is going to be a big issue.

I wonder if a D-bit would work? After all, a gun drill is a single flute cutter. Might be worth a try.


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## MrWhoopee (Dec 7, 2019)

Maybe not doable with what you have, but for maximum accuracy, deep hole drilling is done with both part and drill rotating (in opposite directions of course). Perhaps on a lathe with a live spindle on QCTP and part held in 4-jaw chuck.

*Deep Hole Drilling Process*
*Rotating Tool*

Typically used for non-symmetrical components, or round parts with off-center holes
Cutting speed is determined by tool spindle speed
Drill drift can be significant when compared to rotating workpiece, or counter-rotating process
*Rotating Workpiece*

Typically used for round parts with a deep, on-center hole
Cutting speed is determined by part, balanced to allow high rotating speeds
Drill drift is reduced compared to rotating tool only
*Counter-Rotating Tool and Workpiece*

Ideal process for round parts with a deep, on-center hole
Cutting speed is determined by a combination of tool and workpiece rotation
Provides optimal hole straightness and concentricity


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## T Bredehoft (Dec 7, 2019)

Terry,  No one has mentioned, , and since you might be inexperienced in drilling deep holes, you must "peck drill" the hole. Drill little or no more than the diameter deep before withdrawing the drill and clearing the chips. That'll be at least 22 pecks. Otherwise you run a great risk of binding the chips in the drill and breaking the drill and scrapping the part. I don't know about a gun drill which in effect has one straight flute, but I can't imagine it would flow aluminum chips that far either.

_Edit:_ fix typo


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## mmcmdl (Dec 7, 2019)

Not much information on the functionality of so called part or of its intended outcome . Hard to envision a procedure without some details . Is this a prototype piece , are you designing something etc ? 

Working in an engineering lab for years , you learn there are more ways than one to skin a cat . An engineer makes a simple job overly complicated , a machinist makes it simple again .


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## Liljoebrshooter (Dec 8, 2019)

I have never used a gun drill,  but I think most of them use through coolant that helps flush chips.
They use them to drill a 32" long rifle barrel and stay centered pretty good.
I don't think one that was only about 6" long would be to costly.
Joe Hynes


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## Liljoebrshooter (Dec 8, 2019)

Well I take back the cost part.  Just looked on McMaster,    a  3/16" drill 10" long is about $85.
I guess it depends on how bad you need the precision. 

Joe Hynes


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## ArmyDoc (Dec 8, 2019)

Seems to me that you would want to drill an under size hole first, then use a 6 inch reamer to get a precise hole.  Something like this:








						3/16" X 6" HSS Straight Shank Straight Flute Long Chucking Reamer
					

3/16" X 6" HSS Straight Shank Straight Flute Long Chucking Reamer




					drillsandcutters.com


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## Chewy (Dec 8, 2019)

Here is Guhrings #9050260045000.. $206 from MSC. There is a website calculator that figures it out: https://www.guhring.com/BrowseProducts/Products/Gun-Drills  Just answer the questions.  This will get you just under-size so you will need to ream to final dimension. 
.177 X 4.54 long. Might be other manufacturers that are closer or exact size.


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## bigblock61 (Dec 8, 2019)

Let us know how this turns out. I was considering making a 4 inch hollow tube for the oil can project here but didn't know how to do it. Not as precision as you seem to need but the procedure would be the same.


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## JPMacG (Dec 8, 2019)

Find a shop with wire EDM capability?  One hole might not be too costly.


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## pdentrem (Dec 8, 2019)

Need to find a shop with a hole popper. Wire EDM will not work, as it needs a hole first to feed the wire through. We have one at work but we have never used it over 2” in making our stamping dies.





__





						Small Hole EDM | Sodick
					

Need high precision hole poppers? Sodick’s K Series (our small hole EDM line) features easy operation, the latest servo technologies and high-speed capability.




					www.sodick.com


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## tjb (Dec 8, 2019)

Okay, all this discussion is causing me to wonder if I need to re-think this project.  I added DRO to my lathe a couple of years ago and ran the z-scale along the backside of the cross slide.  Has worked great, but it presents two complications.  First, the scale and reader stick out the back of the cross slide by approximately two inches and interfere with positioning of the tailstock.  Second, the set screw that locks the cross slide is accessible but is directly below the reader rendering usefulness doable but difficult.

I saw a myfordboy video on youtube where he added DRO to his lathe, and made an extension on the back of his cross slide so that the scale was mounted to the rear of center.  I would like to do the same thing and, on my lathe, I had the idea of simply making a 4 1/8" extension (my available space) to attach to the back of the cross slide.  That distance would be sufficient to allow proper use and access of both the tail stock and the set screw.

It would be a rather simple matter to mill a piece of 5/8" aluminum, which I have on hand, to 2" by 4 1/8" and bolt that to the end of the cross slide.  The long holes would only be necessary for a long #10 screw or threaded rod to snugly slide through, hence, the need for accuracy.  The idea seemed simple to me, but now, I'm beginning to wonder.  Is the potential for wandering significant enough to distort the alignment?  I've never drilled anything this long and narrow, so I'm in uncharted waters.  I can think of a couple of other ways to attack this but, frankly, this seemed to be the easiest and most straightforward.  So much for my logic.

What do you think?

Regards,
Terry


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## MrWhoopee (Dec 8, 2019)

Ah, now we're at the meat of the matter and the job looks entirely different from the original description. Cut a window in each side of the piece of aluminum to  allow the use of short bolts. Here's a pic of how I did it on my Heavy 10.


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## mikey (Dec 8, 2019)

Terry, it might help to show a pic of the area involved, with the hardware you're trying to install. I bet the guys could come up with an alternative (like MrWhoopee's above) to extremely deep hole drilling.


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## pdentrem (Dec 8, 2019)

Mr Whoopee’s solution is very good. What about the weight that is cantilevered off those bolts? Maybe give a thought of using hollow extruded stock or mill a slot on the underside and epoxy a tube for the attaching hardware.
Pierre


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## tjb (Dec 8, 2019)

MrWhoopee said:


> Ah, now we're at the meat of the matter and the job looks entirely different from the original description. Cut a window in each side of the piece of aluminum to  allow the use of short bolts. Here's a pic of how I did it on my Heavy 10.
> 
> View attachment 307422


Thanks, Mr. Whoopee.  That's exactly the thought that's been running through my mind, but I wasn't sure it made sense.  That is now definitely way up high on the alternative list.

Regards,
Terry


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## tjb (Dec 8, 2019)

mikey said:


> Terry, it might help to show a pic of the area involved, with the hardware you're trying to install. I bet the guys could come up with an alternative (like MrWhoopee's above) to extremely deep hole drilling.


You're right, Mike.  I didn't really see drilling those holes, initially, as being such a complicated issue.  I really expected to get a simple answer with regard to feed rates, tool material, etc.  On the surface, it seemed pretty straightforward, so long descriptions and photos didn't strike me as particularly necessary.  So in the grand scheme of things, I'm glad I asked.  No telling what a disappointment it may have turned out to be.

Unfortunately, I can't get out to the shop this afternoon to take pictures, but Mr. Whoopee's photo is right along the lines of the direction I was headed.  Looks like he made his the full width of his cross slide; I was only going to make mine 2" - easily wide enough to mount the hardware.  Also, I have some aluminum extrusion end pieces left over from who-knows-what that might be worth considering a la Pierre's suggestion.  Never even thought of that one.

Thanks again.

Regards,
Terry


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## tjb (Dec 8, 2019)

pdentrem said:


> Mr Whoopee’s solution is very good. What about the weight that is cantilevered off those bolts? Maybe give a thought of using hollow extruded stock or mill a slot on the underside and epoxy a tube for the attaching hardware.
> Pierre


Thanks, Pierre.

That one's worth considering.  See my answer to Mike, above.

Regards,
Terry


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## Cadillac STS (Dec 8, 2019)

Since you mentioned doing a test piece and it is just aluminum consider making the test piece(s) the same size of part you need.  That way if your experiment works you are done.


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## Cadillac STS (Dec 8, 2019)

Consider drilling the deep hole large enough to put the head of the screw in. Drill down with 1/2 inch drill for example to half inch from the bottom. Then drill your precision placement hole half inch through the face side so it will fit right where you need it, not needing to be exactly on center with the big hole.

think deep deep counter sink for the bolt head. 

Then use a 1 inch bolt Deep down inside the larger hole.


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## tjb (Dec 8, 2019)

Cadillac STS said:


> Consider drilling the deep hole large enough to put the head of the screw in. Drill down with 1/2 inch drill for example to half inch from the bottom. Then drill your precision placement hole half inch through the face side so it will fit right where you need it, not needing to be exactly on center with the big hole.
> 
> think deep deep counter sink for the bolt head.
> 
> Then use a 1 inch bolt Deep down inside the larger hole.


That's a good idea which I had considered, but I'm only starting with 5/8" stock.  I've been pondering this today and thought about using some 3/4" stock I have available.  We'll see what we come up with.

Regards,
Terry


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## mmcmdl (Dec 8, 2019)

Got it figured out ?


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## tjb (Dec 8, 2019)

mmcmdl said:


> Got it figured out ?


Brainstorming.  Won't be able to get to the shop until tomorrow.


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## Cadillac STS (Dec 8, 2019)

tjb said:


> That's a good idea which I had considered, but I'm only starting with 5/8" stock.  I've been pondering this today and thought about using some 3/4" stock I have available.  We'll see what we come up with.
> 
> Regards,
> Terry



I just mentioned a half inch hole as an example. You could use a smaller head Allen head bolt.  

Also if needed you could chuck up an Allen head bolt in your lathe and take the head diameter down a bit to fit a smaller hole if needed.  Just put 3 or 4 nuts on the bolt and tighten them so the hex sides match. Chuck that up and make the head smaller.


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## tjb (Dec 8, 2019)

Cadillac STS said:


> I just mentioned a half inch hole as an example. You could use a smaller head Allen head bolt.
> 
> Also if needed you could chuck up an Allen head bolt in your lathe and take the head diameter down a bit to fit a smaller hole if needed.  Just put 3 or 4 nuts on the bolt and tighten them so the hex sides match. Chuck that up and make the head smaller.


That's a good idea.  I mentioned 3/4 stock after looking at Mr. Whoopee's photo.  Looks like he used 3/4 or maybe even 1 inch.  I'll study it some more tomorrow.  Thanks for the input.

Regards,
Terry


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## MrWhoopee (Dec 8, 2019)

tjb said:


> That's a good idea.  I mentioned 3/4 stock after looking at Mr. Whoopee's photo.  Looks like he used 3/4 or maybe even 1 inch.  I'll study it some more tomorrow.  Thanks for the input.
> 
> Regards,
> Terry



I used 1x6 stock to replace the original cast tailpiece that covers the crossfeed screw and connects to the taper attachment. It provided a flat surface for mounting the scale for the DRO.


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## John TV (Dec 8, 2019)

Could you mill long pockets on the underside of the extension leaving 1/2 inch of solid aluminum at each end then drill from each side followed by a reamer from one side to ensure alignment. Or use a long drill from one side? The pocket would remove most of the "wandering" I would think and the 1/2 inch would be more than strong enough to hold everything without flexing much. I'm still a nuub but might work. 

John in Minnesota 


Sent from my iPhone using Tapatalk


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## Illinoyance (Dec 8, 2019)

I would drill from both sides.  Because location is important I would drill undersize then bore to .1875 as deep as your tooling will permit.  The undersized hole should be just a bit deeper than you can bore.  The bored portion of the hole will act as a drill bushing to keep the hole on location.


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## tjb (Dec 9, 2019)

Success on Step 1!!!

Milled my piece of 5/8" aluminum with cutouts similar to Mr. Whoopee's and it fits perfectly.  Sorry, no pix tonight, but I'll post some tomorrow.  The most challenging part was drilling for the tapped holes in the end of the cross slide.  Fortunately, I have an 8" angle plate that I mounted and indicated on my mill, but it took almost all the tolerance I had to mount the cross slide standing on end.  Clamped it to the angle plate, drilled and tapped the holes and it matched up perfectly.

I suppose in the grand scheme of things, there's a silver lining to my asking an abbreviated question instead of giving a full-blown description of my objective.  Having never drilled a long, skinny hole, I was not aware of the complications associated with such an effort.  Now I know.  Hopefully, some of our other rookies were able to learn from this as well.

Now on to the big challenge - cutting the glass scale.  At the moment, I'm considering the best course of action is to reassemble the cross slide with the extension plate on it, and go through some exercises to determine optimal length.

To be continued...

Regards,
Terry


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