# Deep Hole Drilling In Aluminum



## prasad (Oct 11, 2015)

Guys, 

I want to drill a deep "through hole" in a 2.65" long aluminum block. The hole will be 0.25" in diameter. The alu block is 1"x1" square. I know I must start with a center drill. After that I am not sure. What should be done to prevent the drill bit from wandering? I have drill bits that are 4" in length and I hope they should be sufficient? 

Next step (not immediate)  I want to attempt will be to make the same hole into an elongated hole (oval shape) of similar depth - 0.25" x 0.4". I think that will be even more tough. 

My machines are G4000  9x19 lathe and G8689 Mini-mill  by Grizzly. 

Regards
Prasad


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## kd4gij (Oct 11, 2015)

I would use a 4 jaw chuck and drill it in the lathe. As long as the drill is ground properly it should drill strait.


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## 4GSR (Oct 11, 2015)

Start your hole with a drill bit long enough to drill the hole in one setup.  A standard jobber length drill bit should do the trick.  Use a cutting oil to lubricate the drill bit so it does not gall up the aluminum and get stuck.  Retract your drill bit often to remove chips and add cutting oil.


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## Round in circles (Oct 11, 2015)

I've done a similar hole job a few days ago in 6 mm  & 5 mm diameters . My drills are hand ground and fairly accurate even if I do say it myself .
I'd prefer to drill the long hole first so nothing jumps or moves around .

First time was in the 4 jaw chuck with the 5 mm drill  , it was a doddle , plenty of WD 40 to lube on the drill bit as the clean drill goes in and  a small brush to keep the drill clean as it's withdrawn . Never sink the drill in past the end of the flute unless you are desperate because this often traps swarf & leads to a broken drill bit . Only go in for say 1.2 " maximum at a time withdraw and use a paint brush brush to clean the drill bit don't use your fingers as the swarf is usually razor sharp . Never used a rag on a rotating drill or lathe

Drilling the 6 mm holes in the aluminium was done with it sitting  on the drill table under the drill press as it was four inches thick and would not go in the four jaw chuck because of the length of the pieces .

I turned up a small  parallel test bar three inches long & an inch and quarter in diameter undercutting the  faced end so that when it sits on the table only the outer edges touch the table . I used this to check & set up the table so it is at right angles to the vertical doing it fore & aft and again left & right to the spindle into which I'd put in a four inch long turned half inch round test bar & gently tightened it up using all three key holes so it sits as near to perfect as possible ...sometimes if you only tighten it on one key hole the part will be ever-so  off centre and at a very slight angle too boot.  I needed to make a slight adjustment to get the table set correct


I then carefully found the centre of the bar using a steel ruler across the diagonals , then checking it with a pair of dividers by drawing the biggest circle possible to see it almost touch each side before giving it a decent clout with a hammer & center punch to fix it & then marked the other end face in the same way .   I set it up again this time using the table vice  & found it wouldn't fit as the overall height was too big for the throat available.

Had to do vertical rechecks from the foot plate ( OK ) and then set it up in the vertical in the table vice and bolted it down to the table did a vertical recheck then did a cold run at the drilling to see if it did actually hit the desired point .

With everything OK  I went a head and drilled the first hole with caution & care.
I drilled in with a 5.5 mm drill from each end face so as not to have to worry too much if the drill wandered off a tad internally . Then followed through with the slightly longer 6 mm drill from each end to take out any deviations .  There was very little deviation  with the 5 mm drill runs to the middle  which really helped a lot .


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## Wreck™Wreck (Oct 11, 2015)

Get yourself a parabolic flute drill, this will work a charm in high D/L ratio holes in aluminum, use a spotting drill rather then a center drill to start. this should give you a fairly straight hole then ream or bore as needed.


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## prasad (Oct 11, 2015)

Thank you all. Great ideas. I will try that and will report back on how it went. 

Any ideas on how to make the hole into an oval? 

Thanks
Prasad
AB3EH


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## RJSakowski (Oct 11, 2015)

When drilling deep holes, it is easy for the drill to wander.  A less than perfect grind, on the drill, drill not perfectly aligned with the start point, not clearing chips properly all can cause wander.  If I need  drill to come out exactly on center on the far end, I will drill approximately half way with a smaller drill, reverse the work piece and drill completely through with the same drill.  Then I will finish with the final size drill.  When the second hole hits the first, the drill will  follow it and if there is a misregistration at the intersection, the second operation will ream the surfaces slightly creating a straight through path.  The finishing drill then drills a straight hole on center on both ends.

Your hole has a 10:1 depth to diameter ratio which is not too extreme and it should not be a problem.  I have successfully drilled through holes using the above method with as much as a 20:1 ratio.

Bob


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## RJSakowski (Oct 11, 2015)

prasad said:


> Thank you all. Great ideas. I will try that and will report back on how it went.
> 
> Any ideas on how to make the hole into an oval?
> 
> ...


I think HF drills cut oval holes. 

Seriously, you would want to use an end mill for precise holes.


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## Wreck™Wreck (Oct 11, 2015)

Round in circles said:


> I then carefully found the centre of the bar using a steel ruler across the diagonals


This I find fascinating and perplexing at the same time, correct me if I am wrong.
You machined tools  and fixtures to make a part as accurate as possible then the last operation is eyeballing the hole position with a rule, what am I missing?


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## T Bredehoft (Oct 11, 2015)

Yes, I'd centerdrill both end on a mill, after locating true center.  Then drill through on a drill press.  Neither my lathe or mill has two inch stroke.


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## Wreck™Wreck (Oct 11, 2015)

T Bredehoft said:


> Yes, I'd centerdrill both end on a mill, after locating true center.  Then drill through on a drill press.  Neither my lathe or mill has two inch stroke.


Jewelers lathe? That is a very small Z axis even for a screw machine or turret lathe, the few small turret lathes that I have used in the past have 4-5 inches of Z travel, excellent machines for making a LOT of small simple parts manually, as mentioned before I prefer drilling and tapping round parts in a turret rather then a CNC lathe that doesn't support rigid tapping, much faster and less of a chance of leaving 1/2 of a tap in the part, if you know what I mean.


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## T Bredehoft (Oct 11, 2015)

The quill in the tail stock of my Clausing/Atlas MK2  has just over an inch of travel.  Yes, I can advance it, but once advanced I can't pull the drill out comfortably without using the entire tail stock as a hand drill. The quill in my  PM 25 mill has 1.78 inches of travel. The quill and the table on my drill press are square, after quite a bit of fussing.


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## Wreck™Wreck (Oct 11, 2015)

T Bredehoft said:


> The quill in the tail stock of my Clausing/Atlas MK2  has just over an inch of travel.  Yes, I can advance it, but once advanced I can't pull the drill out comfortably without using the entire tail stock as a hand drill. The quill in my  PM 25 mill has 1.78 inches of travel. The quill and the table on my drill press are square, after quite a bit of fussing.


Have you tried drilling from the tool post on the lathe? It works well but can be a bit fussy setting up a chuck in a V holder or MT quick change tool post block, if you have to rotate the post then you need to dial it in again every time. I only move the QCTP's on the lathes where I work by accident (read Crashes) as every tool has an offset relative to a base tool so rotating the post requires resetting the offsets for dozens of tools, this is not fun at all .

Drilling from the toolpost beats the hell out of cranking the handle all day. Also you set the drill feed at an optimum rate rather than the hurried feed that one might resort to after several hours of boredom cranking the handle by hand, do not ask how I know this (-:


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## prasad (Oct 11, 2015)

prasad said:


> Thank you all. Great ideas. I will try that and will report back on how it went.
> 
> Any ideas on how to make the hole into an oval?
> 
> ...




Thought about it again. I think I will try it using the mini-mill. My lathe (G4000 9x19) does not have travel sufficient for this depth. The mill has. I know mini-mill has flexure problem but I will try and see how it goes. I generally got the idea but will understand it better when I do it. 

Thanks everyone, 
Prasad
AB3EH


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## T Bredehoft (Oct 12, 2015)

Wreck™Wreck said:


> Have you tried drilling from the tool post on the lathe?



While I have done that, in the dim past, I didn't think of it in this application. My little lathe will only swallow a 7/16 rod, so I dont' have many opportunities for deep drilling, but I will keep it in mind.


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## stupoty (Oct 12, 2015)

Wreck™Wreck said:


> Jewelers lathe? That is a very small Z axis even for a screw machine or turret lathe, the few small turret lathes that I have used in the past have 4-5 inches of Z travel, excellent machines for making a LOT of small simple parts manually, as mentioned before I prefer drilling and tapping round parts in a turret rather then a CNC lathe that doesn't support rigid tapping, much faster and less of a chance of leaving 1/2 of a tap in the part, if you know what I mean.



You just have access to to many big lathes 

My leblond 13 inch was my first lathe with over 2 inch tail stock stroke, its got about 31/4" wow 

Seriously though, it's very handy.

Stuart


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## jbolt (Oct 12, 2015)

Wreck™Wreck said:


> Get yourself a parabolic flute drill, this will work a charm in high D/L ratio holes in aluminum, use a spotting drill rather then a center drill to start. this should give you a fairly straight hole then ream or bore as needed.



+1 on parabolic drills.


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## Paul in OKC (Oct 12, 2015)

You can drill the depth of the hole regardless of the travel of the quill in the tail stock. It is a bit of a pain, but drill what the stroke is, then you will have to slide the tail stock up a bit and lock it with the drill in the part. The one thing you will need to do is advance the drill a bit, then unlock the tail stock and slide it back to clear the chips, then slide it back up, lock it down and drill. Repeating as needed to get the hole through.


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## T Bredehoft (Oct 12, 2015)

Paul in OKC said:


> Repeating as needed to get the hole through.



Yeah, I know. not my choice. But I do it.  I'll look into drilling with the saddle, too.


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## Dave Smith (Oct 12, 2015)

to make your hole oval use a shaper---Dave


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## Fabrickator (Oct 12, 2015)

I would use a stubby screw machine drill to go as deep as possible using my dual-air blower to keep the chips cleared and minimize overheating.  Then I would switch to a jobber drill to complete the hole if needed.  Always best to keep the drill as short as possible and chips clear to prevent wandering.
Another trick I use on deep drilling to use my QCTP/compound to apply a very slight side load to the bit itself. to keep it running true.

I made a dual-nozzle chip air blower (w/regulator) to keep the 2 flutes cleared.


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## Round in circles (Oct 12, 2015)

Wreck™Wreck said:


> This I find fascinating and perplexing at the same time, correct me if I am wrong.
> You machined tools  and fixtures to make a part as accurate as possible then the last operation is eyeballing the hole position with a rule, what am I missing?




On my work piece  , I couldn't get it in the lathe to bore the four inch dimension , as the piece was far too long  & I don't have a milling attachment or a crutch pad to do it , so I had to resort to the old Mk 1 eyeball old way  . I did try using the cross slide with the compound removed but it wouldn't play for me .


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## Wreck™Wreck (Oct 12, 2015)

Paul in OKC said:


> You can drill the depth of the hole regardless of the travel of the quill in the tail stock. It is a bit of a pain, but drill what the stroke is, then you will have to slide the tail stock up a bit and lock it with the drill in the part. The one thing you will need to do is advance the drill a bit, then unlock the tail stock and slide it back to clear the chips, then slide it back up, lock it down and drill. Repeating as needed to get the hole through.


I do a repeat part several times per month, 9/16 hole through 12" of 440 Stainless linear shafting, the surface is cased and ground the ends and center are not. I position the carriage so that after retracting the tail stock (by sliding it down the ways) and clearing the chips one may just push is back in without the risk of driving the drill into the bottom of the hole, works a charm, advance the carriage when you run out of tail stock travel.

 In the past my employer has considered purchasing gun drill tooling for this type of work, I do not see this happening in my lifetime however.


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## Paul in OKC (Oct 12, 2015)

Gun drills are nice. We have one we use regularly at the shop. Run as small as 3/16, and up to 1  1/4".  The small bits scream at up to 4k rpm and 2 IPM feed. Drills great.


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## prasad (Nov 1, 2015)

Guys,

I went ahead and drilled the deep hole with a 1/4" parabolic flute drill. The hole came out great. Thank you all for your advice. I have one question on my experience in drilling with the parabolic flute drill. I did the drilling operation on my 9x19 lathe in small steps, withdrawing the bit frequently to clear chips and to spray WD40 into the hole. I noticed one odd behavior. The chips  appeared to come out in spiral form only from one of the flutes of the drill bit. The other flute did have some accumulation but not as much as the first flute. I felt that only one cutting edge was properly cutting. Could this be due to drill bit faulty or defective construction? The drill bit is of unknown make and was bought from an ebay seller.

Thank you again for your comments and advice.

Prasad


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## prasad (Nov 1, 2015)

Wreck™Wreck said:


> Get yourself a parabolic flute drill, this will work a charm in high D/L ratio holes in aluminum, use a spotting drill rather then a center drill to start. this should give you a fairly straight hole then ream or bore as needed.


Hi Wreck, I did it with a parabolic flute drill. The hole came out good. Offset at the other end was under .005". Exactly as you said. However I noticed that only one cutting edge of the bit was producing spiral shaped chips. The second cutting edge did produce some chips though. Could the drill bit be faulty/defective? 

Thanks
Prasad


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## janvanruth (Nov 1, 2015)

the drill was not properly ground
but as the result is fine i would say dont change a winning team


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## Wreck™Wreck (Nov 3, 2015)

prasad said:


> Hi Wreck, I did it with a parabolic flute drill. The hole came out good. Offset at the other end was under .005". Exactly as you said. However I noticed that only one cutting edge of the bit was producing spiral shaped chips. The second cutting edge did produce some chips though. Could the drill bit be faulty/defective?
> 
> Thanks
> Prasad


This is not uncommon when using conservative feed rates, push the drill harder. Do a test for your own education, chuck a piece of aluminum, spot drill it and then drill as you normally would, do this again with another test specimen but crank the tail stock wheel fast enough where you are afraid of breaking the drill, you will then see 2 chips coming off of the bit.

If one were to purchase a drill from a highly reputable manufacturer, Guhring  for example, it would be likely that you would observe the same chip formation at less then optimal feeds, this does not mean that the tool is "not ground properly", you simply may be using it incorrectly.

Last week, Warner & Swasey # 5 turret lathe, 1  1/4" twist drill straight through 1018 steel parts 1 5/8" thick, no center drill or spotting drill, no pilot hole just ran the drill in and let it find it's own center and eat, accuracy was not important as they were later bored in a CNC lathe to 1 1/2" +.010 - .000". 44 parts at less than 40 seconds each actual drilling time. 1:45 from chucking to finished hole, it took longer to change parts then the actual machining time. I bored soft jaws with a step in them to hold the part because that much feed rate with a drill will push the part right through hard chuck jaws, even with a 15" chuck. A large W & S Turret is a powerful machine make no mistake about that.


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