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How did I mess up this "crooked" drilling?

hobby ist

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#1
I was trying to drill a "long" hole. The tube was aluminum and 2 inches long. I used a centering bit to start, but clearly the other end was not centered.... what did I do wrong "technicically" :) ?


Thank you. drill-tube.jpg
 

RJSakowski

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#2
It is common for a drill not to run true on long holes. A number of factors contribute. Improper grind of the drill, drill not on true center of spindle axis, not clearing chips often enough, and sometimes, I fear, just plain being obstinate. The problem increases geometrically with the aspect ratio (length of hole/diameter). You can reduce the problem by drilling the hole from both ends, of possible. I usually will drill an undersized hole just over half way, flip the part and drill through all the way. Then I will switch to the finish sized drill and drill through the part. the reason for this is to remove any misalignment where the two holes meet. Using peck drilling also helps as you can clear the chips and have better cutting.
 

woodchucker

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#3
Let me count the ways. Ok, no really.
A drill bit MAY wander no matter what you do. The center of the bit maybe ground off center, your tube may not have been perfectly perpendicular in all planes.

Drilling a smaller hole and boring on the lathe is the best way to proceed. The boring can taper though if the boring bar is a narrow diameter. so go with light cuts toward the end.

If you can put it in a collet, that will help also, and it will grab the piece equally all around.
 

Bob Korves

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#6
Drilling holes is not a precision operation. Drills only remove metal. Drills do not go straight. Drills do not stay on the axis they start on. Drills do not drill a hole the diameter of the drill. Drills are only for removing metal. If you want the hole to be in a specific place, or to a specific diameter, or even better to the right diameter AND in the correct place, both at the same time(!), then you need to pay a lot more attention than just punching a hole with a drill. An under sized drill, then boring bar followed by a reamer, or a precision bored hole following a drill, are the best ways to get there.
 

Chipper5783

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#7
Hi Hobby ist, your result looks about right. As others have pointed out, drill bits will do all sorts of crazy things! Managing those issues is what machinists do. There are lots of things you can do (most of which have been described above) to improve the result. What you have not described is what sort of a result you are looking for. How good, is good enough? The formal description is "Tolerance".

A drill bit is generally considered a roughing tool. Drill bits are great. I use them frequently, when I am not really concerned about the size of the hole, the location of the hole, don't care about the surface finish and if the hole does not need to be round. Before I got into machining I thought I knew something about drilling holes in metal, after working at it pretty diligently for 30+ years, I recognize that I don't actually know very much about drilling holes in metal (please, no comments on being a slow learner).

Anyway, I'll assume you were using a lathe and tailstock drilling. I'll assume you held the aluminum rod in a 3 jaw chuck (1" bar and a 3/4" hole?). So you chucked up said bar, and then you simply stabbed in the center drill, then you switched to a 3/4" S&D drill bit and punched it through (even cleared a few times and hit it with WD40 a couple time). Probably didn't take very long.

That is fine, if your tolerance is pretty broad. It is real easy to improve significantly. 2" deep on a 3/4" hole is not really a "deep hole". Certainly not gun drill territory.

I find that when I amgoing in on a starter hole with a larger drill, the drill will often wobble and produce exactly the result you achieved. There are a couple easy fixes: 1. drill undersize for about 1/2", then bore a starter hole to size and follow through with the drill, 2. bring a piece of bar up to the side of the drill as it is wobbling on the start, just touch close to the business end of the drill enough to stabilize the drill in one position - because the whole thing is going around it will come to center (can simply use the back side of a turning tool).

On a short piece like that, it should be within about 0.01" of how well the staring end of the hole was centered (you didn't start perfectly in the center, it won't get better as you go - but it shouldn't be a lot worse).

For better results?
- be careful of the 3 jaw chuck on thin materials - you can make a round hole, but it won't be round after you remove it from the chuck. A 4 jaw will give better results. Of course, don't grip too hard.
- drill undersize, bore all the way through (if it isn't too deep). At least get a starting bore size, then follow drill, still undersize (if you can't bore that deep), then ream.
- this still does not address the jaw centering or the jaw axial alignment - switch to a collet chuck and it will be better.
- machine the entire sleeve OD & ID without removing it from the chuck: rough the ID, machine the OD (depending on the length you may need tailstock or steady rest support), finish ream the ID & part off.
- and no doubt numerous additional strategies depending on your requirements and the facilities you are working with.
- keep asking, you'll get lots of idea.
 

Chipper5783

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#8
Drilling holes is not a precision operation. Drills only remove metal. Drills do not go straight. Drills do not stay on the axis they start on. Drills do not drill a hole the diameter of the drill. Drills are only for removing metal. If you want the hole to be in a specific place, or to a specific diameter, or even better to the right diameter AND in the correct place, both at the same time(!), then you need to pay a lot more attention than just punching a hole with a drill. An under sized drill, then boring bar followed by a reamer, or a precision bored hole following a drill, are the best ways to get there.
You beat me to it Bob (I had an edit underway), and said it all much more concisely. :)
 

Dave Smith

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#9
what you may learn from this problem---is the method to best approach it---I first look for a tube that is already close to what I need-----since your project is only 2" long and a thin wall needed, then if you can find an aluminum tube to modify will be easier than trying to drill a round solid rod----it helps if like me you grab all the tubes for stock and keep them close to the lathe for projects-----I am not an experienced machinist like the many good ones giving you insight on how to do the best method to use when keeping the hole as perfect as possible when drilling from a solid rod----being a good scrounger is a big benefit for me to make up for my lack of machinist skill ability and lack of perfect tools----Dave
 

Bob Korves

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#10
what you may learn from this problem---is the method to best approach it---I first look for a tube that is already close to what I need-----since your project is only 2" long and a thin wall needed, then if you can find an aluminum tube to modify will be easier than trying to drill a round solid rod----it helps if like me you grab all the tubes for stock and keep them close to the lathe for projects-----I am not an experienced machinist like the many good ones giving you insight on how to do the best method to use when keeping the hole as perfect as possible when drilling from a solid rod----being a good scrounger is a big benefit for me to make up for my lack of machinist skill ability and lack of perfect tools----Dave
I like Dave's ideas here. I will even take it farther. Where possible and practical, change the design to use a commonly available size, without having to make a custom piece of tubing. Heaven knows that there are LOTS of options of off the shelf materials. Going even beyond that, start your search at your metal rack and box of drops. If you can find a piece of something in there that will do the intended job, then use it! You can get started right away, and get it done, without paying for retail tubing and the shipping of it. It is worth being a scrounger and having some free or cheap material on hand for your future jobs. Did I mention that one of the joys of being a hobby machinist is that you never need to work off someone else's drawings, much less follow them to the letter?
 

Bob Korves

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#11
Drilling holes is not a precision operation. Drills only remove metal. Drills do not go straight. Drills do not stay on the axis they start on. Drills do not drill a hole the diameter of the drill. Drills are only for removing metal. If you want the hole to be in a specific place, or to a specific diameter, or even better to the right diameter AND in the correct place, both at the same time(!), then you need to pay a lot more attention than just punching a hole with a drill. An under sized drill, then boring bar followed by a reamer, or a precision bored hole following a drill, are the best ways to get there.
I should also mention the perverse, inverse laws of making holes in metal. Or wood, plastic or whatever. When I punch a quick hole in scrap metal, with a dull drill on a mediocre drill press, it usually comes out perfect. When I need a perfect hole, in an exact location, that really looks nice, on a fussy and important (to me) job that is 99% done, there is absolutely no way I am going to nail it...
:headache:
 

chips&more

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#13
When I do mirco machining and specifically making small holes. I turn the work in one direction and also the drill bit (in the opposite direction). This method helps hole alignment and gets your cutting speed without just cranking up the headstock or drill chuck to crazy rpm’s…Dave.
 

Charles Spencer

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#14
I like Dave's ideas here. I will even take it farther. Where possible and practical, change the design to use a commonly available size, without having to make a custom piece of tubing. Heaven knows that there are LOTS of options of off the shelf materials. Going even beyond that, start your search at your metal rack and box of drops.
Yep. I know exactly how I'd make that part. Find a piece of pipe that I scrounged that was close, turn the outside, drill to close the right dimension, bore or ream to finish (depending on my needs), cut off the part and face it.

I frequently find various sizes of pipe at the dump. I used one to make spacers for my old horizontal mill. Now I know that spacers are supposed to be hardened and ground, but the ones I made work for me.
 

Wreck™Wreck

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#15
When I do mirco machining and specifically making small holes. I turn the work in one direction and also the drill bit (in the opposite direction). This method helps hole alignment and gets your cutting speed without just cranking up the headstock or drill chuck to crazy rpm’s…Dave.
Live tooling?
 

rgray

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#16
One thing I don't think was mentioned yet is facing the end of your stock off before drilling. I know I had that bite me when starting out. I'd center drill and then drill but it could be misdirected early if the end of my project was not faced square first.
 

umahunter

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#17
One thing you can try if they're not super deep hols is some stubby drill bits to minimize flex I got a set at a pretty good price from drill hog on ebay they say they're usa made with lifetime warranty I like mine so far I got a stubby set and silver and Deming set
 

jmarkwolf

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#18
Interesting discussion.

I've always wondered how they got long straight holes in gun barrels.

I kinda figured they drilled the deep hole, then turned the OD of the round stock "about" the hole!
 

rgray

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#19
I kinda figured they drilled the deep hole, then turned the OD of the round stock "about" the hole!
They do.
But just getting a hole with in .030 in 20-28 inches is quite an accomplishment.
The Green Mountain barrel blanks I have gotten are .006-.010 off on one end and usually .030+ off on the other end. Not bad for drilling 30" per minute.
 

Sblack

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#20
Go buy The Model,Engineer's Workshop Manual buy G H Thomas from Tee Publishing. Best general machining book EVER. There is a whole chapter dedicated to this. Another on parting off. He wrote for Model Engineer, but the info is gold for anyone who turns handles.

Drills cut best when only the outer part of the flute is working, so you start with a small dia. and use several drills of increasing size to drill your hole.

Drill 2 diameters deep, the retract and clear the chips

Buy good USA (UK, German) made drills and keep them good by using reasonable speeds and cutting oil and don't drill concrete with them.
 

Desolus

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#21
Iv'e had some limited experience in making gun barrels and since no one here has mentioned making your own D bit I thought I'd mention it. In the past what I have done is use a round bar and grind(with my tiny bench grinder and belt sander), then polish a D bit cutting surface onto the end of it and taking the drilling very slowly. Then use a reamer to take the cut to final depth. In my case followed by a rifling broach. This worked for me on pistol barrels using a less than new lathe I had access to at the time.

If you'd rather not make a bit, I have purchased gun drills from eldorado tool and they work fine.
 

EmilioG

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#22
Makes me wonder how they made a Henry Rifle back in the old days. A precision octagonal barrel with a straight bore.
 

RJSakowski

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#23
A local blacksmith made a number of flintlock rifles. The barrel was made by coiling 1/2" x 1" flat stock and jump (forge) welding the coil into a tube. The tube was straightened with a mandrel. drilled using a homemade gun drill and reamed. The rifling was then cut and the exterior of the barrel was then finished to an octagonal form on a Bridgeport. As I recall, he was self taught, having examined a number of historic pieces to figure out how they were made, and his method deviated from the traditional methods.

"The Modern Gunsmith" by James V. Howe (1934) has a good section on barrel making tools. It also has some good information abut machine shop topics in general. It is available for download on line if anyone is interested.
https://archive.org/details/The_Modern_Gunsmith_Vol_1_Howe_1941
https://archive.org/details/The_Modern_Gunsmith_Vol_2_Howe_1941
 

Bill Gruby

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#25
I'm going to swap methods. In tubing I would never drill, it's time to bore the hole. The slightest imperfection in the original bore will throw the finished drilled bore off. A drill bit will not correct imperfections, boring bars will. Just my way of doing things.

"Billy G"
 
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owl

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#26
A local blacksmith made a number of flintlock rifles. The barrel was made by coiling 1/2" x 1" flat stock and jump (forge) welding the coil into a tube. The tube was straightened with a mandrel. drilled using a homemade gun drill and reamed. The rifling was then cut and the exterior of the barrel was then finished to an octagonal form on a Bridgeport. As I recall, he was self taught, having examined a number of historic pieces to figure out how they were made, and his method deviated from the traditional methods.

"The Modern Gunsmith" by James V. Howe (1934) has a good section on barrel making tools. It also has some good information abut machine shop topics in general. It is available for download on line if anyone is interested.
https://archive.org/details/The_Modern_Gunsmith_Vol_1_Howe_1941
https://archive.org/details/The_Modern_Gunsmith_Vol_2_Howe_1941
Also, if you look at the old manuals, you will find that after reaming, but before profiling, they typically stretched a cord or wire through the bore, on a simple bow to tension it taut, then looked through the bore at the light pattern and used those patterns to figure out how to straighten the bore with a machine that pressed at a particular spot. This was considered a high skill that took years to master. After the bore was straightened, and the outside was profiled, they generally did it again, as the profiling could warp the bore. Even then, some barrels would move point of impact as they heated up, while others would not.
 

Silverbullet

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#27
Are your headstock and tailstock in good alignment with each other?
Mark S.
So many times I've seen and helped with holes not drilling straight , yes drill bits will and do wonder but not that much usually. Many drill bits will drill oversized even undersized if the bits not sharpened correctly. They get bent ,,yes bent,, that accounts in many cases. Times it's the alignments of the head and tailstock. Even wear in the ways will affect the drilling straight holes problem . Simple fixes make sure the LATHES in alignment. Then that the piece is turning true in the chuck or collet , even after all that take the precaution to drill halfway turn the part end for end and drill from the other. Still it can wonder , for really straight holes drill smaller and bore to size. Just seems it's about the only way to somewhat guarantee a true hole.