1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.
  2. PLEASE: Read the FORUM RULES BEFORE registering!

    Dismiss Notice

How did I mess up this "crooked" drilling?

Discussion in 'A BEGINNER'S FORUM (Learn How To Machine Here!)' started by hobby ist, Mar 24, 2017.

  1. hobby ist

    hobby ist Iron Registered Member

    Likes Received:
    1
    Trophy Points:
    3
    City:
    San Antonio
    State:
    Texas

    -Return to Top-

    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
     
  2. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

    Likes Received:
    2,412
    Trophy Points:
    113
    City:
    Barneveld
    State:
    Wisconsin

    -Return to Top-

    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.
     
    Steve Peterson, brino, mikey and 5 others like this.
  3. woochucker

    woochucker United States Active Member Active Member

    Likes Received:
    440
    Trophy Points:
    63
    City:
    Pittstown
    State:
    New Jersey

    -Return to Top-

    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.
     
    brino, gregc and mikey like this.
  4. rgray

    rgray Active User H-M Supporter-Premium

    Likes Received:
    306
    Trophy Points:
    83
    City:
    Helena
    State:
    Montana

    -Return to Top-

    Tozguy and pdentrem like this.
  5. chips&more

    chips&more United States Active User Active Member

    Likes Received:
    1,179
    Trophy Points:
    113
    City:
    Danville
    State:
    California

    -Return to Top-

    Drill both ends about half way in and not just from one end, that helps. Drill a smaller hole, then bore it out, again maybe from both ends because of length. Boring could be smaller diameter, then ream to size…Dave.
     
    mikey, Charles Spencer and Bob Korves like this.
  6. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

    Likes Received:
    3,386
    Trophy Points:
    113
    Location:
    USA
    City:
    Sacramento
    State:
    California

    -Return to Top-

    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.
     
    mikey, cmantunes, woochucker and 3 others like this.
  7. Chipper5783

    Chipper5783 Active User H-M Supporter-Premium

    Likes Received:
    342
    Trophy Points:
    63
    City:
    Red Deer
    State:
    Alberta

    -Return to Top-

    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.
     
    brino, Cobra and mikey like this.
  8. Chipper5783

    Chipper5783 Active User H-M Supporter-Premium

    Likes Received:
    342
    Trophy Points:
    63
    City:
    Red Deer
    State:
    Alberta

    -Return to Top-

    You beat me to it Bob (I had an edit underway), and said it all much more concisely. :)
     
  9. Dave Smith

    Dave Smith United States Active User H-M Supporter-Premium

    Likes Received:
    134
    Trophy Points:
    63
    City:
    Rochester
    State:
    Minnesota

    -Return to Top-

    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
     
  10. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

    Likes Received:
    3,386
    Trophy Points:
    113
    Location:
    USA
    City:
    Sacramento
    State:
    California

    -Return to Top-

    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?
     
    rock_breaker likes this.
  11. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

    Likes Received:
    3,386
    Trophy Points:
    113
    Location:
    USA
    City:
    Sacramento
    State:
    California

    -Return to Top-

    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:
     
    JimDawson, Z2V, rock_breaker and 7 others like this.
  12. markba633csi

    markba633csi United States Active Member Active Member

    Likes Received:
    314
    Trophy Points:
    63
    City:
    Mountain View
    State:
    California

    -Return to Top-

    Are your headstock and tailstock in good alignment with each other?
    Mark S.
     
    Silverbullet likes this.
  13. chips&more

    chips&more United States Active User Active Member

    Likes Received:
    1,179
    Trophy Points:
    113
    City:
    Danville
    State:
    California

    -Return to Top-

    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.
     
    brino likes this.
  14. Charles Spencer

    Charles Spencer Active User H-M Supporter-Premium

    Likes Received:
    894
    Trophy Points:
    93
    City:
    Worcester
    State:
    Massachusetts

    -Return to Top-

    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.
     
  15. Wreck™Wreck

    Wreck™Wreck United States Active User H-M Supporter-Premium

    Likes Received:
    1,246
    Trophy Points:
    113
    City:
    Riverton
    State:
    New Jersey

    -Return to Top-

    Live tooling?
     
  16. rgray

    rgray Active User H-M Supporter-Premium

    Likes Received:
    306
    Trophy Points:
    83
    City:
    Helena
    State:
    Montana

    -Return to Top-

    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.
     
    brino and Randall Marx like this.
  17. umahunter

    umahunter United States Active User Active Member

    Likes Received:
    88
    Trophy Points:
    28
    City:
    yuma
    State:
    Arizona

    -Return to Top-

    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
     
    ddickey, mrjbinok and brino like this.
  18. jmarkwolf

    jmarkwolf United States Active User Active Member

    Likes Received:
    113
    Trophy Points:
    43
    Location:
    Southeast Michigan
    City:
    Pinckney
    State:
    Michigan

    -Return to Top-

    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!
     
  19. rgray

    rgray Active User H-M Supporter-Premium

    Likes Received:
    306
    Trophy Points:
    83
    City:
    Helena
    State:
    Montana

    -Return to Top-

    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.
     
  20. Sblack

    Sblack Canada Active Member Active Member

    Likes Received:
    13
    Trophy Points:
    8
    City:
    Montreal
    State:
    Outside US / Canada

    -Return to Top-

    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.
     
    brino likes this.
  21. Desolus

    Desolus United States H-M Supporter - Premium Content H-M Supporter-Premium

    Likes Received:
    11
    Trophy Points:
    8
    City:
    fort worth
    State:
    Texas

    -Return to Top-

    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.
     
  22. EmilioG

    EmilioG United States Active User H-M Supporter-Premium

    Likes Received:
    294
    Trophy Points:
    63
    City:
    HUNTINGTON
    State:
    New York

    -Return to Top-

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

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

    Likes Received:
    2,412
    Trophy Points:
    113
    City:
    Barneveld
    State:
    Wisconsin

    -Return to Top-

    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
     
    EmilioG likes this.
  24. EmilioG

    EmilioG United States Active User H-M Supporter-Premium

    Likes Received:
    294
    Trophy Points:
    63
    City:
    HUNTINGTON
    State:
    New York

    -Return to Top-

  25. Bill Gruby

    Bill Gruby United States Global Moderator Staff Member H-M Supporter-Premium

    Likes Received:
    1,802
    Trophy Points:
    113
    City:
    Bristol
    State:
    Connecticut

    -Return to Top-

    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"
     
    Last edited: May 1, 2017
  26. owl

    owl United States Active Member Active Member

    Likes Received:
    35
    Trophy Points:
    18
    City:
    Missoula
    State:
    Montana

    -Return to Top-

    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.
     
  27. Silverbullet

    Silverbullet Active Member Active Member

    Likes Received:
    691
    Trophy Points:
    113
    City:
    Marlton
    State:
    New Jersey

    -Return to Top-

    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.
     
    Bill Gruby likes this.

Share This Page