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How did I mess up this "crooked" drilling?
- Thread starter hobby ist
- Start date
- Joined
- Feb 1, 2015
- Messages
- 9,984
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.
- Joined
- Nov 25, 2015
- Messages
- 9,741
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.
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.
- Joined
- Nov 26, 2012
- Messages
- 1,307
It's a hole can of worms.
https://en.wikipedia.org/wiki/Gun_drill
A little excessive for 2" but you'll need something longer eventually.
I find them on ebay.
https://en.wikipedia.org/wiki/Gun_drill
A little excessive for 2" but you'll need something longer eventually.
I find them on ebay.
- Joined
- Mar 19, 2014
- Messages
- 2,682
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.
- Joined
- Jul 2, 2014
- Messages
- 7,594
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.
- Joined
- Sep 25, 2014
- Messages
- 1,152
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.
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.
- Joined
- Sep 25, 2014
- Messages
- 1,152
You beat me to it Bob (I had an edit underway), and said it all much more concisely.
- Joined
- Mar 10, 2013
- Messages
- 1,429
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
- Joined
- Jul 2, 2014
- Messages
- 7,594
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?