Set-up question

Just thinking this through a little - starting with the artificial impossible. First imagine the perfection of a drill, and zero run-out drill press, and infinite stiffness, and utterly symmetric cutting faces, etc. and then play through all the things that can start the tip doing a little twirl. Consider why the hole being cut is, at some points down there, temporarily not exactly "round", and able to head off course. Different case, I know, but it begs the question of how the oil drilling guys can "steer" their drill bit to places not exactly below their start point.

It's a good start to use a spotting dill, that being short and therefore stiff and uncompromising.
Maybe shift up so that the quill is extended as little as practical at the start of the hole-making.

But then I think, the one thing that that will limit drill flexing, and wandering about, is to force it to stay straight. Maybe drill a hole in some thick(ish) steel, and put it onto the drill bit before lining up. Then, with the bit where you want it, clamp on the steel guide, and drill some of the hole deep enough to become it's own guide. Test alignment gently at first, or things might snap!

I don't really know. These are just thoughts about what I would try in that situation. Coincidentally, for myself, I am currently trawling catalogs, and "reviews", and eBay, and Machine Mart, etc. checking out drill presses with a view to ending up with something that won't disappoint!
 
A pilot hole serves to accurately locate the hole position. It will not ensure that the subsequent hole will be true. In particular if the spindle is not repositioned directly over the pilot hole or the drill is bent it is almost guaranteed that the hole will stray.
 
RJSakowski said:
A pilot hole serves to accurately locate the hole position. It will not ensure that the subsequent hole will be true. In particular if the spindle is not repositioned directly over the pilot hole or the drill is bent it is almost guaranteed that the hole will stray.
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Hi RJ
I was thinking about that. Once the pilot hole with a generous first countersink is made, and the drill gently centered on it, at that stage, if the guide is clamped so that all is spinning true, before any real pressure is applied, you have the guide insisting that the drill will not buckle, because it is supported over a shorter length.

There is a quantity L/Ryy appled to stanchion buckling that seems to have a direct application to drill bits. It is the length of unsupported steel divided by the radius of gyration across the weaker axis. Like take a plastic ruler and push it's ends together. It bends in the obvious way, because the second moment of area in the other axis is such that it will be harder to bend the ruler that way. In the same way, when I press hard on a drill bit, so that it "curves", it is not going to take too much of that kind of treatment if it is rotating at the same time. So OK - it snaps. When a drill free length to thickness ratio allows "bend", it is for sure also going to wander off course.

It is a long time since I dozed off during that lecture, but I think if L/Ryy exceed factor 18, (I think .. it may possibly be another value), then buckling is likely.

To my mind, if the drill is so forcibly supported along it's length that it is constrained to rotate only on it's axis, that will minimize the opportunity to "go off course". Pehaps, despite all this, it can still cut unequally, and wander off course with a force so large that it can take an angled route through the material, regardless of forcible upstream alignment constraints! Maybe - I just don't know, but if it happens, I would consider that the more remarkable. My mind says that if you force it to stay straight, it is likely to stay that way.
 
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Hi Doug,

I think your problem has less to do with the setup than it does with the material. If you had satisfactory results with wood, then you just need to alter the process for the aluminum a bit. First you need to be a pecker. That's right!. You should peck the work while drilling. Make sure it's securely clamped and feed the drill in pecks. Don't push. Let the drill do the work. Take a small bite then back the drill out of the hole, over and over.

That will do two things: keep the part cool, and minimize the wandering caused by excess pressure or improper tip geometry. Aluminum is renowned for being gummy and heating up quickly. When it heats up, it moves like crazy. These factors make it very easy for the drill to get clogged with material that welds to the tip and then wander off center.

Give the pecking a try on the next piece. I think you'll be surprised. Also a bit of coolant wouldn't hurt either. Hope this helps.

Best Regards,
Bob
 
rjs44032 said:
Hi Doug,

I think your problem has less to do with the setup than it does with the material. If you had satisfactory results with wood, then you just need to alter the process for the aluminum a bit. First you need to be a pecker. That's right!. You should peck the work while drilling. Make sure it's securely clamped and feed the drill in pecks. Don't push. Let the drill do the work. Take a small bite then back the drill out of the hole, over and over.

That will do two things: keep the part cool, and minimize the wandering caused by excess pressure or improper tip geometry. Aluminum is renowned for being gummy and heating up quickly. When it heats up, it moves like crazy. These factors make it very easy for the drill to get clogged with material that welds to the tip and then wander off center.

Give the pecking a try on the next piece. I think you'll be surprised. Also a bit of coolant wouldn't hurt either. Hope this helps.

Best Regards,
Bob
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I have to agree with all of this - it worked for me! Exactly that technique, simply explained!
Be a "pecker"?? Great!

P.S. THis whole thing has got me drooling over --> THIS
 
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