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I have often opened a 6mm hole to 8 or 10 mm without any wobble and my machine is not "Top-of-the-range" model, just a cheap Chinese Monday morning job. Very seldom do I need to bolt down the vise, the larger drill just centers itself.

But for anything bigger, such as 12mm, yes I do bolt it down, got fed up chasing the vise and job around the floor !

A pilot hole does not need to be any larger than the chisel point but for 8mm a pilot is not really necessary. This is virtually a counterbore job and they usually have a pilot to locate the counterbore but as they produce a flat bottom then there is no tendency to self centre. I would expect the work to dance as the drill needs to be sharpened perfectly and be absolutely concentric before starting to cut and even then it stands a good chance of grabbing. A normal length jobber drill is not rigid and any tiny misalignment or uneven cutting is going to start the wobble. I don’t know why you didn’t have the problem with your old drill but what you describe is to be expected in my experience, the dancing also tends to leave a rough edge to the top of the hole. A heavy vice and accurate alignment help but clamping is the best answer.

Mike

Sounds like one lip of the drill is cutting while the other is not. Consequently, the drill is trying to rotate the work.

This may be because of being loose, the drill / work alignment is poor.

If the vice is bolted down, it is far less likely to move, because you have greatly increased the rigidity of the whole system.

If the vice grip is inadequate, the drill could still pick the work out of it. .

Also you will have greater control over the feed rate, reducing the cutting force, and with it then tendencey to move.

Howard

Edited By Howard Lewis on 16/01/2020 14:18:00

If you have a Bullet-style drill in the target size (ie with pilot nose) you can drill a pilot to match and the Bullet drill will then start cleanly and follow the pilot hole.

Edited By ega on 16/01/2020 14:40:26

Hi Bill, not a good idea if the hole is more than a few mm deep.🙂

Perhaps a point in favour of the notoriously sloppy, affordable, import cross vices! As I've said before mine is good enough to quickly bring the work under the drill in, hopefully, dead nuts alignment. However if it is a touch out there is sufficient slop for the drill to bring the workpiece exactly where it wants it with no risk of the whole kit and caboodle being slung across the workshop.

A very large drill running slowly can also wobble the table on my big Pollard 15AY floor standing drill. That machine has proper square section vertical ways for the table to run on and a double screw jack to lift it. My gibs are set so it lifts and falls without undue effort so clearances are very small. But a big drill on bottom speed can still wobble it. There is provision to use one adjuster as a table lock screw but I've never bothered to actually use it. Given that it appears to have been painted over in the factory around 1950 something when, I think, the drill was made Mr Pollard clearly didn't consider it very essential for normal folk either. But there for the just in case jobs.

I get the impression that most folk are far too tentative with drill feeds and speeds. OK the book values probably assume good lubrication but push it in firmly at something approaching the correct speed and it will settle in cleanly without wobble. If you pull back before the drill has reached full diameter and the cut surface has visible radial ridges running across it you are probably not feeding hard enough and quite likely running too slow. If the grind is a bit off centre or one cutting lip doing all the work this sort of thing is much more likely. Despite what the experts say hand sharpening drills properly is a considerable skill needing regular practice. A good jig system is far better for normal folk. Unfortunately all the affordable ones are, objectively, imperfect in greater or lesser degree. Often "crap". Some tools should just work. Properly. Its wrong that it takes Graham Meek or someone of equivalent skills to figure out how to rework a commercial product so it does what it said on the tin.

As Mike said a pilot hole the size of the chisel point is plenty. The more of the cutting edge actually engaged in the workpiece the more stable it will be. Nibbling a mm or a few tens of thou off the edge is a recipe for disaster, probably wrecking the drill in the process. I have a, fortunately, elderly and duplicated drill with approaching half an inch from the end down undersized by 80 thou due to being forced into a pretty hard workpiece to enlarge the hole. Needs must and sacrificed for the job but the final kick to getting my Clarkson drill grinder attachment sorted and fitted as being the only think I have capable of bringing it back to size with a truly central point.

Clive

Come to that, neither was the material. if it's brass and using a pilot drill first with regular drills, I wouldn't be too surprised at this behaviour.