Drill flute orientation

Hi Chaps

As you all like pondering odd subjects how about your thoughts on this one.

When drilling from the tailstock it is clearly posible to orientate the flutes of the drill any way one chooses. The question is 'does it make any difference'. The assumptions are that the drill is in perfect condition but the tailstock is slightly out in the lateral direction but is vertically on axis. The drill is small enough to flex slightly.

When starting the drill in a small centre hole is the the drill more likely to start true if

1 The flutes are horizontal.

2 The flutes are vertical

3 It doesn't make any difference what-so-ever.

regards Martin

PS The question arises because purely out of habit I mount drills with the flutes vertically.

I was wondering also. I think of a drill in the tailstock as a boring bar, so if the tailstock is out in any direction a flute will be out. This flute edge then cuts a little more, assuming it's stiff enough.

I don't think it makes any difference unless your tailstock is wildly out, in which case you should correct it or not use it for drilling (Unless Taper turning etc).
BobH

My thinking is that, as speedy says, for normal small errors you cannot practically notice any difference. However my thinking is also that for most reasonable lathes there is always going to be a side to side error rather than a vertical error. For small misallighnment the contact surfaces of the drill are going to be the two linear cutting edges. shaped like a V. If they are vertical and there is a small misalignment horizontally each flank will still touch the centre drilled hole at the same time. If they are horizontal and the tailstock is out in that direction one flank must touch first and be unsupported by the oppsite flank at that instant. So as it's as easy to mount with the flutes vertical as it is horizontal all other things being equal you may get a better start to the hole.

What I really wondered was had anyone ever heard of this being mentioned as good practice before. It may be that it's just a curiosity and of no practical value but I am if anything a curious person.

regards Martin

Edited By Martin Kyte on 19/09/2017 12:35:53

Edited By Martin Kyte on 19/09/2017 12:36:40

I also tend to mount drills vertically - when it occurs to me to think about it - because I think the chips can clear a little more easily and evenly that way. But of course that only applies in the first diameter or so of depth, and may be spurious anyway.

It seems to me it's more important to give plenty of time to cut until the full diameter of the drill is engaged - so that if the drill is deflected by uneven lips, even by an invisible amount, you give it time for the elasticity of the drill body to spring it back nearly to truth, and so the full diameter enters a hole as near size-and-centre as makes no difference.

And if your drill is slightly bent, drill chuck errors or made by "Back street China" etc, etc. - I think you worry too much Martin. If you want a really accurate hole, drill undersize and then bore it out, (then ream perhaps?).
BobH

I'm not worrying at all, as I said I've never noticed any difference, it was purely a whimsical question.

regards Martin

I cant say I've ever heard advice mentioned pertaining to their orientation. It's all rotating past the same points on the drill, I spose.

Michael W

Possibly a fourth alternative. If the tail-stock is off centre such that one tip acts a single point cutter, then the best solution might be to rotate the drill to minimise the effect. Not vertical, not horizontal, not random, but an angle related to the tail-stock's XY error. The position that makes sure there's flute space rather than tip at the outer point.

Actually, I doubt it makes any difference because the cutting axis is rotating. Whatever position the flutes are in, the drill cuts

along the axis of the rotating work. That being so the effect of any tail-stock offset will just be an oversize hole. I guess!

Dave

Best solution is to rotate the drill too in a saddle mounted drilling head and then you can have auto feed at the same time, provided you sort the alignment issues.

Rather than think about the question, why on earth don't you fix your tailstock alignment. Then you won't have to ask the question!

Andrew.

Assuming that you have already centre drilled the work, the drill will tend to follow the pilot on the centre drill

Advocates of four, or six, facet drill grinding claim that centre drilling is no longer needed.

Unless the drill has been ground with equal length faces, it will cut oversize.

If the Tailstock is off centre, you will get an oversize hole even with an accurately ground drill, and a good, accurate (concentric) chuck

Howard

OK, it was just a whimsical question.

Judging by some of the responses some people perhaps didn't quite understand why I asked the question.

It arose because of late I have noticed that I habitually set drills with the flutes vertical and thought "that's strange I wonder if it makes any difference and if it does why".

So I was really talking about lathes that are in good alignment, but recognising that nothing is ever spot on. It could be assumed that horizontal alignment is going to be worse than vertical on amachine with low wear as there has to be some clearence so that the tailstock can slide. Clamping holds it down onto the bed but doesn't really ensure tight alignment horizontally on flat shears. The argumant does not really hold on prismatic beds. Therefor if generally the alignment assumed to be less good horizontally in general and if there is no time cost in orienting a drill one way as opposed to another and there is a preferrential orientation it probably makes sense to do it if you could be bothered.

In reality, I think the practical benifits are almost certainly un-measureable to the precision we are ever going to need which is why it was just a rhetorical question. I just wondered if there were any 'old wives tails' out there.

regards Martin

If the flute is vertical then, if it is producing chips rather than a long spiral, those chips will fall away during the first mm but thereafter be lodged in the bottom of the hole just by the lowest cutting edge possibly blocking it and wedging it. However if the edge is horizontal the chips will vibrate down the sloping inner face of the cutting edge, out of the way.

There is a notion that the lathe defines the centre line of the workpiece with the slowest moving material. It moves faster as you move away from the centre.

If there was any way to persuade the drill to follow that line it would be wonderful, but a Jobber bit has no cut in the centre so I thought it would shy away from that non-moving centre line.

Then I realised that there was no way the Jobber drill could tell it had shied because as far as it was concerned, it's own centre is always the slowest moving.

Then my brain imploded

If you put the cutting edges horizontal you can apply a rigid sideways displacement to a wandering drill tip by running the cross slide up against it. This cuts a perfectly centred conical dent which guides the bit back on course as you release the pressure.

I had a Boss that said to orient the cutting edges horizontal made it cut closer to size, seemed to prove out.

Yeah, yeah, but haven't you now actually got a truncated conical dent, with a flat at the bottom that's wider than the effective width of the chisel point of the drill, so losing any guidance to continue cutting on centre?

Apart from internal elasticity, that is. That's why I think it pays to pause and let it cut on springback to centre. Or maybe that's just another variant of what you're suggesting.

Maybe it's easier just to leave some mysteries alone...

Yeah, yeah, but if the name of the game is remembering some way the flute orientation could possibly matter then I think I can claim a Brownie badge. There is no fun being a smart arse if there are no badges to collect you know

You need Mozart drills, the ones with a magic flute.

Neil