Having to `make-do’ with a very limited amount of workshop equipment and tools, I was preparing to make a soldering jig to hold a couple of clock parts together while silver soldering them.

I marked out a piece of 8mm thick gauge steel ready to drill some 1/8″ pilot holes. Each hole position was centre-popped ready for picking up with a centre drill. Rather than drilling sideways in the lathe, using the tailstock to align and feed the steel towards the drill, I chose what I thought would be the easier option, ie. to use a friend’s vertical pillar drill.

With eyesight leaving much to be desired, I’ve used a 4″ binocular magnifier for most of my work on the clock. However, judging angles etc. through these devices is less than satisfactory, while my friend seems to pay little attention to securing his machines to the bench. Some of the albeit small equipment tends to wobble or wander a little, requiring special concentration on several things at once. As I began to apply pressure to the almost new centre drill aligned with the first of the centre-pops, the centre drill began to travel sideways. Before I realised what was happening, I had machined a slot into the surface of the jig.

It was about then that I noticed the quill of the drilling machine was tilting to starboard, relative to the support column. Closer inspection revealed that the drill head had not been correctly manoeuvred down into place over the column. Instead, it was being held up by one of the locking screws sitting on the top edge of the column.

Feeling somewhat concerned about machinery drifting across the bench, it was time to leave. I returned home and have since completed the jig using the lathe as a horizontal drilling machine.

Apart from the obvious ones about safety etc. questions arise like :-

Edited By Sam Stones on 03/08/2010 01:43:13

Hi Bogs & Nigel,

Thank you for your very useful replies. I’m pleased too, that others are also finding your information useful.

I had a feeling there was a CNC connection, especially when spot drills are produced in carbide. I might (eventually) have come across them had I not sold my Taig Micromill.

Your point about a centre pop ` . . being even a tiny bit out . . ‘ etc. is very true.

Wrt the link, Nigel’s question regarding 120 and 90 degrees suggests to me that 120 deg suits the normal drill-tip angle, but where does 90 degrees fit into the picture? Could it be that a 90 deg tip is even more `stable’?

There’s a reference to cobalt and carbide, and I can see a significant price difference. I understand that carbide will have a longer life, but is cobalt just another name for one of the HSS’s which, according to Wikipedia (and a couple of `still connected’ neurones in my brain), sometimes contains a percentage of cobalt?

Interestingly (I trust), the stem and ball of my right hip joint is cobalt chromium. This alloy comes close to matching what we often used, when `drilling’ through hardened steel in those early days, ie. Stellite.

Thanks again,

Sam

Posted by

Andrew Johnston on 17/09/2010

I hate centre drills! You’ve only got to look at the smaller ones and the centre bit goes ping.

Hi Andrew,

I’m inclined to agree with you, having on a (very) few occasions had to dig out the tip of a centre drill from a workpiece. However, over the past 60 years of my engineering career both practical and academic, I have either been too blind or too stubborn to notice the alternatives. I have to admit to never having `discovered’ spot drills until quite recently, thanks to you kind people who have tugged at my reins with your postings.

Like me, when you know no better, you become quite skilled at getting the best results from a particular piece of equipment. For me, centre drills have burned their place into my brain, and thus became my automatic choice. Considering the amount and range of specialised equipment I have built over the years, it now seems quite remarkable how I’ve managed to get away with using nothing else for locating a `marked-out’ hole position.

Getting the most out of a piece of equipment has reminded me of working on the apprentice’s lathe back in the early 50’s. Driven from a 10HP electric motor via an overhead counter-shaft (running the length of the shop), the lathe had a three-step pulley and when it was running, it had about 5 yards of flat belt flying past your left ear.

It was a cow of a machine!

My main tasks were turning ejector pins for plastics moulds, and much larger aluminium shrink-pins (used for controlling the diameter of hard rubber textile bobbins during their steam curing process). Applying more than a ten thou cut, the long thin ejector pins were likely to leap over the tool bit, and the tail-stock never seemed to stay on centre no matter how many times it was re-adjusted.

Changing speeds was also a skill in itself. Aided by a five foot long `spare’ wooden lever which was slightly notched at one end, the out-of-reach (overhead) end of the flat belt had to be jabbed from below to flick it from one pulley step to the next. Then, down at lathe level, the belt was give a swift slap with a flat hand to get it to jump onto the lathe pulley. I suspect that the entire workshop (even the factory) would be closed down under current `work-practices’ regulations.

In closing, does anyone know the name of the steel which we referred to as BND? This was a tough steel which was later hardened, tempered, and then ground to size.

Happy centring.

Regards,

Sam

Nice to know about your experiences, Ian.

I can’t remember whether it was before or after my RAF National Service stint, that the company where I was serving my time, actually motorised individual machines. However, by the time I was back in the toolroom and close to getting my ONC Mech. Eng. I was operating one of their brand new Super 7’s, with lots of Myford add-ons. Not forgetting those centre drills of course.

A couple of years later I was in the DO, the place where I had set my mind to be at age thirteen.

It’s amazing where this centre-drill posting has taken us!?