Let's talk about Drill bits, specifically twist drills.

For the lathe I bought some extra 2nd hand old drill bits up to 20mm, cut the rear ends on lathe so they run truer, use them to cut holes, I don't care just resharpen, before using a boring bar.

If I just want to cut a hole I used new ones in lathe.


If I want to drill a small hole op to say 6mm between two edges in the centre, without having DRO, I mark it accurately, then punch a smallest hole as I can using magnifying glasses, then work it from 1mm drill to the size, a bit time consuming(Chuck must run true).

I recently find that the carbide cutters I aquired rather like to plunge down and drll better if I just paint the cutter with cutting oil, wipe it off, and go ahead, the chips fly ou/evacuatet nicely, after many use nothing sticks to the cutter tips not even alinimium, unlike oyher cutter tips I have.. If I flood it with cutting oil by hand, the chips/swarf tends to stick around, and on replunging down, (CNC floodcooling probably properly solve that problem), it may wonder on previous chips before cutting. I am not sure if this is true for any carbite 4 flute endmil cutter. The cutters comes from Gesag base.
 

Edited By Chris Mate on 12/12/2022 22:10:45

When I did my apprenticeship, drill sharpening was essentially the apprentice job to keep them sharp and on drills all over 4mm. Under 4mm they were discarded. So I got a lot of small drills free. Now days , people don't like learning, and anything that seems like hard work is avoided as there are now drill sharpening tools that do a very good job in a timely manor. Often the home shop does not have the best grade of wheel for sharpening drills on, as often they come with hard wheels , suitable for general grinding of soft steel. Few know about using diamond dressers to re dress a wheel, and if they need a fine dress or a course dress. Touching up a dulled bit is easily done with a fine dressed white wheel. But a drill with chips or heavy edge rounding will be best if started with a course dressed wheel as it cuts cooler. Some my be lucky enough to have fine or course desic CBD wheels to sharpen drills on. But that is what often the serious wood turner has at their disposal and sometime come up for sale at a very good price.

One thing I do, is use a basic clearly graduated rule, I like the small Toledo ones, and measure the length of the drill sides. In general they will be about 1/2 the diameter of the drill or so, and of equal length to drill an on size hole, assuming that they are held at the same angle to the wheel. After a while , you get used to making your hands the fixture to get the angles even and adjust the back off to suite the material and rate of drill advance etc.

When you have a drill, and the hole is oversized, the side with all the chips is the one doing all the work. So just take a little more off the side with no chips to get it back closer to cutting evenly on both edges to get it back to size.

Another trick, when we did not have reamers, was to radius the outer cutting edges with a stone, and run that through at a slower speed, to get a very close to size hole. When done with castor oil, it would be very close to the drill size. This was for things like odd sized ejector pin holes in plastic dies etc.

Where ever possible, would drill the hole with the largest closest drill we had, up to 1.5 inches or 38mm diameter. Just start with a spotting drill, or centre drill, and in with the drill. This is when you find out, how important web thinning is.

Yes, learning the bench grinder to sharpen drills, and make and resharpen HSS turning tools and form tools of all types, is time excellently well-spent that repays itself for ever.

One useful point in favour of centre drills is that the pilot cuts on the side as well as the lip, which means 2 things:-

i) the centre hole is effectively bored - truly concentric on the rotation, irrespective of any minor misalignment, providing it's been allowed to cut till it idles, and

ii) you can use the pilot as a slot drill for narrow and shallow slots - it's at least as strong as a standard slot drill in those size ranges.

Did my apprenticeship in the 1970's, and although I was taught how to grind a drill by hand, I could never get the knack of it.

I eventually made a drill grinding jig to a design in the ME by "Duplex", works very well. I have never used spotting drills but using some drills already ground to 4 facet was a revelation!

Derek

My experience is that sharp, really sharp, adequately solves 90% of drilling problems. Assuming decent quality drills to start with of course. Most of the economy ranges are really for hand drill and the rougher end of pillar drill jobs so wider tolerance bands are fine. You might get a nice one, you might not. Generally the expectation is that such will be broken or bent before blunt becomes an issue.Often the pretty TiN coated ones turn out to have only a thin crust of hard material under the make-up so sharpening isn't possible. Not necessarily a bad thing if the drill is also less brittle. I've seen such cheapies pushed so hard by big guy in a hurry that they are significantly bent and survive.

Even with a conventional point bumping a sharp drill into the work a few times will get you a clean start. But you will have to re-sharpen more often.

Given that both Andrew and I have Clarkson drill sharpeners its interesting to see how different our drill practices are.

Andrew finds that by the time his drills need sharpening they are often in poor enough overall shape that new replacements are appropriate.

Given that the default state of my Clarkson T&C grinder is with the drill sharpener set up any drill whose sharpness is even the slightest bit debatable gets mounted and restored to proper condition. As it's about a minute, on a slow day, between a beady eyed "Hmmn" on picking up the drill to putting something sharp enough to shave with into the machine chuck I see no reason to accept anything beyond the most minor wear. After 10, maybe 20 holes in steel you can feel that the drill has lost its best edge. Still perfectly good for, probably, 'undreds more holes but ....

Clive

Hate to disagree, but in industry as opposed to hobby work, that idea is a 'Dark Pattern'. That is, a practice that seems correct, but actually has negative consequences.

Industrial workers cost money and their output pays their wages. A worker who stops to regrind drills isn't productive, so he's potentially wasting money.

The firm should balance the cost of the worker and lost production against the money saved by sharpening blunt drills. It's usually better to minimise downtime by swapping new drills for blunt ones, and to only send big drills off for resharpening.

Resharpening in-house is an option, but the owner has to consider the cost of the machine, the space it takes up, and paying someone to drive it. And a machine that isn't busy resharpening most of the time is unlikely to be paying it's way. Thus it's often cheaper to outsource than to own a drill-sharpening machine.

Assuming it's sensible to resharpen drills and other failures to tackle cost efficiency partly explains why so many British engineering firms went bust, even though everyone in them was working hard and thought they were doing a good job. Dark patterns are nasty because they often go unnoticed for decades...

Dave

Edited By SillyOldDuffer on 13/12/2022 17:25:28

Yes Dave but that hardly applies in the home workshop. If you take that literally then you either need the means to sharpen to a finished degree - for the most part which isn't necessary - or have new drills for every time one gets blunt.

Sorry mate but can't agree with that principle from a home perspective at all.

That may be fine in highly commercial enterprises but in the myriad of support jobbing shops - without CNC machines - not really a viable proposition. Not many without CNC these days I grant you, but then how long have they been round in comparison to previous machining practices.

For the last couple of days I've been making small 'castings' from solid for the valve lay shaft on the marine engine all drilled with hand ground drills and milled with cutters that have had hand ground radii on them.

As Mick says learn something worthwhile and it stays with you for life.

Best - Tug

Yeah, yeah, yeah... bin there, done that ... it depends on the industry and the type of work. In a repetition shop putting out a steady range of products in a cost-competitive market, of course you wouldn't train operators to sharpen drills, and any who took extra time to do so might lose a piecework element of their pay.

You might have a tooling department to sharpen them along with milling cutters in batches if the cost/benefit sums were right.

In toolroom and instrument shops where the variety of work is very wide and specially adapted tools are often needed on an ad-hoc basis, long lead-times are often saved if you have people who can knife-and-fork a suitable tool capable of delivering the required dimension.

Industry ain't where most of us are - it's a hobby done for fun, so we don't always plan in detail and we're often faced with something we have to make in order to do the work in front of us. So we're much closer to the working environment in the previous paragraph.