How do you Drill?

[Mosey]

Which do you use, a center drill or a spotting drill to locate and start holes?
Do you sharpen them when dull, if so how? On a drill doctor? What angle?

 

[Blogwitch]

Mosey,

If you look at the smallest centre drill, basically the nose on it is a standard 1/16" twist drill, so it can easily be deflected, like normal drills and the end will snap off.

With a small spotting drill, the tip is ground into a very fine pointed four facet design that allows it to start very easily, so you should encounter less breakages, if at all.

Spotting drills are designed specifically for starting off holes for larger drills, whereas centre drills are not, they should really only be used for drilling a centre into the end of a job when supporting the piece between centres on the lathe or mill.

In fact, I always spot drill now before using a centre drill, less breakages all around and you are almost guaranteed you will be spot on centre.

Neither are really, in the small sizes, worth resharpening. Both spot drills and centre drills, because of their lower cost, should be classed as disposable.

Here in the UK, this is where I get my small cobalt spotting drills from, and they really do last a long time, unlike centre drills, which snap the tip off at the slightest excuse.

http://www.engineeringsupplies.co.uk/drilling-c-160.html?page=2&sort=4a&9=172

I hope this helps


John

 

[Mosey]

John, thanks.
I never broken a center drill, but sometimes they burn or dull when used on tough stuff. I have eliminated tough stuff wherever I can (coward).
But, having said that I will explore the world of spotting drills, which are Not cheap on this side of the pond (nothing is).
I take it, I could sharpen center drills just like a twist drill if so inclined?
This week, taps are breaking!!!! I am going to evaluate what brand I am breaking. They ain't cheap either!

 

[hobby]

I use center drills, because I don't have spotting drills, and it seems center drills are the most common around here for starting holes on center for drilling, with that said, I have had my share of center drill tips snapping off, it would happen when I go in to deep without backing out to clear the chips, if those chips don't clear out, it seems that the tips will twist and break off.
(on the #1 center drills)

 

[Paulsv]

I switched from center drills to spot drills for locating and starting holes, and I really like the spot drills. They cost more, but I think they are more accurate, and no worries about breaking one. Never tried to sharpen one. They seem to last forever.

 

[Blogwitch]

Mosey,

For really tough stuff, I purchased a couple of the solid tungsten spot drills, but I don't use them very often.

You are quite right, centre drills are sharpened to a standard twist drill tip, in fact, if you could grind them four facet with a 118 degree angle and 7 degree relief, they would centre and cut a lot easier, but it seems that no manufacturers do that. Lubricate them as you would a normal drill, in fact, for spotting with a small centre drill, you could use an old machinists trick of putting a bit of spit on the tip before drilling, instead of oil. It used to work for me when I couldn't find the oil.


John

 

[firebird]

Hi

John I have just looked at the site where you buy your spot drills from and I see they list two types, 90° and 120°. Which one do you use?

Cheers

Rich

 

[Blogwitch]

Rich,

I use both, the 90 I use mainly as countersink bits, hole deburring and for very small drills, the 120 for starting off drills of say over 3mm.

I have made up a set with both angles, from 3mm to 8mm, all in cobalt plus doubled up 3 & 4mm in tungsten. All are still cutting like brand new, despite being used almost continually when I am in the shop.


John

 

[Mosey]

I found a couple of these spotting drills mixed in with my countersinks, and they have dull tips, so how would I sharpen them? They are HSS.

 

[Blogwitch]

In all honesty Mosey, I personally wouldn't even try to sharpen them, unless you have a good tool & cutter grinder.

They are ground to perfection on the tips, just so that they work so well in the job they have to do. If you try to resharpen them yourself, all that precision and accuracy will be lost, and they will be no better than a hand sharpened twist drill.


John

 

[Smifffy]

A very informative thread gents

I'm off to buy some spotting drills.....

Smifffy

 

[Mosey]

Thanks, Bogs,
I think I'll get a couple and try them. Cobalt, I guess.
I constantly amaze myself at how little I know!

 

[Blogwitch]

Mosey,

You could make little handles for the dull ones you have, stone the edges a tad and use them for deburring holes or as small hand countersinks, they will be just the job for that sort of work.

So nothing lost


John

 

[Mosey]

Great Idea!
Then I'll market them in a designer-collection called "Bogstandard" and send you royalties.

 

[Blogwitch]

That idea is nothing new Mosey, I have been using similar things for many years. I have a favourite one that I use for deburring holes on the lathe, I must have made it about 30 years ago, and it is still doing a great job nowadays.

As I said, if an old worn out tool can be used for another less demanding job, nothing lost at all, in fact, you could call it a gain.


John

 

[xo18thfa]

Spot drill is the correct method, but a #3 center drill is all I ever use. Toss them when the get dull.

 

[firebird]

Hi

Thanks John, I'll order some and give them a go. I bought a pack of small centre drills a while back at a show (cheap of course) and have chucked them in the bin. They kept snapping off, at first I thought it was me but on closer inspection they are not even ground centrally.

Nice tip on the centre from arceurotrade as well. I was in there yesterday buying some new gears for my mill if I'd read your post earlier I would have bought one. Next time though.

Cheers

Rich

 

[Captain Jerry]

I use a spot drill because I learned of their existence on this forum. Another thing that I learned here, I think, is that a center drill is used to make a seat for a tailstock center, and that the hole made by the tip is just to provide clearance for the point and that the center drill must penetrate the stock deep enough for the shoulder of the drill to form a counter sink that provides the seat for the tailstock center.

So the real problem with cheap center drills is that they break, and that because of the simple geometry of the point, they produce a small flat area at the bottom of the hole which doesn't guide a very small drill bit very well.

Jerry

 

[Blogwitch]

Just a little more information about centre drills.

There are a few other types that you may come across in your travels, and maybe don't know about.

The first is a 'protected centre' centre drill. These are usually used in shafts that go through bearings, where to disassemble, the ends of the shafts are beaten with hard things like hammers etc. So when the end of the shaft gets damaged, the centre drilling should remain untouched, so allowing easy mounting again between centres on the lathe, to get rid of the end damage to the shaft.
I don't have a picture of one available, but I have shown what they are like on the C-o-C at the bottom, the top sketch.

The next, and more important one for what we do is a radiused centre drill. This is a piccy of what they look like.

These are used mainly when turning between centres when the tailstock is set over for taper turning. If you can imagine, the centre can't sit correctly in a straight sided V centre, purely because the shaft is at an angle to the centre in the tailstock, but can sit correctly if the sides of the V are curved. I have tried to show what I mean in the C-o-C. On the bottom half of the sketch, the top picture is a normally drilled centre and the bottom one is done with a curved centre.

I have had a couple of these in my collection for many years, and use them whenever I am doing offset taper turning. I also have a few protected centres, but because they are too large for my tailstock, I have never used them. I suppose I should buy some smaller ones rather than relying on freebie donations.

I hope this helps


John

 

[Mosey]

Learning never stops!
thanks Bogs.