# How do you Drill?



## Mosey (Mar 29, 2012)

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?


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## Blogwitch (Mar 30, 2012)

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


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## Mosey (Mar 30, 2012)

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!


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## hobby (Mar 30, 2012)

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)


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## Paulsv (Mar 30, 2012)

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.


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## Blogwitch (Mar 30, 2012)

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


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## firebird (Mar 30, 2012)

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


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## Blogwitch (Mar 30, 2012)

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


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## Mosey (Mar 30, 2012)

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.


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## Blogwitch (Mar 31, 2012)

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


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## Smifffy (Mar 31, 2012)

A very informative thread gents 

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

Smifffy


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## Mosey (Mar 31, 2012)

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


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## Blogwitch (Mar 31, 2012)

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


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## Mosey (Mar 31, 2012)

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


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## Blogwitch (Mar 31, 2012)

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


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## xo18thfa (Mar 31, 2012)

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


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## firebird (Apr 1, 2012)

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


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## Captain Jerry (Apr 1, 2012)

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


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## Blogwitch (Apr 1, 2012)

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


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## Mosey (Apr 1, 2012)

Learning never stops! 
thanks Bogs.


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## vcutajar (Apr 1, 2012)

John

Thanks for all the info. I have learnt many things from this thread, primarily the use of the spot drill. Now to get hold of some spot drills. I doubt I will find any locally but there is nothing wrong in hoping. Thanks for sharing your knowledge as I have started this hobby with no machining knowledge and have learnt things hands on and by reading.

Vince


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## Blogwitch (Apr 1, 2012)

Just to make things a little clearer, I have been out to my shop and had a root through my drill boxes. So here are a few pics to show what I was on about.

On the right are the older style of spot drill, almost a flat plate drill, but still with four facets, and on the left, the normal type of spot drills, these are all 90 degree ones.








I now hope you can recognise these ones as 60 degree protected centres, clearly showing the outer cutting edge that forms the recess. The left hand one has an angled bottom recess cut, and the right a flat.







These are my pair of old and well used radius centres, for when doing between centres taper turning.







Now a couple of ones I have never used, and doubt I ever will.
First a 90 degree centre drill. Where and when it will be used, I have no idea.







This is one I really need help with, it is almost a standard protected 60 degree centre, with an angled recess bottom, but what is the bulge for?








John


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## mocaquita (Apr 1, 2012)

I use stub length drills without spotting almost all the time. With a little care starting, they're plenty accurate.
For critical positions, I'll use a spotter. For really close positioning I'll drill an undersized hole and bore it in postion and usually to size.


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## wongster (Apr 2, 2012)

Hi John,

I'm wondering what sizes of spot drill I should get if I usually drill holes between 2 to max 10mm diameter?

Regards,
Wong


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## rake60 (Apr 2, 2012)

I have spot drills in my toolbox but the center drills are at the lathe within arms reach of my mini mill.
I do use the center drills in place of the spot drill, but I only use them to spot!

I do not drill deeper than the the end angle of the center drill.
That is all you need. Drilling deeper than a spot can cause your drill bit to grab.

Rick


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## AlanHaisley (Apr 2, 2012)

John,
To make a guess about



			
				Bogstandard  said:
			
		

> This is one I really need help with, it is almost a standard protected 60 degree centre, with an angled recess bottom, but what is the bulge for?
> 
> 
> 
> ...



I wonder if someone ever developed a ball end center for more radical taper machining?

Alan


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## Blogwitch (Apr 3, 2012)

Wong,

I have a set that goes up to 8mm, and like Rick has stated, you don't need to go the full width or start to penetrate with the side flute. I just use enough depth so that I clear the width of the flat face of the drill tip, that ensures that it is the cutting faces of the drill than are starting first, and they guide the drill perfectly straight. The only time I would use the large 8mm one would be if I was using say above 1" drill bits.

Alan,

I should really get it mounted up and drill down the centre between a couple of plates mounted on the mill, just to see exactly what shape it does give.
But even then, I don't think it would be of any use in my shop.

Just curiosity really.

John


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## wongster (Apr 3, 2012)

Thanks John. That mean that I don't have to go grab a full set but a few pieces and vary the depth from there. Good stuff! I'll go get some when I happen to be around the tool shop.

Regards,
Wong


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## Smifffy (Apr 7, 2012)

The spot drills I ordered arrived on Thursday and are a pleasure to use.

So much nicer (and with no fear of a broken tip) than using centre drills.

Cheers

Smifffy


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## robcas631 (Apr 21, 2013)

I've done that John and it works but I now use a center drill.


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## robcas631 (Apr 21, 2013)

If a drill is incorrectly sharpened what will happen? Will it drift? In my opinion this is a important question.


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## aonemarine (Apr 22, 2013)

For me it seemed to cause a slite drifting problem and also excessive pressure to drill as it wasnt center cutting well.


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## robcas631 (Apr 22, 2013)

Aone, on youtube there was a training video. A center drill was used first then of course a drill. What was interesting was the emphasis on not using lube as that might cause drifting. What do you think of that?


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## aonemarine (Apr 22, 2013)

Rob,  I dont have the experence to make an honest comment....But to not use lube to stay on track?? sounds a bit hokey...


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## robcas631 (Apr 27, 2013)

smitty, How many flutes?


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## robcas631 (Apr 27, 2013)

Aone, I never have as well. I believe if a drill is cutting at proper speed, drifting should not be an issue. The reason I brought the no lubrication topic up is because I observed it on a youtube lathe training video. I wish I could find these videos.

Rob


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## goldstar31 (Apr 27, 2013)

robcas631 said:


> If a drill is incorrectly sharpened what will happen? Will it drift? In my opinion this is a important question.


 
A drill with two lips of unequal lengths will certainly drift. Again, if a drill chuck is inaccurate in holding a perfect drill- it will also drift or cut an oversize hole. Again, if the chuck is 'out' of alignment or worn or whatever, and the drill is similar, the fault will remain.

You MAY get away with using a thinner drill but the words are 'you May'

This is only 5 lines of reply to what is  a very long, difficult but fundamental subject. I can say that 'some' of my drill chucks perform more accurately than others. They were made to more exacting standards and consequently performed better. The others are worn or  cheap and nasty and are kept for woodwork, drilling holes in bricks and garden gates.

I have no doubt that someone will tell me that I'm wrong. So be it.


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