Spotting Drill or Centre drill.

[thaiguzziParticipant @thaiguzzi]

Both. Whichever I get my hands on first.

[larry PhelanParticipant @larryphelan54019]

Hi Everyone,

Looks like I got my sums wrong regarding spotting drills/stub drills. I,ve just been looking them up and they are a different beast altogether,so well they might be,when you see the price of them !

No doubt it depends on your level of expertise,but I suspect that not many could justify the cost of them. This might explain why I have never seen them offered by any of the usual suppliers we use,I dont think they would exactly fly off the shelves.

I never heard of them until now [like a few others ],never saw one even,so I think I,ll stick to my center drills,for now.

One thing I love about this Forum is the amount of information to be had,to say nothing of the advice,and all for free !

Keep it up,and I,ll check before I make another blunder.

[JasonBModerator @jasonb]

By the time the average beginner has snapped the pilot off a couple of ctr drills they work out no more expensive and as I said earlier £2.50 is not that expensive. Also depends on what you are paying for ctr drills, a BS0  (1/8" dia shank) Dormer has a list price of £20!

They will also save you having to buy a small dia CSK bit as they will do that task too

Edited By JasonB on 10/02/2018 09:35:48

[Chris Evans 6Participant @chrisevans6]

I gave up using centre drills to start drill holes 20 years ago. Spotting drills are they way to go and once purchased are cheap because they last for years and are easily regrindable. Look out for offers from MSC but avoid the solid carbide ones they chip easily.

[VicParticipant @vic]

Well I’m pleasantly surprised. I had thought I may be in the minority but it seems the majority of you use spotting drills.

I now wonder how many of you use it’s bigger brother, the Drill Mill? I only have one in carbide.

[Mike PooleParticipant @mikepoole82104]

Is the spotting drill something that was developed for CNC machining that has found another use in general manual machining? There seems to have been strides made in cutter technology possibly driven by CNC, but as NC and CNC have been around for 65 years or more it may be coincidence that cutter technology and CNC have walked together.

Mike

[MuzzerParticipant @muzzer]

Spotting drills and chamfer mills seem to be almost the same thing. As far as I can tell, the main difference is whether or not they have a sharp end ie can drill directly into stock.

Not sure what a "drill mill" is?

Murray

[robjon44Participant @robjon44]

Hi all, spotting drills are indeed used comprehensively in industry especially in CNC machining, a centre drill is for centring a component that is to be held between centres or to be supported by a revolving lathe centre, it is not however the preferred weapon for starting a twist drill. On a CNC mill or machining centre when all hell is being unleashed particularly when drilling large matrixes of holes it is the easiest thing in the world to blink & miss the centre drill breaking on the 2nd hole, unusually it would be your backside that the bootprint of blame ends up on, in these circumstances a spotting drill solves the problem with the added bonus of allowing the chamfering of said holes before they are drilled, bargain!

Now I realise we ain't all got CNC machines in our private caves (apart from the lucky few) however the same logic applies, whether you use manual, what used to be called "automatic", or full blown computer controlled lathes the same logic applies, for many years I campaigned two 2" capacity bar machines producing 960 various components the large majority of which had holes drilled with HSS twist drills, once I had settled in I invariably spot drilled to chamfer size then drilled to size, in 14 years I never had a spot drill break, I rest my case.

Bob H

[egaParticipant @ega]

I suppose it must be easier to re-sharpen a spotting drill than a centre drill.

[David ColwillParticipant @davidcolwill19261]

I use stub drills in the lathe and mill and have no problems.

Regards.

David.

[Mike PooleParticipant @mikepoole82104]

I seem to remember that JS advocated shortening the fragile tip of a centre drill to preempt it breaking. It serves no purpose when long apart from allowing the possibility of a regrind. From Bob's insight it would seem the spot drill is the cutter of choice for good reasons. If the spot drill was not an option when the text books were written the the centre drill being short and ridged would be best thing to start a drill even though it was probably designed to make centres and not start drills, it just found another use. A carbide spot drill has all the desirable features to provide a start for a drill with the bonus of finishing the hole entry as Bob illustrates.

Mike

[VicParticipant @vic]

Posted by Muzzer on 10/02/2018 11:02:20:

Not sure what a "drill mill" is?

Murray

This is a Drill Mill.

**LINK**

Handy for cutting small V grooves without resorting to rotating the work or the head of your mill.

[MWParticipant @mw27036]

Posted by Mike Poole on 10/02/2018 12:25:41:

I seem to remember that JS advocated shortening the fragile tip of a centre drill to preempt it breaking. It serves no purpose when long apart from allowing the possibility of a regrind.

Mike

I think it gives clearance for the point, for when you actually want to use it for accommodating a lathe dead centre.

Michael W

[HopperParticipant @hopper]

And possibly a little reservoir for lubricant for the old fixed centres.

[Mike PooleParticipant @mikepoole82104]

Posted by Michael-w on 10/02/2018 12:32:51:

Posted by Mike Poole on 10/02/2018 12:25:41:

I seem to remember that JS advocated shortening the fragile tip of a centre drill to preempt it breaking. It serves no purpose when long apart from allowing the possibility of a regrind.

Mike

I think it gives clearance for the point, for when you actually want to use it for accommodating a lathe dead centre.

Michael W

It is usually much longer than needed just for point clearance so can stand a bit of shortening, a fair point Hopper about lube reservoir I do remember ramming as much tallow as I could get in the hole.

Mike

[Chris Evans 6Participant @chrisevans6]

When I started my toolmaking apprenticeship one of the first thing taught was shortening a centre drill point.

[CHARLES lipscombeParticipant @charleslipscombe16059]

I had never heard of a spotting drill when I started my workshop activities and have never used one.

Can someone please tell me how a spotting drill differs from a conventional drill? They are much more expensive!

Is the difference in material? Grinding? helix angle? or what?

Secondly if a hole is started with,say, an 8 mm spotting drill, would you then continue to drill the hole with the spotting drill, or change to a conventional drill?

Chas

[David Standing 1Participant @davidstanding1]

Posted by CHARLES lipscombe on 27/02/2018 12:00:43:

I had never heard of a spotting drill when I started my workshop activities and have never used one.

Can someone please tell me how a spotting drill differs from a conventional drill? They are much more expensive!

Is the difference in material? Grinding? helix angle? or what?

Secondly if a hole is started with,say, an 8 mm spotting drill, would you then continue to drill the hole with the spotting drill, or change to a conventional drill?

Chas

Have a read here **LINK**

[Neil WyattModerator @neilwyatt]

My new spotting drills only have about half a turn of helix and quite sharp points, more pointed than ordinary drills, about 90 degrees.

They are very stiff. You only need one so cost isn't a big issue (I got lucky in a private seller's eBay auction and got 4 and 5mm HSS and 6mm carbide one, all new for £1 plus 1.99 postage ).

You can't drill very deep because of the short helix, but you probably wouldn't want to do a lot of drilling in hard materials in order to prolong their life.

My old 'spotting drills' are smaller diameters and more like stub drills – they have a couple turns of helix but again the sharper point. They were a random inclusion in a set of mini-tool bits.

Once you have used one you will always use one.

Neil

[MuzzerParticipant @muzzer]

Centre drill provides clearance for the point of a lathe centre. Spotting drills are often also usable as chamfer mills. However, chamfer mills aren't always usable as spotting drills – they need to have pointy ends for that. You can also get "mill drills" which have a 90 degree point and double as (side cutting) end mills. In that instance, I think you are paying for grinding you won't get to use – either get a chamfer OR an end mill.

Murray

[David Standing 1Participant @davidstanding1]

By coincidence, I just found three 6mm spotting drills (good makes, Titex etc) in a job lot of milling cutters I bought!

[Bob RodgersonParticipant @bobrodgerson97362]

I use Spotting drills on my CNC Mill a lot they are very good for spotting holes and also for machining small chamfers on work.

[Anonymous]

Spotting drill in use marking "rivet" holes on smokebox:

For scale it's a 12" rotary table.

Andrew

[SamsarandaParticipant @samsaranda]

Spotting drills come with two angles 90 degree and 120 degree, as mentioned are expensive particularly carbide but so useful.

Dave W

[Philip RoweParticipant @philiprowe13116]

I've only recently switched to using a spotting drill thanks to advice on this forum, initially to be able to get chatter free countersunk holes in brass, but have found them so useful in other areas. So much more rigid and no annoying pip to get broken off. Expensive in comparison but I think money well spent, well so far for me at least.

Phil

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