I hate centre drills…………..

[Clive HartlandParticipant @clivehartland94829]

Ebay has spotting drills, but dont confuse the type used to remove weld spots on vehicle bodies. There are several sellers who have varoius sizes and even up to 20mm.

Clive

[Anonymous]

Some interesting ideas here. I use centre drills mainly for creating holes for centres when turning, and for starting drills in the lathe. Hadn't thought of using spotting drills in the lathe for starting drills, although I do use them on the mills.

Gray: My drill chuck isn't keyless, athough that's not to say I haven't been damaging the ends. I'll have to have a look nexy time I use one.

The bits of the centre drill I broke last night came out easily with a pair of small pliers. The one I broke a few weeks ago was removed by plunging in with a centre cutting carbide endmill in the drill chuck. Goes through HSS with no bother. Fortunately I needed a bigger hole in the part anyway.

Spot drills are usually carbide, so much stiffer than HSS. They're also used to provide a chamfer on the hole as well as providing a start for a twist drill; two for the price of one.

I'm pretty sure my tailstock is on centre; the lathe turns parallel to within a few tenths when using tailstock support.

I've extracted the centre drills from the bin, and transferred them to the 'Broken HSS' bin instead.

I think that part of the problem is the 'quality' of the no name centre drills. They might be hard but they seem to be brittle. I've got boxes of small centre drills for use on the repetition lathe, and I've never had a problem with them. But they're Dormer, and also all left handed.

Basically I'll have to be more careful in the future.

Regards,

Andrew

[Roger Williams 2Participant @rogerwilliams2]

Same daft question from me too !!!!!.

Roger

[JasonBModerator @jasonb]

Same answer at the top of this page, assume you missed the second page

[speelwerkParticipant @speelwerk]

Long time ago during traveling the UK I bougth the smallest centre drills I ever came across, shaft of 2.34mm with a tip of 0.38mm. Very delicate to work with and now only one left, searching the internet found nothing this size but perhaps someone know where to buy them. Niko.

[Tony Pratt 1Participant @tonypratt1]

The bottom line is, use centre drills only if you have too. I don't know when purpose made spotting drills were invented but CNC seems to have given them a high profile these days, they are some much more robust than centre drills.

Tony

[alan-lloydParticipant @alan-lloyd]

Buy Dormer don't be tempted by cheap prices, run fast, will last you for years, regards

[David Clark 13Participant @davidclark13]

Hi There

An engraving cutter makes a great centre drill.

Works on angled surfaces as well.

regards David

[Ian PParticipant @ianp]

David

Be good if you could elaborate on the engraving cutter. The ones I have used have tapered shanks and only fit into the right spindle. They are ground a bit like 'D' bits so do not really have a point.

How much of an angle will your cutters tolerate before skidding off?

Ian P

[John Stevenson 1Participant @johnstevenson1]

David,

?????????????

You been at the pop early tonight ?

[Clive HartlandParticipant @clivehartland94829]

You can buy parallel shank engraving bits as Gravograph use them and so do Alexander machines. They come in HSS and Carbide. All pre-ground with clearance etc.

Clive

[Ian PParticipant @ianp]

Yes, I understand that Clive, but they are ground presumably as engraving cutters so are they good for centering purposes on sloping faces though?

Ian P

[John McNamaraParticipant @johnmcnamara74883]

Yep centre drills are easy to break…. Particularly if you run them slow with a heavy feed. Centre drills have little clearance and a fairly blunt point for their diameter. I find if you crank up the speed and use a gentle touch on the feed they last a lot longer. (don't forget a little cutting oil)

I guess most lathe work is done at a lot less than the operating speed of a HSS drill of say 2.5mm (The tip of a medium size centre drill in my kit measures about 2.5mm.)

A standard 2.54mm high speed steel jobber drill 2.54mm in diameter should be run at between approximately 1000 RPM and 2000 RPM drilling steel depending on the alloy and hardness. even more for brass and aluminium.

I guess most lathe work is done at a lot lower speed, say 500 to 1000 RPM. And there lies the problem the setup for the work is too slow for centre drilling.

I suspect most breakages are caused by excessive hand feed for the speed used, causing an excessive tooth load.

Whenever I break one it reminds me to be more vigilant. If your speed is too low easy on the feed handle.

Regards
John

[NJHParticipant @njh]

John

I'm sure that you are right – speed coupled with, I suggest, the lack of "feel" by feeding the drill into the work with the tailstock handwheel .

Regards

Norman

[BazyleParticipant @bazyle]

Good point about using too much feed & force. I think my eyes see the fat body so brain goes into big drill gear and forgets the end is a little drill.

[FMESParticipant @fmes]

I must be honest I had never heard of a spotting drill prior to this thread, so consequently have never used them.

I can't see how they would be useful for drilling lathe center holes so I don't have a use for them there.

Looking back over the years I can only think that the times I have broken a center drill was when it was used in a jacobs type chuck rather than a R8 collet, and I don't think the center drills that I have are anything special make wise.

The last job that needed a 1mm pilot hole through some 1.6mm brass, a spotting drill would not have fitted in either my chuck or collet whereas a standard center drill did, owing to its larger shank.

I don't think i do anything that requires 'micron' tolerances – the nearest 'thou' is good enough, so effectively I cant justify the expense of buying spotting drills for a limited application.

Horses for courses I think.

Lofty

[FMESParticipant @fmes]

I was thinking more along the lines of 'ouchiness' involving **LINK**

[jason udallParticipant @jasonudall57142]

A futher benifit of spottin drills…they cut very true,,straight and to size.finish is good too.

[Sub MandrelParticipant @submandrel]

Crikey John, you nearly gave me a heart attack! The first one on the list is:

20.0mm Carbide Spot Drill (120 Degree) £90.34

But then it is carbide and 20mm diameter! More useful general purpose 3-5mm cobalt (HSS) ones are less than £3,

I found mine in a one of those 'several hundred mini drill tool' selection kits bought cheap in Costco.

Neil

[mechman48Participant @mechman48]

Me too! just broken a BS1, fortunately had enough material to machine away & release broken pilot & start again. Also broke a 4mm tap in a QC tool holder adjusting screw.. didn't realise it was so hard… ended up making another, so had to machine away the collar, left me with a surplus knurled 'bit' for my odds 'n' sods box

George.

[JasonBModerator @jasonb]

Lofty they are not used for drilling lathe ctr holes, they are used to start a drilled hole so you must have a use for them whenever you want to drill something in the lathe? Or use a CSK to finish the edge of a hole.

Also if you were able to fit a ctr drill into your chuck whats to stop you fitting a 3mm or 1/8" spotting drill into the same chuck?

I would say in my workshop that ctr drills now have a limited application eg just drilling for when you want ctr support and the spotters every time I drill a hole in the lathe or use the DRO to set hole positions on the mill. I just have 1/8" and 3/16" ones no real need for the big ones unless using to CSK or de-burr at the time of spotting which start getting a bit more expensive.

[FMESParticipant @fmes]

My point exactly Jason, no good for a center hole, and to date the simple center drill and follow up drills have always sufficed in the lathe.

I think I said I wanted a 1mm pilot hole, my chuck doesn't close down that far and will not hold a 1mm drill, so the center drill with its larger shank was used – no probems.

I can understand that if running a CNC setup and having to drill a large number of holes to correct size in one go rather than two is far more practical.

Edited By Lofty76 on 14/10/2013 14:12:32

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