I hate centre drills..............

Thanks Jason

Where can I come across some of these?

Dougie

Oh dear Rik!!

I don't know about spats but how about cod liver oil and malt , school milk (yuk), Bengers, food parcels from Australia, milk in glass bottles with cardboard tops left by the milkman with his horse & cart, groceries delivered weekly by the grocer's boy who would also take down the next weeks in an exercise book. Lorry chassis, with no bodywork, being driven to the body plant by a driver swathed in coats, scarves, hat and goggles. Radio sets powered by accumulators, eating breakfast in the winter with just one small black "Valor" paraffin stove to heat the freezing room .............

Ah the good old days!

(They seem good in retrospect though and I don't remember feeling at all deprived at the time !)

Centre drills? -good reliable, traditional tools - Spotting drills? bah humbug!

Regards

Norman

Edited By NJH on 29/09/2013 20:05:37

I use the HSS Keo ones from J&L/MSC as I like the imperial sizes Page 115 of their virtual cataloge.

But you can also try Cutwell, Engineering supplies etc

I thought I had posted this method of recovering from a broken off centre drill previously but I cannot find it so took a picture today of one that I reground a few years ago.

It was a 3/16" diameter slocumb bit that I broke the point off in a stainless steel job. The tip was stuck in a part that I had almost finished machining and the material was not long enough to shorten and start again.

I cut a deep 'screwdriver like' slot just a fraction wider than the diameter of the drill and just went in again with the modified bit which just removed the metal surrounding the broken tip (which fell out when I withdrew the cutter)

Basically the same as JS's single point trepaning tool but has the advantage that it is stronger and self centres itself. Another benefit is that the end result is just a slightly deeper centre hole.

Ian P

PS, I cut the slot with a 'Dremel' type cutting disk

Edited By Ian Phillips on 29/09/2013 21:11:26

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

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

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

Roger

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

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.

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

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

Hi There

An engraving cutter makes a great centre drill.

Works on angled surfaces as well.

regards David

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

David,

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

You been at the pop early tonight ?

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

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

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

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

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.

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