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Starting Small Holes

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Brian H29/07/2020 08:11:14
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What methods do people use to start small holes?

I've had a job of drilling 1/32" holes in the end of 1/8" dia brass bar, in the lathe. Normally I would start with a centre drill but the smallest centre drill pilot is to large.

I remembered that I had some solid carbide 0,8mm circuit board drills left over from another job and tried one of these. Worked very well but it set me wondering how others would tackle this.

Brian

JasonB29/07/2020 08:15:08
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Spot drill works for me, I often use 0.8mm for split pins in small shafts and have no problem locating with a shallow spot drill dimple followed by 0.8mm drill.

Bob Stevenson29/07/2020 08:27:54
437 forum posts
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Yes, I use the same basic method as Jason, however I frequently encounter people having problems with small drilling and it also depends very much on what is being drilled and why...... I do have a drilling jig for making lantern pinions which I made from steel by use of a 'too big' centre drill....the holes are in the centres of the 'cones' made by the centre drill and the idea is that the smaller drill will self pilot down the centre o fthe cone.

 

There is no doubt that drilling small holes in flat material is very challenging for new clock makers and others....I always suggest use of a good glass at every stage from the initial marking to checking the finished hole. An optical centre punch is a great aid for many, but perhaps the best method is repeated practice in some scrap until it's no longer a challenge!

Edited By Bob Stevenson on 29/07/2020 08:29:43

Martin Kyte29/07/2020 11:21:05
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A 1/32" drill will go completely inside a larger jacobs chuck so if you install it with only the end sticking out it can act as it's own centre drill. Then you can simply extend the drill to a suitable projection and proceed as normal. I don't need to say run the lathe at top speed.

Even when drilling in the mill or drilling machine I have no more drill length extended from the chuck than I need purely for stiffness on smaller sizes.

regards Martin

John Ockleshaw 130/07/2020 03:22:03
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Hello Brian,

Drill Service (Horley) Limited supply centre drills with a pilot diameter down to 0.3mm diameter, the same as a number 80 drill. I am a very satisfied customer.

Regards, John

Stewart Hart30/07/2020 07:28:15
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I've been having problems centring brass bar for injector cones I've tried various methods but still don't always get it correct a friend uses a little hand engraver it looks a bit like a D bit with the front angled I tried this but that didn't work for me, I found the best way is a spotting drill. I've got a high speed drilling attachment but that doesn't work with a spotting drill, I found the best way is to run the lath at top speed and use the spotting drill, then fire up the high speed attachment and start the drill off with both the high speed and the lathe running then when its going in the correct direction to switch the lathe off. I've started using those circuit board drill to rough the holes out they don't drift off line the only problem is they are a bit short, but get enough of the hole drilled to get the number drill going in the correct direction.

The small drills drill like high speeds they go through like a hot knife through butter with the high speed drilling attachment, only problem I've got is getting them on centre and stopping them drifting off line this is best done by pecking the drill. even though with the high speed it will go straight through.

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John Baguley30/07/2020 09:27:42
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When I was making injectors I used a bit of hardened 1/8" silver steel rod with a sharp point turned on the end. That seems to work quite well for putting a little centre in.

John

Nigel Bennett30/07/2020 09:56:21
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I've had a job of drilling 1/32" holes in the end of 1/8" dia brass bar, in the lathe. Normally I would start with a centre drill but the smallest centre drill pilot is to large.

Why is it too large? It isn't necessary to make the centre drill open up the hole to its full pilot diameter; all you need to do is to make a small dimple, slightly smaller than the hole size you want. (Same with spotting drills.) If you make the dimple slightly larger than the final size, you'll be left with a tiny countersink around your final hole size.

Emgee30/07/2020 10:10:40
1718 forum posts
232 photos

Stewart

Just a thought about your drills wandering off line, perhaps a little run-out on the chuck could cause this ?

Emgee

Barrie Lever30/07/2020 10:18:19
688 forum posts
76 photos
Posted by John Ockleshaw 1 on 30/07/2020 03:22:03:

Hello Brian,

Drill Service (Horley) Limited supply centre drills with a pilot diameter down to 0.3mm diameter, the same as a number 80 drill. I am a very satisfied customer.

Regards, John

I ordered from Drill Service at 14:45 yesterday afternoon and the tools were with me at 8:15 this morning, this is the norm not the exception.

Plus everything from them is top notch quality.

B.

Brian H30/07/2020 15:36:40
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1797 forum posts
108 photos

Thank you all for the replies. A few observations;

I didn't realise that centre drill went down past the No 0 that I have. Also the same with spotting drills of which I bought one recently but the width of the land between the cutting edges is wider that 1/32". I shall now buy a 3mm one.

The smallest centre drill that I have has a pilot greater than 1/32" and I was hoping to use the full length of the pilot to avoid swapping tools.

The service from Drill Service sound good, especially with the huge range of tooling that they do; now saved in favourites.

Brian

Andy Carlson30/07/2020 23:06:56
296 forum posts
123 photos

I've had plenty of success using a No 0 centre drill and conventional tailstock drilling to start small holes (down to 0.3mm). You don't need to go very deep at all, but you do need to make sure that the centre drill has not cut a 'donut'.

Sometimes I find that the centre drill can start with a 'donut' and will then 'find' the centre and make a proper dimple.

If you are working with an over-long piece of bar and the centre drill hole gets too big, you can always face some metal off after you have drilled your small hole.

That's what works for me anyway.

Brian H31/07/2020 08:42:21
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1797 forum posts
108 photos

Thanks Andy, that's a very good point about the donut effect and the facing off.

Brian

John Ockleshaw 101/08/2020 06:30:58
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48 forum posts
7 photos

Hello All,

Centre drills with small pilots will not tolerate any miss alignment between the lathe spindle centreline and the drill centreline Miss match may be due to ,wear on the bedways, wear on the underside of the tailstock body, inaccuricies in the drill chuck or its mounting or the tailstock being twisted sideways.

It is worth the trouble of making a holder for that size centre drill body.

Onto the end of a piece of free cutting mild steel bar machine a taper to match the tailstock barrel. Where it will be clear of the barrel machine a flat, say 8mm square, so you can put the taper back in the barrel in the same orientation every time. If you intend to lock the centre drill in place with a grub screw, rather than Loctite, drill and tap the hole for it now. Cut the taper off the bar leaving say 8mm clear of the tailstock barrel.

Mount the taper in the tailstock, retract the barrel as far as it will go, without ejecting the taper and clamp it. Using a boring head in the lathe spindle, or a slot drill or D bit machine a tight sliding fit hole for the centre drill body into the end of your holder. Fasten the centre drill in place.

Regards, John

Michael Gilligan01/08/2020 06:45:47
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16389 forum posts
715 photos

A few seconds with a graver seems much the simplest way to put a small dimple accurately on-centre.

MichaelG.

Kiwi Bloke01/08/2020 07:53:57
461 forum posts
1 photos

You could poke the drill through a previously-made hole in a bit of flat plate, held in the toolpost, just clear of the end of the workpiece. This improvised drill bush can be well-enough aligned by setting it to the drill shank, as it emerges from the chuck. A well-sharpened bit - even with a chisel point - will then enter the work with no drift, wobble, or need for a centre.

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