Spotting drills

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21 Jan 2017
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Hi folks,

I'd like to make something with accurately placed holes of various sizes, and thought I'd look at what the options are. It sounds like lip-and-spur bits might be a good solution for sizes for which they are available, and another improvement I should definitely make is getting some better bits than the cheap-all-in-one set I got decades ago.

But reading the archives, it sounds like spotting drill bits are another possibility; I believe a 120deg bit for use with your average twist drill. I guess a single 5mm(?) spotting bit would work with pretty much any drill size, as you don't want to actually make a hole as wide as the diameter of the spotting drill anyway, or the edges of the twist bit will hit the edges of the hole before the point hits the bottom.

But when I went looking, I was surprised to not find any brands that I recognise. The sites I found ( ... pot-drills, ... drill_bits and ... ng-drills/) all seem to be selling these for cutting non-wood in not-drill-presses.

So I was wondering whether anyone knows whether I'm barking up the wrong alley, or is this worth a punt? And if it is, any brands to favour or avoid? Finally, are the cheap HSS bits fine for wood, or would I be better off with TiN or TiAlN coated, or carbide?

Thanks for any hints
Spotting dills are used a lot in the metal industry because they are stiff (short flutes) and locate the hole with minimal deflection. I use one for drilling into end grain and plastics for pens. I don't know if it will make a lot of difference when drilling side grain in wood but it isn't a huge amount of money to try one....unless you bought a carbide one. :shock: The carbide ones are the stiffest but also brittle and easily broken. I don't get excited over the titanium coated bits because we don't push them hard enough for woodworking to benefit a great deal from it. I do prefer Cobalt bits as they hold an edge longer and generally made better. Any of the bits in the links will serve you well as they are meant for industrial use and won't be junk.

There are occasions where we spotted holes bigger than the drill bit following. That was for holes being tapped for threads. It provided a chamfer to the hole after the hole and threading was complete.

Spotting drills are usually used on lathes and mills for metal rather than wood. They need a rigid setup to work well because they have a thick web to help keep them stiff.

You might want to look at Stub length, sometimes known as machine length drills. These are about half the length of a standard jobber drill but have the same grind web size. They are available in all sizes and are quite cheap as well. I use them a lot for long hole drilling on the lathe, start with a centre drill (lathe specific) then a stub length, then jobber, then extra long and finally aircraft drill if needed.
The Fisch lip and spur drill are excellent for clean accurate holes you can get a decent ser for under £50 or a set of 5 for under £20 .They are very sharp,I buy the HSS ones.I think Axminster sell them or on ebay.As has already been said the centre drills are really for use in a lathe and not very good for wood anyway.I find it amazing that people are still using the long hole boring techniques that are being used a gun drill linked to a compressor is far more accurate and infinitely faster.I have posted about this before.If I was tech wise I would love to show how good it is by making a short video,but I can't even manage to post a photo on this site ,it's taken me 15 minutes to write this short reply.For turners the place to look is Sterling Gun Drills,a handle for them has to be made but it's a simple task for a machinist.For example I can bore a 12 inch lamp base in less than a minute,perfectly clean and centred.
Thanks all. I think I'll get a lip-and-spur, jobber, stub and spotting bit of the same diameter and see how I get on.

I finally got back to this.

I got one side of a piece of softwood, ash and beech as flat as I could, gathered my 5mm drill bits and made some test holes. All done with the wood against the fence of a Bosch PBD40. Results are below, in case it helps anyone - although not particularly scientifically done by a not very accomplished woodworker, so your results may vary!

The drill bits used were:
I drilled 3 holes with each, with and without using the spot drill first. The middle hole I drilled all the way through (or deeper in the softwood, as it as thicker).

I was surprised that the Lip&Spur bit made the least clean holes. I'd been drilling at 600rpm, so I turned it up to 2500rpm and made another hole with each. Lip and spur was now a lot cleaner, but still the least clean of all the bits. Perhaps they need sharpening, but I'm surprised they don't come ready to use.

I cleaned the surface up a bit with a chisel to look at alignment:

In terms of alignment, the spot drill and the L&S were very consistent.
All the bits did pretty well in the softwood, and not bad in the beech. Ash showed the most variability, and the spot drill didn't seem to help with alignment of the others.

Overall, I think the spot drill was the clear winner, although if I can get clean holes from the L&S bits then I think it will be a tie.


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If you're still willing to experiment further, try "Slocombe" drills (aka "centring drill bits"), primarily used to start holes in metal especially when using a lathe or a mill (though I often use mine in both pillar drill and even hand-held battery drills sometimes).

Available in various diameters, always very short (compared to their dia) and usually double-ended - i.e. you get 2 ready-sharpened drills for the price of one!

Try suppliers like Proops, Arc Euro, or loads of others listed in the sticky at the top of the Metalworking Section".

P.S. Or is this what you've already tried when you said "Center" above?
@Wend. Thanks for the link. No, that's not what I meant. here's what I meant:

Slocombe 12eaab9d-ca9d-4417-beca-a76f00e54f97_180x108.jpg

I lifted it straight from the Arc Eurotrade online Catalogue (usual disclaimers). As so often in "engineering" it's "names". I was taught to call that thing a Slocomber (perhaps a Mr. Slocombe first invented them? Dunno!), but I see that Arc calls them "centre drills". Not shown in pic, but they're doubkle ended and VERY stiff.

@Wend. Thanks for the link. No, that's not what I meant. here's what I meant:

View attachment 92679

I lifted it straight from the Arc Eurotrade online Catalogue (usual disclaimers). As so often in "engineering" it's "names". I was taught to call that thing a Slocomber (perhaps a Mr. Slocombe first invented them? Dunno!), but I see that Arc calls them "centre drills". Not shown in pic, but they're doubkle ended and VERY stiff.

My brother gave me a large set of those years ago. I was under the impression that they were for precision drilling in metal (his original trade was in metal fabrication). I had forgotten I had them until seeing your post.
The intended purpose of a centre drill is to make a hole in the end of a shaft so it could be turned in a lathe. The hole has a 60º angle to match the 60º cone that fits in it. Look at all the products in your shop and home to see how much the metal machining industry rely on them, motor shafts for instance. While they have been used to start holes for drills it was more a convenience than being the best tool. A standard drill has a 118º tip so when you use a 60º centre drill to start the hole your drill bit's outside edges hit the 60º side of the hole you start and they can wander somewhat as they engage resulting in a hole that isn't located properly. A spot drill has a 120º angle (there are other angles to suit the bits being used) and is short and stiff too. To use it you only drill a dimple and when you follow with a standard drill bit the cutting edges locate and engage at the bottom of the dimple and the location stays where it should.

Yup, Inspector is dead right about Slocombe basics. The idea is to get a little conical indent in the end of a piece of bar when working it on the lathe - it's the place for a tail stock centre to go when turning long items - etc, etc, etc. And just to be clear, yup, we're talking metal working here.

BUT never one to "stand on ceremony" (e.g. the VERY small amount of wood turning I do is done on my little Chinese Mini Lathe - "just awful don'tcha know!!); likewise I often use Slocombes quite a lot to start a hole in just about any material, using just about any tool when I want a dead accurate start position. They certainly weren't designed for that job but "they don't 'arf work good". The only "trick" to watch out for is to choose the smallest dia, so you can still see the centre point (they're so short in relation to their diameters that you can often hinder your own view).

And the angle doesn't really matter, especially not in soft stuff like wood n plastic. See below.

Because they're so short in relation to their dia they're also VERY rigid. So IF you do see that you've started your required hole in slightly the wrong place you can use a bit of "BFI" (brute force n ignorance!) to push/pull the work piece better into line to where it should be without much risk of breaking the drill (or anything else).

I GUESS that it goes without saying that when "just" drilling in wood or plastic you use only the small dia at the very end of the Slocombe - as soon as you start to reach the large diameter you stop the Slocombe and change to a "proper" drill to finish the job. Personally I've never found the 118 degree angle of a "normal" drill get bother by the 120 degree angle the Slocombe makes, and of course if drilling wood with a brad point drill it's irrelevant anyway.

I'm sure my old apprenticeship teachers will be weeping in their graves reading the above, but OTOH, no lesser maestro than Tubal Cain (the original one) says in one of his 1940's lathe handbooks that if starting a hole with a Slocombe and if finding's a bit off, you can mount a lathe tool in the tool rest backwards (we're still talking metal working please note) and then push the tool against the Slocombe - a few thou at a time "nudging" the Slocombe back into the proper centre point using the cross slide while the job's turning.

If it's OK for TC Esq then it's definitely OK for me (a bit of "knowledgeable ignorance" does no harm)! :cool:
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Hi Wend, I don’t know if this may help, if you want a flat bottom to the hole an easy way to achieve this is to drill all the way through and then put a piece of ply behind. Simples. Ian