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A recommendation in a book says "The countersink must have only one flute and must be ½" diameter".

As far as flutes on a router/drill bit are concerned - reading other questions here on woodworking - I gathered that the greater the number of flutes - the quality is higher but the process is slower - since the feed rate is slower.

I do not own a countersink bit yet, and the most commonly available ones here are five flute ones - I would like to know what makes a single flute countersink bit better than a five flute one?

Okay - to re-phrase and simplify the question - What are the differences between a single flute countersink bit and a countersink bit with five flutes?

Why do countersink bits with different number of flutes exist?

thanks!

saraf
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    You're really taking the recommendation out of context. The fact that it appears in the Buying Guide appendix of Make: Tools, a book aimed at helping novices succeed at some simple projects using basic tools and materials, is important. – Caleb Nov 30 '20 at 22:04
  • "What are the differences between a single flute countersink bit and a countersink bit with five flutes?" One has one cutting edge, the other has five! What else do you need to know? I think I covered the one thing that's actually important about the choice — whether one works better than the other. So in terms of function my Answer still covers the basic thrust of what you're asking. – Graphus Dec 01 '20 at 08:09
  • okay - to start with, why do countersink bits with different number of flutes exist? – saraf Dec 01 '20 at 09:04
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    I don't believe I've ever seen a single-flute countersink bit. I've owned a single purpose, multi-flute bit, and I've owned several sets of drill-/countersink-bits, and they've all had multiple flutes. I've never had issues with drilling a countersink. I can't say what the differences are, but I can say that a multi-flute bit works just fine in wood (and plexiglass). – FreeMan Dec 01 '20 at 11:44
  • Graphus FreeMan Caleb - thanks a lot - your posts are very instructive – saraf Dec 01 '20 at 15:00
  • @FreeMan, there are countersinks with a single cutting edge. There are two main designs I'm aware of, one where you'd definitely call it a single-flute bit but there's also what historically was called the snail countersink (and modern versions of this exist) where I'm not sure you could say it has a flute per se, although that may be splitting hairs. – Graphus Dec 02 '20 at 07:29
  • @Graphus I didn't say there wasn't such a beast, just that I'd never seen one. And it's only splitting hairs if it's sharp enough - that's the test for plane irons, is it not? :) :) – FreeMan Dec 02 '20 at 12:07

1 Answers1

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As covered in the Comments under your previous Question, this is another pronouncement from the author where he's presenting his opinion as fact, without any evidence or apparently any arguments in support.

The simple fact is that both styles/types work, and can work well.

Style
The specifics of a countersink's shape are more important than the number of flutes, by which I mean it must be shaped properly, which isn't the case with many cheaper countersinks of modern manufacture. They can look indistinguishable from a quality one to the naked eye but the devil is in the details.

While the commonest multi-flute countersinks are originally intended for metalwork this style can work perfectly well on wood if made well, sharp, and used appropriately1.

Size
Now as to size, here's where I have a particular problem with that, achem, "one size fits all" advice. I doesn't take a genius to think of cases where you definitely wouldn't want to use a countersink that's a whopping 1/2" (~13mm) in diameter! 2

Probably also worth mentioning the following in this context.

Countersinking doesn't have to be a separate operation any more
There are numerous variations on this basic idea but the basic feature they all share is that they combine a countersink with the pilot bit so both operations are done simultaneously.

Combination drill-and-countersink bits

Note it's clear that both of the above are directly intended for use on wood due to the design of the drill portion of the bit, yet despite this they have multi-flute countersinking portions.

These could be a huge timesaver in a production environment where perhaps dozens or hundreds of holes are needed daily so they're probably most applicable to that. But they're inexpensive enough that even the casual hobbyist could acquire a small set for the occasional drill/countersinking they do..... if they can't stomach the 30 seconds extra it takes to countersink separately ^_^

1 As touched on in a previous Q&A, see Why is my countersink bit making hexagonal holes?

2 Counterbored #4 screws anyone?

Graphus
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    This is good info, but it's somewhat divorced from the context of the recommendation in question because the OP hasn't provided that context. – Caleb Nov 30 '20 at 22:12
  • @Caleb, the only necessary context we need is that this is woodworking, that the countersink needs to work on solid wood and board materials. And in that context as I say, the simple fact is that both styles/types work, and can work well. Assuming they're well made and sharp there is literally no reason to prefer one style over another; this isn't a matter of opinion, it can be deduced from the fact that there are high-end users of both styles of bit...... – Graphus Dec 01 '20 at 08:03
  • The original statement comes from a book aimed at beginners, and it takes them step-by-step through a number of projects using basic, inexpensive tools, and materials not limited to just wood. The author doesn't assume that the reader can tell a decent 5-fluted countersink from a cheap one. The book is set up to create a positive experience by maximizing the likelihood of success and avoiding choices that could lead to problems such as hexagonal holes from chatter. – Caleb Dec 01 '20 at 14:26
  • thanks Graphus for the informative response, and thank you Caleb for the help and the very instructive answer on my other question. :-) In this question I am now trying to understand the concept of flutes on countersink bits in theory - I have gathered now, that - practically, it will not matter which one I buy. Thanks for all the guidance! – saraf Dec 01 '20 at 17:12
  • Aah ... more light! @caleb I read your update in the other question just now - so, more flutes = better finish, but a greater probability of problems like chatter, but only with a hand-held drill. (btw, I -had- read the question about 'why is my countersink bit making hexagonal holes before posting my question') – saraf Dec 01 '20 at 17:20
  • @saraf I don't think it's necessarily true that more flutes makes for a better finish. There are countersinks out there with zero flutes, and I understand that they're much better for use in some plastics than fluted designs. – Caleb Dec 01 '20 at 18:13
  • @Caleb does more flutes result in a better something? – saraf Dec 01 '20 at 18:43
  • @saraf Possibly a higher feed rate and better heat distribution. – Caleb Dec 01 '20 at 20:05