Countersink Drill Bit Questions

[Geflugenmitt]

Hi,

I would describe myself as a reasonably accomplished DIYer - not professional. I have a C/S drill bit - can't see how to insert a picture but it's 5 fluted and with a 'barrel body' - so behind the fluted part it widens to a smooth 12mm diameter body. [Edit - managed to attach an example picture].

I often use this to both countersink and counterbore. I keep countersinking until the hole widens to 12mm and the body then continues sinking. This gives me a conical countersink that is depressed about 5mm below the surface of the piece and is an ideal to fit for a wood plug.

I have three questions.

1. Not that it really matters (the above system works for me just fine), but is this how these bits are supposed to be used? The alternative method I've found is not to use the C/S bit at all, just a standard 12mm drill bit. That also gives a deep hole with a conical profile at the bottom, pretty much the same result. I just have to be very careful with depth because a drill bit will tend to 'pull' into the pilot hole and run away too fast. I don't have a pillar drill so am hand-holding.
2. When I am not counterboring (just countersinking flush to surface) I sometimes get the usual problem with chatter. I am thinking of getting some unfluted C/S bits but never used one before. Could these also be used for counterboring, or am I better off keeping my fluted one/drill bit method for that?
3. Do I need to worry about getting different bits for different angles of screw head? It's not something I've ever considered before. Are screws mostly standard these days?

Many thanks!

 

[Burnerman]

These bits aren't really ideal for counterboring - but they will do just that if you let the wood chippings clear from the flutes. Possibly forster bits are better for that.
The bit you have in your pic is also good for metal - which is probably its original intended use!
At least, the genuine CSK bits don't pull into the timber so much as a twist drill might, so you get better control of the depth.
As for the chattering you may well expect that with wide grain timber that we get so much of these days - you'd probably find that there would be little or no chatter if you were countersinking oak for example. Failing that, try the csk's with only two flutes and / or vary the drill speed.
Screw head angles do vary - usually in the range from 80 deg to 100 deg - and a 90 deg csk bit suits them all well enough.
John

 

[foxhole]

If you are fitting wood plugs a countersunk bit is pointless , just needs a hss bit to dimension of plugs .

 

[lostinthelight]

I use a lip and spur bit which gives a nice clean cut of the outer circumference, drill to plug depth first and drill a pilot after for the screw

 

[Deleted member 174758]

As nobody has mentioned is, I thought I'd point out that there actually is a difference between the angle of a metalwork screw countersink head and a traditional woodwork screw countersink head - metalwork screws are generally with a 90° countersink, woodwork screws with an 82° countersink head. This means that a woodwork screw driven into a hole countersunk with a metalwork countersink may well not seat properly. Whilst this isn't so noticeable with screws driven into wood, it becomes a glaring error when undertaking tasks such as fixing brass or bone plates onto, say, a gun handle using brass screws, or fixing brass kick or finger plates onto doors. So if you are doing restoration work or high quality work, yes, it will make a difference. About the only firm I've come across in recent years who actually understands this is Lee Vally Tools in Canada who do offer 82° countersinks specifically to deal with the problem (there are others). TBH the only time I've hit the issue has been when installing the aforementioned brass kick and finger plates which have been wrongly countersunk for metal screws and where the atrchitect/designer was being (quite rightly) fussy about the fit and finish on high quality jobs

I often use this to both countersink and counterbore. I keep countersinking until the hole widens to 12mm and the body then continues sinking. This gives me a conical countersink that is depressed about 5mm below the surface of the piece and is an ideal to fit for a wood plug.

Counterboring should produce a hole with a flat bottom so that something like a bolt with a washer beneath the head (to spread the load) can be used. Combined pilot drill/counterbore tool typically looks like this:

When I am not counterboring (just countersinking flush to surface) I sometimes get the usual problem with chatter. I am thinking of getting some unfluted C/S bits but never used one before. Could these also be used for counterboring, or am I better off keeping my fluted one/drill bit method for that?

For woodworking a rose countersink (e.g. a countersink with 5- or more flutes) is very much more prone to chatter than a countersink designed for wood. This is partly because a rose countersink is designed to scrape metal as opposed to cut wood fibres. The traditional form of countersink designed for use on wood is a snailhorn countersink and has only one cutting edge:

Unfortunately, these are no longer on the market, having disappeared some time in the 1970s or 80s, and in any case, they weren't suitable for high speed drilling in an electric drill, for which the modern 2-flute combined pilot drill/countersink is a far better tool:

These drill the pilot hole together with the countersink in one action and have the advantage that matching tube plug cutters are available to produce exactly matching pellets:

(The two examples above are from the Trend Snappy range)

Personally I don't like using rose countersinks on wood, particularly softer materials where chuck run-out (especially in cordless tools) combined with the grain and the poor cutting action of the rose countersink can result in out of round countersinks. In any case the combined drill/countersink tools I use are far faster to use - a big issue if you need to drill 30 or 40 holes several times a day

 

[Deleted member 174758]

As for the chattering you may well expect that with wide grain timber that we get so much of these days - you'd probably find that there would be little or no chatter if you were countersinking oak for example. Failing that, try the csk's with only two flutes and / or vary the drill speed.

The chattering is because rose countersinks, being designed for metal, have a scraping action as opposed to a cutting action, so they will be less or more effective depending on whether they are cutting with or against the grain. Rose countersinks are invariably made from HSS which takes a less sharp edge than the carbon tool steel that woodworking tools are often made from (otherwise we'd all be using HSS plane irons - but we don't). Finally, rose countersinks suffer from poor chip clearance in wood as they have too many flutes, and gullets which are too small, whereas a woodworking countersink with 1- or 2-flutes and much larger gullets tend not to clog anywhere near as easily

 

[Geflugenmitt]

Thank you very much for all the answers. I forgot to mention but I've had most success with shallow (flush) countersinks using my HSS fluted bit in a cordless screwdriver, as this spins much more slowly than a drill.

But given the advise above, I will probably now buy a set of the combined drill and C/S bits.

One further question: If the countersink I am using is actually designed for metal, why does it have such a long 'barrel' (12mm dia cylindrical section) which lends itself to deep countersinking in wood, as opposed to *this* which does not?