Countersinks

theoldwizard1

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More newbie questions !


  • Why are there countersinks with 1, 3, 4, 5, 6, and 7 flutes ? What is best for a newbie ?
  • HSS uncoated, TiN coated, cobalt (coated or uncoated) ? Again what is best for a newbie on a budget ?
  • I am certain there is a reason for all of the different angles, but what is the most common, like for flat head machine screws.
 
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You forgot 0 flute in your question, which is my preferred countersink. Rather than a flute, they have a diagonal hole machined through to make the cutting edge. They are also somewhat eccentric ground such that the body is not quite concentric with the shank.

To answer your questions

All of the number of flutes work. It has been said that an odd number of flutes is less prone to chatter that an even number. In my opinion, any number of flutes greater than 1 is too many.

I find that the single flute work very well, I don't like any countersink with more than 1 flute. Use slow spindle speeds (about 1/4 drilling speed) and good cutting lubrication.

M. A. Ford seems to make the best single flute countersinks. These are available from Enco tools, and several other places. There are less expensive ones available, but you get what you pay for. I'm sure there are other brands that are good, but I have no experience with them.

I bought a set of Hitachi single flute countersinks at Home Depot, they were complete junk, and ground with no lip clearance. Not useable, might have worked in wood but I never tried them.

For normal use, uncoated work just fine. TiN coating might give a smoother finish and longer life, but for the home shop I don't see the need, however, the cost difference is not that great. I have been using my M. A. Ford set for the last 10 or so years, and they still work fine.

82 degree is the USA standard for wood screws and flat head screws, 90 degree is the metric standard.
 
I found this table on Wikipedia

Type of ThreadNormal CS Angle
ISO Metric90°
Imperial BA, BSF, BSW etc.90°
UNC, UNF82°
Aviation fasteners100°
 
I also found out that Amazon carries most of the KEO product line as does Zoro Tools.
 
C'sink material and flute count are going to be based on what you are working on. On 2024/6061/7075, 3 flute HSS piloted are the norm. On titanium, HSS or carbide worked, depending on the person's skill. Carbon fibre then it's carbide or diamond, with lots of flutes for carbide and a single for diamond. Feeds and speeds are dependent on material, thickness and surface finish requirements. Using a c'sink stop or cage makes it easy for repeatability and to have the tool perpendicular to the material for best results. When in doubt about speed or feed, experiment on a scrap piece before you do the real one.
 
I also find the one with a single cutout cutting face the least likly to go wrong.

although i do have 2 faced counter sinks that i use sucessfully just have to be very carfull with chatter.

Stuart
 
I also prefer 0 or 1 flute. 0 flute are easy to sharpen just go inside the hole with a small grind stone in a dremel.
 
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