Best bit for counter sinking flat head machine screws

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Forum topic by MisterCat posted 06-08-2010 07:37 AM 5122 views 0 times favorited 10 replies Add to Favorites Watch
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22 posts in 3101 days

06-08-2010 07:37 AM

Topic tags/keywords: counter sink bit machine screws

A few months back I bought a small stock of 1/4”x20 flat head machine screws to be used for making shop jigs. When I was building a jig this weekend, I found out that I really didn’t have a good bit for countersinking the heads, everything was too narrow. Looking on the McMaster-Car web site, I found out that they had a 0.477 inch head diameter, which is larger than a #12 wood screw. I decided that my 1/2” 90 degree v-grove router bit would work in a pinch. It did, and pretty well. The difference in angle (the machine screws are 82 degree) didn’t seem to matter. I think that when the bolts are tightened, the wood fibers near the root of the machine screw get compressed and the angle of the hole changes till it fits the screw head slope.

So my question is: is there a big difference in the counter sink bits I see on Amazon? Some of the bits shown are ‘0 flute’ and have a sort of sharp edged hole

Some have just a couple of flutes
2 flute

and some have many flutes:
Many flute

Right now, my choice would be the many flute design, as I think it would be smoother cutting, and also be less likely to tear out. Does anyone have any experience with the different flavors?


10 replies so far

View ajosephg's profile


1880 posts in 3739 days

#1 posted 06-08-2010 10:56 AM

I like the “0” flute best. They cut smooth, while the others chatter in my drill press.

-- Joe

View a1Jim's profile


117283 posts in 3755 days

#2 posted 06-08-2010 05:13 PM

I use the type with many flutes but have never tried the others.

-- wood crafting & woodworking classes

View dbhost's profile


5767 posts in 3410 days

#3 posted 06-08-2010 05:22 PM

You didn’t list them, but a good number of countersinks only have 1 flute. I have a set of single flute Mibro countersinks. They work, but I wouldn’t buy them again… I had a set of the 0 flutes that grew feet when I had a room mate years ago when I was single. I wish I had bought a replacement set of 0 flutes. Never tried the many flute design you show, but I know the 0 flutes cut super smooth, with no chatter.

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View Gene Howe's profile

Gene Howe

10989 posts in 3606 days

#4 posted 06-08-2010 05:32 PM

Will the “0” flute work in aluminum?

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

View Dragonsrite's profile


136 posts in 3575 days

#5 posted 06-08-2010 05:39 PM

I get a smoother cut with a single flute versus a 5 flute (I think) ... in both wood and aluminum plate.

-- Dragonsrite, Minnesota

View Ger21's profile


1075 posts in 3309 days

#6 posted 06-08-2010 06:00 PM

I’d recommend the Mcmaster Carr 2910A22.

I use the same model but smaller, for 10-32 screws. It’s the best countersink I’ve ever used, by far. Absolutely razor sharp. I used it last night in Baltic Birch, and the countersinks shined like fresh planed wood. They’re not the cheapest, but they’re all I’ll buy from now on.

-- Gerry,

View ajosephg's profile


1880 posts in 3739 days

#7 posted 06-08-2010 06:17 PM

The “0” aka “Crosshole” Countersink will work in metal – in fact it is primarily a metal working tool. You can also get them with a pilot so they will find the exact center of the hole.

-- Joe

View MisterCat's profile


22 posts in 3101 days

#8 posted 06-19-2010 05:46 AM

A quick follow up on this thread:

I ended up buying this set:
wttool link

though I wish I would have found this link before I bought my set (US made)

I’ve used the big bit for the project I was working on, and the other two bits in tests. So far my results are fair to perfect. The countersink hole can move off center of the shank hole, slightly if you don’t concentrate on keeping the bit aligned with the hole. I think with a little bit of experience I’ll get very consistent results. The good news is that there is no chatter, and depth control is very easy because you have good visibility of the hole as it’s drilled. Particular for a hand held drill, the zero flute design is a clear winner.

All in all, I’m very satisfied with the tool and the way it preforms. I would recommend the these sets of bits for people that use machine bolts for wood-working.

View iamwelty's profile


259 posts in 3293 days

#9 posted 06-20-2010 04:37 PM

Gosh, I just use a larger bit…

-- There is a fine line between eroticism and nausea...

View Knothead62's profile


2598 posts in 3139 days

#10 posted 06-20-2010 07:26 PM

I measure the bolt head and match it with a plain ol’ drill bit, put the bit in the drill press, measure the depth, set the depth and drill away.

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