Countersinking 4mm bolt

For a clean cut without chatter, I prefer to drill a pilot hole and countersink, then drill the clearance hole. You can't do a test fit that way but if you cut the head off a screw, you can use it as a test piece. Otherwise, very slow rpm will minimize chatter.
 
The chart he posted is for socket head cap screws. Counterbore dia. 8.25mm.
 
Metric flat head screws can be either 60° or 90°, with that said, 60° is very rare.

The head dia of a 4mm screw is 8mm. C'sink are normally specified to a diameter.

As mentioned, the best way is to go little by little and try the screw till you have the fit you want.

As for what tool to use, there are a lot of choices, depends on your machine abilities and the material you are working with.

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Socket head cap screws have a small fillet under the cap. The countersink is to provide clearance for that fillet.
 
2G's said:
I need to countersink a 4mm bolt, if I'm reading this chart correctly the diameter at the top of the hole is 4.8mm and the depth is 4.4mm.
Click to expand...
Remember, it's metric; for a flathead screw, instead of an 82 degree countersink, it takes a 90 degree countersink.
Presumably, it'll set flush if you use an oversize cutter and only plunge to the depth of 4.4mm.
If there's a need to do lots of these, piloted bits are a good idea.

Rivets and aircraft screws can be 100 degrees... so many standards!
 
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A countersunk flat head would be best on a router table. A counterbored Allen would collect all the debris in the head and bore. A countersunk flush screw would minimize that problem.
 
Thanks everybody for your input and insight you've helped immensely. I have decided per the recommendations to countersink the bolts. I plan on using my drill press for this operation as I do not have a mill. My skepticism on countersinking was I wanted a clean non chattered surface, so with the advice given I believe I will achieve the desired finish.
 
Brento said:
It also has info for a countersink if you follow the table
Click to expand...
That countersink is for the bottom of the counterbore to ensure the bolt will sit flat.

This is the table to use for countersinks of flat head screws.

engineersbible.com

Countersunk Hole Size for Socket Flat Head (ANSI Metric)

Use this chart to find out what size countersunk hole to use for ANSI socket flat head fasteners. This is for ANSI Metric countersinks.
engineersbible.com engineersbible.com
 
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