Countersinking woes!
 

Pretty straightforward question, maybe I'm just a complete dumba$$ when it comes to using countersink bits, but I always get a bit of the screw sticking out of the material I'm working with. The problem is the "squared" edge at the top. If I keep going with the countersink bit to make sure that portion is level with the material, then I end up with a hole that's way too big in diameter. If I go with the right diameter, then I end up with a mm or so of the screw sticking out. Any solutions?

Also, a beautiful Paint rendered jpg of what I'm talking about (not to scale:-P).

http://i14.tinypic.com/4mwjmv5.jpg

Why not start with a drill bit and finish with the counter sink bit?

it must be those canadian fastners....LOL...just kidding.

most "flat head" screws for counter sinking don't have that "flat" spot at the top of the head like in your drawing. if your screws have that flat spot then that's your problem the only way to do what your trying to do is to get a counter sink bit that is the same diameter as the screw head so when you go "deeper" into the material with the bit it will also do a "counter boar" allong with the "counter sink"

"thumbsup"

Well, I exaggerated the flat spot in the top to show what I was talking about, but it's still there and annoys my perfectionist nature! I was thinking of going the drill bit/countersink route, but thought there might be a more elegant solution! I'll have to look around for same sized diameter countersink bits too I guess!

While it is not the best practice for high stress applications (angles aren't quite right), a drill bit the same size as the screw head can be used to countersink/counter bore holes.

If you are countersinking in plastic with a drill bit you need to start with the countersink sized drill, and drill the through hole after. Use a drill press if you have one so you can easily set a depth stop. Hold/clamp the plastic so the drill bit doesn't grab and go all the way through.

Another crude option I have use in plastics is to take a longer bolt of the same style as what you are using. Grind/cut/sharpen the head of the bolt so it will cut on the underside of the head. Push the bolt through the hole you want to countersink and chuck it in a hand drill. Run the drill while pulling back on it to countersink the hole. It takes a while if you have a lot of holes to do because you have to chuck and unchuck for every hole.

Ecoli/all

I would just add that Metric flat head screws have 90 degree- 92degree angles. Where as English flat head screws have 82 degree angles. Are you matching correct countersink angles? I've made this mistake before.

Leigh

Beat me to it.

Make sure you have the right countersink and it shouldn't have the problem you described.
Pat

Dang, never even thought of that. I'll check and see if that isn't the problem. Thanks!

Chris

If your angles are correct and you are increasing the bore diameter with the counter sink, the material you are counter sinking is to thin. There is no getting around this other than grinding the head of the screw down.