countersinking a m3 hole.

[ilovemygt35r]

hi
im trying to csk into plastic, im using a m3 csk screw, can anybody tell me the correct size bit i need for doing this please, ive got a few bits but none really work very well.
thanks very much

 

[pedrobedro]

You really need a countersink, it's the angle of the point that does the job and drill bits are not steep enough unless you regrind them yourself. You could just twist a drill the same size as the head of the screw into the plastic with your fingers enough to recess it.

 

[ilovemygt35r]

yes that was my question what is the correct size countersink do i need for a m3 been searching and there are quite a few countersinks just not sure which is the correct size
thanks

 

[rtbcomp]

As Pedro says, it's the size of the head which matters and this may differ between types of screw. Get a hand-held countersink and open the hole until the head fits flush.

Because of the conical shape one bit will do a whole range of sizes, and using a hand-held one will stop it going in too far.

 

[hareng]

Spot on Rt the head sizes vary even from the same supplier yet alone different suppliers.
Countersinks would be sold and made well oversize to cater for that fact.

Me i always use a twist drill, not the right angle. Countersink with the drill and try the screw in it. If sits too high go in deeper, great when got a dro for this.

The M3 countersunk i have here measure 5.72 to 5.78 round. Bare in mind most screws nowadays are made in china and will be offset to the screw thread.

 

[CRB]

Probably not really what you are after but these are available, I remember enquiring of Cromwell about them.
http://www.deltaintl.com/microstops/Microstop Countersinks.html

What ever type of plastic you are using, you should avoid countersinks if at all possible, and if unavoidable, use very light pressure in tightening. The stresses imparted by forcing a cone into the material will cause fracturing in the more rigid ones. Even the softer types will succumb to similar issues over time.

Ideally you should use a panhead and washer with an ample clearance hole beneath. These will allow the expansion and contraction of the material without buckling occurring. Again, light pressure since forcing a washer into the surface will end in the same problems as stated earlier.

 

[MattF]

Just use a rose countersink in either a handvice of some sort, hand/breast drill or use a depth stop on the pillar drill. Hand/breast drill are handy as you just count the handle revolutions and use that as your general marker for each countersink.

 

[brightspark]

Spot on Rt the head sizes vary even from the same supplier yet alone different suppliers.
Countersinks would be sold and made well oversize to cater for that fact.

Me i always use a twist drill, not the right angle. Countersink with the drill and try the screw in it. If sits too high go in deeper, great when got a dro for this.

The M3 countersunk i have here measure 5.72 to 5.78 round. Bare in mind most screws nowadays are made in china and will be offset to the screw thread.

twist drills arent much cop for countersinking. if its in wood it rips the grain out and bites in metal and doesnt leave a nice round hole. ok if your not that fussy mind

 

[Luke]

If it's tapped m3, it sounds like you're going to be putting a machine screw in it. these are commonly 90 degree countersink, which is different to a wood screw, so a standard countersink rose isn't much use.

 

[Engineer1964]

Countersinks for imperial is normally 82 degrees but for an M3 countersunk bolt you will need a 90 degree countersink bit, then you will find that the countersink you do will be a perfect match

 

[MattF]

If it's tapped m3, it sounds like you're going to be putting a machine screw in it. these are commonly 90 degree countersink, which is different to a wood screw, so a standard countersink rose isn't much use.

If I recall correctly, the standard rose is 90 degrees.

 

[Luke]

Yes, standard for machine screws. A rose for woodworking screws is different.

 

[ilovemygt35r]

thanks very much for the ideas and suggentions

 

[hareng]

twist drills arent much cop for countersinking. if its in wood it rips the grain out and bites in metal and doesnt leave a nice round hole. ok if your not that fussy mind

Never done me any harm, every one a gem in steel, brass, aluminium, woods and plastics.
Nothing worse than using the supposed proper tools for the job and seeing a massive gap between head and csk.
Heres 8 csk that went out yesterday http://i1140.photobucket.com/albums/n563/Jonhareng/Shooting/SteyrLG110RAILMiguel0001DSCN4034.jpg

Woods can admittedly be tricky to counterbore and countersink, none beaten me yet.