Hi guys, what's the best way to countersink holes for socket-head cap screws? I have been drilling the holes to diameter and then CNC pocketing out the recesses for the heads, but the pocketing is slow and rather ugly as my X-1 is riddled with backlash.

I have been thinking about getting some countersink cutters, but won't they leave a conical base to the recesses? I'm also a bit worried about the X-1's ability to drive a 13mm countersink, but I suppose as the centre 9mm of the hole have already been drilled out, it should work.

Cheers.

I just typically use 135degree drill bits for this.
Not ideal by any means.
They sell a cutter designed just for this.
They are a little expensive, but do look like they will do a good job.
Actually, this price isn't too bad.
http://www.use-enco.com/CGI/INSRIT?PMAKA=368-4200&PMPXNO=949264&PARTPG=INLMK3

Drill the through hole then drill the counter sink with a normal drill bit, then flat bottom it with the same size drill bit with the end ground flat plus the necessaery clearance angle. Reasonably neat and tidy and a lot cheaper.

Regards
Phil

Hi guys, what's the best way to countersink holes for socket-head cap screws? I have been drilling the holes to diameter and then CNC pocketing out the recesses for the heads, but the pocketing is slow and rather ugly as my X-1 is riddled with backlash.

I have been thinking about getting some countersink cutters, but won't they leave a conical base to the recesses? I'm also a bit worried about the X-1's ability to drive a 13mm countersink, but I suppose as the centre 9mm of the hole have already been drilled out, it should work.

Cheers.

That Enco set seems pretty cheap - I've only seen those things for £20/$40 each!

I only really need to be able to do M8 and M6 cap-screws, but I do have a lot of them to do, so I might invest in a couple of dedicated cutters.

I take it that the ones with the conical cutters are for countersink screws, rather than cap-screws?

Philbur - I tried drilling out 7mm pilots and then opening them up with a 9mm drill, but it chattered like mad - the 9mm drill is way longer than a dedicated cutter and only has 2 flutes. Before I invest, I might try a 9mm 4-flute endmill instead, that might work a bit better.

Cheers.

Without looking it up I think an M8 cap screw has a 12 mm head so to keep it neat you need to go for say 12.5mm diameter counterbore for clearance. Its the odd sizes that make using using endmills a bit difficult. Odd sizes means high prices. A 12.5mm drill bit costs very little.

However as you say if you need to do a lot then the right tool for the job would be the best idea.

Regards
Phil

That Enco set seems pretty cheap - I've only seen those things for £20/$40 each!

I only really need to be able to do M8 and M6 cap-screws, but I do have a lot of them to do, so I might invest in a couple of dedicated cutters.

I take it that the ones with the conical cutters are for countersink screws, rather than cap-screws?

Philbur - I tried drilling out 7mm pilots and then opening them up with a 9mm drill, but it chattered like mad - the 9mm drill is way longer than a dedicated cutter and only has 2 flutes. Before I invest, I might try a 9mm 4-flute endmill instead, that might work a bit better.

Cheers.