[adam_m]

A little off topic but what tool would you use to countersink an 82 degree bolt in 6061?

3/8"-16 x 1-1/2" Black Oxide Finish Flat Socket Cap Screw | Fastenal


Adam,

[fizzissist]

I'd use a 1" 82deg countersink.

[CarveOne]

Fastenal and other tool sellers have counter sink bits for standard flat head screw/bolt shoulder angles. They usually have 1/4" shanks for use in hand drills or drill presses. Not very expensive. Get the one best suited for the screws you will use. Drill the hole for the screw shank and then counter sink the hole(s). Countersink just deep enough for the screw head to be flush or slightly below the surface.

[mactec54]

adam_m

If you have lots to do, & want the best, there is the nine9 tooling that will do a perfect job, they cost, but are worth every cent, most tool suppliers sell them MSC Etc

Nine9 2013 45° Indexable Chamfer Mill

[adam_m]

C1, I tried the standard countersink with terrible results, chatter marks, etc.

Are indexible countersinks the way to go? replaceable bits, etc?

[CarveOne]

C1, I tried the standard countersink with terrible results, chatter marks, etc.

Are indexible countersinks the way to go? replaceable bits, etc?

What kind of metal? Did you use any kind of cutting oil type lubricant? Did you use a corded/cordless drill. a drill press, or milling machine? Use moderate pressure, not light pressure, to reduce chatter. The type of cutting edges your countersink has will make a difference in how much chatter it produces. They're not all the same.

[MI370]

Keep in mind most 82deg. HSS counter sinks are for RPM around 200 +/- (less than 500) WAY less than thousands from a CNC router.

There's no way you can use one in a CNC router with any good results.

Maybe an indexable bit would be good in an ultra rigid machine but a CNC router is pretty far from being rigid enough.

[CarveOne]

Keep in mind most 82deg. HSS counter sinks are for RPM around 200 +/- (less than 500) WAY less than thousands from a CNC router.

There's no way you can use one in a CNC router with any good results.

Maybe an indexable bit would be good in an ultra rigid machine but a CNC router is pretty far from being rigid enough.

I just assumed that he was using hand operated tools, but would agree that a router would be much too high of an rpm. I haven't used an indexable type countersink. Having straight flutes on all countersinks I've seen probably doesn't help stabilize it while cutting at higher rpms.

[adam_m]

C1, I tried the standard countersink with terrible results, chatter marks, etc. using a drill press at its lowest speed.

I was under the impression I could do this on the CNC and not in a drill press.. actually I thought that was the preferred method. I'm fairly certain that in the manufacturing process they don't countersink holes on a drill press when the part is in the CNC...

Adam,

[mactec54]

adam_m

Like I said in the above post if you want perfect, then you need to buy the right tooling, If doing them on a drill press a single flute 82deg countersink would work the best
For CNC you need good tooling, I found the nine9 tooling to be the best at doing this, & I do hundreds of countersinked holes like this

[adam_m]

C1, I tried the standard countersink with terrible results, chatter marks, etc. using a drill press at its lowest speed. Although it was a multi-fulted (sp.) bit maybe my mileage will vary with a single flute?

I was under the impression I could do this on the CNC and not in a drill press.. actually I thought that was the preferred method.

Adam,

[CarveOne]

Some folks do it that way successfully, but I haven't (so far) tried it. I would think that a step-down drill operation with very shallow steps at the lowest rpm might do it. I'm thinking that it would "kiss" the surface many times quickly so that the chatter doesn't happen. ger21 and others here would know more than I whether this has any merit. Maybe someone here who has done it on a solid aluminum table will speak about what they did.

[dbsharp]

like others have said you need rpms much lower than you will get with a cnc router for a regular countersink. I have countersunk 82° holes in a hand drill with no bad chatter, the key is LOTS of pressure and low rpms. If you are using a knee mill, you can get great results out of a standard countersink.

I have used carbide center drills and carbide drill mills to countersink holes in aluminum with my cnc router at 8-10k rpm. You will need a powerful spindle and a very rigid machine to do this IMO.

[Geof]

Try using a single flute countersink in a very small pilot hole, say 1/16", not the full size bolt clearance hole; only drill the pilot hole as deep as you will go with the countersink.

You can even try using the countersink without any pilot hole in aluminum alloys.

[adam_m]

Thanks, sounds like a single flute and SLOW speed is the ticket...

Appreciate all the input.

Adam,