Counter Sink - Feeds & Speeds

[RJS100]

I am counter sinking a few holes for M5 flat head screws in 6061 aluminum. I am using a nothing fancy single flute 5/8-inch 90-degree counter sink (see below).

The manufacturer said to run it at 300 surface feet per minute and 1.5 though per revolution. If my figures are correct, this would mean about 1800 rpm and a plunge rate of 2.75 inches per minute. I ran a couple holes today and since I did not previously test it first, I dropped the feed rate to about 30% so I was plunging at around .8 inches per minute. The counter sunk holes looked great, but I was surprised that it was removing what looked to me like lots of material fairly quickly. I am pretty sure that if I had run at the full speed (2.75 ipm), it would have been too fast.

I have never used a counter sink before. Is there something I should be calculating differently?

Thanks... Richard

[suntravel]

If it works the cutting rate is ok.

I do not use counter sinks on CNC, because there are most times chamfers to mill, so I use this also for the holes.

Uwe

[RJS100]

Thanks Uwe. I thought I would try them because Fusion allows you to specify the chamfer diameter and the counter sink depth is automatically calculated. The counter sink actually looked great. I think I am going to try it again with a chip breaking to help clear the chips.

[Max]

My experience with machining c'sunk holes is use a low speed and feed. This applies for manually machining say on a drill press and on an NC machine. This will reduce chatter and improve tool life. There is a large surface area when cutting a counter sink hole. My practice is to double the clearance for the screw hole ie make the clearance hole larger. This will make cutting easier and will not degrade the holding power of the screw

[RJS100]

Thanks for the tip! Really appreciate that.