[aarvig]

I purchased a #30 countersink bit new (among others) when I started my build on my RV-9A. I used it slightly on my empennage but now I am countersinking my wing spars. I am curious...what should I look for to know that my countersink ain't quite cutting it any more (no pun intended)?

 

[rickmellor]

You'll notice two things: first it'll start taking longer to CS the hole and second, you'll start having to apply more down force when cutting.

 

[Av8torTom]

Long Time

Good question - they do seem to last a long time though. I completed the countersinks on the empenage and both wings and there's no sign of it slowing down (pun intended).

I imagine it's an insidious thing, but I would say as long as you're getting acceptable countersinks with no overheating, drill on...

T.

 

[bruceh]

If you have used it on fiberglass, it will dull up quickly.
These counter sink bits are easy to get replacements for, so stock up on a few extras.

 

[Noah]

There is only one reliable way to know that your countersink cutters are dull. When you are working in your buddy's shop, helping him out and using his new countersink cutter, and you exclaim "Wow, these cut like they're going through butter"! Then you will know that yours are dull. And that is the only way you will ever know.

 

[Wayne Gillispie]

Like above poster, time/pressure increase...it is time to reorder.

I used the same ones the entire build. The reason they lasted so long is I used boe lube and bought separate ones for just steel and fiberglass. I had four cages so very little switching. Every minute counts.

 

[aarvig]

Thanks for the replies everyone.