Hey Fellas,

What is the best size bit to countersink 4-40 screws on the underside of the chassis, ie servo mount screws.

Thanks

1/4 diameter x 82 degrees
You will need to be carefull, since all the screws we use aren't the same head size, just go slow and check each screw.

Thanks

or you can use the Mavrick 05 chassis, it has the holes for an adjustable servo mount already in the chassis. It is great, I love not drilling graphite!!

Niftech makes and drill bit and counter sink in one piece. They make them for 4-40 and 8-32. I have both.

I use a tapered stone on my dremmel. Do a little at a time and check often!

I use a tapered stone on my dremmel. Do a little at a time and check often!

I have used this method as well. Just make sure you keep a firm grip and press pretty hard otherwise the bit can slip and make a nice mark all the way across the chassis.

I use a tapered stone on my dremmel. Do a little at a time and check often!


i have done the same thing for years now. :thumbsup:

Go to Mcmaster.com and get a 1/4" diameter, 60 degree, single cut solid carbide bur, it's part # 43035A92 it's cost just over $9 and it will last you a lot longer than any high speed steel countersink when cutting into carbon. That's what my machinist uses for all of my production chassis work.

-E

60 degree? all the screws we use are 82 degree, why would you want to put that extra pressure on the head of the screw?

What type of tooling are manufacturers using (upcut/downcut sprials, compression)? Also, what type of material is the tooling made out of (HSS, carbide, carbide tipped).

Maybe you could start the cutting with the 60 degree bit and finish with a proper angle countersink?

Seems to me if you were really doing this on a production basis you would get McMaster item number 29245A11 instead. It uses replaceable carbide inserts. But at $93.17 it is not something most of us would buy for a few holes.