I figured I'd put this in a seperate thread - I posted a problem I'm having with the surface quality of a 6061 AL octagon shape I am machining. The exterior is an octagon, the interior is a circle. Looking at the top, I am drilling 8 holes - one in each of the triangular "corners" between the inner circle and outside octagon shape. I need to tap them later and I do not have much room to work with. They are for #0 screws, so I was using a 3/64th drill bit (HSS). We're doing 4000rpm (max on the machine) and 1.5ipm plunge rate. We've tried doing it in a full pass and also tried peck drilling. It doesnt help - we tried to drill one piece with 8 holes and snapped 3 bits off in the holes after only 6 holes - not good.
Any suggestions? Machine is a Bridgeport series 1 with retrofit CNC control. No flood coolant. I am using a collet toolholder that fits well.
Do my RPM and plunge speed look correct? I used the suggestions MasterCAM came up with.
Would going to a carbide drill help? HSS drills are .80/ea, carbide are about $3/ea so before I snap a bunch of carbide bits I wanna solve the problem
Would centerdrilling first help? It wouldnt matter if the top of the hole was sligthly oversize because its covered later so I could use a larger centerdrill to start the hole - although the bits didnt seem to be walking at the start of the hole, rather they would break when they were 1/2 way into the hole.
Any other suggestions? Peck drilling is better? What depth should I do in each peck?
Thanks!
Mike