Need help with machining a long bushing

[MoyBien]

I am working on a long bushing with an outer diameter of 0.8125 inches inner diameter of 0.5625 inches, and a length of 4.8 inches. im using a 13.8mm solid carbide coolant-through drill from Nachi Aqua. After 40 pieces it broke. Before that it was giving me a concentricity of 0.004 inches. i think the drill starts going off-center after 3 inches. i tried pecking and not pecking. Right now im using a 120-degree 5/16 drill to make a 0.5-inch deep guide hole for the 13.8mm drill which has a 140-degree tip. I dont have a 142 degree spot drill. im pecking 1inch deep keeping the drill in the hole and backing off 0.1 inch each time. My speed is 600 and feed is 0.006. Any tips to make this work better??

 

[verywhiteman]

That drill walking after 3 inches sounds like deflection or chip packing, the 120 degree guide hole might not be helping since the Nachi has a 140 degree tip, so try matching the angles. 600 RPM seems low for solid carbide; bumping that up might help. Also, make sure your coolant flow is strong enough to flush chips properly. If it's consistently breaking after 40 parts, wear might be the issue, all these little tips here and there, I hope they help