T-Plus programming question??

[Bobesmo]

I am turning a shaft that requires a 4" radius and am having a problem with it under cutting about .010 at th start of the radius,...I know this will be hard to explain without the print but here goes...

The shaft is 12"long, turned to 1.25",...... in the middle it is turned to .868 +- .002 for 6" with a 4"radius and .125 radius going up to the 1.25 Dia. on either side of the .868 Diameter in the middle.The 4" radius needs to start 1.0" from the 1.25 Dia. on both sides.
I am using the "U" symbol in Bar Out, and 4" as the final radius, using seperate tools to make each side(one doing a back turn)
any help would be appreciated!!!

[CNCRim]

it's hard to mental picture without the print, .010 undercut what I'm confusing.

[Bobesmo]

The .010 undercut is at the transition from the .868 turned Dia. to the start of the 4" radius.

[j-radkemachine]

Could Be Tool Deflection... How Much Are You Leaving For Your Finish Pass?