At 09:48 AM 1/16/2009, you wrote: >One thing to keep in mind when considering the tapered end mill idea >is chatter. > >The existing stepped design limits the depth of cut (width of >cutting edge engaged) to the height of one step. If you use a >tapered end mill, the cutting edge will be engaged in the cut over >its full length. You are much more likely to get chatter in that >case. A high helix cutter will help, as will ensuring that the >finish cut isn't too deep. > >Another chatter risk is cutting inside radii with a cutter that is >the same as (or very close to) the finished radius. If the cutter >radius is close to the part radius, then the path of the tool >centerline has a sharp or nearly sharp corner. Just before the tool >reaches that corner, the amount of tool perimeter engaged in the cut >increases dramatically. (Hard to explain in words - see the >attached sketch. The heavy red line is the portion of the tool >perimeter that is cutting.) The result can easily be chatter and a >crappy surface finish. > >If you decide to use a tapered end mill for the finishing cuts, keep >both of these issues in mind, and take some test cuts. It would be >a shame to have the very last cuts in the part start chattering and >make a mess of things. > >I'm sure both of these issues are old-hat to the experienced >machinists here, but I learned them both the hard way - hopefully >this will spare someone else the same experience. > > >Regards, > >John Kasunich
Yep, were it me I would put some bigger radii in the corners and run a carbide ball end mill finish pass with say 0.005" or less down steps. Wind it up as fast as it will turn and feed it as fast as it will go. In the video that squawking that John is referring to in the corners is something you can get away with in aluminum and softer steel but if you are cutting 60Rc tool steel and you hear that you may as well just stop and change the cutter because it is done cutting. ______________ Andre' B. ------------------------------------------------------------------------------ This SF.net email is sponsored by: SourcForge Community SourceForge wants to tell your story. http://p.sf.net/sfu/sf-spreadtheword _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
