Hi Kirk, Most plastics like a really sharp edge with lots of positive rake. You want to slice it off rather than scraping it off. The xxGT inserts generally use a micrograin carbide which allows them to hold a finer edge. The down side is that they wear faster. However in a plastic like Delrin that probably isn't an issue.
I would also take deeper cuts. For instance with your part, I probably would only use two passes, one roughing at 0.160 and one finishing. If you are doing a lot you may be able to even cut that down to one pass though you may have to tweak the dimensions slightly to compensate for flex. > Is it reasonable to use one tool for all > directions; facing right and left, turning in and out? I tend to work on the principle of 'if it has a cutting edge, use it'. For instance if I am roughing to diameter I sometimes cut alternately left and right with the same tool. This is obviously faster as you don't have to return for the next pass and it spreads out the wear on the cutter. Of course this depends very much on the tool and part geometry Les Kirk Wallace wrote: > > Thanks for the replies, Leslie and John. > > I was using a triangular insert with a front angle of 89 degrees (almost > parallel with the workpiece face) and a back angle of 29 degrees (29 > degrees from the OD surface). The insert has a chip breaking groove > approximately .030" wide. It worked fine in aluminum. The Delrin part > path is here. > > http://www.wallacecompany.com/machine_shop/retainer_side_1-1a.png > > I take two roughing passes (~.080" each cut, violet lines), starting > from the left on the first pass and finishing the second pass on the > left. I then lead in (gray line) on the left and follow the finish > profile (blue). > > I got a torn melted finish. Is it reasonable to use one tool for all > directions; facing right and left, turning in and out? The more I think > about it, I think the insert isn't sharp enough. I may dress it on my > diamond wheel and see if it works any better. > > I like the DCGT inserts, but I am having a little trouble finding a > holder (3/8" square shank) that will work on my Hardinge HNC. Youtube > seems to have the best picture of the turret: > > http://www.youtube.com/watch?v=vwhz3Ho_Gx0 > > I need to get some still shots. > > ------------------------------------------------------------------------- Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW! Studies have shown that voting for your favorite open source project, along with a healthy diet, reduces your potential for chronic lameness and boredom. Vote Now at http://www.sourceforge.net/community/cca08 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
