Well today I got to play around with the new MariTool 45 deg shell mill (3.15" OD) and it is really nice! It took about 10 iterations to find a good recipe for what I am trying to do. As a reminder, I have (x2) 10" x 3" pieces of bar stock 6061 mounted on a pallet and I need to deck off 0.110" and achieve a mirror finish. This is a production item that runs all day every day so reliability and speed is everything. I started out with a 0.100" DOC and 3" WOC at 5100 rpm and 20 ipm and the machine was bogging down hard so I reduced immediately to 10 ipm. I quickly realized that this tool needs to be run in the max torque band (2500-3000 rpm) or else you are leaving a lot of material removal on the table. I found that at 3000 rpm I had the least amount of bogging and I was able to push the tool to about 15 ipm (4.5 in^3/min) but I really didn't like this recipe and it seemed like the machine was working very hard just to keep up. I figured that I would get a more reliable and efficient cut by reducing the WOC so I made quite a few iterations and landed on a pretty solid roughing recipe that I am happy with.
For roughing I like a 0.100" DOC and 0.7" WOC running 3000 rpm and 60 ipm (4.2 in^3/min). I am not pushing the machine to the absolute limit with this recipe. In fact, as time goes on and I am more comfortable with the tool I will probably ramp things up a bit. Based on my tests I think an aggressive recipe would be something like 0.100" DOC, 0.8" WOC at 3000 rpm and 70 ipm (5.6 in^3/min). This is just about the same material removal rate that the superfly and the shear hog boast but I would rather run this tool for decking down a surface. The tool is balanced and cuts very aggressively without any signs of chatter. The chips are more compact than what I had with the superfly and if I push it too hard the machine bogs down but the cutter is not going to explode!
For finishing I liked a 0.005" DOC and full 3" WOC at 3000 rpm and 60 ipm. It is important that I have minimal tool marks on my parts and I was able to achieve a BETTER finish and a flatter part with this shell mill than I was with the superfly! I did not expect the surface finish to be as good as it was. In fact, I would go so far as to say it would be hard to improve the finish.
After only 1 day with this tool I feel that I am ready to retire the superfly. Although I got a lot of good use out of the superfly, it is a punishing and unbalanced tool that can do some costly damage if it fails. I do have one concern about the MariTool shell mill and that is the weight. This is a VERY heavy setup and I plan on storing it in the ATC. I am concerned that the nylon screws are going to stretch under this weight and become loose. Only time will tell...but I will say if the Tormach drops this tool or punches it out of the ATC you will definitely do some damage to the surfaces below. I think there is an opportunity to make a Tormach friendly face mill that can cut a 3" diameter. I will say that I wouldn't try running a tool that is any larger than this on a Tormach machine. That is an awfully large diameter and a huge amount of torque is put on the spindle components and at the end of the day we are relying on an R8 collet not a large taper spindle that this tool was designed for.
Tomorrow I receive the Tormach collar so I can use the ATC. I will put together a quick video/pics to show the final production run cuts.