Surfacing help!

[Thorpydo]

Hey,

I'm making a two part mold with some surfacing. It's the most complicated part I've made so far and am a bit over my head.

First the background:

I've setup a rough surfacing feature and a fine surfacing feature in mastercam for a 3/8" carbide ball end mill. I will follow with a fine surfacing feature with a 1/8" ball end mill. The surfacing path that I'm using is parallel. The rough feature leave .1" to the surface, the 3/8" fine leaves .02" and the 1/8" fine takes off that last bit.

The problem I'm facing is this:
During the 3/8" fine cut, it's taking off .08 down, but also .08 at the edges, and these edges can be a half inch deep. The machine doesn't like that and I have to slow the feed rate way way way down to make it even manageable.

If I was doing this over, I probably would have 3/8" roughed to .03, then 3/8" fine to .015, then 1/8" fine to the surface.

But I'd like to hear from you guys, what would you recommend? I've looked at the contour surfacing path in hopes that if it starts from the top, then I'm only ever taking a little bit off. . . but that doesn't look to be the case and the path is pretty funky.

Would you guys recommend roughing with a flat endmill instead? The ball doesn't seem to cut as well (my guess would be because towards the center doesn't rotate as fast as the outside)

Thanks!
Aam

[MRM RCModels]

What RPM are you cutting at? I would have used a 0.25 carbide rougher to cut within 0.05 of the surface. Then, use the ball end mill. Also, try reducing your step over to a few mm. 3D work is not a quick process.

[Thorpydo]

RPM is the stock 2000. Stepover is .100 on the roughing and .06 on the finishing. Unfortunately I don't have any roughers. Would you use a flat rougher or ball rougher (there is such a thing, right?)

I'm re-running the work.
20 thou to surface on the 3/8 roughing
10 thou to surface on the 3/8 finishing

Would a flat endmill work better for the roughing?

[DeusExMachina]

I'd suggest using a flat end mill and leaving 0.05" or so for roughing, finish or roughing end-mill, then finish up with a 1/4" or so ball with a 0.0025"-0.01" step over depending on how smooth you want it, it'll take a while... Actually this is more or less what MRM RCModels just said...

Your 2k spindle is going to limit your feeds a lot....

[pete from TN]

While I am not yet able to intelligently help you with your question, I would like to congratulate you on an ambitious machined part on your X3.... that thing looks pretty cool and I am wondering just what the hell it is? Man I cannot wait to be able to make stuff like that on my machine. What is the approximate run time on that part? Anyways, not to hijack but nice work and that is probably the most intricate part I have seen done on that type of machine here lately... keep up the good work...peace

[pete from TN]

can you post a video of that machine running that part for the folks here that right now can just drool over it!! peace...

[Thorpydo]

Thanks. I've seen much more intricate work done but nothing this large. I've just about maxed both the x and y axis. Makes me wish I sprang for a bigger machine. . . then again I really don't have the room in my apartment.

The part is for my next million dollars It's the handle to a daggerboard (basically a small removable keel for a sailboat) that I'm prototyping. The daggerboard will provide a larger righting moment for the sailboat (in theory).

The cavity will be filled with urethane.

[pete from TN]

Amen brother.... I hear that and I hope to make some cash with the machine once it is done too... SO this is a MOLD huh, I love sailboats, I used to borrow a neighbors small hobie cat at my grandparents house down in florida and I ran that thing all over that lake. Nothing cooler than when the wind picks up and you get it going on one side and you only head the rush of the wind and the water getting ripped aside by the single pontoon. Feels like you are going 100mph man, it is a total sensory experience I think. I also spent some time in the Coast Guard and found new respect for sailboats when you get way out there and there is not a motorboat anywhere but a small sailboat is on a round the world trip!! Nothing more seaworthy than a well built sailboat.... try to post some completed pics and a vid if you can, that is real cool...peace

[Thorpydo]

The batteries in my camera ran out as I was finishing up the video. . . I'll hunt around for some spares.

Yeah, sailing is great. I'm planning a trip with some buddies to sail the California coast at the end of summer, maybe down to Mexico.

Have you heard of the Maltese Falcon?

[pete from TN]

WHAT VIDEO>>>> and if you mean the book then yeah but if you mean some special sailing vessel by the same name then no.... fill in the blanks please...peace

[Thorpydo]

I took a short video. My camera batteries died as the video ended. Without batteries, it's hard to upload the video to my computer

Maltese Falcon:
http://www.symaltesefalcon.com/index2.asp

It's the largest sailboat in the world (depending on how you measure) built by the venture capitalist Tom Perkins . It's almost 300 ft long with 3 carbon fiber masts. The sails are rigidly attached and the masts themselves rotate to adjust the sails. IE, no rigging, computer controlled boat, which admittedly would take some of the fun out of it.

Check out the 'submarine' on that page. Also a very interesting concept.

[escott76]

Originally Posted by Thorpydo Hey, I'm making a two part mold with some surfacing. It's the most complicated part I've made so far and am a bit over my head. First the background: I've setup a rough surfacing feature and a fine surfacing feature in mastercam for a 3/8" carbide ball end mill. I will follow with a fine surfacing feature with a 1/8" ball end mill. The surfacing path that I'm using is parallel. The rough feature leave .1" to the surface, the 3/8" fine leaves .02" and the 1/8" fine takes off that last bit. The problem I'm facing is this: During the 3/8" fine cut, it's taking off .08 down, but also .08 at the edges, and these edges can be a half inch deep. The machine doesn't like that and I have to slow the feed rate way way way down to make it even manageable. If I was doing this over, I probably would have 3/8" roughed to .03, then 3/8" fine to .015, then 1/8" fine to the surface. But I'd like to hear from you guys, what would you recommend? I've looked at the contour surfacing path in hopes that if it starts from the top, then I'm only ever taking a little bit off. . . but that doesn't look to be the case and the path is pretty funky. Would you guys recommend roughing with a flat endmill instead? The ball doesn't seem to cut as well (my guess would be because towards the center doesn't rotate as fast as the outside) Thanks! Aam

Couple of things. For finishing your stepovers sound rather large. I get real nice mold finishes running in the 0.002-0.001 range. I also use a "constant stepover" cut, which makes the stepover constant over 3 dimensions, in other words just not moving over in X and Y and taking another pass at variable Z, but keeping this pass a constant distance from the last in X Y and Z at all times. No finish work on the mold, and plastic comes out really nice. I don't prototype molds in aluminum though, I do it in plastic, and pour liquid plastic with a release agent. Works good, and is faster than cutting metal. Of course injection molding is kind of out.
There are a couple different kinds of toolpaths you can use for roughing. If you are having trouble with the total DOC in some areas, set your CAM system up to take multiple Z passes that are within the range of your tools spindle. I don't use mastercam though, I use Gibbs, so I can't help with specific function names. I use a proportionally much larger stepover, more like 1/2 the tool, take shallower cuts and more of them. I also leave much less for a finish pass, in the 0.01-0.02" range.
As the others have said, the finish pass sucks on the time. Just part of the deal when it comes to 3D work. Getting the most of your CAM system will take time and experimentation too. The more complex types of toolpaths will require some tweaking and tuning, and experience with them will let you know the kind and values within that toolpath type that give the results you want in the material you are using. Play around with some scrap material, make a simple shape, and do comparisons between them to tell you what works best. That way you don't scrap lots of expensive mold blanks.