Problems with 3D cutting

[44henry]

I've been using our Shopbot PRT96 Standard for a couple years now, but I have not done much 3D carving with it until the last couple days. I purchased a 3D file from VectorArt of an Enfield rifle and used the VectorArt 3D Machinist program to plot a tool path for my ShopBot. On the screen everything looks great in preview modes, but the actual cut is still fairly rough in places and I don't seem to be getting all the detail that I'm seeing on the machine. I've scaled the drawing up to about 3X its original size and I'm using a 1/4" ball nose cutter on it for both roughing and finish passes. My finish pass is going about 60 ipm and 30 for the Z and the stepover is set to 5% the depth of cut is .062". Would it be better if I did the final pass with an 1/8" ball nosed cutter? Thanks

[rcnewcomb]

The previewer should give you a very accurate representation of the finished item. I usually use an 8% stepover. Can you post a photo?

A few things to check:
1. Material movement. How is the material being held? If it is vibrating then you could get poor resolution. If you are removing a lot of material there may be cupping or bowing coming into play.
2. Material. What material are you carving? Soft pine does not machine as cleaning as something like hard maple or HDU
3. Bits. Are the bits the correct size? High quality bits make a tremendous difference on the end result. I've had some bits that left a line in everything because there was a tiny nub on the end.
4. Z play or runout. Is the Z axis solid or does it have some play? Does the router have some runout?

[myxpykalix]

Your problem is you are using a ballnose on both the roughing and finishing pass. Typically when i am doing relatively small 3d(less than 12"x12")
I use a 1/4" endmill for roughing and a 1/8th" ballnose for finishing. Try that combo and let us know if it is any better.