Roughing bit: Ball or Square

[PW2008]

Hello,

I was machining a 3D surface up to 6mm deep in a block of alluminiun using a 4mm Square-end End-Mill (SQEM) for roughing and a 1.5mm Ball-nosed End-Mill (BNEM) for finishing. However, the 1.5mm BNEM broke and I don't know why (I'm still a novice).

1. One suggestion was that using a BNEM for roughing would make life easier for the finishing bit. Is this true?

2. Would it be preferable to use more than two bits (eg a second roughing stage using a smaller bit)?

3. As a good example, can anyone quote a set of tools and parameters for the case above?

Thanks, Pete

[big_mak]

Can't be done with out a description of your part, and the parameters you are using and the specs of your machine!!!

Supply some more info and you may get some more response.

You may be able to do a semi finish pass with your roughing tool to makes the stairsteps smaller before you finish!

[ckirchen]

Your 4mm end mill is probably leaving areas of thick finishing stock (the stair steps). When the ball mill hits the thick area, it overloads and breaks.

Take a look here: http://haascnc.com/solutions_3D.asp#toolpath

Chris Kirchen

[PW2008]

Thanks for the haascnc.com link, it's exactly the sort of info' I'm looking for. If you know of similar sites I'd very much like to know.

I can't quote all the tool details because I'm typing this at home, not at work, but generalized answers would be just as useful. I'm using ArtCAM 2009 to machine into aluminium a toy train (artwork which comes with ArtCAM) with dimensions approx 80mm x 50mm x 6mm deep, recessed into a slightly bigger rectangle, so the train is not proud of the surface. Roughing was done with a 4mm SQEM with step-down 0.4mm, 12000rpm and 0.5mm Z allowance. Finishing was done with a 1.5mm BNEM with step-over 0.15mm and 12000rpm. I believe all the other settings were correct for this job and the "Many" machine used is quite capable.

I have some idea of what may have caused it to break: 1. The contianing box was too small, not leaving enough room between the train and the outside wall for the 4mm roughing tool and 2. The roughing step-down and Z allowance were too big, leaving too much material for the finishing bit.

However, my problem has 'evolved' slightly since I wrote the first question:
1. I wish to know how to get ArtCAM to do roughing with more than one bit.
2. The bit broke in a region where ArtCAM left more metal after the roughing stage than I can account for. That is, the 1.5mm finishing bit ran into a significant volume of metal that the 4mm roughing bit could easily have removed. It is difficult to show what happened by text, hopefully someone will know what I mean.

(Sorry for any vagueness on my part, it seems to be a flaw I'm stuck with.)