Getting my head around CNC capabilities

**beefs** · 11th March 2010, 08:22 AM

Hi there everyone, just came across this CNC stuff and find it fascinating, needless to say i'm about to order the Solsylva plans and build myself one...just need to clarify some capabilities of the machine first in respects to 2.5D/3D.

For example could a 3 axis machine route a baseball bat? I'd consider that to be a 3D project and the answer to be "no it can't be done". However what about if you cut down to half way, then flipped the work over and cut the other half? Is this a difficult (or possible) thing to do?

What about if the baseball bat was a weird mishapen one and had bezier curved edges rather than perfect circular edges - could this be cut using the above method (as long as there was no overhangs?). Can cut3d/mach 3/homemade cnc routers handle bezier curves?

I've seen the 3D carving of the fish by rodm which makes me think it's possible but just want to double check. Hope my examples describe the question clearly enough

Thanks

**seafurymike** · 11th March 2010, 03:52 PM

Quote:
could a 3 axis machine route a baseball bat

A. Yes, but you would be better doing this type of work with a 4th axis. This is a rotational axis, just like a lathe which is added generally to the table top of the machine. As you mentioned you can mill away the top half, use location pins, flip the piece over and route the other half. Alignment is difficult to achieve using this technique.

Can cut3d/mach 3/homemade cnc routers handle bezier curves

A. If you draw it, the post processors will output the G-Code

/M

**beefs** · 11th March 2010, 05:28 PM

Thanks SFM, that's good news on what the post processors are able to do with the G-Code.

The fourth axis seems ideal but for a first machine i'll start with the 3 and index/flip my work pieces I think. Once i'm on top of that a 4th could be a possibility though.

**rodm** · 11th March 2010, 08:50 PM

Hi Beef,
If you are after proper 3D then you need a five axis machine. Even with a 4th axis it is not proper 3D as you cannot machine the ends or make undercuts.
You need to be able to rotate the router upwards to make undercuts.

I would love to see plans for 5th and 6th axis knuckle as it is something I am seriously considering. I've seen a few of these rotary joints but they are based on pulleys and belts which just don't provide enough resloution or lack of backlash. Harmonic drives are the key but so far I can't get my head around construction of these into a knuckle.

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