[ArnieJr]

Hey Guys

I’ve tried to machine a dome with a ½” ball end cutter and found out that if I machine it using 3axis approach (from top only ) it comes out different from 5 axis!
Basically the 3 axis approach digs further into the part the further it cuts away from the tool center, while the 5 axis approach cuts the part perfectly. The difference between the two approaches is about 0.3mm but the implication is far more daunting as it means I cannot cut a part with both approaches in it as it would have a step between the toolpaths!
I thought it could be the tool but after I tested with 3 different tools I realized that they all do the same thing !
Is it how it should be or is there a post-processor problem here ???

Thanks
Arnie

[awerby]

Hey Guys

I’ve tried to machine a dome with a ½” ball end cutter and found out that if I machine it using 3axis approach (from top only ) it comes out different from 5 axis!

[There's a reason people spend the extra money for 5-axis equipment and software.]

Basically the 3 axis approach digs further into the part the further it cuts away from the tool center, while the 5 axis approach cuts the part perfectly. The difference between the two approaches is about 0.3mm but the implication is far more daunting as it means I cannot cut a part with both approaches in it as it would have a step between the toolpaths!
I thought it could be the tool but after I tested with 3 different tools I realized that they all do the same thing !
Is it how it should be or is there a post-processor problem here ???

Thanks
Arnie

[I think you're noticing the difference between horizontal (waterline) milling and parallel milling. If you set a step-over distance and start milling on the top of the dome, all will be fine for a while. But as the angle gets steeper, going down the side of the dome, the horizontal distance translates into a much greater vertical distance, so your cusps (the uncut places between the cuts) get larger. I think if you measure the bottoms of the cuts, the dimension will probably be accurate, even though the surface doesn't look good. The solution would be to use a different type of toolpath for the sides of the dome than the top, one which drops the tool a certain amount vertically each go-round (those are the waterlines) rather than just stepping over horizontally.

[Superman]

Hey Guys

I’ve tried to machine a dome with a ½” ball end cutter and found out that if I machine it using 3axis approach (from top only ) it comes out different from 5 axis!
Basically the 3 axis approach digs further into the part the further it cuts away from the tool center, while the 5 axis approach cuts the part perfectly. The difference between the two approaches is about 0.3mm but the implication is far more daunting as it means I cannot cut a part with both approaches in it as it would have a step between the toolpaths!
I thought it could be the tool but after I tested with 3 different tools I realized that they all do the same thing !
Is it how it should be or is there a post-processor problem here ???

You haven't given ALL the variable details...
- toolholder used, Shrink/collet etc.......sidelock should not be used,
- quality of tool...... HSS, CBD, balanced, actual tool build (holder+tool.... short as possible is best)
- constant machining depth, finishing path only
- quality of machine
- calibration of "swing point" ( 4/5th axis)
- temp difference when calibrated & when machined

If tool is new & quality brand, I would put more faith on a 3 axis path being correct before a 5 axis result
- a 5 axis path and the machine kinematics have a major effect on any result

3 axis path would allow the cutting contact point on the tool to be the tip ( at the top ) moving round to the side of the tool when machining the lower area of the dome
- where a 5 axis path would use the same section of the tool radius of the cutter to cut over all of the dome.

[ArnieJr]

Thanks for your reply Andrew

I did a test prg where the 2 approaches ( 3 axis and 5 axis ) would overlap each other by 1/4 of the dome area so as to enable me to measure the difference between them .I could clearly see that the 2 toolpaths don't actually meet ( by 0.3mm roughly)
Arnie

[ArnieJr]

Hey Superman, thanks for your reply

These are the variables:
Toolholder used: HSK50 / collet
Tool : Solid Carbide ½” Ball nose cutter
Tool length : 70mm ( Cutting edge 25mm )
Stock: Model board (SikaBlock M700) Density : 0.7 g/cm3.
Machine : Multicam 8000 series( Not a very good machine I must admit )