Been a long time, making chips again.

[harryball]

Hey Nev! How you doing? My only question, why would anyone WANT a pool! I'm trying to fill mine in. I know what you mean about the plastic one's breaking, but I think filling in the pool is a much better solution than making an aluminum wrench. I understand every body is different, just poking at you a bit.

Glad to see you back. Hope to see more posts in the future. Next time we get over to Austin I'll have to remember to give you a call.

/RB

[dubliner]

Great to hear from you Robert, and yes after owning a pool I totally agree with you. Glad to back on the forum and on the machine too.

[Gary Campbell]

Sean..
A little of both (machine & trickery). Machine is on linear rails and is 5mm pitch ballscrew driven. There is no substitute for mechanical reduction. (as long as machine can withstand the additional forces created by it) This gives 3.3 time the mechanical reduction as a 7.2 alpha system. AS911 motors have 2 times +/- the torque of the AS98AA's, resulting in somewhere around 6+/- times the ability to hold a given position under load.

Then we introduce the trickery: Drives were reprogrammed to full step operation only. Results in unit value over 2500 FULL steps/inch. Each layer of micro stepping reduces the ability of the motor to hold that position under load. (see doc: http://www.micromo.com/microstepping...-and-realities) stepper motors lose about 30% of their holding torque (or more) when in motion, and even more based on the charts in the doc.

This creates "torque detents" that when the tool is under load, it will, depending on that load, move to the next detent that will withstand and hold that load. This phenomenon creates a rippled effect on angular or circular cuts. These ripples, often being uniform from top to bottom of material, are usually described as "chatter". My opinion is that chatter would be non uniform and not be uniform thruout multiple passes.

Increasing microstepping is often prescribed as a solution. I disagree and believe its a myth started with Gecko's 1/10 stepping years ago. Increasing reduction and decreasing microstepping seems to dispel the myth, albeit not in a scientific manner. There are 2 schools of thought on this and they are the exact opposite. You will either buy into one or the other. Although un scientific, I have tested Nev's machine with a 3/8" O flute at 1.5ips at .080" per pass. This is a force beyond what most small CNC guys could/should expect from their machine. Using the alpha drives 500/1000 switch, it will consistently impart more edge ripples with the switch set at 1000. If I was Jamie Hyneman, I might say "myth busted"

[Brady Watson]

I concur with Gary's findings. Full stepping is best combined with mechanical reduction to get both resolution and full torque. Torque is your friend when it comes to machining - especially materials that have no give, such as AL.

Once you understand torque detent points on steppers, it all becomes clear. All of this mumbo jumbo for those with cognitive dissonance, boils down to edge quality and the reduction of 'chatter' or dime-edged marks, provided that your machine is in good tune & maintained. Torque loss from microstepping contributes to chatter.

The screws also add to the smoothness without introducing the cyclical pattern of gear rack patterns on the part. (Which also assumes proper maintenance and aligned rack & pinion). Good ballscrews 'ain't cheap', but then again - neither is hand finishing aluminum edges to erase the sins. Everything has a price...

Well done by the way...It is clear that you did your homework. I certainly wouldn't mind having one of these puppies in my own shop

-B

[dubliner]

Indeed Brady & Gary, Im having a renewed love affair with cutting aluminium : ). Garys build is awesome and thank you Brady for your immeasurable assistance too. Both of these guys knowledge is impressive and their willingness to share is equally so. Beyond that, being friends with them for as many years is a treat, and Im sure there are many many of us that can say the same thing. Monty MaGill, my machine is at your disposal should you need some aluminum parts with shiny chatter free sides : )
PS Gary - that explantion was very succinct. I must have been glazed over looking at the machine when you told me that first time.