Feed Rates and cutters for wood panels

[jimbo_cnc]

I'm listening and using the advice I get.

I'm not hell bent on that machine, but no one has suggested any alternative yet. That's not a criticism, just a
fact.

And it appears to meet my needs. Even if it doesn't meet your idea of how fast I should cut wood. (I'm up to about 6000mm/min now, just in case you think I'm still at 3500)

As to ballscrew size, I've asked for 2 proposals from the seller, 25mm ballscrew and 32mm ballscrew, with details of motors and drivers. When I get that info, I will try to analyse the overall performance of the options. Apart from acceleration, what else is there to consider?

[jimbo_cnc]

as anticipated, next question is acceleration.

I've got some specs:

Motor: 85BHX450B current：4.0A resistance: 0.5Ω, inductance：3.0mH, torque：6 Nm
can't find that on google, but I can just use the values given.

Driver: Leadshine MA860H


I've plugged the values, along with some guesses on gantry weight into the motorcalc spreadsheet, and for 25mm ballscrew it all looks good.

I deconstructed the spreadsheet so I can see the acceleration being used is based on time to achieve feed rate. This results in 0.57g requirement for my cutting.

Is that an appropriate value for this machine?

I'd also like to use this machine for my small plastic parts. I haven't paid any attention to acceleration settings on my 6040, although I might have followed some advice without remembering it. I'm going to run some of my cutting jobs in Mach3 with different motor tuning to see what difference it makes.


32mm ballscrew:
When I plug in the 32mm ballscrew, it's clear the ballscrew dominates. I can get about 0.3g from the motor above. Or I can ask for a larger motor. I was quoted +$100 for 32mm ballscrew, but wasn't given a price for a bigger stepper.

[JAZZCNC]

32mm ballscrew:
When I plug in the 32mm ballscrew, it's clear the ballscrew dominates. I can get about 0.3g from the motor above. Or I can ask for a larger motor. [SIZE=2][COLOR=#000000][FONT=&] I was quoted +$100 for 32mm ballscrew, but wasn't given a price for a bigger stepper.

It'a not just as simple going Bigger on stepper motor. The drives they are providing now only just about cuts it for that size stepper so going bigger only makes things worse.
It's a Classic mistake often made thinking bigger is better when reality is it's often the worst thing to do. Bigger motors spin slower and require much more power and those drives won't handle larger steppers and give great performance from them.

You Get the performance thru correctly matching screws and motors to rest of machine. Just going LARGE only leads to COSTLY under performing Mistake.!!

[jimbo_cnc]

Turns out he's not offering a bigger motor, so I have to trade speed for acceleration.

In what aspect is the drive just about cutting it? (for the 25mm design)

Here's an updated calcsheet.
I'm still workig on what an appropriate accelration is to plug in for my two requirements.
Using Mach3, dialling back the acceleration made next to no difference on my plastic parts, but that might be because I cut so slowly in the first place.

[Ger21]

If you can achieve .2G, I think you'd be doing very well.
Calculating stepper motors for a target acceleration is very tricky.

Most inexpensive controls use a linear acceleration, meaning you need the same amount of force from start until you're up to speed.
The problem with that, is that steppers lose torque as rpm's increase.
So you have to base your acceleration on the amount of torque your motor will have at your target speed. This may be only 1/4 of the motors rated torque.

[jimbo_cnc]

As I understand it, I'm below corner speed even at max feedrate, so I have full torque available.

Advantage slow machine! :)

[Ger21]

The only time you have "full torque" available is when the motor is not spinning. That's why it's called holding torque. As soon as it starts spinning, the available torque starts decreasing.
If you're spinning so slow that you don't lose much torque, then your resolution is probably poor.