# Thread: Feed Rates and cutters for wood panels

1. 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.
Last edited by jimbo_cnc; 10-03-2015 at 03:21 PM.

2. 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.

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

4. 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.

5. page 3
https://www.geckodrive.com/gecko/ima...cs%20Guide.pdf

Torque doesn't start reducing straight away, it's not until corner speed it falls off.

Resolution is what it is. It's 10mm pitch direct drive and I don't have the option to gear the motor faster on this machine. Driver has serious micro-stepping capability, depending on how you think theoretical resolution translates into real-life accuracy.

When I add power into the calcs, it may reveal some acceleration problems at lower speeds.

6. Look at a chart from a motor manufacturer. They don't look like the one from Gecko.
Torque starts dropping immediately.

7. At very low speed the torque is approximately 2/3rds of the rated holding torque. The then gradually lowers from that value then quickly drops off at the corner speed.

8. The first chart from the first hit on google looks a lot like the gecko chart :)
http://www.orientalmotor.com/product...-only-1-8.html

But I see many different characteristics, so yes, new torque model needed before I look at power and stall.

9. Yes, 60oz motors have flatter torque curves. But we don't use those.

10. Originally Posted by Ger21
Yes, 60oz motors have flatter torque curves. But we don't use those.
And if you find a Chinese supplier that gives you an accurate Chart for that particular motor then Frame it because it will be a Rare thing.!!

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