Different speeds X and Y?

This is a curiosity question mostly, as I assume I can change the axis speeds in controller settings.

I’ve noticed that the machine (Chinese 1000x600) moves faster on the X axis than the Y axis. I’ve seen answers to questions about cut/engrave times where it was suggested to rotate the image 90% to speed things up. My question is why?

I’ve worked with CNC routers for a while now, and designed and built my last two so I know about machine control and motion. None of the machines I’ve had ran X and Y at different speeds. Why is that the norm with lasers?

Interesting Topic.
I have couple of 3D printers which the Cartesian one moves a 2Kg heavy bed on the Y axis and i found out that you can change accelerations for X & Y separately in Marlin’s firmware.

Lasers have significantly less mass to move in the X direction than the Y - just the weight of the head with mirrors, bearings, and belt. In the Y direction, you add the weight of the X gantry, X stepper motor, Y bearings, belts, and coupling shaft.

As a result, most lasers can travel and accelerate / decelerate in X significantly faster than they can in Y.

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That’s true of CNC routers too though. The gantry itself is usually at least equal to the mass of the Z axis, the spindle mount and the spindle that moves on it.

The same physics apply, though. At least in gantry style CNC.

  • X axis has to move gantry + Z-mount, Y/Z steppers, and spindle
  • Y axis only has to move the Z-mount, Z/stepper, and spindle
  • Z axis only has to move the spindle, but also has gravity to deal with.

You can’t get away from each of those having more/less mass. Some steppers and drivers are spec’d differently for each axis so you can keep the same acceleration settings. Some configurations are just a case of it’s easier for a one-size fits all.

For the latter, you could probably adjust the accelerations for each axis and get better performance.

Acceleration is delta-V/delta-T (change in velocity over time).
Force = Acceleration * Mass

No matter what else you do,more acceleration or more mass requires more force. More force requires more energy. The stepper, driver, and power supply all need to be able to provide and handle the required energy.

I’m not sure if you’re relying to me or not, but you simply expounded on my last comment (and brilliantly I might add).

I probably wasn’t clear in my original post. All of my CNC routers have moved the X and Y axes at the same speed. The gantry on one of them was easily three times the mass of everything that was mounted to it, but they moved at the same speed. My question wasn’t about the physics involved but the difference between this laser I have now (and presumably others from what I’ve read) and the CNC routers I’ve had.

The question was WHY do the axes on lasers move differently when they don’t on a CNC router, especially when the difference in mass is much more pronounced on the router?

In hindsight it’s got to be a software compensation issue. The physics can’t be avoided so the motion controllers I’ve used in the past must have some sort of compensation algorithm that slows the faster axis down to the speed of the slower. The more common laser motion controllers evidently don’t.

The question was WHY do the axes on lasers move differently when they don’t on a CNC router, especially when the difference in mass is much more pronounced on the router?

To be more “brilliant”, there is a difference between speed and acceleration. You can have the same/different speed or acceleration on each axis.

Speed is actually velocity; how fast something is moving.
Acceleration is how quickly you get from current speed to desired speed.

Consider a sports car, pickup truck, and tractor/trailer (“semi truck”), each governed to no more than 60Mph (it’s OK, this is an analogy, not real life :)). They all have a top speed of 60Mph but the sports car will get up to that speed quicker than the pickup which will be quicker than the tractor/trailer.

All axes on the CNC may be the same speed, but they would not be the same acceleration (unless the axes capable of more acceleration are artificially limited).

The acceleration may be different, but quick enough that you don’t see the ramp up/down and just see them moving at the same speed. Or, the speed is intentionally limited.

I’ve only used a 6040 CNC with a UCCNC controller. It, as well as Mach3 and others, allow you to set acceleration and speed on each axis independently.

There may also be an additional design consideration; lasers just need to move stuff around. CNC has the additional load of milling and mechanical resistance.

This may well be the answer in a nutshell.

CNC machines (and lasers too) when cutting, move at a fixed speed, but that’s more about feed rate through the cutting bit. My CNC machine could (and did) move much faster in X than in Y, so rapid moves that were primarily in X would go much faster than moves that were primarily Y.

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