How fast are you engraving?

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How fast are you engraving?

Postby BenJackson » Fri Dec 30, 2011 5:14 am

Right now my steps are limited to 37kHz and with 8x microstepping that limits me to 470mm/s (or F28200). My acceleration is 7500mm/s/s which means it takes about 15mm to get up to full speed. I haven't really tuned the acceleration and I suspect it could go much higher.

In order to engrave faster I would have to reduce the microstepping on X. Dropping to 4x would still have 1mil resolution and I could reach 940mm/s, which is about half of what something like an Epilog claims to be capable of (I saw suggestions that low end models could hit 75 IPS, or about 2000mm/s).

So my question is: How fast are people driving their 2.x laser carriage? Has anyone hit 1000mm/s or even 2000mm/s using DSP/Retina type solutions (or a smoothstepper)? Is it practical for the makerslide carriage? Most commercial engravers really minimize the size and weight of the final mirrors.
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Re: How fast are you engraving?

Postby dirktheeng » Fri Dec 30, 2011 5:33 am

Ben,

With 16x microstepping, I can get to 1,200 mm/s with the 2.X system. I don't recall what acceleration I had to use, but it wasn't too slow. I don't know what I could get to if I cut the microstepping. Bart Dring would say that we should stick to 1-3 microsecond pulse widths to be in the best power band for the drivers. That means about 1MHz step rates max... though I found you can go over that without a problem. The SS is capable of driving 2MHz. I'll have to try a few things and let you know.
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Re: How fast are you engraving?

Postby Greolt » Fri Dec 30, 2011 7:24 am

I don't have a 2.X but this is a very timely subject for me.

My Gantry assembly is built and awaiting the frame construction.

I have been doing some testing to see how the Z axis performs with this "how fast are you engraving" question very much in mind.

A long time Mach3 user, so this is my first choice to get started. With a SmoothStepper I am getting 130,000 mm/m (5000" ipm) or just over 2 meters per second. At 1000 steps per inch (40 steps per mm)

However I believe that using the Mach3 engrave plugin, I must use the LPT (not the SS) and at 25khz kernal speed I can only get about 38,000 mm/m

However I believe the Mach3 plugin only works at about 20,000 mm/m any way, so if I stick with Mach3 then engraving speed is going to be sloooow. :cry:

So I am wondering what sort of step rates are the DSP and Retina Engrave products capable of.

And as you originally asked...how fast are you engraving?

Greg
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Re: How fast are you engraving?

Postby BenJackson » Fri Dec 30, 2011 8:39 am

Greolt wrote:A long time Mach3 user, so this is my first choice to get started. With a SmoothStepper I am getting 130,000 mm/m (5000" ipm) or just over 2 meters per second. At 1000 steps per inch (40 steps per mm)

As I mentioned that sounds comparable (75IPS) to the low-end Epilog. What is your acceleration profile? You need enough overscan on each side (0.5 * v^2 / a) to hit top speed before the engraving starts, so 2m/s is only useful if you are able to use accelerations of something like 200,000mm/s/s. That would mean you could hit full speed in 10mm. That's 20 g's.

Is the carriage smooth at that speed?

Greolt wrote:So I am wondering what sort of step rates are the DSP and Retina Engrave products capable of.

I'm not sure about this, but I doubt they have a true electrical limit, only the physical limit of your laser carriage. So if you can make your SS do 2m/s I bet they can too.

Greolt wrote:And as you originally asked...how fast are you engraving?

Sorry, I thought that was obvious: As fast as possible! 470mm/s (feed rate F28200). This is as fast as I can go on the PC I'm using. I'm configured for 2000 steps/inch, though. If I reduce that to 1000 steps/inch I could go twice as fast, assuming the mechanics are up to it. To get the same overscan (I'm at 15mm right now) I'd have to quadruple my acceleration to 30000mm/s/s, which might actually work. 3 g's.
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Re: How fast are you engraving?

Postby Greolt » Fri Dec 30, 2011 11:47 am

BenJackson wrote:As I mentioned that sounds comparable (75IPS) to the low-end Epilog. What is your acceleration profile? You need enough overscan on each side (0.5 * v^2 / a) to hit top speed before the engraving starts, so 2m/s is only useful if you are able to use accelerations of something like 200,000mm/s/s. That would mean you could hit full speed in 10mm. That's 20 g's.


Acceleration was about 20,000mm/sec/sec or 2Gs. How much is my acceleration distance at that?

My axis travel is larger than a 2.X, so hopefully I will have that little extra room for acceleration margins.

Anyway if electrical limitations mean that engrave speed must be slower that that then it is a bit of a moot point.

What matters is how fast can I engrave. I need to get this machine frame built before I can explore those questions. :)

Just wondering what the Retina Engrave and DSP specs were like.

BenJackson wrote:I'm not sure about this, but I doubt they have a true electrical limit, only the physical limit of your laser carriage. So if you can make your SS do 2m/s I bet they can too.


But would not the limitation be how fast the laser can turn on and off?

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Re: How fast are you engraving?

Postby BenJackson » Fri Dec 30, 2011 9:46 pm

Greolt wrote:Acceleration was about 20,000mm/sec/sec or 2Gs. How much is my acceleration distance at that?

The formula I mentioned above: 0.5 * v^2 / a. So 0.5 * (2000mm/s)^2 / (20000mm/s/s) = 100mm. That would apply to any rapid move: You should see acceleration to top speed happen over that 100mm distance. Any move shorter than 200mm (accel, decel) would never hit top speed.

That's a perfectly good configuration for most purposes: Most cuts will be far, far slower and that's a very high acceleration relative to those cuts. And for rapids you don't care about the acceleration. But if you intended to try to reach that speed for engraving it would be impractical.

Greolt wrote:But would not the limitation be how fast the laser can turn on and off?

Other similar lasers seem to manage ok even at high speeds. I haven't measured what's going on.

In some sense it's a tradeoff, though: At low speeds you can get huge horizontal resolutions. 1000DPI is no big deal in X because it's the same sweep of the carriage, just faster laser modulation. But 1000DPI in Y takes a long time because it's so many passes. If doubling the speed cuts your X resolution in half you can now make twice the passes in Y in the same time, and Y was your limiting resolution anyway.
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