I had made a video previously about calculating the maximum speed of the Glowforge in mm/s. Since I had this video before the update, I was able to do some before/after comparisons with the effect of the speed and acceleration changes. Check out the video here:
It’s cool that you had video of both before and after and could compare apples to apples. Do you intend to write up the results to make the data a little more accessible to people who don’t prefer to learn via video?
I think it would be interesting if somebody had video like yours of a tall engraving instead of a wide one. In theory you’ll see the greatest increases in speed on a tall thin engrave rather than a wide short engrave. Since most if not all of the benefit comes from the acceleration portion, a vertical, thin, high speed, high lpi engraving spends most of its time accelerating into an out of lines. That’s where you’d really expect the update to shine.
Glowforge was cagey about releasing numbers with this release for this very reason. There are just too many variables to get into it in a short format.
You’re correct that wide things benefit the most. I did that shape because it was the shape I had done originally. I can’t go back and re-film the pre-update one. Glowforge never released original top speeds either, but people calculated it at 140 to 150 mm/s.
Tall. 
Wide things benefit most from the top speed increase. Tall, skinny things probably won’t benefit too much from the acceleration increases because the head doesn’t have room to get up to full speed anyhow. Greater acceleration, but at low speed won’t change much. But that small increase over many, many lines might add up to significant differences.
You have it backwards. Or at least we’re not talking about the same thing.
Top speed – to an extent – who cares, the laser only has so much power, you alluded to that. Going too fast will often not get great results.
But for a given speed, more time is spent accelerating the shorter the individual scan passes get. For a tall thin engrave, it spends very little time “up to speed” compared to a wider engrave.
Thus, comparing the old to the new, you’d expect a major reduction in overall job time if you cut out the acceleration times, which is what that update did. Ergo, tall engraves (with far more passes and much shorter passes) should see more benefit than wider ones if speed and power are unchanged.
And if you want the same results, you can’t mess with the power and speed. This is why I think the engraving top speeds are a waste of time as a general rule. There are some materials that get good contrast with very little laser (cork, for example, and some mahoganies, etc) but in general, the top end of speed is for edge cases, not for hardwood engraves – at least not the way I like them, aesthetically speaking.
I agree that top speeds are overrated. But I disagree about the effect of acceleration on tall, skinny jobs. Since the head never has time to go very fast, it doesn’t really matter how fast the acceleration is. It’s like running back and forth in a 2-foot room. Your acceleration and your top speed won’t matter much because there’s no room for either one to have much effect. Acceleration is really only important when you’re accelerating to a significant speed. Tall, skinny things will never get to significant speeds. It’s like a Yugo and a Corvette racing from 0 to 2 miles per hour. There won’t be much difference.
Great conversation!
I think again we’re talking about different things. All engraves get up to the same speed, regardless of aspect ratio. This is why the margins get wider with higher speeds. It gets up to that speed, but doesn’t stay at that speed for long, that’s the rub.
Let’s pick 1000 speed (highest reasonable speed more or less) means that the laser will be cruising at 1000 speed when it’s engraving the actual art (as long as you’re not using the beta margins feature). That means it needs to get up to 1000 speed for the engraving area no matter how wide it is. That acceleration process is the same no matter how wide the engrave is, and therefore takes some amount of time. Let’s call that time X.
Therefore a row goes like this:
Accelerate to 1000 speed (X time) + cross engraveable area at 1000 speed (Y time) + decelerate to zero (X time).
Therefore a total row is 2X + Y. Old or new version, Y time was the same, but with the update, X is strongly reduced. Lets put mythical numbers of 0.5s (old) and 0.2s (new) for X and two examples of a wide engrave (Y = 3s) and a narrow engrave (Y=0.375s).
For a 270 LPI engrave that is 1" * 8" let’s do some math.
Wide:
OLD total time = 1" * 270 LPI * (2X + Y) or 270 * (2 * 0.5s + 3s) = 1080s
NEW total time = 270 * (2 * 0.2s + 3s) = 918s
Or about a 15% time reduction.
Narrow:
OLD total time = 8" * 270 LPI * (2X + Y) or 2160 * (2 * 0.5s + 0.375s) = 2970s
NEW total time = 2160 * (2 * 0.2s + .375s) = 1674s
Or about a 43% time reduction, about three times the benefit you see in a wider engrave.
Now I don’t know what the actual numbers X and Y are but since they’re constants the math will always work out where the larger increase between old and new will be felt on taller engraves. I’m ignoring the travel time to and from the engrave start and end (doesn’t scale up with engrave size so can be discarded), and ignoring the step time between rows (scales up per row. but negligible)
So this is what I mean when I say you’ll see the greatest improvements with taller narrower engraves. I am assuming that power and speed are the same, and that you’re not using the margin beta.
I do see what you’re saying and the answer depends on a few things. Some lasers accelerate all the way to full speed before they begin engraving at the full power. Others ramp up the power as the speed increases. Many Ruida lasers can do the latter to save time. I don’t know if we know for sure which way the Glowforge does it, but some informal measurements that I did on the video today suggest that it is not at full speed during the entire engrave. We do know that the Glowforge has the ability to actively change the power settings as it does so when the head slows down to go around corners while cutting. If, however, the laser gets up to full speed before it begins firing, then your analysis would be correct. Either way, we can agree that the additional acceleration is a great thing!
It’s an option when you’re engraving, they call it the beta margin function.
By default it doesn’t try to engrave in the margins, It gets up to full speed.
As for whether the acceleration changes are good or bad, that’s a difficult thing to say. It’s definitely more wear and tear on the machines and there may be edge cases where people were right on the limit of their belt tension or something where it could cause issues. It’s a complicated system, and for most people it probably is nothing but positive.
Anyway, it’s great to have technical discussions like this, I like the way you think and the knowledge that you bring to the discussion!
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