View Full Version : Slate - Considerations and settings

Bob WrightNC
05-11-2016, 9:36 AM
Well, after talking a big game, I decided I too needed to be a contributor and at least put someone in the ballpark if I can. I tested pretty extensively and would love some feedback from some of the more experienced guys.

Looking at what you find when you search for slate on this forum brings up few threads on slate and few of those are on Trotec machines although Keith Winter did post some settings for a machine like mine and when my wife wanted a demo piece, those were the settings I used(100P,8S,1000PPI). I initially ran this at 500 dpi and the end result was a deep engrave with a goldish color. Gotta admit when it was running it was a little freaky/sparky as the laser was literally chiseling the slate away and you got a very noticeable deep engrave that would be perfect for color filling. My version of Job Control(10.4) had no settings for slate so I knew that this would be a testing scenario as others have suggested. My test grid consisted of holding either power or speed constant (100) and then varying the other by 5 points across the entire range. I did have some settings that yielded no mark so I knew at least that I had the lower end of the range covered. I held PPI at 1000 for no reason other than all the stone in Job Control used that setting and I had to make some assumptions. My initial runs were at 250 dpi as I had seen in one of the threads but it quickly became apparent that with much variation in the surface, it became pretty "gappy" and I had read in the one of the threads that 600DPI had given a consistent mark. So we went with the 600 knowing that once I found the color I was looking for, I'd test saturation to look for consistency.

Our slate was mineral oiled and a nice black ready for retail piece that we buy wholesale. They(the vendor) also laser engrave but after some conversation with them, I knew that my results were going to be about color and consistency/uniformity of the mark. I didn't want the gold, but as crisp and bright a color as I could get which turns out to be a nice gray/whitish gray.

Where did I end up? 100P, 70S, 1000PPI. When I looked at DPI, I found that the 600 gave a very good mark but with a very uneven surface, I'd go to 1000DPI even though it adds about a 35% increase in time. Once we got the color, it was uniform across a very wide range of speed/power settings which suggested that almost anywhere in that range, I could probably tweek DPI and end up with a good mark.

Observations - Speed is a real consideration with the Trotec as very few settings that I see on here on the forum correlate over to my machine unless they are from someone with a Trotec. Even within the same exact model, there are variations in power that make true 1-to-1 conversions from one machine to the next anything but a sure thing. The bottom line is that this is a good ballpark setting for someone that has the same machine that I do, but not many others. But it is a very different group of settings from what's on the board, and maybe it can help someone else at least get close and save a little time tweaking out their own settings.

Am I giving away trade secrets? Anyone who wants to do slate can do exactly what I did and get to the same place and find what others have said is "what looks good to them". It's much easier with slate, than say glass which brings so many variables to the table. The fact is, it's about customers and how many you have that come to your site or your storefront - that's where the battles are won and lost. And for that reason, I had no problems sharing if it will help someone.

Speed is a variable that I'm still trying to understand and one of the big differences between machines that make "translation" of what you see in the forum tough. But as I get to know my machine better all the time, I realize more and more that it's about testing your substrate in YOUR machine. That's where the rubber meets the road. Still, listening to those who are more experienced gives me other perspectives to consider which can impact how I test.

Thanks again to all who contribute.

Mike Chance in Iowa
05-11-2016, 6:39 PM
Wow. So many "reads" on this thread, yet no thank you. So, thank you Bob for writing up the post and sharing your results. While I do not have a need to engrave slate at this time, I may need to search for this information at a later date!

Kev Williams
05-11-2016, 8:13 PM
Concerning speed, I've found that with higher speeds you compromise overall engraving quality. Could be why my 1997 ULS to this day still produces outstanding high-detail results, it just plain ain't fast!

Concerning detail, in some cases (not all, but might work on slate?) changing the black to 70% black and creating a 300dpi bitmap can give much more consistent large-area results, I suppose due to the more 'random' firing of the laser. However, "in some cases" is the key- I've found the sweet spot with my LS900, whereas I can engrave a full sheet of glass and it'll literally look like it's been sandblasted, but I've yet to even come CLOSE to those results with my other lasers. Unless really fine detail is necessary, I've found the 70% method gives me better results than extremely high dpi settings...

Doug Fisher
05-05-2017, 7:22 PM
Thanks for taking time to create this detailed post.

Keith Outten
05-06-2017, 7:07 AM
I haven't engraved slate but you might try coating it with Armor All before you engrave to see what happens. I have been using Armor All to engrave black marble for years, you can find more information about this in our archives.

Mike Null
05-06-2017, 7:27 AM
How about some pictures?