Engraving glasses revisited (long)

[Don Gares]

First of all I realize that there have been several threads concerning this subject and I think that I have read them all. I have a 40 Watt Pinnacle M Series machine and the related rotary attachment. I have been experimenting engraving beer mugs, flutes, wine glasses, etc. with reasonably good success.......probably not perfect but presentable as far as I can tell (never seen any done by other people). Obviously, I have not tried every combination of DPI, speed, and power but I have tried a lot of them with my best results being with 100 speed, 60 power, and 1000 DPI! Yes, I have found 1000 DPI to work the best but 600 DPI is almost as good. I have not been using any wet wraps or dish soap on the glasses.

Ok, now my questions:

1.) Most all of the posts that I have read recommend a dramatically lower DPI, why am I getting the best results with a high DPI?

2.) The previously posted speeds and power are all over the place but this may well be because of different powers of lasers. Does my settings sound in line and if not, what would you suggest?

3.) I have also seen liquid dish soap recommended several times. I would like to try this but isn't it a real mess dripping in the machine?

4.) My print driver has both a "Black and White" and a "3D" setting which the manual really does not fully explain the difference. For engraving on glass I have been using the "Black and White" mode, does this sound correct? In, fact, I have only found the "3D" to be useful on wood plaques. What am I missing?

All in all, if this knowledgeable group of individuals could shed some light any or all of the above it would be greatly appreciated by this person that has only owned a laser for about three months and had never even seen one before.

Cheers,

Don

[Tim Bateson]

I can help with a couple of those questions:
1) Good question - I'd be interested in that answer myself.
2) Yes, you are correct every laser - even the same wattage is a bit different.
3) When properly applied, the glass will be slippery with a thick coating of liquid dish soap - not to the point of dripping or running - almost like an oily film.
4) Never tried it, but I don't think you want 3D for glass. That mode digs a bit deeper & may be too much power for the glass to handle or may weaken it. Again, I'd be interested if someone has tried it.

[Hilton Lister]

I have a 25 watt Mercury and I get the best results at 1000dpi. 100% speed and 85% power. I do use sign-vinyl application tape as well though and often give the article a light sandblast before removing the tape. The tape seems to have quite a dense adhesive and will take quite a good blast. Indeed, you must make sure you have completely lasered through the tape, otherwise it is almost impossible to blast through the adhesive (at least, at the pressure I blast) Another advantage, is that you can actually see the crystallised deposits from the laser being blasted away during the process, leaving no shards.

[Darren Null]

1) Possibly your software is reducing the dpi of the image on the way through. Don't know otherwise.

2) Sounds about right.

3) You don't use enough to drip. Smear it on with a finger.

4) Black and white turns the laser on to the power you specify or turns it off for the white bits. 3D uses the power you specify for the black bits, but steps down the power through various shades of grey (how many shades depends on the machine). With a specially-prepared graphic, it's possible to make a 3D image. It takes ages and I usually end up with charcoal. Technically, the image is 2.5D, because you can only fire the laser from one direction. Most of the laser manufacturers have some sort of demo; this is the first one I found on Google:
http://www.gemengraving.co.uk/laser_engraving.htm

With my 10W, 3D is nowhere near cost-effective...much quicker to vector cut layers of plywood for 3D. Your mileage may vary.

[Frank Corker]

When it comes to engraving glass, I always put my settings on 1200 dpi, it results in a much smother finish. I always use thin paper with a dollop of concentrated washing up liquid which I smear with my finger across the glassware. On the Epilog rotary you have to be careful about having too much soap in the wrong place or the workpiece will slip.

[Don Gares]

Ok, for a few hours this morning I have been trying many of the suggestions that I received and the end result was dramatically better than I had originally obtained. It appears, at least on my machine, that the increased DPI and dish soap is what moves the engraving from just "ok" to "great".

First I increased the DPI to 1000 and wiped the glass with dish soap and got great results. Of course I didn't know if it was the increased DPI, dish soap, or both that helped so I continued to experiment. The end result was that it was both.

In short I get my best results at 1000 DPI, speed = 100, power = 70, with the glass wiped with Joy liquid dish soap. This is with a 40 watt Pinnacle M Series machine. Of course, the drawback is that it takes 66% longer to engrave something at 1000 DPI than it does at 600 DPI.

All the replies were appreciated and I must say that this forum is probably the best that I have found, all subjects included (from gardening to lasers). So many forums get off subject with their replies but you people stray right on tract and that is definitely appreciated.

Thanks again,

Don

[Richard McMahon]

I would love to know how you can get 1000 dpi from your laser. I have a home built one and the very smallest I can get my dot size seems to be about 0.006" or about 160 dpi.
My lens is a 2" focal length and I think that the smaller the focal length the better the dot size. i.e smaller
I usually engrave at about 300 dpi but lately I have reduced the size to 96 dpi with better results

I now have a sheet of granite to engrave for a memorial plaque on a headstone and I am just a little bit reticent about doing it with no test sheet and as such I am torn between doing it at 96 dpi or somewhere between that and 300 dpi.

for testing I usually use the cardboard from our local X-Ray department that the X-Ray negatives come in and it is coated but takes a good burn so I may use that as a test plate. They throw it away by the hundreds so you may try that as well if ever you want to try it. The plastic X-Ray sheets cut ok too and there are usually a few blank ones you can use for stencils etc which are free.
Does anybody else use them?

All my mirror tiles have come out ok and Photograv 3.0 has helped a lot but it is still a science to get it right.
Rich.

[Mike Null]

I'm definitely in the minority here but I use a lower dpi (333) to get the result I consider best. What a I like is a frosted look without the micro-fractures.

If you want to practice get some window glass from the hardware store. It's cheap and will allow you to experiment with settings, masks and lubricants.


Additional comment: I usually run these twice at this resolution. 45 watts at 90 ips.

[Albert Nix]

You guys have a lot more laser time than I do but it would seem like 1000 DPI would be way over kill. If you had a lens that could reduce the beam width to .001 the dots would be end to end at 1000 DPI so with the 1.5" lens that fires a .003" spot, would'nt 600 DPI give you a nearly 50% overlap on the dots? Or am I looking at this all wrong?
Al

[Don Gares]

Okay, I can't argue with the math because it certainly makes sense so I just tried the various DPI's (300, 600, & 1000) on a piece of flat glass. All were engraved on a 40 watt machine at 100 speed and 65 power. I then scanned the engraved glass with a black mat board behind it and attached is the result.

As you can see the 600 and 1000 are dramatically better than the 300 DPI. What I found interesting is that the 600 and 1000 are basically a "toss up" with the 600 possibly being a bit better when engraved on this flat glass. OTOH, when I tried the same thing on a beer mug with my rotary attachment the 1000 was by far the best.

And yes, I had too much time on my hands this morning.

Don

[Albert Nix]

I think I agree with you that the 600 may look a little better. If the math does work, then the 1000 DPI pass may have been over kill for that particular piece of glass. 1000DPI may be fine at a lower power setting. The mug may be a different grade of glass and be able to stand the pounding or a higher power setting (or slower speed) at 600 DPI. The reason I am so interested is that it looks like you have the same machine that I do and I like doing glass. Mine has mostly been glasses and mirrors. For the most part I also use 100P/60S 600DPI

[Jack Harper]

Ahhhh, but what about a photo where you need to control gray scaling? Over driving the resolution may just make a photo lose all detail.

[Bob Cole]

I was having trouble with glass engraving and still fine tuning. I first went by the settings in the ULS book and they came out horrible. Another post had the link to a colorfill demo on ULS web site and the settings for the 2.0 lens were:
pwr=100
spd (use your laser wattage, so if you had a 60 watt, put in 60)
ppi=500
img=5 (500dpi)

The kicker that modified how well it looks was having the mask on the glass and changing the black to grayscale of about 60%. I tried 70%, but it turned out better at 60%. I haven't tried any other % but wondering if either lower power or reducing the grayscale even more would help it out.

Using this formula got me the closest to the look of sandblasting (obviously without the depth).

My goal is to colorfill but all the rattle cans I try just don't work well. I also tried some Amaco for glass/ceramics and wasn't thrilled with that. The gold rubnbuff came out the best but still having difficulty getting it to look exactly the the picture on the tutorial page 3 and page 4.

I am getting a little nervous due to having 50 glass awards to do and still don't have my settings dialed in perfect. I may be expecting too much. Most people I show the samples to say that looks great before I tell them I am unhappy with it. Not sure if it is my obsessive compulsive behavior or what.

[John W. Love]

Bob, I am with you on the colorfill of glass. I have tried dyes, inks, paint, rub n buff, etc. and just have not had any luck producing something that not only looks really nice, but also lasts. I do remember about a month ago somone posting about using craft paints from Michael's. Americana brand? Not sure if that is right or not. not sure exactly what the thread was about, but I am most certain it was within the last month.

BTW Bob, we are our most critical critic.

[Dan Hintz]

Bob,

Hmmm, I think you have that backwards... you want 100P and a speed that matches your wattage (in your case, and mine, 60S). I use 60S/100P/333dpi with good results (though I'm still tweaking, as time permits). To use it your stated way doesn't work. Imagine someone with a 100W laser... they'd be running at 100S/100P (blowing 100W into the glass at 'X' ips), whereas someone with a 10W laser would run at 100S/10P (blowing 1W into the glass at the same speed).

I haven't yet played with anything other than pure black, but that's my next step. I believe most have received great results with 80-90%.