Unsatifactory Laser Engraving (Shenhui Laser)

[Johan de Waal]

I had similar issue on my 80W Reci and I found that the shape of the laser beam coming out of the tube didn't burn a perfect circle on a piece of paper and it also seemed to deteriorate after around 80 hours. So test the beam pattern at the first mirror at multiple power settings. Shenui replaced my tube and I am now able to cut blond mdf cleanly at 65% power at 40mm/s

[Kev Williams]

I've never seen a lens get so dirty so fast as the one on my triumph. And for what it's worth, my cone is gone. You may need air for cutting (I don't, but all I cut is up to 1/8" wood or rowmark) but you don't need air for engraving. Now the cone isn't in the way, and cleaning the lens is a breeze...

One thing I didn't see mentioned (or missed?) is the "CARVING BACKLASH" settings as it's called in my PHCad software. I've painstakingly tested over several hours, the reverse offset numbers that need to be entered at many different raster speeds. If these numbers are incorrect, or simply not there, the engraving will have duplicate shadows caused by the left-to-right sweep not lining up with the right-to-left sweep. I'm not sure how this is done with a Shenhui or its software, but I'm pretty sure backlash settings DO need to be adjusted---

[Rich Harman]

I think it is called reverse interval or something like that. Before messing with that setting, first make sure that you can make a nice engraving in one direction (unidirectional) instead of bidirectional. That way the reverse interval setting does not come into play.

[Steven Cox]

I see, it is probably the same as the interval setting in my software. Will give it a try.

Interval is the space between the lines, its kinda like DPI is to printing but in reverse. The higher the interval is means the lines are more spaced apart so you'll get a crappier result, On my machine depending on the material being engraved I set the interval between 0.1 and 0.25

0.15 interval works for me on standard MDF. That said there are a few of different grades of MDF, Lite is softer than Standard and MR (moisture resistant) is harder than standard so depending on what you are using you may need to play with your power settings as well.

[Rich Harman]

Interval is the space between the lines...

Yes, and reverse interval is where you tune the left to right, and the right to left lines so that they line up - similar to backlash. For unidirectional engraving it does not matter.

[Walt Langhans]

Here's something else for you to check. I ran my laser for a while before it even dawned on me that the mirror on top of laser head is adjustable. (yeah I know... nice noob move right, lol). If you haven't checked it, put a piece of tape over the end of the nozzle and pulse the laser. The dot should be centered.

[Kev Williams]

A rose by any other name...

I have 2 versions of the "PH" software that came with my Triumph.

the old version's backlash setting is simply "engrave reverse offset" (notice the higher the speed, the more the offset)





the new version calls it "carving backlash"-- (one reason I don't use this version of the software is because
it puts its own gibberish numbers in, and the results can be quite entertaining!)





As for "interval, this software calls it "scan gap"...




Speaking of interval/gap/aka Lines Per Inch-- on my "western" machines I usually engrave at 500 lines per inch, or more. 400 is okay for larger words and such, but 300 is almost too choppy in anything but wood or glass (for my taste).
At 500 LPI your line spacing is .002".
400 LPI, spacing is .0025"
300 LPI, spacing is .0033"
200 LPI, spacing is .005"

in mm "gap" or "interval" spacing--
.05mm = .00196" / 510 LPI
.06mm = .0024" / 417 LPI
.07mm = .0027" / 370 LPI
.08mm = .0031" / 322 LPI
.1mm = .0039" / 256 LPI
.15mm = .0059" / 169 LPI-- assuming a .006" dia. laser dot, at this point the beam paths are likely barely touching but not overlapping;
.2mm = .0079" / 126 LPI-- at this gap there will likely be an un-engraved space between the beam paths..

SO-- IMO, high-quality engraving requires no less than 400 LPI - or no more than a .07mm interval/gap. And good backlash settings, IF your machine/software requires YOU to make adjustments, are imperative to getting good results ...

[Alexis Martial]

My two cents in addition to all above very good answers:
1) check your laser beam, preferably near the laser tube
Reci laser tube quality has dropped drastically over the past few years, at least for their high-power ones. My first 130W tube had a near perfect beam shape and energy distribution and lasted 3 years of intensive use. My second one has a very beam and lasted only one year.
To check your beam without expensive equipment just use a piece of 5mm clear acrylic, shoot directly on it for around 5s [you have to blow air on it while doing so to avoid burn/fire], than look at the beam shape:
- it should be circular
- it should look like a cone i.e. with more energy at the center

2) check your focus and ensure it's as good as possible i.e. thinner line

For this just use a piece of clear acrylic. Do a first rough job by just shooting and adjusting focus to have the smaller dot. Than confirm by drawing a circle of let's say 2" diameter at medium to fast speed, low power. Do it multiple time until you find the focus with the thinner line.

Repeat this process at the 4 corners of your working table. Adjust your working table to have the thinner line at each corner. By doing this you will compensate for any beam divergence and get better results than by just keeping your table horizontal ;-)

3) test and adjust your engraving

I got very good engraving results on MDF when following the below conditions:
- use MDF that does not include outdoor type glue
- use a raster spacing of between 0.05 to 0.1mm [I usually go for 0.08 since it match nicely my stepper motor sep and thus I get very consistent results]
- use medium speed, in my machine I go for 200mm/s thus no need backlash adjustments
- use clean air assist at medium PSI [5 to 10 in my case]: this reduce the charring of the MDF and provide a sharper while slightly less contrasted engraving.

If you have any pictures this would help us help you ;-)
Good luck !

Alexis Martial
Plixo Pte Ltd

Owner of two "Chinese" Laser cutter, one from RedSail one from GCC