View Full Version : Unsatifactory Laser Engraving (Shenhui Laser)

Brent Ramsay-Boyd
04-20-2014, 1:55 PM
Hi All

I have had my Shenhui 80W Reci Laser for a few moths now, and cannot seem to get my laser engraving to a satisfactory level.

When I engrave, I cannot seem to achieve the crisp detailed work that I have seen produced on other lasers, could this be a downfall of having a chinese machine, or am I doing something wrong, I am hoping that someone with a Shenhui could chime in and help guide me. The edges of the engraving seem to slope inwards instead of having a well defined edge, and the engraved surface has a very uneven and undulating texture. I will try to get a decent camera to get photo's of what I mean, but at the moment all I have is my phone camera and I cannot get any decent pictures.

At the moment I am engraving mdf, and I know it may not be the best material for engraving, but I have seen much better engraving on mdf before, so I know a better finish is possible. I am using a 40mm lens at 25 power and 300mm/s speed (Although I am not sure the head is actually moving that quickly). I have tried to adjust the interval setting but it does not seem to help.

I am just starting out with my own business and I would hate to supply my customers with sub standard work. Any help would be greatly appreciated.



Rodne Gold
04-20-2014, 2:36 PM
Without pics its difficult to say , invest in a cheap printers loupe or a magnifying glass (5x or so) to see exactly whats happening , a loupe is a must for any laser engraver , it is an invaluable diagnostic tool.

Travis Wizniuk
04-20-2014, 3:32 PM
Hhmm that doesn't sound right.. Sounds like you are not focused correctly..

Also have to adjusted the SCAN GAP in Lasercut? I find is should be 0.055 to get nice crisp engraves..

Walt Langhans
04-20-2014, 9:21 PM
Yeah.. where to start...

To begin with.. I have the same tube and a Shenhui as well, and work primarily with MDF.

MDF sucks for engraving. I used the same file with the same machine set up and had 2 VERY different results and the only thing that changed was the the MDF. No idea but I'm assuming it has something to do with inconstancy in the way MDF is made.

Your speed is WAY too high, I if you want crispness on MDF (well as crisp as you can get it) I don't go over 150ms.

And it also sound like you could be a bit out of focus or alignment.

The other issue is your 40mm lense, if you want really detailed work the smaller the dot the better.

BUT like Rodney said.. we need pic for a proper diagnosis and this advice is based on my 'best guess"

Dee Gallo
04-20-2014, 11:53 PM
Hi Brent, welcome to the Creek! I cannot help you with your laser since I don't have your make, but there is a sticky at the top of the Engraver's Forum for tips and tricks on Chinese lasers... you might want to read those posts for general knowledge.

I'm hoping you will get yourself to a better place soon, the help already offered should start you on your way. These guys know what they are talking about.

cheers, dee

Rich Harman
04-21-2014, 1:55 AM
This is something I engraved on MDF and posted about it (http://www.sawmillcreek.org/showthread.php?170732-Lasers-do-you-get-what-you-pay-for&p=1757099#post1757099) a couple years ago. I don't remember the settings exactly but it was probably around 300 to 400 mm/sec at full power using a 65mm lens. My version is lying on top of the sample that Epilog sends out to prospective customers. The size is about 2" across.


Brent Ramsay-Boyd
04-21-2014, 6:29 AM
Thanks for the replies, I will try to get some decent photo's and post them as soon as I can. I am also going to try some different materials to see if it is just poor quality MDF. While testing I have come into a second problem, I have noticed that the power from my laser has dropped, I have only got about 20 hours or so on the laser so I don't think it is the tube, but where I was cutting 3mm mdf at 35 speed and 100 power, it is now not cutting through. Is it normal for a new tube to loss power so quickly. The reci site states that for optimal tube life to keep the amps under 25mA, I have set it a bit lower that that, but this is only when it is running continuosly, between cut lines when the laser pulses it jump to approx 40mA for a split second, have I set it correctly, or should I be tuning it down?

I did have a problem the other day when I auto adjusted, the table bed crashed into the head and when I stopped it and the head tried to return to the origin and messed up my honeycomb table a bit. A very terrifying experience but all seems to be ok. I think this may have messed up my focus etc.

Brent Ramsay-Boyd
04-21-2014, 6:46 AM
Is scan gap the same as interval?

John Bion
04-21-2014, 7:12 AM
I did have a problem the other day when I auto adjusted, the table bed crashed into the head and when I stopped it and the head tried to return to the origin and messed up my honeycomb table a bit. A very terrifying experience but all seems to be ok. I think this may have messed up my focus etc.

Hi Brent,

I do not have Shenhui so I will let others comment on your software settings, however I would Strongly recommend you get rid of autofocus, this is nothing but trouble. It is very easy and quick to focus manualy. I would check for right angle alignment between the head and carriage after a crash like that.
MDF is very dirty material to cut, have you checked the cleanliness of your optics/mirrors? Is the end of your cone almost blocked with residue? MDF also jams up the autofocus very quickly.
Pictures definitely needed.
Kind Regards, John

Brent Ramsay-Boyd
04-21-2014, 7:44 AM
Hi John thanks for the advise.

I have decided as you suggested not yo use the autofocus any longer. My optics are clean, and there is no residue on the nozzle. How do I check for right angle alignment?



Khalid Nazim
04-21-2014, 9:38 AM
Get a carpenter's square to check if your laser head is perpendicular to the laser bed. And like the other shenhui owners said, ditch the autofocus. I had a similar accidend due to autofocus and had removed it afterwards. I dont miss it at all.


John Bion
04-21-2014, 9:50 AM
Get a carpenter's square to check if your laser head is perpendicular to the laser bed. And like the other shenhui owners said, ditch the autofocus. I had a similar accidend due to autofocus and had removed it afterwards. I dont miss it at all.


as Khalid said.

Regards, John

Travis Wizniuk
04-21-2014, 12:24 PM
I have a G.Weike with Lasercut software.. I just assumed the Shenhui used the same software..

If so, the Scangap can be found in the same location where you set the power and speed. Anything over about 0.065 will give super crappy results (you can actually see the individual laser lines).

Brent Ramsay-Boyd
04-21-2014, 12:38 PM
I see, it is probably the same as the interval setting in my software. Will give it a try.

Brent Ramsay-Boyd
04-24-2014, 5:36 AM
I have check for that the laser head is still perpendicular, and it seems to be ok. All the optics are clean and aligned, but still I am low on power. Any Suggestions?

Johan de Waal
04-24-2014, 8:44 AM
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
04-24-2014, 12:00 PM
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
04-24-2014, 2:52 PM
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
04-24-2014, 10:25 PM
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
04-24-2014, 11:04 PM
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
04-25-2014, 8:53 AM
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
04-25-2014, 11:12 PM
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
05-01-2014, 5:31 AM
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