Blue Residue on Mirror

[Brent Ramsay-Boyd]

Since getting my Shenhui Laser I have been plagued with problems which have not allowed me to run my machine reliably for any prolonged period of time, not good a it was supposed to be my main source of income.

When I first got the machine, it was happily cutting 3mm MDF at 35mm/s with no problems. This lasted about a week and then things went downhill. Cutting speed declined dramatically since then. I have changed the tube, swapped out the power supply and checked the optics regularly, but have never been able to get more than 20mm/s cutting speed again, usually having to drop down to 15mm/s to get a good cut.

Unfortunately, where I live I have not been able to find a local technician to come and help me get my machine cutting correctly.

On recent checks of the optics, I have noticed a blue residue on the q-tip after cleaning the mirror closest to the laser output. My cutting ability is almost non existant and I can't for the life of me figure out this machine. I think it may need a new tube, which is next on my list to try, but funds are low and the tube I have which although unused has been sitting for over a year on the shelf.

Has anybody else had a similar experience with there machine. I have an 80W Shenhui laser with Reci Tube, is 30-35mm/s a reasonable ask on 3mm MDF of was that just some sort of fluke that I got that? Obviously, I would like to get my machine back up and running, and at full speed, so I hope someone can shed some light on my situation.

Thanks

[John Lifer]

I expect that a lot of others will chime in, but I expect that your tube is toast. And from what I've heard, life of a tube is not just operational time but overall time from manufacture. So your tube on the shelf is probably not much better. But I'd swap it out to see. Is your exhaust working well and air assist on since you are cutting mdf? Check those out too.

[Bert Kemp]

you didn't say what power your running at,or how old the tube your using is. Have you aligned your mirrors? Checked to make sure the lens is ok and not being blocked by part of the lens tube. Are you using air assist? Is you bed level and are you using the right focus tool.?

[Matt McCoy]

Hi.

For loss of power, these are the usual culprits.

1) Check the alignment.
2) Inspect mirrors and lens. Clean, if necessary.
3) Inspect the laser tube. Should be a bright purple/Pink color, when firing.
4) Check power supply. Can be very dangerous and you will need to read information until you have a solid grasp on how to safely inspect/test it.

I suspect if you have already replaced the tube once, that the power supply or alignment will need to be addressed.

Good luck.

[Wilbur Harris]

That "blue residue" is somewhat suspect. If the mirror was clean to start with, check your exhaust capability. Is that the only mirror that has the blue stuff on it? I don't think that's why your machine is not working properly but something that needs addressed once it is working.

[John Blazy]

Everybody nailed it, especially Matt's list. Always do a spot test by test firing into white paper or masking tape, and if the spot is kidney shaped, then the beam is hitting the inside of the cone. We reamed out our cone a bit, but I tested last month and the beam wasn't perfectly center on the lens - fixed it, and it cuts great.

The residue is likely smoke depositing, because when I cut 3mm hardboard (HDF) bluish white smoke fills the laser box. This will deposit on mirrors. Also remember that if the entire chamber is filled with the smoke, the smoke blocks the laser beam to some extent, so if it cut good initially, then tapers off, maybe its smoke blocking. Gotta have lots of exhaust.

Then focus across entire bed is crucial. My custom MDF grid actually warped over time, and didnt realize it - 1/8" low in middle. So I power planed it flat. Then easy to check parallel across the WHOLE table, but took some time.

Another issue I noticed was that if the second mirror is too low or high, and you adjust the 1st mirror to hit center of 2nd mirror, but don't check it both close AND far, then its center will be off center at the 3rd mirror, only in certain parts of the bed. Always check that the beam is hitting center on the 3rd mirror in all four corners of the laser bed. You might be hitting center in the front, where most cutting is done, but the laser might be eclipsing the nose cone at the rear of the bed, or left or right rear, or any combo imagineable.

Are you using the same brand of 3mm MDF as you did when you got 35mm/sec? Different MFR's use different binder resins, and all absorb IR differently. Especially true in plywood with exterior glue vs interior glue.

[Kev Williams]

The blue stuff could be fried spider, or who knows what. I fried a miller parked inside my lens tube one day. My lens still has a dark spot from that. Your mirror might be stained too--

Funny thing about blue, is if any of the reflected light from that mirror is blue, the lens will absorb it. I have a blue laser pointer that's these yellow lenses completely absorbs. Red & green pass right thru, the blue is totally invisible.

does that machine have a milliamp meter? If so, are you keep the needle at 26 or below? Running above will give your tube a lifespan of days or weeks at best. If you don't have a meter, you should get one. FWIW, I have an 80 watt RECI tube, and depending on water temp, 70% is my "100%", as 70% power as entered to my machine usually hits 26 on my meter, and that's as high as I've ever ran it. My machine will be 3 years old next month, no tube issues so far... and last week was the first time I ever checked the tube while it was running, nice pretty pink...

Also of note, I've never cut MDF with my machine, but I cut a lot of 1/8" acrylic, and a good one-shot pass with a 2" lens I run the machine at 20mm/sec. @ 26mA. I can go a bit faster, but as the water heats up (I don't have a refrigerated chiller) the power drops a bit and I end up with un-cut spots. I could crank up to 80% and probably cut like gangbusters, but I'd rather trade a few minutes cut time for a few years of longevity ;)

[Brent Ramsay-Boyd]

OK I am going to try and respond to all questions in one go.

Bert, I am running the laser at full power and the tube is about 14months old, but it only has maybe 200hrs of running time on the tube itself.

Matt, The alignment is all correct and the lenses have all been cleaned. I have not yet checked the tube, but that will be the first thing I do, and I do have a spare power supply, so changing that out will be an option if nothing else appears to be causing the problem.

Wilbur, the mirror closest to the tube is the only mirror that shows this blue tint on the q-tip after cleaning. The blue tint has shown up several times after cleaning the mirror. As for the blue, I doesn't actually seem like its a deposit, so much as possibly some kind of tint that may be coming off of the mirror itself, the mirrors are silver in color, but when checked before cleaning there does not seem to be any buildup on the mirror surface itself. Could it be that the mirror itself is faulty and is slowly deteriorating and giving off the blue tint? Also this mirror sees by far the least amount of smoke so I doubt its that as not showing up on the other mirrors.

John, Second on my list will be to check that the beam is not hitting the cone, but i am pretty sure it is not as I am getting a fairly tight spot size on the test fire. As for the smoke blocking, although I do need better exhaust I don't think its that as the cutting power actually starts off incredibly poor, barely marking the surface and then improves as the cut goes along. Parrallel across the table might be slighlty out, but I am not decent getting cutting power on a small area at any point on the table so that is secondary to the main problem. I have been getting the MDF from the same place the whole time, so unless they have at some stage changed their supplier, the MDF is the same.

Kev, I don't think the blue is from a spider/bug as it seems to be a recuring problem. When you mention the tube lens, is that the lens on the actual tube itself. I cannot see any problem on that lens, but I remember reading somewhere that that lens is very sensitive and that you should not touch it, not even for cleaning purposes. I may be wrong there though.

The machine does have a milliamp meter. I have been very careful to run the tube at 26mA or below, I set the power of the machine to 80% and the power from the software to 80%. Which put m the ammeter at just below 26mA, though this has dropped slighty to around 24mA over time even though the power setting have not changed. That said, the ammeter reading does shoot a lot higher when the the laser first fires on any cutline, then settles almost instantly down to 24mA. Is that normal?

Initailly I was getting 20mm/s on 1/8 inch acrylic, but since the first tube I never got more than 15mm/s. Mostly around 10mm/s. As you would imagine running at half the speed does not make for a very profitable business. I do have a chiller, which sits at between 18-20 degrees Celcius depending on the temp outside and the time the laser has been running.

As for the tube life, if it is the tube. My 200hrs or so of cut time is no where near the 10000hrs that reci claim, not that I expect 10000hrs. And when people are getting 3 years life with no problem, and I am sure you have done a fair bit more cutting than I have, I don't think that shelf life is the problem either.

Hopefully, there is a solution somewhere in all of this.

Thanks all for your help. I will keep you posted on the outcome.

[Kev Williams]

If you haven't yet, REMOVE THE CONE and see what happens. None of my older machines ever had a cone, so I don't use the one with my Triumph. I did test the beam with it on right after I got the machine, beam alignment everywhere was near perfect, and the beam thru the cone was pretty much dead centered too. One time for fun I cut thru a piece of 1/2" thick wood, just lopped off the corner. Then I put the cone on, wanting to see if air-thru-the-cone would keep the lens cleaner longer. But with the cone on the cut only went about 3/4 the way thru. I put a piece of tape over the cone hole and fired the laser. Not dead center, but what I thought should be 'within tolerance'. Cone off, it cut thru the wood just fine again.

Now, I don't know if laser light waves will reflect off the side of the cone and affect the rest of the light waves, but I'm pretty sure any light waves that may hit the cone will scatter and can never focus, substantially reducing the power at what's left of the beam spot. It's the only explanation I got for not getting thru the wood--

I've heard another reason for the cone is to keep the lens cool. I've never had a non-coned lens ever get hot. With that, it's my opinion that if your coned lens IS getting hot, it's because the laser's heating up the cone, not the lens... again, just my 'untested' opinion... ;) As for air itself, I've only found it necessary to keep flame-ups from happening, I've never found it to help with the cutting process specifically. My air line just hangs down not bothering anything when I'm just engraving... if I'm cutting, I hold the airline with a MacGyver special hose holder...

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My diaphragm blower pump pushes plenty of air to keep fires out and blow the smoke away, but not so much air that it moves around what I'm cutting. No worries about the beam hitting the cone...

[John Noell]

Beware "full power" on a glass tube. Running at 90% (the maximum mine was set to when it came) resulted in a tube losing power in a matter of a few weeks. From there it is down hill. I was recently told (by Yarde Feng, originally from Shenhui, now with Lontgtai) that running even at 85% can be damaging. Yarde says stay below 85% for maximum tube life.

[Dave Sheldrake]

The Blue tint on the mirror is Molybdenum DiOxide...Moly mirrors aren't coated...just highly polished

Take it out and clean using fine printer paper and de-ionised water (the solvent for mdf)