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View Full Version : 100W RECI tube.... Black coating on tube lens creating odd burn pattern



Kevin Cowan
04-06-2017, 11:55 AM
So..... I bought a 100W machine with RECI tube a year ago. Works great, fires great etc etc

Bought a second 100W machine this year with a spare RECI tube as well. I verified with RECI site that tubes are legit.

The tube on the original has a normal looking lens at the end, yellowish in color and if you look at it head on can see down the tube. Produces a nice crisp dot when you pulse the laser.

With the new machine and two new tubes that came with it, if you pulse the laser it produces a circle with a dot in the center. I took a look at the lens on the new tubes and they both have a solid black circle (slightly smaller then the lens itself) which I suspect is what is causing this to happen. This is not the case with my original tube purchased a year ago from RECI as well which I also verified is a legit tube.

I have seen a number of tubes over the last few years and never seen a tube lens like this before.

Attached is a picture showing what Im talking about, I removed the metal collar for a better picture.

Anybody know what this may be about? Am I doing something wrong here?

Pretty new to all this and learning as I go so................

I haven't ran the machine like this yet until I can figure out what the deal is with this.

Any insight appreciated.

I did email RECI just now looking for more info but have yet to hear back, hoping somebody here might know.

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Rich Harman
04-06-2017, 11:27 PM
None of my tubes look like that. Cant tell from the blurry photo but it looks like it is on the outside of where the window normally is. Could it be a removable protective cap?

Mike Lysov
04-08-2017, 10:28 PM
It looks to me that you have some smoke built up on the output window. And that's a lot of it. It is possible that it has had been run like this for a long time burning the whole lens.
Have you tried to clean it with alcohol and see what will happen?

I had a similar spot of blackish colour on my tube once but it was nowhere that big and that dark as you have.
In my case it did not burn the lens and I could remove it with methylated spirits.

It got there when I was aligning two tubes laser machine. TO do it I was firing one tube at a time covering the other tube path with a piece of Corian at about 50mm distance from its output window. Sometimes I used a piece of MDF instead of Corian Smoke/debris from a burn mark on Corian/MDF got stuck and built up on the output window.

Kevin Cowan
04-10-2017, 6:35 PM
None of my tubes look like that. Cant tell from the blurry photo but it looks like it is on the outside of where the window normally is. Could it be a removable protective cap?
Well thats what I thought at first so I carefully inspected the sides of the mirror and very gently picked at the sides with my nail to see if there was a film or cap that might peel off but......... nadda. Upon closer inspection it seems as though it maybe a coating on the INSIDE of the lens.

Kevin Cowan
04-10-2017, 6:37 PM
We have never run this tube once, except for a few pulses to setup alignment.

We did clean lens to see if it was in fact build up or something from the factory, but nothing comes off with cleaning. It is a very perfect circle with no irregularities like build up would show.

Kevin Cowan
04-10-2017, 6:41 PM
So I havent had time to work on this much since my post but today I did.

Upon much closer inspection and playing with lights it appears to be a coating like found on some some lenses as it is reflective when looked at from the correct angle. But again the coating only cover the center of the lens producing this odd burn pattern of a circle with a dot in the middle when the laser is pulsed. If it is pulsed for a full second or two, it produces a solid dot that is oblong shaped.

So...... I figured that the odd burn pattern may have been due to the pulsing not firing the laser hard enough and maybe everything was as it should be. So I did my best to setup alignment with it like this and ran the machine but all the engraving comes out VERY blurry and the engraving is quite shallow for a 100W tube. So its clear that whatever this is and whyever it is firing with such a weird burn patter, is causing the laser to not focus and lose power.

And apparently the RECI site was down when I sent my message to them because it bounced back to me and now the RECI website is still down so I wont be getting an answer from them for who know how long ;(

UGH....

Kevin Cowan
04-10-2017, 7:18 PM
Here is a picture of the burn pattern it produces when the laser is pulsed quickly.
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Kev Williams
04-10-2017, 8:27 PM
could it possibly be that what's on the end of the tube is a protective cover?

Kevin Cowan
04-10-2017, 10:15 PM
Checked that. Nothing I can see indicates there is any type of covering on the lens that can be removed.

I picked at the edge of the lens trying to find a film that may be covering it, but nothing there.

I also inspected it closely with a magnifying glass and could see any indications of a protective film/covering/cap that might be able to be removed.

With my more in depth inspections today, it appears to be a ZNSE coating or similar as it seems to be reflective when in the right light. But then I dont get why they would only cover PART of the lens with this? Its not expensive.

So, in my testing this evening, I pulled that tube out, popped in the one from my other machine and it works fine. So there is something with this tube/lens that just isnt right or IM doing something wrong.

Im going to try popping the replacement tube that I got with this machine in tomorrow that has the same black spot/coating on the lens to see what that tube does.

Rich Harman
04-10-2017, 10:48 PM
Here is a picture of the burn pattern it produces when the laser is pulsed quickly.

A simple way to get an idea of the beam's profile is to fire the laser into a piece of 1/4"+ cast acrylic for a few seconds. Place the acrylic in front of the first mirror taking care to keep it away from the tubes output window to avoid contaminating it. Fire at full power to burn the pattern into the acrylic.

Here are two examples, the first is from a failing 130W Reci, the other from a good 80W Reci.

Dave Sheldrake
04-11-2017, 1:05 AM
It's a Gallium Arsenide PVD coating on the output lens to prevent scratching. Most higher power tubes have it now

Kevin Cowan
04-13-2017, 10:49 AM
In the event anybody wants to know the outcome of what I figured out...........

The brand new tube was in fact bad but it wasnt due to the coating itself. I think that something internally is simply misalinged. But none the less, the tube cannot be used.

First, thank you for the comments, it has been helpful. Comparing the burn on acrylic to what it SHOULD look like made be believe there is in fact something wrong with this tube when when it wouldnt burn very deep and still made the strange donut pattern.

So, to test things out I got everything lined up and made a test run. It came out really shallow and blurry. No matter how much I aligned things I couldnt seem to get it in focus or to burn very well.

Based on what Dave said of the marking being an anti scratch coating I figured there really cant be much out of normal to getting these tubes to work compared to the ones without the coating.

So I finally plugged in the second tube we got with new machine that also has this coating on it. Low and behold it worked without a hitch. No strange burn pattern, engraves great and no problems getting it setup whatsoever.

All in all something new learned despite a bunch of frustration.