View Full Version : does somebody know why lasertube putsout a ring instead a point

walter hofmann
01-27-2012, 3:52 PM
HI all
I am wondering if somebody know why my lasertube puts out a ring instead of the regular point ( see picture)
the other day I was engraving and all of a sudden the power did go down. I checked the cooling water it was fine on 70 degree F

the power meter shows the right current . I checked all mirrors and the focal lense all clean I just cleaned it before this job
the last what I could think off was that maybe the alignement was off.
I startet with the first mirror on the laser tube and shot a beam and the result was that the beam createt a ring instead off usualy a point.
I was not aible to find the reason for this water flow was good everythings else was good no arking. I dont know.
my machine is 3month old one of this small K40 CO2 chinese machine converted to the newest DSP from lightobject. the tube has only about 250hour light engrvaing and about 2 hour cutting (70%) on it
maybe some one can help me out.

Dan Hintz
01-27-2012, 4:13 PM
Two reasons:
1) Loss of gas
2) One of the internal mirrors shifted position

Mark Sipes
01-27-2012, 4:26 PM
Are you sure the focal lense is installed in the proper direction.

Is there a way to take a photo of the ring Output you are seeing.....unless I am looking at the photo all wrong...

Test beam shot.. Oh there it is .... the blue tape on a blue machine ........ now I see a ring

Dan Hintz
01-27-2012, 8:41 PM

That shot is of the first steering mirror, so the ring is from straight out of the tube. It's one of the two things I mentioned above...

walter hofmann
01-28-2012, 8:14 AM
Hi guys
thanks for the respond thats what I assumed and have allredy ordered a new one hope the new one will fix it
I dont have time to much work

Eric Ucci
03-24-2012, 1:23 PM
Hello All,
So, I've been working on my machine setup for a while in my spare time. I finally got around to aligning the tube. When I pulse the laser at the 1st mirror it makes a ring about 1/4" dia. (see photos). Does this mean that my tube is shot? I have a spare to swap out if I have to. Also, by the time I get to the 2nd mirror it start to appear as a crescent shape. what could cause this? The 1st mirror has some soot on it so I'll clean that. What is a good method for cleaning the mirrors?

Also, this is a 150w reci

Neal Schlee
03-24-2012, 3:16 PM
Bad Mode, Dan's probably right, one the internal mirrors may have shifted. A Co2 lasers beam Mode can be more important than tha actual power measured, especially when cutting or engraving. I spent 15 years rebuilding and aligning our 2 Apollo (LMI) 80 watt flowing lasers, and will NEVER go back to a glass tube no matter how cheap it is. At least the Apollo's had adjustable mirrors.


Eric Ucci
03-25-2012, 11:54 AM
I'm new to all this, so I have no frame of reference for what to expect from this 150w reci tube. I installed the 2nd tube and it definitely does not fire a "ring" the way the 1st one did. The 2nd tube fires a spot about 3/16" in dia. What I'd really like to know is whether or not firing a "ring" directly out of the tube verifies that the tube is damaged. If so, then I need to talk with Shenhui about getting it replaced. I'm just concerned that they will disagree with that diagnosis and refuse to send a replacement.


Neal Schlee
03-25-2012, 2:38 PM
I'd compare the engraving quality between the two tubes, see what you get. If it's a dramatic difference then try and get them to exchange it based on the test. It does not take much for a mirror to get out of alignment, it may have been that way from the factory or jouseled in shipping.
As I understand it, these mirrors are not adjustable. How do they mount these tubes? Sometimes just too much pressure in an area on the tube can change the mode and/or power significantly. Temperature can also affect performance, NEVER fire the tube without the chiller on.


Dan Hintz
03-25-2012, 3:29 PM
I installed the 2nd tube and it definitely does not fire a "ring" the way the 1st one did. The 2nd tube fires a spot about 3/16" in dia. What I'd really like to know is whether or not firing a "ring" directly out of the tube verifies that the tube is damaged.
The 1st tube is ****ed and there is no hope in fixing it for a reasonable price... throw it in the glass recycling bin.

EDIT: Really? The forum software stars out the word B O R K ?!

Rodne Gold
03-26-2012, 6:19 AM
Our 80w RECI doesnt put out a solid dot at the first mirror , its more like a ring with a darker crescent. However it cuts and engraves just fine. I was concerned and was going to swap for our spare tube , but I decided that if it's working acceptably , not to try "fix" it. Align the tube and try it.

Dan Hintz
03-26-2012, 7:40 AM

If that's true, it may explain how the RECI tubes are able to get increasing powers out of shorter tubes (as compared to the standard tubes)... if you'll remember my complaints about them not being able to get the claimed power out of that length of tube. If these guys are using higher-order modes (in this case, TEM01), they're trading reduced focusability for more raw power. A standard tube would be TEM00 (a true Gaussian).

Interesting... wish I had one of those tubes (and the time) to play with it, see if my theory is correct. If so, the tubes would not be as useful for fine work...

Rodne Gold
03-26-2012, 7:52 AM
I compared my 80w Reci to a cheapy 60w to my RF tubed machines , they all seemed to give more or less the same output , albeit the 60w and RF tubes did maybe seem "finer" , tho it was real hard to detect...
I recon most of us are far more critical than our customers will ever be.. all my lasers have more than acceptable output to them.

john banks
03-26-2012, 8:46 AM
I have nothing to compare them with in terms of the spot shape on the first mirror, but both my 100W RECIs didn't look any different to each other and they may well have had a ring appearance at the first mirror, but I didn't think anything of it, will recheck.

I do notice that when pulsing the laser because I haven't programmed a time (I maybe should) then it runs as long as you hold it and depending on this time and the power, it is easy not to make a clear mark or to frazzle the tape. Sometimes what looks like a crescent is not a crescent when it has enough power or time to make a circular spot. It may be that a brief pulse produces a circle outline and a longer pulse produces a spot. Someone did comment elsewhere that the vast majority of the power of the laser is in the perimeter of the beam when there was discussion about narrowing the nozzle tip, I wonder if this applies after the focus lens though, I'd think not. If it applies before the focus lens though, it would explain why the extra power around the perimeter makes the mark first, along with any possible effects from what Dan is describing which I do not yet understand?

Rodne Gold
03-26-2012, 8:52 AM
According to sam's laser FAQ , a co2's beam can be either ring shaped or spot shaped , obviously the focus lens will focus the "donut" or the spot to a "spot" , probably the donut will be a blunter spot than the spot spot.. but maybe the difference is negligable in what we use the lasers for?
Yeh , there's a fine line tween spot and incinerated tape . so maybe the brief pulses are too short..