One weak tube and one that lights up but no output. Please advise.

[CronusCNC]

I have a small 4'x4' laser system that I recently built that makes use of an import 40W CO2 laser tube. Knowing that there have been issues with tubes from China I went ahead and purchased 2 tubes and 2 power units and unless I am doing something very wrong there is in issue (a different issue) with each tube.


Problem 1


The first tube has very poor output power. I can't make it all the way through 1/8" acrylic in one pass even with up to 25 PSI air assist and feed rates of 5 IPM (which is the setting for 10W lasers according to most generic CO2 laser charts). It appears I am getting less than 10W output.


The machine is steel frame, very rigid and capable of moving very quickly with great precision and no mirror or nozzle vibration. The alignment is spot on (pun intended) and was checked at all 4 corners, center and various positions on the machine. Visible laser was used to get the initial alignment and bronze backed paper targets were used at all reflection points and the nozzle outlet (before lens install) to insure the beam was dead center.


In all the 40W charts I have checked they report that you should be able to glide through acrylic at a minimum of 27 IPM. The cut speed I am having to use is recommended for a 10W CO2 laser unit! At this rate I would not even dream of 1/4" cuts (which is what the unit is rated at).


It lights up with what appears to be a nice purple glow and doesn’t make any odd noise. I even tried the backup PSU and the results were exactly the same.

Can this be a lens issue?




Problem 2


Since I bought 2 tubes I decided to try the backup tube to check if the first tube was a dud. The second tube lights up the ubiquitous purple albeit a bit brighter but will not fire a beam. I can put paper directly in front of the output and it won’t even make a spot.

I have inspected the tube and there doesn't appear to be anything wrong. The output lens looks good, there are no cracks and no indications of other visible problems.


Any idea as to what could case a laser tube to light up but not fire?





With having 2 for 2 problems I have to assume I have done something wrong but I can’t figure out what this may be…






Thanks in advance for anyone who can offer help with this.




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[Gozzie]

Does your machine have an amp meter ? Does it register when you fire it ?
Does your software have an adjustable power setting for firing the laser through the button?
Make sure your setting isn't to low. Try for 20% or higher.
Check all of your controller settings.
Some controllers can be set up for different styles of tubes. (RF, DC, etc..)
Double Check all of your wiring and settings, it could be something simple that you wired wrong or set incorrectly.

Try to start at the basics again. Tape a paper target at the first mirror and test fire. If it burns a hole there move to the second mirror and so on.
Next make sure your lens isn't upside down. It happens a lot. Then make sure your focus distance for that lens is correct.

Gozzie

[CronusCNC]

Gozzie,

Thank you for your quick response.

I am fairly confident alignment isn't the culprit. I just retested. My jig consists of covers that go over the mirrors and have a piece of thermal paper attached with printed crosshairs. The beam is hitting dead center of mirror 1, 2 and the beam is centered in the nozzle tube. I have checked this alignment at all four corners of the table and the center line. Just rechecked.

The lens is a good point. My lens is currently installed with the convex section accepting the laser and the concave section facing the workpiece. Is this correct?

Tube one is just acting weak. I was able to get a little more speed with playing with the focal length. I used the "ramp" method to determine the cutting sweet spot but the feed is still far below what I feel 40W should do (based on reading what a 40W should be capable of). Getting a 1 IPM increase from 5 to 6 is not that big of an improvement.

And the second tube issue is just odd to me. Tube 2 lights up but makes no beam. I can put something directly in front of the laser tube output and the tube ignites but will not burn the paper directly in front of it.

Any chance I simply got 2 bad tubes. They are by Bill Laser and if I am reading the tag correctly it looks like they were originally manufactured in late 2013...




Is this old for a laser?

[herby08]

could you post a picture from the whole tube this looks strange to me
greetings
waltfl

[CronusCNC]

No problem. Here are some pics of tube 2 - tube 1 and 2 are identical.

[CronusCNC]

Gozzie,

Thank you again. To answer your other questions.

1. 20ma at 90% power
2. Ran it from 50% to 100%. The cut depth is relative to the power setting. We have a POT and PWM. Bypassed PWM and went straight POT to eliminate PWM issues. Also ran without POT to eliminate it from the equation and it appeared to be at around 75% power without it.
3. Always at 50% or above.
3. The tube and PSU are supposed to be a matched set. I don't see any configurable options. The PSU has simply 2 types of trigger inputs (high or low), +5v, Ground, Power level and a safety circuit on the signal in side. It has AC/AC/EARTH/Tube Ground on the mains side and has a single HV insulated wire on a transformer for the tube +.

If I understand the wiring digram correctly I have the HV from the transformer going in to the back of the tube. The ground is at the front of the tube where the beam comes out. The HV positive where terminated to the tube is very well insulated to prevent arcing. Is this the correct way to wire the PSU to the tube?

[fixtureman1]

are you sure that the beam is not hitting the side of the lens holder.

[CronusCNC]

are you sure that the beam is not hitting the side of the lens holder.

Thanks for your reply.

Absolutely. I have checked beam alignment several times. Paper in front of mirrors, paper under the nozzle without a lens - everything is dead on.

I'm cutting a job now allbeit very slowly. I'll post a pic of the output as soon as it's done - perhaps this will help.

I'm very thankful you all are helping me soundboard this. I'm guessing it's a bad batch of tubes at this point. One tube appears week and the other tube doesn't fire at all. It lights up but there is no beam.

I'm now just very curious how tube 2 lights up and there is no output. If the gas leaked from the laser would this happen?

[Gozzie]

Hi CronusCNC,

If you have the specs for your tubes you may want to check the milliamp ratings.
I believe 20 ma is running it too hot for a 40 watt tube and that can cause adverse reactions to the power output.
Someone else could chime in with the proper ratings but I think 18ma is the max rating and you shouldn't run but 85% of that.
So I believe 15 ma should be your max output. I may be wrong so double check that.
If you run them too hot they can burn out really fast or not last very long at all.
Don't let me scare you, that's not my intentions. Just be safe for now and run it at no more than 14 until you know for sure.

Regards,

Gozzie

EDIT.. I went to http://www.billlaser.dpes.com.cn/product.html but they don't list a 40 watt tube, only a 100 watt
so I cant find any specs on it.
Here is a very good article on your setup I found DIY Laser: Laser Power Settings Via PWM Can Fool You

One last thing, check your physical dimensions on your tube and compare them to the bills website. Your picture and bills picture
look very similar. It would be a laugh if you really have a 100 watt tube.
Then what happens when you run a 100 watt tube on a 40 watt supply ?
Just a thought.......

[CronusCNC]

Excellent info!!! Thank you so much Gozzie! I greatly appreciate it.

I am very used to building CNC routers and Plasma units as this is what I have done for a living for years but Laser is very new to me so I am a "DIY noob" in that area - LOL. I made some assumptions in the setup regarding PWM and outputs and I am glad you brought that article to my attention.

I am going to hook up some test equipment and check the settings (and get my settings dead on for this tube) and try to re-run a few of the parts for the 3D puzzle I just made.

I will let you know if re-tuning helps.

In the meantime - here is what I ran.





I ran it at 6 IPM one pass, 25 PSI air assist. The results are great - the laser is consistent - just low output power.

[Dean448]

Is the power supply PWM? Be carful not to overdrive the tube by simply setting high to 5v on the PS. Use the amp meter to make sure you don't exceed the rating on the tube.

Did you say this is a 4'x4' machine? Is it possible that the distance the beam travels has an effect in power? I would try cuts in the back left of the machine where alignment is good and distance is short


Sent from my iPhone using Tapatalk

[CronusCNC]

Problem solved. The vendor sent me a new tube from a different maker and I cut 1/4" today at 15IPM! The new unit works fantastic.

Thank you everyone for all of your help

[Gozzie]

Good job from the vendor. That's what I like to hear. You may want to post who the vendor is and brag on them a little.
I know they would like to see a positive feedback and it sounds like they deserve it. Enjoy your machine.
Cool looking puzzle your working on. That's what it is all about.

Gozzie

[CronusCNC]

Good point. The vendor is a small outfit out of Houston. Buildyourcnc.com.

The company I work for doesn't make laser machines so I was looking for someone close to me and happened on them. I am glad I did. They have been really great and they back their products.

Also, If you want the DXF for the puzzle just let me know.

Thanks again everyone.