Full problem with half focus -Help needed

[Dave Vigness]

Don't forget the curve up vs curve down option. It will change your focal length position a bit, but I have mine set curve up as I do mainly cutting.

I also noticed a significant difference when I was able to switch from my low air flow, large nozzle opening, and 20mm tip to work 'engraving' setup, to a true cutting setup. It's the same lens, but a different physical configuration of the tip and air flow. It makes a world of difference. With the lens mounted high in the tube for a 4 - 6mm tip to work gap and healthy air flow I was getting much cleaner and deeper cuts on the same power and speed.

[Gene Uselman]

Dave, you have mentioned this before- what are you using for air supply? And do you use Russ' [or similar] Ultaircontrol?

I use a shop air compressor and an altered Ulta air control system and have not needed different nozzles. Is this from Russ' videos?

[Dave Vigness]

I use the standard little compressor supplied with the machine, but yes, it is from one of Russ' videos and followed up when he made my custom lens tubes. I don't know what video it was that he specifically covered it, but I do know it was also mentioned in passing in a few others as well. I have a custom air assist set up, but also added a tee and valve for burn test air supply.

The manufactures do not specify the engraving vs cutting on purpose. There is a big difference between engraving and cutting setups. You may be pumping a fair amount of air flow if you're using a shop compressor, but the little one supplied with the machine will do just fine IF you have the right nozzles. That was mentioned in the video that shows his compressor hanging from the underside of the cabinet. Mine sits on a piece of that super soft styrofoam that was around the laser in shipping. Just a matter of isolating the vibrations.

With an engraving nozzle, the lens is set closer to the tip giving you around a 20mm gap between tip and work surface. The nozzle itself has a 3 - 4mm or larger hole and a restricted air flow. That large hole is necessary because the beam as it exits the nozzle is still fairly wide with the focal point so far away. It's also the reason they like to push the red dot. It helps to see where the nozzle is aiming for since it's so far from the work surface.

The cutting nozzle setup has the lens set higher in the nozzle / tube giving you a 4 - 6mm gap tip to work surface. The nozzle has a much smaller opening, around 2mm or less, and a wide open air flow. The high velocity air flow keeps the cutting out-gasses away from the beam. It would be the same but on a smaller scale of not having your exhaust fan pulling all the gasses away and clouding up the work area. The less in the way of the beam, the better cutting you get.

With a proper cutting set up compared to my old engraving setup, I am either cutting the same materials faster, or cutting thicker materials I was unable to cut with the engraving setup. Example: With my old 2" engraving setup, I could only get about 60% of the way though a 9mm piece of Premium MDF at full power and 5mm/sec. With the cutting setup I get about 90% using a 1.5" lens. When I get to playing with the 2.5" lens in the cutting nozzle there is a good chance I will get all the way through with the longer usable focal length.

Use a little plastic zip tie and put it up your nozzle to your lens and add the 20mm */- focus gauge. If you have the normal 2" supplied with the machine, you could make a world of difference just in swapping out to the 1.5" by getting the air flow deeper in the cut.

It's enough of a difference in nozzle air flow I thought I had broke something the first time I fired it up with the cutting set up. Russ was probably chuckling at my not realizing the difference.

With some necessity and a lot of inspirations from Russ' video's, I have made a large number of modifications on my unit. I'm not far from completing them and will post them in the appropriate section when I do. New controller, new integrated red dot tube, rearranged and expanded on the electrical, moved exhaust to allow for partial pass through. I went from a new magical toy, to wishing I had just built it from the ground up.

You can probably relate to some of my mods Gene, I had to keep the water from freezing in the winter. I escaped MN 30 years ago, but keep getting dragged back for work every now and then.

0110201822.jpg

0110201823.jpg

[Henrik Horlin]

2nd Update.

After the initial "success" of the focusing becoming better after mirror fiddling was temporary (and very intermittent) and I think it might be because it wasn't the mirrors at all. It is basically a shitty tube from start.
I've done tons of research about CO2 laser tubes now and can conclude fairly confidently that I'm experiencing a "TEM mode 01" artifact, i.e. Transverse Energy Mode 01 https://en.wikipedia.org/wiki/Transverse_mode. This is basically a result from improper mirror alignment in the resonance cavity in the tube itself.
The method to conclude this was to put a piece of acrylic in front of the third mirror at different distances and look at the point of destruction and see if they appeared differently at different distances, they did. The closer I got to the tube opening a very pronounced "dougnut-shape" impression/hole appeared instead of a (more) Gaussian distribution. The crater diameter did not change in any distance.

When I get the time, I'll see if the power setting does have any affect on severity on the TEM-artifacts since the beam is pulsed at lower settings than 100% and some constructive/destructive interference could be more noticeable at some settings.

[Gene Uselman]

Henrik- I think I have more or less the same problem going with not one but two Reci 130w W6 tubes.See this post-
viewtopic.php?f=139&t=5451

I am afraid that the Chicoms have caught on to highgrade copying and buying second [or worse] class tubes that fail the normal quality control tests.

I am looking at SPT and GIS tubes from LightObject in California- they claim to test every tube and I have somewhat of a relationship with Tech_Marco going back 5 years. This will not help you being in Europe but I am afraid that may be the only way to get a good tube. Gene

[Dave Vigness]

My machine came with a QC reject EFR F2 tube. I get the TEM 01 when ever the tube is cold. Once it warms up it's okay.

If you're looking at the SPT, consider the TR series tubes. They have the red dot integrated into the tube output. Ruka down in Florida is another SPT distributor, and when I thought my tube was going, I got a much better price with shipping from them than I did from LightObject when I contacted Ruka via email. Their web price was a bit better than LightObject, and when I wanted to confirm the price, they gave me an even better one in the email.

[Gene Uselman]

Thanks Dave... I have never heard of them. They claim to test their tubes too and we are in the Keys for two more weeks and could stop in Jacksonville on our way back to the north country. I have always liked the idea of the red dot inclusion but have not heard any feedback.

[Dave Vigness]

Well, Russ highly recommends SPT, and says they tend to under rate their tubes. The other nice part is the rated output on the SPT TR tubes is after the built in red dot combiner, not before. Of course you are screwed either way if you have the GaAs lens, they don't transmit the red dot so you are stuck with a lens tube mount if you really have to have it. Russ found that out with his bench top lens tester. He used a red dot pointer as a beam source, and the GaAs lens doesn't transmit it.

[Gene Uselman]

Dave, I would like to start a thread with CO2 laser tube information, I have two bad tubes now [I have a video template from Reci for evaluation purposes but I am guessing if they ever are warranted, it will be a long while] and in the meantime I have a 5 year old EFR F6 to work with. I will be unhappy if the next tube does not perform.
Please post any knowledge you [or anyone else] have on where the CO2 tube market is today. I get the sense that things are getting shaken up in China and that we need to know all we can gather. Thanks Gene
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
LightObject claims to test all their tubes before shipping, and they have a forum to communicate with customers.
they sell, Reci, GSI ,SPT and TL tubes of several series- I will expand upon their offerings.

[Dave Vigness]

Gene,

I'm afraid I can't add much more. I try and tell anybody on any of the forums about the relabelers of quality control rejects. Mine shipped with a KH relabel, which Russ identified as an EFR. The specs were just above minimum, and I later found out the glass work was restricting my water flow to just above minimum as well.

Beyond telling them that if it's not a world wide known brand to be VERY careful. I only found the Ruka distribution because I was researching the SPT TR series tubes. At that time LightObject wasn't selling them yet. I know Reci and EFR, seems like there was another highly regarded brand name, but I don't remember what it was.