Problem with 4" Lens with a CloudRay Head

Hi at all, i have a problem with a 4" lens because doesn’t wants to cut … my spec is 6040 with 100W tube, mirror 25mm and focal lens II-VI 101.6. After ramp test the optimal focus is 25mm from the nose to material but if i measure the 101.6 from the shoulder of 4" of lens tube my focal should be 17mm. But if i use 17mm or 25mm the problem is always the same doesn’t cut… I would like to cut a MDF of 10mm but i can’t… If i use a 50.8 lens i can cut until 6mm with a power of 24ma but if i use a 101.6 and i set a power of 26ma doesn’t cut. I link some images with the lens that i use the head setup and the ramp test just to explain fine… All is correct ? or i mistake something ? Or maybe is the tube that is not really 100W ? the size is 1430mm from VEVOR … Thanks

Firstly make sure you have the lens the right way up. I use the 4" also.

Hold the lens on your finger and you should be able to see your entire head in the lens…this side goes upward.

I have 1200x900 with 100w (99% power is at 29ma) it will cut 10mm MDF power 90 speed 12mm/s.

My focal distance is 7mm from the end of the tube. (tube could be different)

Make sure your mirrors are clean, and alignment is good. Put a piece of tape over the end of the lens tube and fire a pulse make sure it is in the middle and not clipping the metal of the tube…

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Maybe this will help.

Engraving and cutting have different configurations. Notice the ‘engraving’ setup for a 4" lens with the short nozzle. Has a focus to the finest point at 17.8mm. The cutting version is using the longer lens cone and it’s focus is 4.5mm.

What is important is the kerf is 2.5mm not the focused ‘point’ you’re probably expecting.

Hope this helps…


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I believe the long nozzle is used for cutting as it allows you to get the air jet closer to the work piece. Having a good speed of air coming out the nozzle really helps when cutting as it clears the burnt debris away allowing for a better cut.
Something for the OP to also consider…Increasing the air pressure.

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Hi, thanks for reply me, the lens convex side is up (receive the laser beam) and concave down then the position i think is good… mirror are cleaned and the alignment is good also because if i change the lens with a 50.8 this works fine… I did also the test with the scotch on the final part of lens tube without the nozzle … pulsed and the shot stay in the center also i tried to put the scotch on the nose of nozzle and also there the shot stay in the center… only the focal lenght confusing me now… because at the moment the ramp test give me the optimal focus at 25mm but if i measure the lenght from the shoulder of my tube lens 4" position until the material (101.6mm) it show me that the focus should be at 17mm (the distance between the nose of the nozzle and the material)… well which i must use ? I saw also the @jkwilborn picture and it seems that i have the configuration for engravers and not cutting … but the head of Cloudray type C it’s only for engravers and not good for cutting ? From my picture you can see if the nozzle is for engravers or for cutting ? your opinion …
Thanks in advance for reply.

I don’t think the length of the nozzle really makes that much difference. I have put the 4" lens in the lower holding position and the focal length from end of tube is 62mm, and it still cuts ok (not quite as good as closer but will still cut 10mm MDF!) So I don’t think this is of any issue to you.
a 4" lens has a reasonable tolerance for focal distance (maybe 2mm either way) as the beam is so long. Unless you are way out of focus you should still be getting mostly through 10mm.

You can get something to measure the actual power of the beam (laser power meter), might be worth looking into.

you have a good chiller? what is the temp of the water when running the laser? mine runs at about 9 - 11 degrees

Hi Neil, my question is when you put the lens wherever you want (upper pos or lower pos) after you measure the distance betyween the lens and the material and then you have the focal distance (from tip of nozzle and material) or you do a ramp test ? just to understand fine this step because i would like to have a solid start point for my tests. And , unfortunately i don’t have a meter power but because my problem in these days i started to think to buy one. (About the meter, do you have some suggestion of which product i can buy ?) Also, i want to try the reverse beam alignment mirrors to see if the beam is fine paralleled. But i start to think that is the quality of the tube is not very good … this measure 1430mm the label tell 100W but i don’t know if is true or else… the product is this… … can you give a look about it … what do you think that is cheap about money but also about the quality ?
And … i have a CW-3000 chiller and when i use the laser the temp is about 15-16 degree celsius.

From what I know about Vevor tubes they are ok, and the length 1430 would indicate 100w yes (1400mm is min for 100w afaik) 400euro for a tube is not cheap or expensive, my tube is EFR and cost £700.

I would be interested to know what your mamps are at 99% power, i would expect 29 or 30 max, if power supply is set correctly.

I would get a power meter, they are not expensive and will show you power at all stages around the machine

Hi Neal, my 99% is set by me at 30ma because I have a power supply of 150w and also i have the regulator that is optional with my PS but I bought it… and then i can regulate the ma vs % of power…

Actually never cared or measured that difference. All I care about is what it’s like when it hits the material. So nozzle to material, like with a ramp test, who cares where the lens actually resides in the system.

Need to make sure there’s enough length for the beam to get small enough to pass though the nozzle.

I think when you are cutting thick material, you are less interested in a focused beam. By that I mean, the 2.5mm kerf, stays that way for a relative long distance when cutting with the 4" lens. That is a ‘wide’ beam, lower power density than when it’s focused. Have to go slower since the laser isn’t really ‘focused’ to a dot.

I’ve also, been advised and find that a lower pressure cutting with acrylic seems to work better.


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I’m curious about the 2.5mm kerf. I have a 4 inch fl lens in my basic k40. As an experiment, I tried cutting a hex shape in some 3/4 inch pine. It did cut all the way through it in one pass (slow & steady), the cutout fit quite tight in the hole, I will measure the object and the hole. in any case the kerf is considerably less than 2.5mm.

I use it for cutting. For me it has a wide kerf, much like the drawing.

I will have to look to get a clue myself, it’s been so long.

Never have tried to cut anything that thick. I think 25mm foam is thick…


Follow up, just measured the cutout and socket, On top, kerf ranged from .020" - .025" on the bottom exit side, ranged from .004"-.007".

The kerf on my 4" lens is very tight. always remember the tightest part of the cut is underneath so you should always put your face side on the bottom (inverting image as necessary) this will give you the tightest finished kerf. cutting say 10 mm MDF my joints are push fit touching.

@jkwilborn where did you get 25mm foam example from? I don’t see it in the chat. I cut 40mm foam in 1 pass no problem btw (cut out gun shape cases for a arms supplier)

I will have to revisit this myself. These discussions bring up things that you thought, but… Kind of tied up with a modification right now. So I will get back to it.

Probably start with a long ramp test…


I think Jack mixes up my post a bit with this one :wink:
(My new 60 Watt OMT…)