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  1. #1
    Join Date
    May 2012
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    CNC Laser Cutting - Edges not square ??

    hi all

    i'm still learning how to use my CNC laser cutter,

    i'm trying to cut 9mm MDF is cuts thru the material really well but for some reason the edges of the cut aren't square they seem to be angled ..

    can anyone tell me why this is and is it possible to fix ?

    thanks

    Justin and Kasey

  2. #2
    Join Date
    Dec 2011
    Posts
    75
    If the edges aren't straight (90 degree) then it is highly possible that the laser power isn't strong enough to cut the material decently. So what to do? Raise the laser power and/or drop the cutting speed. Off course if you cut too slow, there's a chance that your material will ignite or at least the edges will get charred, which you wouldn't want. So be sure that you have a strong enough air assist. Experiment with the laser power and cutting speed. I don't know the power of your laser tube, but in some cases your laser tube might not be strong enough to cut the material you want. Cutting 9mm MDF isn't the easiest job for a mid power CO2 laser. The reality and what the laser salesman promised you might differ drastically. Could you please tell me your machines brand, model and specifications?

    Then there's the second possibility: Your laser tube or mirrors might not have been aligned correctly, so the laser beam might hit the cut material at an angle. Check your tubes, mirrors and alignment.

    Lastly, be sure to clean your machines lens and mirrors regularly (once a week generally) with alcohol and cotton sticks or whatever the manufacturer recommends. Cutting MDF will pollute the lens and mirrors quite fast.

  3. #3
    Join Date
    May 2012
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    0
    Quote Originally Posted by [B
    Could you please tell me your machines brand, model and specifications? [/B]

    Then there's the second possibility: Your laser tube or mirrors might not have been aligned correctly, so the laser beam might hit the cut material at an angle. Check your tubes, mirrors and alignment.
    hi there thanks for your reply, it's a cnc laser we brought from China

    Brand - Wisdon 1200 x 900 table
    Laser Tube - RECI 130w Glass C02

    how do i tell if the laser bean is hitting the material at 90 degrees ? - when i can't see the beam of light.?

    also do i still focus the laser on the top of the 9mm MDF or should i focus it half way thru the MDF?

    what speed and power settings should i use to cut 9mm MDF ?

    at the moment i'm using 80% power and 5-7mm/s cutting speed

    thanks

    Justin

  4. #4
    Join Date
    Sep 2011
    Posts
    58
    Hi

    What is difference betteen two diagonal?
    Lucy (Jinan Consure Electronic Technology Co.,Ltd) 0086-18254116182
    Web:http://www.jncslaser.com Email: [email protected] Skype:consurelaser

  5. #5
    Join Date
    Sep 2011
    Posts
    58
    Hi

    What is the difference betteen two diagonal for that not square 9mm MDF sample.

    Lucy
    Lucy (Jinan Consure Electronic Technology Co.,Ltd) 0086-18254116182
    Web:http://www.jncslaser.com Email: [email protected] Skype:consurelaser

  6. #6
    Join Date
    Sep 2011
    Posts
    296
    Quote Originally Posted by Just-In-Kase View Post
    hi there thanks for your reply, it's a cnc laser we brought from China

    Brand - Wisdon 1200 x 900 table
    Laser Tube - RECI 130w Glass C02

    how do i tell if the laser bean is hitting the material at 90 degrees ? - when i can't see the beam of light.?

    also do i still focus the laser on the top of the 9mm MDF or should i focus it half way thru the MDF?

    what speed and power settings should i use to cut 9mm MDF ?

    at the moment i'm using 80% power and 5-7mm/s cutting speed

    thanks

    Justin

    Hi, Justin,
    Frankly speaking, 130W Reci's top ability is cutting MDF 8mm-9mm. And that is under the case everything is excellent. So it is very common that it can not cutting a MDF of that thickness well.

    do i still focus the laser on the top of the 9mm MDF or should i focus it half way thru the MDF-- to the top


    how do i tell if the laser bean is hitting the material at 90 degrees ?-- You need to find a thick acrylic(20mm) to press the test button, to check the laser throught that. You can measure the distance from the dot to the edge at the top of the material and also at the bottom to see if they are the same.

    You can try more power and less speed. Maybe 90% and 4-5.

    After all efforts, if your laser still can't cut MDF well, you can consider upgrade that to 150W.

    Melody
    [email protected]

  7. #7
    Join Date
    Dec 2011
    Posts
    75
    After seeing what Melody says I can say that your laser tube isn't strong enough to cut 9mm MDF. Don't be mad or disappointed, you might upgrade to even a 195W RECI tube if your Power Supply is strong enough. If not ,you can buy a new Power Supply too. Be careful that both are RECI. Now that sounds though, but you have to spend more $$$ if your main purpose is to cut 9mm MDF. My salesperson tolde me that I could cut 20mm acrylic with a 150W RECI tube. Another told me that I could cut 30mm acrylic with a 200W GSI tube. :bs: Don't believe everything they say, especially the Chinese.

    If your salesperson told you before buying the machine, that the machine can cut 9mm MDF, you should talk to him again. If you imported the machine yourself, there's no way they will want to reimburse you. If you bought the machine from a company in Australia then you can try to get a refund. If nothing works and the machine isn't suitable for your work, you can try to sell it in Australia. You might actually profit from the sale if you imported it yourself. Then you can buy a better machine that will suit your work. I don't know the delivery time from China to Australia, but it's definitely shorter than to the US or South Africa. Actually you might receive a new machine in a month. Buying a new machine is the worst case scenario, but if nothing works, it's the way to go. (Don't mistake me for a salesperson, though.)

  8. #8
    Moot point on cutting ability, in theory a 30 watt laser will cut 24mm MDF....at around 1mm per second / 100% power and about 50 passes.

    What a laser will cut and what a laser will cut efficiently are two very different things.

    I tend to agree with Mel, above 9mm (and in some cases for 9mm) a router is a far better tool.

    The chances of getting a straight cut in both X & Y axis in 9mm MDF is slim, the beam itself is a Gaussian curve ergo not straight so your not starting with a level playing field.
    Acrylic is a different matter, it acts as a wave guide so can be cut at much bigger thickness's and still retain a straight edge.

    9mm MDF on a laser? unless it's a 150 watt RECI or a GSI you aren't going to be impressed by it.

    best wishes

    Dave

  9. #9
    Join Date
    May 2010
    Posts
    112
    With 50PSI of clean shop air, a modified (extended) air blast nozzle and a 100mm focal lens I can blast through 1/2" MDF in a single pass with my 80W RECI tube. I run about 10mm/s for a speed at 90% power.

    Air is your friend. Toss the cheap POS pump that came with your laser and get it set up on some real adjustable air pressure.

    The adjustment knobs on the last mirror are for adjusting the squareness of the cut. You need to have the laser beam enter the carriage dead center from the nozzle or you will never get it right. This may take some adjustment of the carriage or position of the 2nd mirror on the long X axis rail, mine came straight from gweike way too far out of alignment to ever get a square cut.

    After that you need a thick piece of clear acrylic. Test fire the laser into the acrylic and fiddle with the last adjustment mirror till it appears to be exiting at a perfect 90 degrees. If the laser does not enter the carriage properly you will hit the side of the air blast nozzle before you find the "sweet spot." You'll know this is happening when you see semicircles appear on top of the acrylic.

    It takes forever and a day to get a laser to cut right and true. After it's set do your best to not bump or move it at all. Set the rubber feet, don't rely on the wheels. Be extremely careful when you clean the mirrors. Don't touch them, drag an alcohol soaked cloth across them. They are clean when the alcohol evaporates and you can no longer see any crap stuck to the mirror.

    Hope that helps!

  10. #10
    Join Date
    May 2012
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    0
    Good morning All

    wow thanks for all your replies so far, i have learnt alot from reading your posts so far..

    so what kind of PSI does the little air compressor that came with my laser put out ? it's a HC-388D 90L/Min

    so i need about 50 PSI ? so a small direct drive compressor from the hardware store or something different??

    so about adjusting the mirror on the laser head, i have the beam hitting center of the nozzle, but ur telling me that if the last mirror isn't correct it could be giving me the angled cut ? should the laser dot the comes out of the nozzle be dead round or slightly oval ?

    ok so i'll have to track down some thicker acrylic if i can't find any is there any other ways of testing it out..??

    i was thinking could it be my cutting speed is to high and there for the laser beam is cutting half way thru and then it's moving and the beam is getting bent (skew)? i have found the angled edges are on acrylic as well

    yes i clean the mirrors often, but not as much the focus lens (i'll do that today)

    thanks all i hope to hear from you all again soon

    cheers

    Justin and Kasey

  11. #11
    Join Date
    May 2010
    Posts
    112
    Good morning All

    wow thanks for all your replies so far, i have learnt alot from reading your posts so far..

    so what kind of PSI does the little air compressor that came with my laser put out ? it's a HC-388D 90L/Min

    No idea, but the pressure and volume are extremely low. I would hazard a guess around 2.5-5PSI

    so i need about 50 PSI ? so a small direct drive compressor from the hardware store or something different??

    Yes, that should be OK. You will need to filter the air very well, any contamination that gets on the lens (especially water) runs the risk of cracking the lens. Use a series of filters, preferably 20 micron -> 5 micron -> coalescing filter in that order. You can skip the 20 micron filter and just use the 5 micron, but it may plug easily. Don't just use a coalescing filter by itself, it will be plugged in minutes.

    so about adjusting the mirror on the laser head, i have the beam hitting center of the nozzle, but ur telling me that if the last mirror isn't correct it could be giving me the angled cut ? should the laser dot the comes out of the nozzle be dead round or slightly oval ?

    It is possible to hit the center of the nozzle while still being out of alignment. The laser beam needs to make a perfectly perpendicular turn down towards the table. There is no conceivable way to correct an out of square cut if the beam does not come towards the table perfectly perpendicular in both the X and Y axes. When in focus the laser beam will make a perfectly round spot on a test fire. If it makes an oblong dot you are hitting the focal tube somewhere. Don't ever trust the red dot for anything. It is a very inaccurate novelty and not good for much of anything but sapping laser power. You certainly don't want to use it to align your laser, and you most certainly don't want to use it to determine problems with the CO2 laser.

    ok so i'll have to track down some thicker acrylic if i can't find any is there any other ways of testing it out..??

    Not that I know of. Acrylic is readily available at almost any hardware store. .220" should do just fine. If you can find thicker stuff go for that, you will be able to see the angled cut a lot easier the thicker the material you test with. This is true to an extent, if you go too thick you will start seeing the taper caused by the laser focusing. Test fire close to corners of the acrylic, this way you can see what it is doing in both the X and Y axes. You should be able to distinguish the difference between an out of square beam and the natural focus pattern of the laser this way.

    i was thinking could it be my cutting speed is to high and there for the laser beam is cutting half way thru and then it's moving and the beam is getting bent (skew)? i have found the angled edges are on acrylic as well

    Laser (light) beams do not skew or bend. It is physically impossible. What you will see, should you go too slow, is the laser superheating the surrounding material causing it to ignite. The weak air pump that comes with the laser only acts to flame this fire, pushing it along your half finished cut. Since the cut is not all the way through those hot embers stay in the "pit" of your cut burning the entire thing to a giant mess. These things are easily to distinguish from an alignment problem. If the cut is straight but out of square it is alignment. If the cut is real wavy or full of holes you are trying to cut too much. Try more passes at a faster speed.

    yes i clean the mirrors often, but not as much the focus lens (i'll do that today)

    thanks all i hope to hear from you all again soon

    cheers

    Justin and Kasey

  12. #12
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    May 2012
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    0
    Thanks for your reply i'll re read it and work thru all the steps you have outlined

    also what roll does the compressed air have is it just to cool down the focus lens ? or to help with cutting ? if so how does it help with cutting?

    thanks

    Justin and Kasey

  13. #13
    Air keeps carbon out of the cut line, assists in the combustion in the case of wood and suchlike and keeps dirt off of the final lens

    Air is the god of laser cutting without a doubt, lots of it at high pressure is the way to go

    best wishes

    Dave

  14. #14
    Join Date
    Jun 2012
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    0

    lens focal length

    I was having problems cutting acrylic and getting edges that were not square. The problem turned out to be that I was using a lens with a short focal length (1.5"). That lens is great for detailed surface engraving, but cuts are always v-shaped, leading to non-square edges. Also, the fumes from cutting made the lens dirty quickly since is was so close to the cutting. I was having to clean frequently. A longer lens, 4" or 5", will cut 1/8" acrylic nice and square.

  15. #15
    Join Date
    Oct 2012
    Posts
    72
    Quote Originally Posted by pontiacg5 View Post
    With 50PSI of clean shop air, a modified (extended) air blast nozzle and a 100mm focal lens I can blast through 1/2" MDF in a single pass with my 80W RECI tube. I run about 10mm/s for a speed at 90% power.

    Air is your friend. Toss the cheap POS pump that came with your laser and get it set up on some real adjustable air pressure.

    The adjustment knobs on the last mirror are for adjusting the squareness of the cut. You need to have the laser beam enter the carriage dead center from the nozzle or you will never get it right. This may take some adjustment of the carriage or position of the 2nd mirror on the long X axis rail, mine came straight from gweike way too far out of alignment to ever get a square cut.

    After that you need a thick piece of clear acrylic. Test fire the laser into the acrylic and fiddle with the last adjustment mirror till it appears to be exiting at a perfect 90 degrees. If the laser does not enter the carriage properly you will hit the side of the air blast nozzle before you find the "sweet spot." You'll know this is happening when you see semicircles appear on top of the acrylic.

    It takes forever and a day to get a laser to cut right and true. After it's set do your best to not bump or move it at all. Set the rubber feet, don't rely on the wheels. Be extremely careful when you clean the mirrors. Don't touch them, drag an alcohol soaked cloth across them. They are clean when the alcohol evaporates and you can no longer see any crap stuck to the mirror.

    Hope that helps!

    I have changed my lense to 100mm.

    I also changed the nozzle to the one that was provided for the 100mm lense.

    From the top of the lense to the material surface this is measured at 100mm.

    I have a 14cfm compressor with a 10 metre hose that is connected to the laser cutter. Regulator reads 50 psi at the compressors end.

    I have a regulator on the laser cutter which is not reading 50psi.

    Yesterday I re aligned the mirrors.

    Did a test cut and I can't cut through 12mm acrylic or mdf in 1 pass. Not even in 2 passes.

    I own an 80 watt Reci Wk Laser Cutter.

    What am I doing wrong?

  16. #16
    I also changed the nozzle to the one that was provided for the 100mm lense.
    The nozzle needs to be as close to the work as possible the ensure you get a good directed airblast at the actual cut point.

    From the top of the lense to the material surface this is measured at 100mm.
    Lens focal lengths vary by quite a bit, even within the same batch, lens's are also imperial, a 100mm Lens is actually a 4" lens so the base line focal length is 101.6mm, you will need to do a ramp test to get the exact focal length though.

    I have a 14cfm compressor with a 10 metre hose that is connected to the laser cutter. Regulator reads 50 psi at the compressors end.
    Pressure drops with expansion and distance, 33 feet of hos is a LOT to expect the compressor to handle. Re-site the compressor as close as possible to the machine.

    I have a regulator on the laser cutter which is not reading 50psi.
    See above

    best wishes

    Dave

  17. #17
    Join Date
    Oct 2010
    Posts
    27
    Quote Originally Posted by pontiacg5 View Post
    With 50PSI of clean shop air, a modified (extended) air blast nozzle and a 100mm focal lens I can blast through 1/2" MDF in a single pass with my 80W RECI tube. I run about 10mm/s for a speed at 90% power.
    Would you be so kind to share a couple of pics of the setup you describe? That 'modified (extended) air blast nozzle' sounds just like what I need. Also, do you think a temporal / trial setup where the air is blown into the piece from outside the nozzle is worth trying?

    Quote Originally Posted by pontiacg5 View Post
    Use a series of filters, preferably 20 micron -> 5 micron -> coalescing filter in that order. You can skip the 20 micron filter and just use the 5 micron, but it may plug easily. Don't just use a coalescing filter by itself, it will be plugged in minutes.
    Again, a couple of pictures of your setup in the 'filters section' would be of great help! I'll be heading to the hardware store soon but don;t really know where to start from...

  18. #18
    I also changed the nozzle to the one that was provided for the 100mm lense.

  19. #19
    Join Date
    Nov 2012
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    42

    Re: CNC Laser Cutting - Edges not square ??

    We're having similar problems with a 40W laser cutter that is producing a V-ee rather than perpendicular to the plane of motion.
    The optics appear to be aligned but I'm wondering about the beam quality. The tube is a bit older more importantly, the tube has been overheated on a few occasions.
    Any links to troubleshooting CO2 laser cut quality problems?
    Thanks
    Doug

    I should ad that the acrylic is only 3mm thick. The lack of perpendicularity of the cut is obvious even over that thin range. It affects the fit between interlocking parts. The is air assist, but it is pretty low pressure.

  20. #20
    Join Date
    Aug 2004
    Posts
    780

    Re: CNC Laser Cutting - Edges not square ??

    I dont have a laser, but do know the physics..

    How close is your air blast nozzle to the surface ?
    If the air blast is high above the surface, it will not have good airflow into the cut. As post#16 said..

    Change the air hose from compressor to machine to a thicker one.
    Going to a bigger hose will reduce the load, and thus restriction, dramatically.
    Even if the nozzle at machine is small.
    A small hose can drop your effective air 50%, even more, over 10 m with small compressor.

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