Optics Alignment Problem

[Brent Ramsay-Boyd]

I have spent the day trying to properly align my lasers optics but have run into a small snag.

I have managed to get 3 of the 4 corners of the bed (top and bottom left, and bottom right) to hit the exact same spot, but I cannot get the top right to hit the same mark. It is hitting about 4 - 5mm higher than all the rest.

If I adjust mirror 2, the other corners go out of alignment. Can anybody help me figure out what adjustments to make to get the optics all properly aligned.

The machine itself has only been leveled with a simple spirit level. Could it be that this whole corner is sitting low and the actual foot on that corner needs to be adjusted up?

Regards

Brent

[Bert Kemp]

check Rabbit Laser USA website under manuals and tutorials look for flying optics this is a very good way to get it right.
http://www.rabbitlaserusa.com/Manuals/BeamAlignment.html

[Brent Ramsay-Boyd]

Thanks Bert.

I have read through that link before, but it does not have any information that addresses my specific problem.

[Bert Kemp]

yes to the table sitting low check level again

[Jerome Stanek]

yes if your rail is low or high in one corner that would do it

[Rich Harman]

Yes, a corner sitting low can cause a problem. Could be other things too.

Is this a new laser? Have you aligned it before?

It would be helpful if you would add your machine to your signature line so that we know what equipment you have.

[Brent Ramsay-Boyd]

Hi Rich

I have added my machine details to signature, so I hope that helps. Its not a new laser, I got it back in 2014, but I have been plagued with various problems since I got it so have never got it set properly. I have had 3 Reci tubes, none of which have lasted more than 200 hours. I am on my fourth now so am taking it slow setting up the machine properly so that I can try sort out all the kinks and make sure this one lasts, though no one has been able to help me figure out why my tubes die prematurely.

Have tried to align it before, but have always ended up with bad spots on the bed where it doesn't cut properly. I have also just replaced the 1st mirror. its a Molybdenum Mirror which was leaving a blue tint on my q-tips when I cleaned it. Someone told me it was Molybdenum dioxide, and just to clean it off. I took the mirror out the machine and under close inspection under good light, the surface though free of scratches and deposits seems to have a very dotty stippled appearance, almost looks like its under the polished surface. This is not the same on the new mirror, so hopefully that will sort out my power problem.

[Bert Kemp]

Does you machine have an amp meter? if not I highly suggest you put one on. The tube problem could be caused by over driving it. do a search here on how to install an amp meter and what reading you should get for your tube.Lot of Chinese MGF's turn up the power on the PS .that causes premature death to the tube.

[Brent Ramsay-Boyd]

The last time I leveled the machine I obviously did it wrong. I leveled the machine taking measurements on the bed, but measuring now I see that the rails and the gantry are not level. I have re-leveled the machine as best as I can taking my measures from the gantry and rails. This has somewhat improved my problem but its not completely solved yet.

While leveling the gantry I have noticed that the measurement taken at the center of the gantry and the measurement taken at the extreme ends are not the same. So if I get it dead level in the center, the extreme ends are slightly out of level. They are still within the level markings, but very slightly out of center. I am not sure if this means there is a slight bow in the gantry, or if there is something else I am missing. I would expect to see the bottom right mark also out if the problem was solely down to the gantry.

The top right mark is now hitting 1-2mm above the marks made in the other 3 corners. I am not sure if this is an acceptable tolerance. I am a bit of a perfectionist, but I can let it go if this is acceptable. If not any suggest on the next step?

The other thing is that although aligned my marks are not hitting center on any of the mirrors, they are centered left to right, but are hitting low on the first mirror and high on the second and third. I can only assume mirror 1 is slightly higher than the other 2.

Bert, I do have a amp meter and a potentiometer on my machine, and my max power has been set on the machine so that the amps do not go over the 25mA recommended by Reci for max tube life. I had a friend come and test the amps from the tube with a high quality multimeter, so I could make sure the power supply was not a problem, and I found no issue there.

My machine also will not run without water, and I always check to make sure the water is at the right temp before running the machine.

The only change I have noticed is that the reading on the ammeter has dropped slowly over time from 25mA to approx 22mA. I have not ajusted it up any further, but my friend multimeter did show a slightly higher reading of around 24mA.

[Bill George]

Tubes only lasting 200 hours and mA reading ok? I would replace the power supply regardless.

[Kev Williams]

1390's are big machines. Just getting tables that big level and flat is a trick.

As for aligning things- If the machine is making a decently square square- no short sides or angled sides- then you only need to align the mirrors. If you have 3 corners dead on and one corner high or low, then it's likely one corner is low or high, and low corner needs to be raised. If you have 3 corners dead on but one corner is hitting left or right, the the gantry may be out of square... The thing is, how far off 'dead on' is acceptable? I've found when playing with the red LED and beam alignment that almost anywhere the beam hits the mirror over the lens is acceptable, because the beam spot moves less than .005" on the table within a 3/8" move on the mirror. So, for me anyway, spending great amounts of time to dead-center each mirror only to get a .005" (if that) improvement isn't worth it. I just get the beams to hit the mirrors as close as possible to the center and call it a day. The most important thing is for the beam to hit MIRROR and not mirror HOUSING so there's no beam reflections/retractions and no power is being needlessly absorbed. Beam alignment thru the cone is pretty important, which is another reason I refuse to use a cone. If you prefer a cone, IMO the end needs to be sanded down so the hole is at least 3/16" diameter so the beam won't hit it.

Belt driven lasers are not high precision machines. Even making a decent, accurate ruler with one is a pretty tough chore. So unless there's a huge beam alignment error present that WILL require adjustments (which usually just lead to infinitely more adjustments), then do your best to average out the errors- if 3 corners are good, one is low 1/8", then adjust until both are low and high 1/16" inch. The most important is the one over the lens...

To level the gantry, just level the whole machine until the gantry shows level. Then you need to adjust the table to 'fit' the gantry. Cut a 2" or so shim using Romark or wood or whatever, then adjust the table at the home corner so the shim just fits between the table and lens. Then check the other 3 corners. Assuming you have a raising table, adjust the table's lead screws until all 4 corners are the same. Easiest way to adjust the screws is to find and remove the big drive belt, then turn the screws by hand, then put the belt back on. :)

If you have a stationary table like mine, it's a simply matter of a adjusting the table's pads, or adding a few shims..

If you're machine doesn't make a decent square, then you may need some gantry adjustments...

[Brent Ramsay-Boyd]

Thanks Bill. I do have a spare power supply, so I will swop that out in the morning.

Kev, I think I have the laser as level as I need, might try a few small adjustments, but I am not going to kill myself to get if perfect if its not necessary. Maybe when I have more time to fiddle, but for now I have work that is backing up so I need to get cutting as soon as possible.

I still have to align the final mirror which might be harder than I would like as the cone housing actually holds the lens on my machine, so I can't even remove the cone to align the beam, which I am sure is hitting the housing at the moment.

[Jerome Stanek]

I would try a shim under the top right rail

[Jeff Body]

You don't show your location?
Do you have alot of condensation when you're at temperature?

[Brent Ramsay-Boyd]

Hi Jeff

I am from Durban South Africa, It does get quite humid here. Especially in Summer. I wouldn't say I have a lot of condensation, but I did notice today that I had a bit of condensation around the on the glass nipple where the outlet tube for the water attaches to the laser tube. Although the laser should not have generated much heat today, as I was only pulsing it to align the optics today.

[Bill George]

Condensation moisture from your cooling water for the tube could cause a High Voltage arc over that might affect your tube or power supply. We have the same problem here in Iowa July / August and about the only thing you can do is run your air conditioning to lower the humidity.

[Rich Harman]

It would not be surprising that the gantry is not square with the Y axis rails. Mine wasn't and required adjustment. To test, vector a square on a piece of MDF (or whatever) as large as you can and measure the diagonals. If they are not equal then you can adjust by loosening up the clamp that connects the two sides of the Y axis rod at the back of the machine and adjust as necessary. Use a sharpie to mark the starting position.

It would not be surprising at all that the Y axis rails were not lying on the same plane. I had to shim one end of mine using a piece of thin plastic.

I also did not have the beam hitting the center of the mirrors. I needed to raise the first mirror slightly, then raise the second mirror a bit more. I used the third mirror as the guide because it's height was not adjustable.

[Jeff Body]

Condensation moisture from your cooling water for the tube could cause a High Voltage arc over that might affect your tube or power supply. We have the same problem here in Iowa July / August and about the only thing you can do is run your air conditioning to lower the humidity.

You beat me to it......

I'm pretty sure condensation is what killed my last tube. It arcing a few times through the condensation and within a day the tube was dead.

[Brent Ramsay-Boyd]

Thanks Bill and Jeff. I will have to take that into account. Will probably mean I have to install a aircon, or at least a dehumidifier.

Looking at the predictions it looks like we are going to have in excess of 70% humidity for the next week.

I have never noticed the tube arcing, but it may have happened while I was not near the machine.

Rich, I will try your suggestions when I get a chance, though I am weary to adjust too much as I don't want to screw it up more.