Vertical Beam Alignment

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Meta-Concepts
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Vertical Beam Alignment

Post by Meta-Concepts » Mon Oct 31, 2011 10:27 pm

Wasted half a day trying and failing to get my beam aligned perpendicular to the table on this 1290.

The beam is off in XZ and YZ planes by about 1mm in 40mm, which is enough to mean that significant features like tab joints are not cutting square or to size.

I have tried adjusting the laser tube height so the beam is more central to the mirrors and I have tried adjusting the final mirror, but the beam hits the side of the nozzle before it becomes even slightly more perpendicular to the table.

I've even tried realigning the entire head assembly with no joy.

Not quite sure how the vertical alignment is supposed to work, because if you shine a visible beam through a single lens element, angling the beam doesn't move the focal spot, it just changes the intensity?

tweakie
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Re: Vertical Beam Alignment

Post by tweakie » Tue Nov 01, 2011 8:36 am

Ideally, it's the final mirror you have to adjust to get the beam perpendicular to the work table (assuming all other mirrors are adjusted correctly). If necessary the nozzle may need packing to align with the beam and prevent the beam hitting the side.
I found this adjustment could be checked, quite easily, with a small block or edgewise piece of acrylic and test firing a hole then checking the result. http://www.laserscript.co.uk/phpBB3/vie ... =406#p2649

Hope this helps,

Tweakie.

Meta-Concepts
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Re: Vertical Beam Alignment

Post by Meta-Concepts » Tue Nov 01, 2011 10:14 pm

Adjusting the final mirror doesn't have any great effect on the beam passing out of the lens. All it does is align the beam with the centre of the lens on the input side, thus ensuring maximum power transmission. If you replace the lens with a paper target, you will see that the beam diameter is nearly that of the lens at this point, so moving the beam across the lens results in hitting the side wall of the tube, burning, internal reflection and heat damage to the thin edges of the glass.

Try shining a torch through a single element lens to see what happens if you angle the beam.

I am testing by running the beam across the edge of a 40mm block of PP. This clearly shows a parallel beam pattern with little divergence across this depth, but with a severe slant to the left and slightly less to the rear of the machine. Adjusting the final mirror makes no significant difference to the beam angle until the beam hits the tube wall when the output splits into two angled beams and the surface of the tube starts to burn. This can be seen if you put tape over the nozzle. Changing the final mirror moves the burn point slightly away from the centre of the nozzle and changes the shape of the cut, but before you get to the edge of the nozzle you start seeing internal reflection and splitting.

On my machine, you would need a bigger nozzle opening before the beam was corrected enough that the output became perpendicular to the bad. Something seems to be flawed with the geometry of the head?

Spooky
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Re: Vertical Beam Alignment

Post by Spooky » Wed Nov 02, 2011 12:17 am

Something isn't right in the optical train.My 1290 if the final lens is replaced with a 2mm thick piece of card gives around a 7mm beam diameter on the input side.

Best wishes

Dave
Please note I am not employed by HPC, any advice or recomendations I give are based on my own experience and are not necessarily the same as HPC's. First point of contact on any hardware issues should be with HPC
Dave@OpticalPower.co.uk

tweakie
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Re: Vertical Beam Alignment

Post by tweakie » Wed Nov 02, 2011 7:00 am

Try shining a torch through a single element lens to see what happens if you angle the beam.
Done it, been there already which is exactly why I say that perpendicular beam alignment is a function of the final mirror adjustment (assuming all other mirrors are correctly adjusted).

Assuming your lens is removed, the beam should leave the final mirror perpendicular to the table.
Your lens should now be fitted central to the beam.
The position / angle of your tube should be adjusted so that the beam does not strike the sides.

I accept that this may not be easy for you to do (neither is riding a bicycle for the first time) but perfect alignment is the secret to successful and efficient laser operation.

Tweakie.

Spooky
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Re: Vertical Beam Alignment

Post by Spooky » Wed Nov 02, 2011 5:09 pm

Hiya MC,

The final lens is positive meniscus not biconvex so moving the mirror will move the focal point without making very much change to spot shape.less than 5 degrees of turn on each screw when adjusting is a good idea any more and the beam will leap about all over the place.
If you have moved the tube mounts you will need to start there to get a baseline set up, getting the tube level is half a day on all the new machines to ensure over the large bed of the 1290 you get the best possible results and maximum power.
I'd look at getting that as close to perfect as possible then move through the optical train until you get to the final mirror,be careful though as if the beam is striking the edge of the lens as you mentioned earlier it will crack or shatter it quite quickly.
You final spot size after the final mirror but before the lens is supposed to be between 6 and 8mm diameter and pretty close to round.
Main thing is though to get the tube bang on first or you're going to be tail chasing for days.

best wishes

Dave
Please note I am not employed by HPC, any advice or recomendations I give are based on my own experience and are not necessarily the same as HPC's. First point of contact on any hardware issues should be with HPC
Dave@OpticalPower.co.uk

Meta-Concepts
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Re: Vertical Beam Alignment

Post by Meta-Concepts » Thu Nov 03, 2011 10:23 am

I haven't been given any procedure for adjusting the tube, so I'm not sure how you are defining 'bang on'?

Chris leveled the machine when he installed it, but didn't touch the tube. I later noticed that the beam path, whilst making it all the way through the system, was not hitting the middle of the mirrors. Chris suggested adjusting the tube to move the beam, but only described how to unlock the screws and move the adjuster nuts.

If I adjust the beam so it is near the centre of all the mirrors and passes through the exact centre of the nozzle, I get the previously described angle on the cut.

I wonder if it might help to work backwards with a visible laser. Make up a mount for a laser diode that is perpendicular and aligns with the centre of the tube, firing up, then note the position on the mirror that needs to be hit and aim the main beam at this?

Given the reliability of the rest of the unit to date, I wouldn't be surprised to discover that the whole frame is jacked off-square.

Daven
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Re: Vertical Beam Alignment

Post by Daven » Thu Nov 03, 2011 11:01 am

Knowing Chris he would have left the machine working to spec. I think it would be best to call HPC and discuss it with them rather than try and fix the problem via the forum. After all you have a new machine and tinkering with it may cost you more in the long run (by saying 'tinkering' I'm not suggesting you are inept - just that Chris has a lot more experience with these particular machines than any of us here and has the equipment to re-align ;-) )

Cheers

Dave
Using two LS3060's and an ex 3020 user
Please note I am not employed by HPC, any advice or recomendations I give are based on my own experience and are not necessarily the same as HPC's. First point of contact on any hardware issues should be with HPC

Spooky
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Re: Vertical Beam Alignment

Post by Spooky » Thu Nov 03, 2011 11:02 am

Hiya MC,

The frame is sheet metal so it's going to be square but not to the nth degree,even temperature over sheet that size is going to make a difference.Working from the final optic back would work if the tube was level and at a direct 45 degree angle to the first mirror but if the tube height/square is out then even though the spot may strike the final mirror in the correct place it will only work in one position on the bed.
Until the tube is set to the correct initialising point there is no real way to ensure all the optical train will follow.
On cut through the kerf will always be at a small taper,its the nature of solo optical systems that don't use collimators,the beam itself over a 50mm length from a 8mm start point will have near a 9 degree taper that cannot be improved on without the inclusion of a second lens.

The main thing is to get the tube alignment right first, without that it becomes an exercise in futility trying to align anything else as you won't have a datum to work from or to.I'd suggest a call to Chris may be a good idea, even on my industrial cutters I won't get into moving the laser source and they have fixed machined datum points so on a machine like the 1290 I wouldn't say tube alignment is a home user job at all.

Overall the machines are very reliable (hell theres isn't much in them that can go wrong) but like with any laser optical system alignment is the "god" of all function.

Like I say,give Chris a call and see what he suggests?

best wishes

Dave
Please note I am not employed by HPC, any advice or recomendations I give are based on my own experience and are not necessarily the same as HPC's. First point of contact on any hardware issues should be with HPC
Dave@OpticalPower.co.uk

Meta-Concepts
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Re: Vertical Beam Alignment

Post by Meta-Concepts » Thu Nov 03, 2011 11:50 pm

Right, enough effing about with bits of masking tape. Here is how to set the laser alignment fast:

Go to Maplin and purchase a Green Laser Pointer (A64JK)

Get some 21mm diameter Delrin rod or similar. On a lathe, bore out the rod to 13.4mm diameter to fit the laser pointer. If you turn a slightly larger rebate on one end, the tube will fit over the power button, holding it on.

Remove the air assist nozzle and the lens tube.

Fit the Delrin adaptor over the laser pointer and press up into the bore of the head where the lens tube normally fits. The laser pointer is now concentric with the tube and shining a visible beam in the reverse direction to the CO2 laser.

You will be able to see the green spot on the surface of the mirrors. Start in reverse order with the final mirror.

In my case, the laser head assembly was so far out of alignment that I couldn't adjust the final mirror to hit the second mirror. I had to re-align the head by slackening the bolts and moving the assembly.

Once it's close, get the laser dot in the centre of the second mirror at both ends of the travel of the X axis using the final mirror adjustments. You now have a beam that is concentric to the output tube and parallel to X.

Repeat with the second mirror onto the first.

Once you get close, you will discover that you have TWO spots on all your mirrors, one fuzzier than the other. This is because your beam is travelling all the way up through the CO2 laser and is reflecting back off the internal mirror and travelling back the way it came.

You can now fine tune the mirrors and the tube if required until both spots are hitting all mirrors at the same point. Your system should be very close to alignment at this point, but not necessarily completely perpendicular to the bed. Small adjustments to the CO2 beam can now be made with the final mirror as per usual, although if you try shining your green beam through the lens tube, you will see that only very small adjustments are possible before reflections start to create artefacts around the image. Better to align the head assembly as close as possible to perpendicular first. This can be done by cutting across the front and side corners of a deep piece of plastic and checking with a small square, or by making a jig to hold a piece of thin acrylic on edge.

I now have good alignment in X-Z but will need to pack the head assembly with a shim to correct the error remaining in Y-Z.

As to reliability, I have not been lucky to date. In the first couple of weeks, this machine has had a leaking brass water coupling that had to be replaced, an intermittent power supply that also had to be replaced and yet another undiagnosed intermittent fault that causes the machine to spontaneously soft reboot periodically.

On top of this, the software doesn't support variable power engraving even though the hardware obviously can and there is no consistent mechanism to specify cutting or engraving actions and powers from your design tool, which means having to re-edit every design laboriously in the LaserCut software. Unfortunately, this renders my business model unviable due to the high cost of multiple handling of design work required.

Frustratingly, other resellers of the same Chinese hardware appear to have a printer-driver based integration model along the same lines as Epilog et al, which allows you to do all your setup in the design package of your choice.

Terry

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