[RogerClark]

Ken

I'm glad things are working a bit better, but I think you still have an alignment issue.

What it sounds like is happening is that the final mirror is not directing the beam straight down, its going off at an angle

So if you push the tube up as far as it can go, the distance between your mirror and the lens is less, so any angular error on the final mirror is not putting the beam too far from the centre of the lens

What I did was pulse the laser with the nozzle completely removed and the MDF around 15cm below the gantry and I'm getting a spot in the centre of the circle I drew around my nozzle

I did not have to align my final mirror, as it was OK from the factor, but I had to align the 2nd mirror and also as I had to remove my laser tube 4 or 5 times already to get rid of air bubbles (and need to take out again today :-( :-( ) I had to re-align my first mirror several times as well.


BTW.

Do not run your laser at 100% power until you know exactly what tube you have. On the 50W lasers, 100% power overdrives the tube and causes it to degrade (See Russ's vidoes' on Youtube, he had to buy a new tube because he damaged his running it 100% power)

I'd recommend that you limit your power to perhaps 75% for the moment.

IMHO you are likely to find that you get a negligible amount of power more, by going above 75% and all it does is wear your tube out much faster.

I common added extra that people seem to fit to their machines is an analog current meter (milliamp meter) to display exactly how many milliamps the tube is taking. But you need to know what you are doing to wire one in, as one end of the tube is at 25kv and one end is at earth and if you get the wrong end you are in serious trouble (it is however obvious)

[KenR60]

OK running out of "Play Time" today, Here is the underneath of the "Wobbly" Squares. I think this must be the best position to be 99.9% cut through without Burn Marks?

I will re do all alignment again and do the Tests again


Attachment 303758

[RogerClark]

No worries

These things eat time for breakfast ;-)

I have loads of bits of MDF with 20mm square cut out of them and the shed smells mildly of burnt wood ;-)

BTW. Ken, where are you. I guess you are on the east coast?

[KenR60]

Ran the test again and all lines are straight, maybe there was a wobble of the 3mm MDF with the Laser forcing it down?? But its gone, so now is cutting the 3mm completely through so back to the drawing board with alignment the next thing on my list.

Now another Question,

Is there Better replacement Parts here in Australia like the Mirrors and Lens? or they all much the same results??

I'm in Brisbane Roger

[RogerClark]

Hi Ken

If you were in Melbourne, I'd offer to drive over and give you a hand, but Brissie is a bit to far to drive ;-) (well I have driven to QLD from here but we did it over 3 days !)

Re: Better quality parts

Perhaps PK can advise.

But I suspect that the mirrors and lens are not the issue.

Its probably still an aligment issue, and if not that, then its probably a tube or laser power supply issue. (or possibly a setup issue in your control software not telling the laser PSU to go as hard as it should)

[KenR60]

Just something I thought of .... Does it matter if I don't "Ground" the machine? it said to Ground it using a piece of Pipe at least a Metre long. My Workshop has a Concrete Floor and I have framed a Timber Floor 70x35 over the top so would grounding make any difference?

[pk7639]

Grounding wont affect cutting, just the interface to your PC. Once the laser is cutting the PC is no longer talking to the DSP controller in the laser, so you don't have a problem.

Better quality lens' and mirrors get you one or two percent more power and a fair bit more life (always remember that lens' and mirrors are consumables. We swap ours out about once every 12-14 months, but we use the machine every day).

The wobble is interesting, and may hint at a loose screw on the head. However, if your beam was alligned correctly, you probably wouldn't see it in the cut.

The reason everyone is harping on about beam alignment is that its THE thing everyone gets wrong when the get their first laser cutter. It isn't hard to get right, there are lots of video's around on the topic. Some of them are dogmatic, some give you enough information to understand the process, and following the instructions in most of them will leave you with good beam alignment.

Rogers sugguested test is a good one. I'll add that you should do it four times, once in each corner of the machines workspace. If the dot moves more than 5mm with respect to the center of the head tube when you compare the 4 tests, then you need to align the machine.

[KenR60]

Thanks for all that, I may not get back to the Laser for a couple of weeks as I am away on Holiday on Sunday, in the meantime, Where is the best place pk7639 for replacement Mirrors/Len just in case I can get better Quality to start with.

[pk7639]

We buy ours from AliExpress vendors.

[MonoNeuron]

Hi Guys,
I haven't been on here for ages but I have 2c to play with.
The way I checked my height for the lens adjustment was to get a piece of card about 50 to 60 mm long and fold one end over so it is about 10mm high to make a wedge.
Adjust the lens so it is about focused in the middle of the 'ramp' of card stock and draw a line in your software the length of the card. You will be cutting a very thin line on top of the card without burning through it. You're just finding out how wide the cut line will be as it focuses and de-focuses as it cuts along the card.
Place this under the lens at the smallest end and " cut " towards the biggest end using about 10% to 15% power and about 50mm/sec cut speed to just leave a mark on the card.
Cut the line.
Look at the line width and see where the thinnest part of the cut is and measure that distance to some point on your laser head that will be accessible every time you use it.
I've been doing that for years and works really well and is much quicker to do than to explain.
Hope this helps.

That wobble in the cut lines will be a loose belt or a pulley coming loose on one of the drive shafts of the stepper motor or the table may be moving holding the part. Tension the belt so it is tight but not like a guitar string. You don't need to have them too tight but they need to not have any droop in the middle.
Rich.

[RogerClark]

@MonoNeuron

As an aside, I have just replaced my 50.8mm lens with a 38.1mm in my 50W (cheap Chinese laser) and have been doing a similar sort of focus test to the one you described, except I was using acrylic and doing multiple passes across the acrylic and then looking at the dept of cut in side elevation

But I'll try you paper test tomorrow

PS. I replaced the lens because the focus point on the 38.1mm lens is supposed to be 8.1 times smaller in area than the 50.8mm lens. However in my preliminary tests, I'm only seeing a marginal difference in favour of the 38.1mm lens - but I need to do a whole load more testing ;-)