[RogerClark]

Robert

I took a look another look at whats happening, and if I leave the machine turned off for a few hours, I get a load of small air bubbles appear in the tube.

I don't think the air getting into the system I think that the de-mineralised water I bought must contain air in solution, and it comes out of solution when I leave the machine for a while.

I found a supplier that has "steam distilled" water, but they are closing early today (new Years Eve) and don't open again until Saturday.

BTW. I tried all the tricks with pinching the tube etc, and the only way to move the bubbles is to lift the end of the tube a lot, 20 deg or more higher at one end.
I guess I could pick the machine up, but I'd need to lift one end almost 2 ft off the ground to get the angle required.

So if I can find a fix that doesn't require me to pick up the machine etc it would save me a lot of problems.

[robertk925]

Hmm, I don't know much about demineralized water, but I would be surprised if it released air indefinitely. Since I would assume your water system is not a closed system (i.e. the tank is not completely full of water), the water is continually exposed to air, and should eventually reach stasis (neither releasing or absorbing air). I use distilled water (in addition to the RV antifreeze) and like I said, only see some bubbles in the very beginning, which are created by air in the water lines due to the water draining when the pump stops.

[RogerClark]

Robert

Its not a closed system. I have a pond pump in a plastic box which has a lid, the lid is not air tight, but it keeps out the dirt and I get condensation on the inside of the lid because its fairly warm here in Melbourne at the moment (40C outside this afternoon and probably 25 deg in the small workshop that has the laser cutter in it

BTW. I know that I need to keep the water cool and in the longer term I'll need to get a chiller unit, but I just want to get the machine working first before I shell out for a chiller and in the mean time I can use camping ice packs to cool the water .

I guess sooner or later all the air would be dispelled from the water, but it could take ages and each time I get a bubble in the tube its a pain to remove.

I think I'll get the 10L can of distilled water (for $13 AU ) on Saturday and try that (I will try to save as much of my de-mineralised water as I can as well)

Thanks

Roger

[the.sniper]

@RC, heres an idea just use a solution of straight antifreeze. I cant imagine you need more than a few gallons.
if your having so many problems with getting distilled water. this should solve that one.
BTW: Happy New Year to all!

[robertk925]

It has been a long time since my chemistry classes, but my point is that I would guess that it shouldn't take long at all for the water to reach equilibrium when in contact with air. Think about a carbonated soft drink, and how quickly it loses its CO2 fizz if left open. Maybe a day or so at most, right? So I believe that your water is already at equilibrium (i.e. has absorbed/released as much air as it can at its current temperature and pressure), and is not the cause of your bubbles. Try this experiment. Put some water in a clean closed bottle or jar. Shake it violently. See how long it takes for the bubbles to disappear. That is how quickly air dissolved in water is released back into the atmosphere.

But I guess you could try different types of water/antifreeze to test it yourself. I would choose something with some color to it so that you can visually inspect your hoses to see if there is air in them.

Sorry, maybe I missed it, but I didn't see if you confirmed that your outlet water tube and your pump are completely submerged in the water tank. Because if they aren't they will definitely introduce air into the system.

[RogerClark]

Guys

My air bubble problem seems to have finally resolved it's self. Yesterday morning when I opened the covers and looked at the tube, there weren't any micro bubbles, and running the pump was fine.

In the mean time I did find a source of "steam distilled water" so I have bought 10L for $13 (AUD) around $10 USD. Which I think is a reasonable price. But as it seems Ok I have not swapped to distilled, and probably will just use it to top up the reservoir.


I had another amusing problem with the machine. The Y axis seemed to be sticking half way along its travel.
Pushing it manually, I could feel it was stiff but not that bad.

Anyway, on further investigation, I found that they had not screwed in the grub screws in either of the two, Y axis drive belt pulled attached to the drive motor !

I don't mean they were not tight, they had not been done up at all, and needed around 10 turns each to get them in contact with the drive shaft, before I could even tighten them up!

I'm sure how it was working at all in the first place. The Y axis drive shaft must be quite a tight fit in the belt pullys

One other thing about my machine.
The focal distance is a lot longer than on other people's machines ( of the same type)

My machine came with the piece of focussing plastic, which is around 18mm wide.
I initially thought this was a mistake, but I have done some basic tests and it is definitely this sort of distance. In fact, I have been doing test cuts on 4mm MDF ( as I have loads and loads of it), and if the distance gets less than 18mm it does not cut so well.
So I actually need to try 19mm and further away to find the optimum.

The only problem with having a nice long focal distance is that the air from the aquarium pump is not powerful enough to quench the burning of the MDF very well.

I have a 2HP compressor for spray painting, So I may try attaching that instead of the aquarium pump, but I wonder if what I really need is a separate air feed from the larger compressor which I could direct to the cutting point.

any suggestions ?.?

[the.sniper]

@RogerClark:
Fwiw: My system consist of (all DIY) a 1 gallon reservoir that feeds into the pump which pushes into the radiator which feeds the co2 tube and then back to drain in the reservoir. all interconnected with a series of hoses.

My system will get an air bubble trapped right in the pump. (a large one.) which causes cavitation(and cannot be seen) And, severely slows down the flow. IF I let it run long enough the trapped air will slowly break up. I typically will burp all the air out. then run the system.
And as mentioned in a previous post I did switch over to a 100% prop-glycol solution.

Not sure what you meant by the 18mm distance thing pics would be helpful!

-S

[robertk925]

Roger:

Glad to hear your bubble issue seems to have sorted itself out.

The focusing distance is dependent on the lens (2"/50.8mm is typical, but there are shorter and longer lenses available). All of the nozzle geometry below the lens surface is dead space (except of course for allowing for threads and the air connector) and has no impact on cutting, so it is very possible that your nozzle is shorter than what many of the other machines have. Also, as I mentioned before, check to make sure your lens is not installed backwards. Mine was, and flipping it around decreased the distance between nozzle and material by a few mm.

The airflow shouldn't really be affected by the nozzle length, since the air velocity is pretty much the same no matter the length (unless there is a significant resistance in the air path). In other words, a properly sized 1 meter long tube will output similar air velocity as a 2 meter long tube.

[RogerClark]

@the.sniper

Sorry. I think I'm confusing things here.

The that was in solution in my water now seems to have come out, and I no longer get micro bubbles in the tube.

The 18mm is distance below the laser air nozzle and the item that is being cut.
I re-measured it, and the plastic tool that came with the machine is 19.8 mm wide.
Attachment 302606

Attachment 302608

From what I've read, the normal distance for this is around 6mm, but I have done some tests and the distance between my nozzle and the item to be cut definitely needs to be about 20mm

The downside of this, is that I don't think there is enough air pressure from the nozzle to quench the flames when cutting MDF or cork. I'm finding it virtually impossible to cut 3mm cork sheet, because using higher power of slower speed just results in more / wider charring rather than deeper cutting. i.e the cut is closing over with carbonized cork.

I was going to attach my 2HP air compressor but I realized that the regulator had packed up, so I will need to get another one before I can have a go at increasing the air supply.

[RogerClark]

I'm not sure if I should start a new thread, as this thread was supposed to be a review of the machine I have...

But can anyone advise if this sort ridging on the edge of an cut on acrylic is normal ?

Attachment 302618

The picture is taken with a USB microscope and the ridges are about 0.5 mm apart, and only occur in the Y axis. The X axis is smooth.

I have noticed when cutting card, I seem to get a series of small perforations rather than a constant cut.

Its as if the laser is being pulsed, but not at a very high frequency, i.e probably something like 20 Hz

But as this effect is only happening in the Y axis and the cut parameters are no different for all sides of the 20mm squares I have been cutting, perhaps its a drive motor issue

Any ideas?

[Storen]

I think we should start a new thread for testing different brands and models and discuss the issues. A thread that will be easy to find from people interested in the subject. I am working on some test files that should challenge different aspects of the cutting and engraving process. In a couple of days I'll post them here so we could use the same geometry and have a more strict comparison.


On your question - mine does the same on both axes and the distance between the ridges depends on the speed. As I mentioned in my previous post, I think this issue is caused by the design of the drive system. Most likely is the motor like you said, but it could be alignment, friction, drive, insufficient torque, etc.

[the.sniper]

one suggestion :One thing to try would be Using the same test file. say a rectangle (easy to identify the X from Y no matter the orientation) Then easily swap the Stepper input cables. this will rule out the gantry from the electronics hardware . if the jagged ness stays with the axis. its prob in the gantry.
otherwise start working backwards some more. motor and or driver etc...
*** NOTE I would not Hot swap the cables. do it while their is no power to the controller~.

[the.sniper]

@the.sniper

Sorry. I think I'm confusing things here.

The that was in solution in my water now seems to have come out, and I no longer get micro bubbles in the tube.

The 18mm is distance below the laser air nozzle and the item that is being cut.
I re-measured it, and the plastic tool that came with the machine is 19.8 mm wide.
Attachment 302606

Attachment 302608

From what I've read, the normal distance for this is around 6mm, but I have done some tests and the distance between my nozzle and the item to be cut definitely needs to be about 20mm

The downside of this, is that I don't think there is enough air pressure from the nozzle to quench the flames when cutting MDF or cork. I'm finding it virtually impossible to cut 3mm cork sheet, because using higher power of slower speed just results in more / wider charring rather than deeper cutting. i.e the cut is closing over with carbonized cork.

I was going to attach my 2HP air compressor but I realized that the regulator had packed up, so I will need to get another one before I can have a go at increasing the air supply.

FWiW I would suggest watching this youtube video. Chinese laser cutter tutorial part 6
Very good a and easy to follow along. should address everything you said here! Might be worth adding a "THANKS" to Russ! his vids have been instrumental in my lasing projects.

[RogerClark]

@Storen

Ok. I will start another thread.

[Storen]

High-Res scanned samples of my good old Shenhui can be found here: http://www.cnczone.com/forums/genera...-software.html