Plywood burning or not cutting thru

[David Borneman]

HI guys,

I am hoping we have a wood cutting expert here that can answer this one.

I am running a chinese (Bogong) 1325 machine with a 100W (130W max) tube with the RD6445G-LM(EC) controller.

We cut 3mm acrylic and 3mm plywood, and are located in Thailand (might be important for this question).

I have cut many different test boxes similar to this:

Capture.PNG

using many different power/speed combinations. This one (85 power) generally allows us to cut thru 22 speed, but 22 will sometimes (frequently actually) not cut every item - only some of them, at least at the moment. I say at the moment because just last week we were cutting at 30-35 speed at 65% power just fine. I strongly suspect part of this is wood quality and humidity. We store our wood in a dry room (aircon unit on DRY mode 24/7), but my supplier does not. And the wood was just delivered yesterday. Thus "Thailand" has to enter in as a variable - both in its humidity and its undoubtedly variable wood quality supply. one shipment is just not going to be of the same quality as the next, etc.

At first I thought we had a optics issue... so I removed and cleaned all the mirrors and lens, and while doing so I noticed there was a small alignment issue so I re-aligned the laser etc. After doing all that, our current wood (the 3 sheets ive cut in the last 2 days) I have to drop the speed down to 18 in order to get a clean cut every time. The problem with this is that the up-side burns quite badly (IMHO) - but the back side looks ok, so we use them backward (we use the back side as the "face").

Now, on top of that... looking at videos online I See people getting nice honey colored cuts after they figure out their optimum cut speed/power... ours are always black. Maybe slightly different degrees of blackness - but all 100% black. Pics of one of todays cuts is attached, front and back plus an attempt to get a closeup of one of the edges - kinda failed, but if you zoom in the focus point is on one of the edges, so you can zoom in quite nicely on that.

Now it is possible... actually probable that I am doing something very wrong here. At least it sure feels like it. But ill be darned if I can figure out what. I am hoping someone here will be able to make me feel really stupid (and thereby solve this problem)

20210715_211948.jpg

20210715_211922.jpg

20210715_211909.jpg

[Gene Uselman]

What are you using for Air Assist- not the supplied air pump I hope? Russ' Ultimate Air with a shop compressor is the best. You need enough air to blow the debris out of the cut and the air flow will tend to blow out any flames on the back side. I suspect you are correct about you quality of wood- you might have to buy more wood so it can dry out as much as possible... drying racks, fans, whatever it takes. We use UV heaters on our wide format prints to help dry the ink, not sure what it would do to plywood. I also buy Baltic Birch plywood which seems to be the best quality and most consistant.

Russ has been experimenting with Gallium Arsenide lenses and they really do cut better in my experience also a wider focus 'zone' so that is not as critical if you have warped wood.

The charring you are getting normally means you need less power of more speed in my experience, alto it could be the wood I suppose.

[David Borneman]

Oh boy. Yes, we are using the included air pump. Pic attached.

20210715_230629.jpg

We do have a good quiet compressor in the shop, and one of the things on my to-do list has been to hook it up instead, but we do not have the right hardware yet (we need some way to limit the air flow - right now we don't have that and the output on the compressor needs to stay high for our other blowing operations).

Another issue I meant to post here eventually is also an issue. Early on in our experiments with this laser when it was news had the controller resetting seemingly randomly during normal use (right when it moved from one cut to another). The "experts" at bogong determined that it was the air valve that turned the air assist on and off. As a result they had me bypass that by just removing the air hoses from the valve on both sides and sticking them together (one hose is slightly larger than the other allowing them to be connected). Then I disabled the ifblow function in the vendor settings. That solved my problem... and they later came back to me with the following instructions, which may seem clear to some of you that know what all this stuff is, but it was obviously badly translated chinese to me:

WhatsApp Image 2021-07-14 at 9.08.38 AM.jpeg

WhatsApp Image 2021-07-14 at 9.10.00 AM.jpeg

here are all the instructions to go with those pics:

Capture.PNG

the... um.. clarity of those instructions are the reason I have not attempted that "fix" yet. So right now the air is blowing full time, no matter if the machine is on and cutting or not - which is the main reason I have slow-rolled my plans to use the compressor instead of the air pump.

now... I take it this is something I need to fast-track? And assuming that's the case, can you make some sense out of those instructions above and translate them in to an actual fix? From what I read it seems she wants me to use 2 new wires attached to the brown and blue in the picture and run them to replace whatever is going to the valve now (or redirecting the wires they are using for that valve to the brown and blue wire positions). Now I am an electronic engineer, so re-wiring something is pretty simple for me, I am just not clear at all on what exactly they want me to do lol.

[Gene Uselman]

The blue and brown wires seem to be to the limit switches- I would figure out what that relay goes to- not sure what that would have to do with limit switches? If you do not have a wiring diagram [which is normal] perhaps this will help to some extent.

.

1318-2_wiring.jpg

[David Borneman]

The blue and brown wires seem to be to the limit switches- I would figure out what that relay goes to- not sure what that would have to do with limit switches? If you do not have a wiring diagram [which is normal] perhaps this will help to some extent.

.1318-2_wiring.jpg

Ya, I am confused too - which is exactly why I have not solved that issue yet. I just don't feel confident in their instructions and that doing what I think they want me to do won't break something lol. When time allows ill get under there and trace the wires and see whats connected to what and go from there.

For now, I just redneck engineered a connection from my compressor to the laser and essentially doubled the airflow that was coming out of the air pump... and so far I like the results. No more burning on the front it seems.. will know in 30m or so. Now just need to figure out how to work it so the compressor isnt on 24/7 lol.

[David Borneman]

Ok so...as with most redneck engineering projects... this one was a fail lol.

The first 4 items in the row cut fine. The 5th and subsequent items in that row all failed. But I think I know the reason. There was water from the compressor squirting thru in enough quantity that I could see it. I assume that was stopping the cutting process - cooling down the material enough to stop the cutting. I will need to buy some sort of a water filter for the air line, if such a thing exists. With the high humidity here the compressor running full time will create a LOT of water. This gives me a direction to work in tho. Its 2am here now, but come morning ill go shopping and see what can be found locally.

So... related question. If I did not want to use my compressor for this, would buying a second air pump and combining them with a simple Y work? would the backpressure from them being connected together cause any issues for the pumps that would stop that from working? Seems like the air pumps produce much drier air than my compressor does for some reason.

[David Borneman]

Ok... So.

I had assumed it was the water stopping the cutting... it kinda made sense. But inspecting my lens I see that I totally destroyed it. I was in the process of trying to clean this thing (luckily I took pics first) when I dropped it...and it shattered. Was my only usable lens at the moment... so im about to hop in the car and boogy to bangkok in hopes of finding someone who stocks these things.

In the meantime... can anyone explain what happened here? How/Why did attaching my air compressor to the laser cause this? Pics attached.

20210716_023009.jpg

20210716_023044.jpg

[David Borneman]

Note, that damage was on the laser side of the lens. Not the material side.

[Gene Uselman]

On the laser side of the lens it almost had to be something landing on the lens and being burnt onto it- I have been doing this for 5+ years and never had anything on that side of the lens. Is there so much smoke/particulate matter floating over the bed that it could settle on the lens. I am not sure what you have for an exhaust fan but with that large a bed it must be substantial. I have a 750W fan evacuating my 4x6 foot cabinet and use auxiliary fans to move the smoke to the exhaust fan- and I have a cabinet which will exhaust better than your flatbed , albeit I cut with the [large] door open. I think you need to take the time to lay in a stock of lenses, mirrors and expendables. I think your shop air compressor is still the way to go- I would think it has a water separator of some sort on it, you just need another regulator/filter feeding the laser- and look at Russ' Air assist setup- I use a variation of it and it is the best I have seen,

[David Borneman]

On the laser side of the lens it almost had to be something landing on the lens and being burnt onto it- I have been doing this for 5+ years and never had anything on that side of the lens. Is there so much smoke/particulate matter floating over the bed that it could settle on the lens. I am not sure what you have for an exhaust fan but with that large a bed it must be substantial. I have a 750W fan evacuating my 4x6 foot cabinet and use auxiliary fans to move the smoke to the exhaust fan- and I have a cabinet which will exhaust better than your flatbed , albeit I cut with the [large] door open. I think you need to take the time to lay in a stock of lenses, mirrors and expendables. I think your shop air compressor is still the way to go- I would think it has a water separator of some sort on it, you just need another regulator/filter feeding the laser- and look at Russ' Air assist setup- I use a variation of it and it is the best I have seen,

My air compressor does not have one, but I purchased one today along with a valve and all the associated hardware. Just need to take the time to connect it all, which I hope I will have time to do tonight.

Yesterday there was a lot of smoke rolling around... that can happen if I don't take the time to stack the bed. I have 2 strong exhaust fans, but with a open bed and no enclosure, it can be tricky. I generally have to lay excess wood/acrylic around the edges of the bed and cover any cracks in the material im cutting etc so that there is a suction from the fans pulling all the smoke down and out the exhaust system. Problem is when cutting a full sheet of material, if items drop thru (as they do) the air will rush in there instead (air will follow the easiest path) and smoke will escape above the cuts. Its a constant fight keeping the smoke going in the right direction. But yes, there was a lot of smoke yesterday since things were not cutting properly. Whatever it was, it totally wrecked a brand new lens :/

I was able to get 1 more lens today, but thats all they had in stock. I have ordered 4 more from china, but it will take weeks to get here... so I am very hesitant on connecting the compressor again lol.