Chinese laser: Tube current and X axis

[William Dillon]

Hi all,

I received my Chinese laser last week, and I've been working on nailing down all the random issues. I think I've got cooling, air assist and ventilation nailed. Last night I tried my first engraving onto cardboard.



There are obviously a few issues remaining. For one, I'm not sure what the tube current is supposed to be. The instructions say that I'm supposed to use .6A. That's clearly nuts. Because of that, I assumed that them meant 6mA. Therefore, I set the tube current to 6mA. It doesn't seem like that's enough. The tube seems to fire up easily enough, but it seems to decay in some cases after it's on for a while (like one raster line). You can kind of see that on the right edge of the raster engraving. What current level to others drive their 40W generic tubes at?

Another issue in the video that is easily identified is the skipping on the x axis. It's obvious that the stepper is losing steps or skipping teeth on the belt. I'm hoping that I'll just have to tighten the belt, is that likely or do I have some other random problem?

Finally, the head seems to sometimes randomly loose its mind and runs headlong into the side of the machine. It is very important to me that it stop doing this! I'm not coming up with anyone who knows what makes this happen and how to fix it.

I would not be surprised if I end up replacing the mosh board (and moshisoft) wholesale.... :/ The LAOS board is looking appealing. Btw, I've built a reprap and other stepper-motor based projects, and sometimes the extra work of figuring out the problems in open source systems is much easier than banging your head against some crappy closed junk.

[Dave Sheldrake]

Hiya Will,

For one, I'm not sure what the tube current is supposed to be.

*if* its a genuine 40 watt then 16mA, the head looks like a K40 so in that case the tube is a 35 watt so 14.5 mA

do I have some other random problem?

Yup, it's moshidraw, likely the worst piece of software/control system that ever came out of China I'm afraid

Just about up to doing some rubber stamps, put it this way, the tube is the most expensive part of the machine

cheers

Dave

[William Dillon]

Hiya Will,



*if* its a genuine 40 watt then 16mA, the head looks like a K40 so in that case the tube is a 35 watt so 14.5 mA



Yup, it's moshidraw, likely the worst piece of software/control system that ever came out of China I'm afraid

Just about up to doing some rubber stamps, put it this way, the tube is the most expensive part of the machine

cheers

Dave

Thanks, Dave!

Conservatively, I'll start at 10-12mA which would already double the current I'm using.

Luckily, I'm not all that broken up about the controller being junky... It's pretty much what I expected

For now, I'll see if I can tighten the belt some. I'm also considering reducing the raster rare to reduce accel/decel loads. I'm just a hobbyist, so roi is not a great concern.

[Bill George]

Try checking all your connections with a small screwdriver, power off of course. Mine was doing the funky chicken slamming the head over to one side, at random times doing a program. Found a couple of really loose wires on the controller wiring, one so loose it came out of the terminal when I touched it.

The sad part about the K40 laser is by the time you get it all upgraded with a DSP controller and more, you have more invested than what its worth.

[Rich Harman]

Also check that the pulleys are secured to the shafts.

[William Dillon]

Try checking all your connections with a small screwdriver, power off of course. Mine was doing the funky chicken slamming the head over to one side, at random times doing a program. Found a couple of really loose wires on the controller wiring, one so loose it came out of the terminal when I touched it.

I just checked all the screw terminals. They all seem to be secure. (bummer, that would have been an easy fix)

The sad part about the K40 laser is by the time you get it all upgraded with a DSP controller and more, you have more invested than what its worth.

Indeed that is true. I'm not really interested in those DSP controllers in part because of the price, and because I've seen videos on it and wasn't that impressed. I'm considering the LaserOpenSource (LAOS) board: http://redmine.laoslaser.org/projects/laos/wiki

The kit, including display, is around $150 and that seems more reasonable.

Embedded systems and robotics are my day job, which is part of why I'm leaning that direction. Never mind the fact that I'm a Mac/Linux person... ;p

[William Dillon]

Hiya Will,



*if* its a genuine 40 watt then 16mA, the head looks like a K40 so in that case the tube is a 35 watt so 14.5 mA



Yup, it's moshidraw, likely the worst piece of software/control system that ever came out of China I'm afraid

Just about up to doing some rubber stamps, put it this way, the tube is the most expensive part of the machine

cheers

Dave

Well, this isn't good... I tried turning up the power and as I turned the potentiometer up it stayed at 6mA for a while then dropped dramatically and the laser basically quit firing. The good news is that when I turn it back down it comes back to life. I have a thermocouple on the narrow part of the tube near the output coupler and it never read more that 21.5c. I'm not sure what to think. It may be time to call the vendor unless you all have some ideas...

[Bill George]

I just checked all the screw terminals. They all seem to be secure. (bummer, that would have been an easy fix)

Indeed that is true. I'm not really interested in those DSP controllers in part because of the price, and because I've seen videos on it and wasn't that impressed. I'm considering the LaserOpenSource (LAOS) board: http://redmine.laoslaser.org/projects/laos/wiki
The kit, including display, is around $150 and that seems more reasonable.

Embedded systems and robotics are my day job, which is part of why I'm leaning that direction. Never mind the fact that I'm a Mac/Linux person... ;p

Looks like an interesting project from someone (me) who purchased a CNC package for a Mill-Drill used off eBay and had a long expensive learning curve. The software that comes with the LightObject DSP package is worth it. I don't own but was going to purchase when I was planning to build a laser. Once I did the math on building vs purchasing a working unit, (not a K40) it did not work out. Very happy with what I have, my experience in past CNC projects helped me on troubleshooting this one.

[Dave Sheldrake]

Well, this isn't good... I tried turning up the power and as I turned the potentiometer up it stayed at 6mA for a while then dropped dramatically and the laser basically quit firing. The good news is that when I turn it back down it comes back to life. I have a thermocouple on the narrow part of the tube near the output coupler and it never read more that 21.5c. I'm not sure what to think. It may be time to call the vendor unless you all have some ideas...

Hummmmm, possibly a faulty POT, they are unreliable at best and I've seen them come in on brand new machines already dead or faulty (although cheap to replace so no great loss if it's not)

I'd give that a go first

[William Dillon]

Hummmmm, possibly a faulty POT, they are unreliable at best and I've seen them come in on brand new machines already dead or faulty (although cheap to replace so no great loss if it's not)

I'd give that a go first

Yah, it should be easy enough to disconnect the output terminal of the POT and measure the voltage across the range, good idea. I emailed sinmic about what they say the tube current should be to get the ball rolling with the several issues I've identified. This is their response:

This is Mr.Zhang from SINMIC.

I am the after-service engineer for your laser machine.

About your problem:
1. What is the tube current supposed to be? It says .6A in the instructions, but that seems wrong. Is it supposed to be 6mA? If that’s true I have doubts that laser will be able to produce the 50 watts that is was specified to.
The laser tube current is 6MA. The tube's peak power is 50W. But in order to extend the life of the tube please let the tube working in 10%~85% power. As you know this mini machine is mainly used for engraving. So normally no need too much power.

Unless they have magic tubes, I smell bovine excrement. I'm deciding how frustrated I'm going to get with them about that. I re-aligned the mirrors and got a lot more power across the bed than I had previously. So much so that with the air assist off it's really easy to set cardboard on fire. It does take me a few passes to cut through 2-ply cardboard box sides; that seems to be a bit weak.

I'm going to move moshidraw off of the windows virtual machine running on my mac to a dedicated computer that will do nothing other than run the laser. I'm hoping that improves things a bit. I did get spousal approval to buy the other controller board, so I'm likely to do that also.

[Dave Sheldrake]

I've yet to see or hear of a laser that produces 50 watts output in that voltage range using only 6mA of current.

At BEST a DC tube will run to 15% conversion efficiency so the maths is pretty easy at 6mA most DC tubes over 820mm length won't fire let alone produce any power

cheers

Dave

ps: The pre-ionisation charge on a RECI tube is quoted at 4mA to give you some ideas

[Bill George]

I'm going to move moshidraw off of the windows virtual machine running on my mac to a dedicated computer that will do nothing other than run the laser. I'm hoping that improves things a bit. I did get spousal approval to buy the other controller board, so I'm likely to do that also.


With a no dongle DSP controller as LightObject sells it can always be transferred to another machine. I have seen them sold used.
Marco at LightObject also hosts a Forum where all sorts of projects and problems are discussed.
On going discussions of converting K40 machines are common.

Another Forum which I can not post a "hot" link to but exists at: buildlog dot net Not Bull dog but Build Log dot net.


IF your "40 Watt" tube is 700 mm long or less its Not a 40 watt, more like a 30 watt.

[William Dillon]

IF your "40 Watt" tube is 700 mm long or less its Not a 40 watt, more like a 30 watt.

Yup, you got it. It's 710mm. Bummer. Well, I can say with authority that Sinmic are scammers. Let that percolate though the collective knowledge of the site.

I ordered the parts I need for the open source laser controller. They came to $150 without the circuit boards. I'm expecting those to cost about $30. Yet another step on the journey. It's good that I'm doing this as a learning experience, because otherwise I would be getting really pissed!

[Bill George]

Yup, you got it. It's 710mm. Bummer. Well, I can say with authority that Sinmic are scammers. Let that percolate though the collective knowledge of the site.

I ordered the parts I need for the open source laser controller. They came to $150 without the circuit boards. I'm expecting those to cost about $30. Yet another step on the journey. It's good that I'm doing this as a learning experience, because otherwise I would be getting really pissed!

Here is another thing I learned before Not purchasing a K40 machine. Some of the tube power supplies (in those units) can not be controlled except with a manual Pot, which means any software control of power is not possible. So that means replacing the tube PSU also and those are not cheap. Check out the LightObject Forums, lots and lots of posts about what you are going to do.
So by the time you have postage and your time in the conversion board your going to have round numbers 1/2 the cost of a decent DSP controller.... that you know will work when you hook it up. Plus decent software that you can use. BTW I am and have been a Ham since the mid-70's and have built lots of PC board projects. Even made my own circuit boards.

[Dave Sheldrake]

Yup, you got it. It's 710mm. Bummer. Well, I can say with authority that Sinmic are scammers. Let that percolate though the collective knowledge of the site.

I ordered the parts I need for the open source laser controller. They came to $150 without the circuit boards. I'm expecting those to cost about $30. Yet another step on the journey. It's good that I'm doing this as a learning experience, because otherwise I would be getting really pissed!

One of the issues I have with DC tube vendors

The 710 mm tube will peak at 40 watts at max current and voltage (such as when the arc strikes) sadly many vendors (including some well known US based one's) tend to take that as the tubes actual power when in fact running the tube at that level will kill it in a matter of hours.

A 710mm tube in reality has a peak of 38 watts and an effective (read safe) run level output of about 30 - 32 watts, for example RECI state the following for the Z2 series

The working current: test current is 29mA. Maximum working current is 29mA. The running current
must be kept below 27mA. The life span can reach 8,000 hours if the current is kept below 25mA.

Tested at 29mA (this will give 100 watts of output)
Running current 27mA (this will give 90 watts of power)
Max Q for 8,000 hours life 25mA (now you are down to around 75-80 watts)
Life span 10,000 hours (but to achieve this you need to run at no more than 16Kv and 22 mA)(so rendering around 65 watts of ERP)

Yet I still see people advertise the RECI Z2 in a machine as a 100 watt laser! it's not lying but it's not being fully honest either. Back on planet earth to get that 10,000+ hours you need to run it at 65 watts and a stable temperature of no more than 23 degrees C with a +0 / -2 degree variation. Yes they will run to 30 degrees C but the lifetime you will lose is subject to the inverse square law once you exceed 23 degrees!

As to the machine, Weike also make a very similar model and even their sales staff DON'T recommend people buy them!

One of my two pet hates with the laser industry.....

cheers

Dave