Not Just Another Laser Engraving with PVC

[Tweakie]

Excellent result Jeff - I'm certainly not going to count them.

Tweakie.

[JJWMACHINECO]

Thanks Tweakie,

I ordered new timing belt and pulleys to change the ratios to the encoder on my router. Theoretically if I have a shade for every .0001" of movement, then the closest I can get would be a 3.33-1 ratio. Since my Z axis screw is 2.5MM pitch (.0984") then dividing that by 3.33 will give me .0295" to work with on the 0-5V range on the encoder without changing any steps to the motor. If I start out at Z-.0005" for Z zero and set PVC to cut at .0284" depth and PVC creates white in the g-code at Z-.0028" depth, then this should give me .0256" from white to black giving me 256 .0001" incremental moves (shades). My Z axis only moves half that much since it's a 2-1 ratio and still should not effect the focus of the beam.

This would the best I could get with the PVC software and it's shade generation count. I know this is only in theory and there is no way I could actually see or even count all the shade differences, but I just want to try and make any improvements I can to the images I am laser engraving.

I also checked the wattage output of my 445nm laser diode with the 3 element lens today and it's the same as my other laser with only 1W @ full throttle. Dave, you are definitely getting more power out of yours if is truly putting out 1.75W.

Jeff

[dlgabry]

Hi Jeff,
You may not need to change the pulley ratio if your stepper driver board can support micro-stepping. My lead screws are 10 pitch, and directly driven by 200 step per revolution steppers. That should work out to 2000 steps/inch, but my stepper driver board is set up for 1/2 stepping - that means I have to tell Mach that there are 4000 steps per inch. My stepper drivers also support 1/4, 1/8, 1/16 micro-steps, so to add more steps (shades) over the .016" depth needed to get 1 rev of the encoder, I can choose one of those. For example, 1/4 stepping should require an 8000 steps/inch setting in Mach. Not sure if your board supports this, or if you're already using it.
Picked up some birch ply this week, and had to boost the laser to 60% at 40ipm to get a good burn. Need to find wood that's a bit darker than birch with less grain than the luan I was playing with.

Dave

[Tweakie]

Hi Guys,

Dave was saying earlier that (at ½ stepping) it took 64 micro-steps to drive the encoder between 0 and 5 Volts.

What do you consider would be the ideal number of micro-steps to drive the encoder from 0 to 5 Volts ??

Would 256 micro-steps be enough or should I consider more ??

Tweakie.

[JJWMACHINECO]

Dave,

when I setup this router the manual said to set the steps at 640 for the Z axis and that was for metric. I calculated the steps for inch by deviding that number by .03937" and got 16256 steps. I varified it by placing a 1" indicator on the z axis and when I MDI it to move 1.00", it did move 1".00". I do not know what the board is set at, but with my settings, when I move it .0001" I see the stepper and voltage move slightly and the counter in Mach changes .0001" at a time.

Tweakie,

if PVC is only able to create 256 shades, then at my settings it would require 416 steps, or .0256" travel (256 .0001" moves).

Jeff

[JJWMACHINECO]

Would something like this work? http://usdigital.com/assets/datasheets/ ... 9802029574

It has 2 analog output voltage settings, 4.095V and 10V. It requires 4096 counts to go through it's full range, according to them. It's made for an incremental encoder, but maybe there is a way to use the step and direction pins to simulate the encoders pulses up and down. Set it for 10V and only go half the steps or pulses to get 0-5V.

I did look at this first using it with an encoder, but total price changed my mind to the MA3 instead. I did like the idea that I could have zeroed it anywhere, but I'm very happy with the setup I have now.

Jeff

[dlgabry]

Hi Jeff,
I think that's not suitable for using the step and direction lines from Mach3. It's going to expect two pulse trains 90 degrees out of phase one way for up, and 90 degrees out of phase the other way for down. And yeah, it's expensive.
I'm thinking of making another try with the counter/dac idea using some cmos counter chips instead of the LS ttl counters. I think the difficulties I had on the first attempt was due to choosing the wrong counters. They wouldn't work with the opto-isolators I used, and their combined current drain would have been too much to drive directly from the parallel port I think.
If this works, I'd define a phantom axis (like C) and use its step and direction lines to control the counters. That way I can take any amount of steps without worrying about the amount of z-axis movement or pulley ratios.
For the time being, I'm sticking with the ma3 encoder.
Dave

[JJWMACHINECO]

Hi Dave,

As you can tell I'm not a Mach expert and how the step and direction pins work.

I did finish the ratio changes on my router and did a test run. Still need to do some refinements and the wood grain really played havoc on the image, but it came out OK. I scanned it to Grey Scale this time.

Jeff

[dlgabry]

Hi Jeff,
That looks really good! Yeah, a strong grain pattern does tend to mess things around. I've been looking for something that burns as easily as the luan ply I had, but without the grain. Something a bit darker than the birch ply but not so dark as to interfere with the image would be great. Haven't found anything yet though.

I ordered some cmos chips yesterday. If I can make that approach work, I'll post the circuit here in case it might be of use to someone. So far though I've been getting pretty good results with the ma3 encoder.

Dave

[JJWMACHINECO]

Hi Dave.

I need to ask you a question. I tried setting the tool to a V-bit and set CV tolerance to .015 and I did get more detail then before, but what I found out is the code did not run as smooth. There was allot of hesitations and in the darker areas, it left some dark burnt spots because the laser stayed in that area to long at full throttle. Was this the reasons you had to cut the power back to 50% and set PVC not to cut as deep? If not, how did you resolve this problem, or did you even have this problem? I like the detail I'm getting setting PVC to that tool, but the engravings are taking allot longer and it has the hard burning issue going on.

Thanks. Jeff

[dlgabry]

Hi Jeff,
I cut back on the power for a couple of reasons. My laser begins to get quite warm at full throttle, and though the temperature levels out near the 90 degree mark or more eventually, I was concerned that I might fry it. The second reason was that the luan ply I was experimenting with burns incredibly easily - it has a slight reddish tint and I think that's likely the reason for the ease in burning it.

I picked up some birch ply last week, and it does need a higher power level to get the same burn. I've been running at 3 volts (60%) or more and 50 ipm (mach says it's averaging in the mid 40's though).

I have the cv tolerance set to .015, and yes, it slows a bit on sharp transitions in shading. I did a test using a horizontal one-pixel-wide line and rastering at 90 degrees to the line. Without a cv tolerance, the line showed up as a double line with about .020" between them. It got worse as the feed rate was increased. Not sure of the reason, but the laser fired differently when traveling in +y vs -y directions. It looked like a backlash issue, but there is none. Turning off cv or setting a small distance tolerance fixed that problem. At the time, I was doing B/W halftone stuff using the z direction line to modulate the laser.
I'm getting much better results with the encoder, but still have the cv distance tolerance set. I'm cutting as close to a full revolution of the encoder as I can get, and adjusting the maximum modulation voltage level with a 10K pot on the encoder's output line.

In the beginning, I was having trouble at the edges of the image with burning too dark, the plasma setting fixed that.
I wonder if boosting the accelleration rate in mach's motor tuning would help lessen the overburn? I cranked mine up till the motors stalled and then backed it off a bit.
Dave

[JJWMACHINECO]

Thanks for the info Dave.

I had the same problem with the temp getting to high before and that is what the guy that built it said that caused it to fail. I never seen it get more then 92 degrees, but it failed anyway. It was a bad design in my opinion. He had a small fan on it and had holes out the side of the box so not all the air passed through the heat sink. The last time he sent it back to me it had a larger fan on it (in my opinion, was still not big enough) and he also added a LasOrb to it which stops spikes to the laser diode. He tried talking me into Tec cooling (peltier), but he wanted to much for that added on. Here is the fan I used on mine and I directed all the air through the heat sink. This dual fan also blows all the smoke away from where the laser beam is burning the wood.

http://www.ebay.com/itm/370509393811?ss ... 2754wt_699

Jeff

[dlgabry]

Hi Jeff, thanks for the info. I'm pretty sure we have the same laser. There are 4 holes in the beam output end of the box with one taken up by the lens. And one smaller hole in each side of the box. The fan's mounted on the opposite end of the case.
I had given some thought to putting it into a larger enclosure with a larger fan, but I'm not all that comfortable about hacking into this thing. I suppose I can pop the cover off and take a look inside without damaging it. Anything I should watch out for when I do?
The new fan you have looks to be about the same size as the original? Are you powering it from the original laser power supply?

Dave

[JJWMACHINECO]

Dave,

This is what it looks like inside. Basically a rats nest of wiring. For the money paid, I expected a more professional wiring job, but it works.

Rats nest picture 1

Rats nest picture 2

I used the same power supply and it has enough amperage output to handle both the laser driver and the fan, but I do notice when the laser throttles up, the fan slows down. This is an indication that the output of the laser can not be linear. One of my next changes I will be doing is wire a separate power supply for the laser driver and one for the fan. I'm also going to add a Tec cooler to it so the diode does not run any higher then 75 degrees.

Here is pretty much the same power supply that came with it. http://www.ebay.com/itm/200584075987?ss ... 1439.l2649

[dlgabry]

Yup, looks like a bowl of spaghetti w/o the sauce. The diode looks like it's just clamped between two heatsink extrusions? And the thermometer is just measuring the air temp in the box and not the diode itself?

So, I could use the original 12 volt supply to run the laser driver, but would need another to run the new fan, and likely need a larger heat sink too, along with a larger enclosure. Sounds like its time to raid the junk boxes again.

Dave