Not Just Another Laser Engraving with PVC

[JJWMACHINECO]

I got this engraving idea from captaingrayhair and the aluminum engraving he did.

Did Auto Adjust and slightly embossed it in Photo Paint before bringing into PVC.

[hdtheater]

Out of curiosity, where do you display that at?

-Eric

[esteeme1]

I'm sorry but part of seeing the boob is seeing the curve. That’s what, makes it so nice to look at. I find blatant censorship more offensive than exposure. I guess I'm trying to figure out why this picture, is she a hand model?

Really nice process I just purchased PS last night and will be doing some experementing myself.

[JJWMACHINECO]

Out of curiosity, where do you display that at?

-Eric

I use these as my mouse pads. I appears that the little eye on the bottom of the mouse is more responsive to the content of the image it's passing over.

[esteeme1]

Now that's funny. It's probably looking for a ring.

Out of curiosity, where do you display that at?

-Eric

I use these as my mouse pads. I appears that the little eye on the bottom of the mouse is more responsive to the content of the image it's passing over.

[JJWMACHINECO]

Now that's funny. It's probably looking for a ring.

Out of curiosity, where do you display that at?

-Eric

I use these as my mouse pads. I appears that the little eye on the bottom of the mouse is more responsive to the content of the image it's passing over.

Yea, at the end of the day, I have to put that little bugger back in his cage so no funny business goes on after hours when I'm not around. I don't want them to start mass production without me.

[dlgabry]

Don't ever forget to lock him up at night, or he might set up the laser so it works like the one in the movie 'TRON'

Dave

[JJWMACHINECO]

Hi Dave.

On a serious note, I did a test to see how PhotoVcarve interprets the colors into different depths of cut or shades in my case and this is what I found. I took a 256 color pallet and ran it through PVC and lasered it at 40 IPM on birch plywood. This test could be done making a lithophane, but who would want to waist a good piece of Corian on a test like this?

It looks like some colors get processed the same as others based on my test with the laser. Click on the photo below and it should open up and start running.

[dlgabry]

Hi Jeff,
UPS delivered my MA3 encoder yesterday. I still have some playing around to do, but I'm already getting much better results than anything else I've tried. Don't think I'll be going back to B/W or halftones anytime soon. I added a 10K pot to the encoder output so I can set a maximum level because it was burning too dark at full depth of cut.
Dave

[JJWMACHINECO]

Hi Dave.

I found that the MA3 is a very precise way to vary the voltage to the modulation. What I have done to keep the laser from burning so hard in darker areas is speed up the feed rate. With mine 50 IPM is a happy medium to run at. Another way is, based on the ratios that you have setup the encoder on your router to drive it off the Z axis. Just back off the full depth of cut you set the PVC software at.

My full range of 0-5V output on the encoder is .0164". I incrementally go down .0001" until the volt meter jumps to 5V and then back off .0002". I then set Z zero at -.0015" from that point because that is where my laser starts burning the wood slightly. I then set PVC to cut at -.0145" with a retract of .0015" so it turns the laser off completely on the edges. When setting at that depth, PVC will interpret white at -.0014" depth and black at -.0145". The .0002" on each end of the travel is to insure the encoder does not jump to 5V. That .0002" tells me how precise the MA3 encoder tracks the Z axis motion. I'm up to 80 hours run time with no failures.

I did another test to see how wide the laser beam is actually burning at full throttle by scanning it into my computer and then I brought it into my cad program. I then zoomed into that area and measuring the width of the burned line and it turned out to be only .007" wide. I have the tool tip set at .002" so the PVC software finds more detail of the image. By setting it at a .01" step over, I'm actually getting a .003" line in between the burn lines that is not burnt and it lightens the image it up some. If you zoom into the image I posted you can barely see the lines.

Dave when you get everything worked out please post some pictures of your engravings.

Jeff

[dlgabry]

Hi Jeff,
I'm thinking that the depth of cut needs to be close to a full rotation of the encoder for the best results. Even though the encoder has 10 bit resolution, it doesn't mean the laser will have 4096 shades. We're limited by the number of steps needed to get a full rotation of the encoder. For my setup, 0.016" translates into 64 steps, so the best I can do is 64 possible shades for one full rotation of the encoder. Backing off on the depth means fewer steps (shades). That's limited further because once the level for the darkest burn is reached, increasing the laser output doesn't buy much. Same goes for the other end of the range from zero volts to the point where the lightest burn begins.
Using a potentiometer to limit the laser output means that I can keep close to a full rotation of the encoder to maximize the number of shades while not burning beyond the darkest level.

Dave

[dlgabry]

A couple of test runs, taken with my cheesy web-cam. These came out quite a bit darker than the photo shows. Laser power was 50% max at 50ipm, max depth 0.012", stepover .010". Same mechanical parts, 60 tooth pulley on the stepper, 10 tooth on the encoder. Found the pictures here - http://vianaarts.deviantart.com/ Just imported them into photovcarve without alterations, each took about an hour or so.

[JJWMACHINECO]

Dave,

Those look very good. What were your tool settings on those and what size did you engrave those at?

I'm not quite sure I understand your calculations, but I know when I incrementally move my Z axis .0001" at a time, I can see the volt meter move slightly. I know with the naked eye you will not be able to see the difference in the laser burn (shade) with that kind of incremental move. If I set PVC to go .016” full travel depth and white will be generated at Z-.0016” that leaves .0144” for full travel or 144 .0001” incremental moves (shades). I do see in the g-code .0001” incremental moves that PVC does generate.

Your right about me setting zero at Z-.0015 and that I lose those initial shades to begin with because PVC would start at Z -.0016 for white anyway. My laser evidently is not outputing the same watts as yours if you have to cut back to 50% power and only go -.012 on your Z depth. I ordered a laser power meter a couple of days ago and waiting for it to arrive. I wanted to see if I'm realley getting 1.7W max out of it like the seller claimed. It seems like it burns the same as my 1W, but I may be wrong.

I don’t know how many shades the PVC software creates from a color photo, but it can not be very many. Maybe 8-bit (256). I wonder if one of the Vectric Staff will chime in and answer that question? Hello, is there anyone out there???

SILENCE Well not really, this is where you would hear crickets chirping.

They must be all hanging out over at the Aspire forum and forgot about us PVC users.

[BrianM]

....
I don’t know how many shades the PVC software creates from a color photo, but it can not be very many. Maybe 8-bit (256). I wonder if one of the Vectric Staff will chime in and answer that question? Hello, is there anyone out there???

Hi,

The number of grey scales for PVC is 256 which is the limit for a 24bit colour image (as each colour channel is 8bit / 256 levels). Aspire can import 16 bit grey scales to give a much wider range (32,000 or so), but not many graphics package support 16bit grey scales.

Brian

[dlgabry]

Hi Jeff, looks like I lost my update, here it is again.....
My steppers are all 200 steps/rev, lead screws are direct drive (no pulleys), driver board is set for half-stepping. That works out to 4000 half-steps/inch, or 0.00025" per half-step, so a move of 0.016" takes 64 half steps. The motor can't move less than one step even if the g0code says to. that. I can see that on the mach3 mdi screen when I try to move less than the .00025 - the dro doesn't change. I think I could set the driver board for 1/4 or 1/8 stepping and get smaller steps. Yes, PVC can generate moves smaller than one step, but it knows nothing about the stepper/driver/mach settings.

Don't have an oscilloscope these days, but I'd bet it would show 64 stair-steps as it ramps down from zero to -0.016.

I have the same pulley setup as yours for the encoder, 1/6 of a stepper revolution gets me 1 full turn of the encoder.

I have a 1.75 watt 445nm blue laser from the ebay link you posted in your other thread. The encoder output feeds a 15 turn 10K ohm pot from the radio shack parts bin, the pot's wiper feeds the laser modulation input.

Nothing was done to either picture other than load them into photovcarve. The housecat picture is about 5x5", the tiger is about 4.5x6". The tool is defined as a 60 degree V-bit, 50ipm. Mach is set for plasma off, cv distance tolerance of 0.015" - need that on small stuff or the results are blurry. The mach feedrate display shows in the high 40's.

Dave