Laser leaves smokey engraveing on vinyl

[Richard De Wilde]

I have a 40w Chinese laser unit. It has been doing a great job up till now.
It has started leaving a burnt or smoke color in the white vinyl layer. It never did this before, it all started when I had to change to a newer computer.
The resolution and axis motion seem great. Do you have any ideas?
Thanks

[Scott Shepherd]

What are you cutting that's vinyl. Cutting vinyl is a no no on a laser. If it's a tiny bit you might get away with it, but it sounds like you've been cutting this for a while to go through to a newer computer. What material are you cutting?

[Dave Sheldrake]

What machine and what Vinyl Richard (Hiya Scotty ltns) :)

In general any chlorinated plastic is going to destroy your machine, it won't really matter though as it will probably kill you long before the machine dies :(

[Kev Williams]

I'm thinking 'his' vinyl and actual vinyl might be 2 different things?

I've engraved (never cut) a crapload of PVC, and there's always soot, and it's always rust colored.

Since he wasn't getting his 'smoke layer' before, and the reference to the 'white vinyl layer', I'm thinking the 'vinyl' he's cutting may Rowmark or some other laminate...

[Richard De Wilde]

You are right, I am using Rowmark laminate. Same material I use for name badges.
It has always engraved clean and neat. Suddenly, with no apparent cause, it is leaving sooty streaks in the cuts. These sooty streaks are burned in, and cannot be cleaned off. I wonder if one of the configuration parameters might have changed on me. But, I don't know where to start.

[Kev Williams]

Out of focus or a loose lens will cause that...

[Richard De Wilde]

You are right about out of focus. I changed my final lens to a new unused one, at it cleared it right up. Thank You-Thank You.
I have been cutting much smaller font lately, and no problem showed up. This project required 1" characters.
Maybe you could answer two more questions. 1-Is there a KEHUE dealer in the states that will answer technique questions?
2-Do you have suggested settings for printing jpegs on wood?
Thanks again,
Richard

[David Somers]

Richard,

Perhaps I am reading more into your message above than you meant. But you said the problem was focus, but that changing to a new lens corrected it? Those two statements don't necessarily go together.

Did you look to see if your original lens was dirty? The last time you removed and cleaned it are you sure you put in back in firmly set on its seat, and firmly held by its retaining screw/ring? And was it put back with the convex side up? Perhaps just cleaning it would have corrected the problem? If you did remove it and clean it did you check to see if it was in its tube firmly with the convex side up? When you replaced it did you put the new lens in oriented the same way as the original lens? (Convex side up is what is recommended) If the original was clean when you replaced it did you refocus after the replacement?

Regarding jpegs on wood....I hate saying this, but it depends. On the wood? On your laser and its alignment and the age, power, and health of your laser tube, the cleanliness of your mirrors and lens, if your table is on a place parallel to the X and Y axis of the gantry, etc etc etc. The best you can do is to have a good method for developing a good graphic to work with. (search for Gold Method in this forum) and then do tests on samples of the wood your final will be on. And remember that the next piece of wood, same species, even from the same length of lumber, may require different settings to get a good result. If my machine were identical to yours my settings are as likely to fail for you as they are to work. Testing is your friend.

[Doug Fisher]

>>1-Is there a KEHUE dealer in the states<<

If you meant, Ke Hui, the answer is no.

[Richard De Wilde]

Dave,
You guess that maybe the lens was dirty could be correct. I thought about that after replacing it.
But I was under pressure to get this job out and took the quickest action.
The material I have been using on another job creates a lot of smoke. Even though I have a beefed up exhaust
system, when engraving furthest from the exhaust port, more smoke than I like is getting to the lens.
I am in the process of figuring out how to add an effective blowing fan as well.

Regarding the jpegs on wood, you are correct about different woods producing different results. But I have yet to find
a satisfactory setting to achieve the quality I want, on any wood.

Thanks for your inputs.

Richard

[David Somers]

Richard,

Do you have an air assist on your machine? That is an air pump that blows air through a tube and into the nose cone of your lens tube, below the lens. The idea is that you have positive pressure air coming out the cone, preventing smoke and fumes from going back up to the cone to the lens. It also can have an effect on your cutting and or engraving since smoke will reduce the effectiveness of your laser beam coming out of the cone. If you do not have that I would had it for a number of reasons. It should not be difficult. Most likely a replacement for your cone tip. Plus some air hose and an air pump similar to an aquarium pump.

On the Jpgs. Make a grid or pattern with a number of small, simple jpgs in them. Burn each one at a different setting, bracketing each different graphic with a different setting. You can test a bunch of settings that way without having to do each individually. If best result is unacceptable, try defocusing the beam a smidgeon. Do the bracket test again and see how that works.

[Richard De Wilde]

Dave,
Thank you for your suggestions.
No I don't have air assist and nose cone yet. But it makes sense, I had nose cone vacuum on my rotary and it really helped.
I will start looking for one. It would make more sense than an added area fan.

On the jpegs. Was your comment to change settings to mean: power, speed, or configurations?
Richard

[David Somers]

Hi Richard,

Normally a test grid would have one axis of the grid be power, and the other axis being speed. You would typically put what you think is the correct setting roughly in the middle of the pattern so you can see how it looks with settings both above and below it. There should be some examples of a test grid here if you do a search for test grid.

This is one short thread with some examples that might get you started.
http://www.sawmillcreek.org/showthread.php?157577-engraving-settings-test-template-what-do-you-use&highlight=test+strip

Hi Richard,

BTW. I don't believe you want to consider a vacuum in the nose cone since you would be pulling smoke/fumes INTO the cone and exposing the lens to that stuff. Use a blower like an aquarium bubbler with a high enough output to push through the cone so it exits the bottom of the cone, keeping smoke/fumes away from your lens. That will also help clear the kerf and work surface and make your cuts more efficient since the beam doesn't have to get through opaque smoke. The little unit you add to the cone will have a nipple to accept the air hose from the air pump, and it should also have a valve on it so you can control the amount of air being send through the cone.