Anodized aluminum - finished look

[Jarami Reid]

I have a 60 watt laser. I have been able to get three basic finished looks when engraving anodized aluminum.

The first is a beige engraving that I get when I use a high power or a slow speed or both.

The second is a white marking when I use relatively low power settings and high speeds

And third is a shiny silver engraving.


The problem is I can't seem to repeat the shiny silver engravings on my first pass!

The first time I got this look I was engraving at 100 power and 100 speed,
I got it again today using 50 speed and 100 power using two passes. I need to reproduce these results and I don't understand what is going on.

I have a Trotec speedy 500 and am using high quality engraving and raster correction 1000 dpi and 1000 ppi correction 10, this info may only be pertinent if you have a trotec. but I don't really know

[Mike Null]

It is a waste of time to use HQ engraving. 500 dpi is adequate also as is 500 ppi. You are gaining nothing by using the other settings except using a lot more time. Contrary to popular opinion 1000 dpi will not produce a sharper image and, in fact, with certain materials, will produce a poorer image.

HQ engraving causes the engraving head to move across the entire x axis with every pass. There are few applications for this mode.

Change back to normal engraving and experiment with your settings. Generally the off white look is considered to be the optimum for AA. More power will remove the anodic finsh revealing the plain aluminum. The beige is something I haven't experienced but it sounds almost like scorching.

[Rodne Gold]

Beige is scorching , white is the right mark (leaches the dye use in anodising) , sliver is beyond scorching.
Problem is , all anodising is different the amount of time in the anodising bath , the dyes used , the sealant method varys from plant to plant so the silver result might not be repeatable.
Stick to the white....it can be coloured and does
NOT remove the protective anodising

[Jarami Reid]

The problem is the silver is the look the customer wants.

The thing about high quality engraving is that it ensures that the laser travels the whole distance of the job on each pass - in this particular instance it ensures that there is an even finish to the engraving (instead of a fading off near the ends in the x axis). I know that you can ensure the laser travels the whole distance by creating a white border around your job, but high quality engraving seems like an easier method to achieve this.

So the silver is beyond scorching? I find this hard to get my mind around. Last time a achieved this finish I was engraving at a higher speed than the settings I got the beige/scorched look?

[Jarami Reid]

Another point worth noting is that I had three sample pieces of AA. On both sides of the first two pieces I produced the silver finish, my settings were 100 speed 100 power 1000 ppi and 1000 dpi and 10 correction. With high quality turned on and raster correction enabled.

I am now trying to engrave on the third piece of AA from the same company (anodized in the same bath inches away from my first two samples)., two weeks later and cannot get the silver color - I figure I'm obviously missing something (such as improperly recording my settings from last time), but I'm stumped and frustrated.

Mike - I wouldn't be so sure about the 1000 dpi setting being useless - try cutting circles out of thin acrylic. there are also some other incidental uses such as adding heat to wood engravings to produce dark lettering and such. Maybe you just mean its not advantageous in my AA predicament.

[Rodne Gold]

Well the easy way is to run a few test plots using lets say a 1/2" x 1/2" square and see what settings get you what.
Anodised aluminium relys on dyes soaking into a pourous layer of oxide - the oxide or anodising is normally a whiteish colour , the dye stains it and the dyed anodising is then sealed. If you get a bright silver - then either you are totally overpowering the anodising and the dye and the sealant and getting down to bare metal (destroying the anodising) or you have leached the dye , vaporised whatever is used as a sealant and exposed and *partially* vaporised the anodising which might have been really thin (maybe left shorter in the bath or less current?) and it shows the metal under the anodised layer and thus you might see a more silver than off white ?
A normal rotary or burnishing type engraver would be better if you actually wanted a true silver look.
What you can try is this - engrave normally for the nice white or off white lookj and than use a silver wax like rub'nbuff or silver gilding paste (at hobby shops) and rub it in and clean off excess with turps , the silver wax/paste will sink into the unsealed and leached white portions and give the engraving a more silver look.

If you engrave anodising as it should be done , ie just leach the dye , you have to think like a printer laying down dots of white.
The laser , if raster engraving , will render all graphics using a 1/2 tone , ie it will interpret various shades of grey as matrices of dots , the spacing between these dots is what will give the shading and of course the detail.
Now what one has to bear in mind is this: Due to the lasers spot size (best 0.003") , the material can only hold 300 dots per inch before all these dots overlap - so in reality , using anything more than 2x this in the drawing/graphic is just making more work for the interpreter and the laser - it will not give any more detail and can actually smear the detail due to whats called dot gain... apart from which , the laser is going to take a lot longer to engrave.
Mike was talking about engraving when talking about limiting ppi and dpi - not cutting.
As to adding more heat - well you could actually do the same thing as 1000dpi by just slowing the engraving speed and increasing power.

[Mike Null]

Jarami

The dpi setting is not functional in the vector mode. My reference was to your question about engraving anodized aluminum. (I also try to get darker engraving in wood using higher resolution)

Unless you've experienced problems with a lightly engraved image at the ramping spots (normally seen at the extreme left and right of the table) there is no reason to use HQ engraving.

I do not have the problem with my Speedy 300 in the normal mode. (if I tried engraving an image against the left ruler I could have the problem)

Rodney's explanation of the effect of dpi is correct and anodized aluminum is one of the materials, plastic is another, where using a high dpi is counter-productive.

[Dan Hintz]

The problem is the silver is the look the customer wants.
As Rodney and Mike have already said, the silver is you totally blowing away the oxide layer. Although a new oxidation layer is created immediately, given some time, that bright silver will oxidize more fully to a dull silver unless you coat it. Defeats the purpose and what the customer was looking for.

[Jon Colley]

I hate to disagree with you Mike, but the DPI setting actually does have an effect on vector mode. It's only noticable on small contours (<0.050" radius) but you can see an improvement in the way the driver interprets the vector line from the design package. If you make a 1/16" diameter circle on a 1" x 1" job and print it at 500dpi and then 1000dpi you can see the difference in the job preview (double-clicked not WYSIWYG).

If you are using a 1.5" lens (not available on the Speedy 500) you can get a very slight improvement running at 1000dpi vs. 500dpi on anodized aluminum but with longer lenses you won't see any difference due to the larger spot size. In general, I would agree that 500dpi is the optimal setting for running anodized aluminum on a CO2 system.

[Rodne Gold]

Does the higher dpi when vector cutting/engraving lower the step distance (IE make it more like microstepping) and thus increases the curve resolution?

[Scott Shepherd]

I can't speak for Trotec, but I had my eyes opened several months ago while working through some issues trying to hold tight tolerances on some small items.

Universal told me to increase the resolution tab to the max setting. I said "That's on the raster section, what's that got to do with it, I already have the vector quality set to the highest setting and the PPI is set to 1000, you're telling me the raster setting makes a difference on the vector side of things?".

The answer I got back was "Absolutely".

I found it to be true as well. If I put the raster setting on a lower setting and cut a row of parts, they vary slightly, very slightly, but for this item, it's got something that slips into it so I can check it easily. I find the sizes to be random. When I set the raster mode to it's highest setting and vector, it makes all the items perfect. No variances from one item to the next. I have done 1000's and 1000's of these things and I beat my head against the wall for many hours. Once they explained that to me, I have almost no sizing issues at all.

It was explained to me that setting it to that level sends a better quality image over, for raster and vector.

Corel can only handle one print setting, so if you set the raster low, when it sends the vector over, it will be low too. That's what was explained to me and I have found it to be very true. Of course I didn't like hearing it because it meant if I had a job that has raster and high quality vectors needed (which I do), then I have to send the job over twice, one for lower resolution for rastering, so it's quick to engrave and then once in higher settings so it will allow for high quality vector cutting. I complained about having to send the job over twice and was told "We can't help what Corel does, and it only allows one print setting to go over with the file, so there is no way to send the raster over at low resolution and the vector at high in 1 file".

[Mike Null]

Jon

I stand corrected. I was told originally that dpi would not influence vector settings but you are obviously more informed than I.

Nevertheless, I also stand with the advice I gave relative to anodized aluminum. Since I do a good bit of it I can tell you 1000 dpi is no advantage.

[Tim Bateson]

Oddly enough from some recent work I've done... A lower DPI on vectoring was most notable when the lens/mirrors were less than perfectly clean. A low DPI was vectoring very poorly, a higher DPI was much better. Ultimately cleaning all of my opticals solved everything. I'll try a few more tests.

[Jarami Reid]

thanks dan,

"As Rodney and Mike have already said, the silver is you totally blowing away the oxide layer. Although a new oxidation layer is created immediately, given some time, that bright silver will oxidize more fully to a dull silver unless you coat it. Defeats the purpose and what the customer was looking for.":

I was actually worried about that.

I think I might try the wax rub and buff - does anyone know the name brand of such a product?

It still perplexes me that one day I get one result and a few days later a different one.

[Dan Hintz]

The quality of an anodized finish is highly variable unless the company knows what it is doing... finding a company that is consistently good for a reasonable price is pretty difficult these days.

One of my clients has gone through three anodizers in less than a year because of quality issues. A poor quality anodize will look more putty-like than a good white.

[Michael Hunter]

I get excellent and consistent results when engraving for white, but when I intentionally went for the "silver look" I found that the results were variable and the bare metal often came out blotchy. Also, there was oxide dust all over the work, which then needed cleaning off ...

All my customers now use quality anodisers, but previously one of them had used "The Worst Anodiser in the World" (thankfully now gone out of business) : each batch from this bloke needed wildly different settings to get even barely acceptable engravings. It shows that not all anodising and anodisers are equal.

I run anodised at 1200dpi, as I was getting some banding at 600.
Perhaps a slight out-of-focus coupled with a tad more power would sort this, but my customers like the quality and I'm able to charge accordingly.

[Mike Null]

I totally concur about the wide variance in anodized finishes and finishers. One of my customers had so much trouble that he switched to powder coating and never looked back.

Good for me too as it takes longer to engrave and two passes==more money.