4.0 Universal laser lens kit

[Keith Colson]

I am considering buying a 4.0 lens/mirror kit for my VLS6.60 but I need some advice first. I do laser engrave some stainless wine buckets that are too big to spin on my rotary so I think the 4.0 would be a win there.

1) If I get one of these kits will my laser cut through 12mm plywood. It is not something I want to do often but would be useful once in a while. I am not concerned about charring but my 2.0 lens is not up for it at all.

2) If it does cut through okay, what is the thickest plywood I could cut?

3) Is there a discount supplier that has good deals or aftermarket parts so I don't have to pay full price. e.g. I got a mirror off Ebay that works perfectly for 20 bucks instead of 100+

Cheers
Keith

[Mike Null]

Keith

Can't answer your questions but I do plates in brass or pewter then curve them and apply to the buckets.

[Scott Shepherd]

Keith, the 4.0 lens doesn't give you more power, so if you can't cut through 12mm ply now, you won't be with that. Also, if the bucket is too large to spin on the rotary, when you put the 4" lens on, there's a great chance you won't have enough travel to focus the 4" lens. The 4" lens is a LONG way from the work piece, so you need to check those measurements. I ran into that same situation not too long ago. Customer had a tall, odd shaped piece and the 4" is the only thing that would work, but once inside the laser, it was too close to the lens, so I couldn't focus it.

[David Somers]

Keith,

I can't add anything to the comments about cutting 12mm stock with a 4.0. But I do have a thought on the rotary issue. I don't know the VLS6.6 construction, but you are clearly handy making adaptations to things as evidenced by your mirror setup for cutting a bevel that we were all following.

So....if there is room in the machine could you remove your main table in the laser and replace it with a shorter pair of tables, one at either side of the laser, that could hold the left and right fixtures of the rotary with an open space beneath them? That would resolve the issue of diameter limitation.

The complication, if I remember a ULS rotary correctly, is that the rotary has a solid piece of metal that runs from the head stock to the tail stock, making it one unit. That is what is limiting your diameter. So this would only work if you could remove that horizontal "bed" so that your head and tail stock are now independent units and that bed is not limiting the diameter of your piece.

Assuming my laser ever leaves the container ship it is vacationing on out in Elliot Bay (dock workers slow down in effect) I have a number of plans in my mind for modifying my rotary to handle odd ball needs like that.

If that didn't make sense just PM me and I will sketch out what I was thinking of.

[Richard Rumancik]

Keith, I think you might be disappointed trying to mark graphics on a round object without rotating it. Although the bucket has a large radius of curvature, you still have to average the focal point. That means that most of the mark will be out of the optimum focal point. If doing a small logo it could be tolerable but if you have .25" or more from "top to bottom" of the mark I don't think you will get a crisp mark. It will probably look fuzzy on the ends of the graphic.

As well, since the 4" lens has a much larger spot size than a 2" lens, this will work against you as well. You can't improve it much by increasing resolution, because if the spot size is .008" or more and you plot at say 300 dpi, the ratio of spot size to step size is not optimum.

I recall a magazine article where the author was marking stainless flasks which had a curvature. What he suggested was to mark the Cermark twice - once at the lower end of the curvature and again at the higher end. This could help improve the crispness of the mark, but it means double the laser time.

If you think it is worthwhile to rebuild your laser table and rotary as David suggests, that could work, but it might be a lot of hours invested. I would probably lean towards Mike's idea of using a separate tag for the graphic, especially if it is a one-time job.

I built a special table for my laser from birch plywood many years ago to be able to mark a large box that I couldn't fit otherwise. It had a recessed center section to accommodate the box height. It took quite a bit of work to design and build it, and it worked fine - unfortunately, the job never materialized and I have never had a need for it since.

[Keith Colson]

Thanks for all the responses

Scott, you are dead right on the nozzle clearance to the bucket. I tested it and when I engrave buckets. Right now I have 2mm left on the Z travel so the 4.0 lens would not work.

FYI I am getting perfect results on my stainless buckets. I am just limited to a width of 45mm before the focus goes "too bad". I also laser cut a fixture which lets me re-run the same bucket if a mistake is made. e.g. a scratch in the Cermark. I cut my first can of Cermark open after it died. I got a lot of paint out of it and its super handy for little touch up jobs on spot painting.

I still have the open question of what is the thickest ply I can cut with the 4.0 lens? I wonder if the local agent has one I can borrow to try.

Cheers
Keith

[Scott Shepherd]

I still have the open question of what is the thickest ply I can cut with the 4.0 lens? I wonder if the local agent has one I can borrow to try.

Cheers
Keith

Why do you think you can cut thicker ply with the 4" lens? That's just not true. If you want to know the thickest ply you can cut, put your 2" lens in and see. If you can't cut it with the 2", you're not going to cut it with the 4". The 4" doesn't give you any magical solution to more power, in fact, it will probably won't cut AS thick. The beam being bigger, the power is spread out over a larger area, making it less powerful than the 2". A long time ago, I thought the 4" would be the saving grace for cutting things. It didn't take me but one afternoon of testing to realize it wasn't.

[Chris Corwin]

A 4" lens would just minimize the angle of your kerf.

[Dan Hintz]

I'll also add (since I don't think I read anyone else bringing it up)... with the 4" lens have a much lower power density than your 2" (roughly 25%), you will need to go even slower than you currently do to use Cermark on stainless (assuming you have enough power density at all to accomplish the mark).

[Scott Shepherd]

I'll also add (since I don't think I read anyone else bringing it up)... with the 4" lens have a much lower power density than your 2" (roughly 25%), you will need to go even slower than you currently do to use Cermark on stainless (assuming you have enough power density at all to accomplish the mark).

Oh come on Dan, I finally say something right and you miss it? :p

"The beam being bigger, the power is spread out over a larger area, making it less powerful than the 2". "

[Dan Hintz]

Oh come on Dan, I finally say something right and you miss it? :p

"The beam being bigger, the power is spread out over a larger area, making it less powerful than the 2". "

I saw that, but I wanted to be specific since he was marking stainless (presumably with Cermark).

[Glen Monaghan]

The longer focal length would keep the beam "in focus" over a greater depth/distance so can be helpful when engraving curved/uneven surfaces to get a consistent result across the height variations. However, as said, the focal image (spot size) will be larger as well so you can't engrave as fine of details as you can with shorter focal lengths, plus the larger spot size means you have lower power density so not as good "cutting power". That said, assuming you can still cut through a particular thickness with the longer focal length/lower power density, you'll have a somewhat straighter or less beveled edges with the longer focal length (more angled or beveled with shorter focal length). Whether the edge difference is significant may be very subjective and highly dependent on material and applications.

[Keith Colson]

I have cut 18mm mdf with my 2.0 and I found the kerf got so wide at the bottom that it would burn badly. I was "hoping" the 4.0 with its longer hourglass would make the last bit of the cut easier. I do understand about the drop in the power but was curious to find out had anyone done the experiment with some quantified results.

Cheers
Keith

[Scott Shepherd]

I have cut 18mm mdf with my 2.0 and I found the kerf got so wide at the bottom that it would burn badly. I was "hoping" the 4.0 with its longer hourglass would make the last bit of the cut easier. I do understand about the drop in the power but was curious to find out had anyone done the experiment with some quantified results.

Cheers
Keith

I haven't charted my results but I do know what works and what doesn't work, and a 4" lens isn't going to cut any thicker materials.

[Keith Colson]

Why do you think you can cut thicker ply with the 4" lens? That's just not true.

I just read through "Lens-Details-Co2-and-Beam-Expander.pdf" by Universal and they clearly state that a 2.5 and a 3.0 lens will cut thicker materials than a 2.0 lens. While they don't say the 4.0 will cut thicker they do say the longer 2.5 and 3.0 focus will. I cannot get a 3.0 lens for my machine but I can get a 2.5

[Scott Shepherd]

They can say it all they want, it's not true. I've been running a Universal for 6 or 7 years now. It's not going to happen. I suspect their words are not for all materials. Will a 4" lens cut SOME thicker materials? Probably. Is wood one of them? No. Is acrylic one of them? No. Is foam one of them? Possibly.

I have the lenses, I'll gladly run the test to prove it won't cut any thicker wood (in fact, the results were worse with the 4" because the air assist doesn't reach the work and it burns the heck out of it all), but the fatter beam wanted to drift off when cutting denser woods and MDF. I had a client insist I laser cut 1/2" thick hardwoods. Despite me telling him it wouldn't work, he insisted we try it. I put him on the clock, put the 2" and 4" lenses in, and ran the tests. Neither lens would do the job and the 4" gave the worst results. I charged him, he paid me, walked out, and I've never seen him again.

[Keith Colson]

Scott, I am in agreement that the 4" lens won't do any better. Its the 2.5 and 3" that's in question.

[Dan Hintz]

I just read through "Lens-Details-Co2-and-Beam-Expander.pdf" by Universal and they clearly state that a 2.5 and a 3.0 lens will cut thicker materials than a 2.0 lens. While they don't say the 4.0 will cut thicker they do say the longer 2.5 and 3.0 focus will. I cannot get a 3.0 lens for my machine but I can get a 2.5

It's a bit misleading, I admit. The reasoning for being able to cut thicker materials with a longer focal length lens is the focal range (that area where the spot size does not increase more than around 50% of the smallest waste size) is itself, longer. However, that assumes you can throw an infinite amount of power at something (or at least a significantly higher power than the material needs at the true focal point to burn). Since we do not have infinite power sources, this only holds true for easily-burned materials (let's say, like foam). Once you add in a hard-to-burn material, like wood, the power density drops off too readily. The HAZ of the material plays a big role in this.

[Scott Shepherd]

Scott, I am in agreement that the 4" lens won't do any better. Its the 2.5 and 3" that's in question.

I have a 1.5", 2.0", 2.5", and 4.0". Will the 2.5" cut thicker materials than the 1.5"? Sure will. Will the 2.5" cut thicker than 2? No.

[Mike Lassiter]

I have been cutting a lot of 1/4" MDF for someone last several months. With my large cutting area (24x48) some of the sheets are less than flat. Some I have to use masking tape on the corners trying to hold the sheet down flat. Sheets are cut down from full sized sheets that actually measure 49"x 97" so every one is wider than the cutting table will accommodate and I have to run a file on everyone to cut the sheet to 24"x48" as the sheet is sitting above the honeycomb on the far right and bottom. Once the sheet is trimmed it will drop down onto the honeycomb. I remove the trimmed part them run the file. What I find is cutting with the 2" lens and air assist cone the kerf is so narrow the parts cut out get pinched in the sheet as I try to remove them, and using a 2" lens cutting if the sheet is bowed there are other areas that will not fully cut through and require running the file again. Most anything cutout results in the parts being bound in the sheet and hard to remove, especially if I have a very large or several fairly large items on the sheet. Using the 3" lens the cuts have a wider kerf, that allows the sheet to be easily lifted and the cutout parts remain on the honeycomb table without binding. The bowed sheets are rarely a problem as the 3" lens easily allows for some less than ideal focus areas to cut fully the first time. I believe the 3" lens did require a slightly slower cutting speed (4.1% 2" lens to 3.8% 3" lens) but having the parts freely cut so the sheet can be lifted off the table and the parts cut out all left in place and slightly bowed sheets cutting the first time more than makes up for the slight slowdown in cutting speed IMO. I have to us the air assist sweep for the 3" lens lowered fully down, instead of the cone. Got both when we purchased the laser. The 3" lens will not work with the air assist CONE on my laser - the beam hits the cone and heats it up ( a hard lesson learned )

[Keith Colson]

Thanks Mike

That is some really interesting quantified information. One thing I thought of that maybe of use. If you got your air assist nozzle 3d printed it would burn a path through the nozzle where needed. It would take the issue of alignment away. If I do buy a longer focus lens I may trey this, I really like using the nozzle as much as possible as it keeps the lens clean and lets you blow out flames on the target work.

I was most interested in your point that the parts come out easily. When I make some complicated cake toppers that would be a handy feature.

Cheers
Keith

[Dan Hintz]

If you got your air assist nozzle 3d printed it would burn a path through the nozzle where needed. It would take the issue of alignment away.

Not the best idea. The outer edges of the beam will not have enough power density to melt/blow through the plastic, and therefore it will always be blocked. This will have the effect of always reducing your possible power at the focal point. Nothing like purchasing a 60W tube and only getting 50W to the substrate...

[Keith Colson]

Not the best idea. The outer edges of the beam will not have enough power density to melt/blow through the plastic, and therefore it will always be blocked. This will have the effect of always reducing your possible power at the focal point. Nothing like purchasing a 60W tube and only getting 50W to the substrate...

It is not possible to dissipate 10 watts in a 1mm ^3 of low temperature plastic. Some ballpark calculations puts it under 1/4W. My laser varies more in power with my room temperature.

[Matt McCoy]

It is not possible to dissipate 10 watts in a 1mm ^3 of low temperature plastic. Some ballpark calculations puts it under 1/4W. My laser varies more in power with my room temperature.

What about adding the baby bottle nipple hack to the end of the 3D printed piece?

http://www.sawmillcreek.org/showthread.php?225296-Optimal-air-assist-configuration-to-prevent-fire!&p=2350207#post2350207

[Mike Lassiter]

both air assist attachments have micro small magnets that tell the driver they are installed. I thought my cone was plastic, until I carelessly left it on and put the sweep on too. (Still cannot understand how I didn't notice thae cone as I had to work around it to attach the sweep) but when the beam hit it it got extremely hot. It in fact is black annodised aluminum and now a grayish color at tip. If either is installed the driver will not start the laser when the air is not turned on. Note I have to manually turn air on I don't have the driver controlled option. So, for my laser while the driver doesn't have to know air is on or off it is a nice safety feature that will pop up a window telling you the air pressure is low and does NOT start the laser.

[Dan Hintz]

It is not possible to dissipate 10 watts in a 1mm ^3 of low temperature plastic. Some ballpark calculations puts it under 1/4W. My laser varies more in power with my room temperature.

The 10W loss was an off-the-cuff figure and not meant to be taken literally, but you also have to remember that we're not talking about all of that power in a tight focal point. Even with the wrong aluminum cone installed, the power loss is quite measurable at the substrate, and the cone may not get any more than warm to the touch... that's not enough to melt plastic out of the way. Plus, I'd love to know how you came up with that 0.25W loss figure...

[Chris Corwin]

You could always use the lasered hole in the print to act as a pilot hole for a drill bit. Then you could maximize your output and have a cheap air assist nozzle. I think I might do this for my epilog!

Edit: changer layered to lasered, damn auto correct......

[Keith Colson]

Chris, thats a really good idea. I would be interested to see if PLA is up for the job, the heat may be a challenge. That said you have the option of ABS or even better Nylon. When I get time I will print one out of PLA for a test. The cool thing is the 3d cad is easy to do. If I do I well let the laser cut the hole and see if my estimation of negligible power loss is correct.

Dan my Ballpark calculation was based on an 0805 resistor dissipating 1/2 watt will easily melt PLA. Divide that by 2 for size and margin gives a 1/4 watt. (an 0805 resistor is not rated for 1/2 a watt but will run for a period long enough to test this if you so desire.)