PDA

View Full Version : Need some advice



Allan Longson
08-25-2011, 2:02 AM
Hi All

We are cutting a veneer wood, front and back on 3mm mdf, veneer is matai. We are currently making book covers which have a lasered logo on them and we laser holes on the edge so we can bind the covers together. We are using 400 x 800 sheets on a 60W Universal laser with a 3" lens. The lens is new and the bed is level, machine is about 2 years old.
The issue we have is vectoring the holes for the bindings. On the sheet we will lay out 16 book covers (A5) and start the print job, the logos cut out fine but for every second row of books the holes for the ring binders will not cut thru. The problem is intermittent, one row is fine, the next row isn't. I don't think it has anything to do with how far the vector is from the laser, top or bottom rows, left or right corners have the same problem.
It's as though on a particular horizontal axis the laser does not have enough power?
Anyone got any thoughts as to why you get intermittent results over a whole sheet.

And can anyone explain the logic that Universal use for a print job? Like why will it start at the top right corner, do a vector and then move to the middle of the sheet for the next vector and then move to the side for the next vector?
Why are some holes vectored counter clockwise and others clockwise? Whateverprint logic they are using seems to be horribly inefficient or are we not setting the job up correctly in Coral before submitting it?

Rodne Gold
08-25-2011, 3:33 AM
Firstly , I would change to a 2" for the extra power density.
You can re arrange the order of cuts in corel , but your laser driver should have an optimisation section , try using it if it does , if not you can only use Corel
Generally only the driver will enable you to change the direction of cuts and their start points , but I don't think you can do this on yours.
The variable power thing is most likely alignement of the beam if it drops off at the same place on the laser bed , it could be a hump at that particular point on the honeycomb or whatever supporting table you use.
Re align the beam making sure it is aligned at all points on the table and check the level again , however check it with the board and support , ie run the head and stop at different points on the stuff you cutting to see that the distance between head and material is always the same.

Allan Longson
08-25-2011, 4:55 AM
How do you organise the order of cuts in Corel? We have tried by using the tab order but this made no difference.

We had a 2" lens and had similar problems however this lens may have been damaged, hence the chinese replacement which works well but has a different focal length of 3". In other words,we order a 19.05" diameter lens with a 2" focus from the chinese supplier and when we installed it the focus point was 1" deeper.
I thought the longer focal length gives a longer cutting zone and as we are working with wood that is nearly 4mm thick (this is at the limits of a 2" lens) therefore a 3" focus lens would be better?

Rodne Gold
08-25-2011, 5:18 AM
You need to use the object manager in Corel.
The 3" lens will allow for cutting thicker stuff , but the 2" should be fine for 4mm albeit at the limits....

The thing is , the energy concentrated on the smaller spot size of a 2" lens will promote a much cleaner cut than a 3" , thus reducing charring , more importantly the cut width will be smaller, the downside is the lens is nearer the material and can get contaminated. Think of it like trying to burn a hole in a piece of paper with either a small pencil blowtorch or a bic lighter , both will do the job but the hole with the blowtorch will be more precise and neater than the messy hole you get with the BIC.
If the 3" works for you , well then leave it be :)

Mike Null
08-25-2011, 6:23 AM
I think Rodney has given you all the correct answers but to emphasize--be sure your laser is focused at all points on the table and that the material is flat.

I cut a lot of wood, usually 3mm, and I find that I have to clean my lens numerous times (at least every hour) during a job in order to maintain quality cuts. I always use air assist during cutting operations.

I assume you have tried slowing your speed and increasing power. Have you varied the hertz/ppi/dpi--whatever ULS calls frequency.

Allan Longson
08-25-2011, 6:56 AM
Thanks Rodney for the tip on Corel, will try that tomorrow.

I forgot to add that I spent 2 hours levelling the honeycomb bed, it would be within 0.5mm to the head of the laser over the entire bed, measured every 10cm! Our material is flat as it is stored flat in sheets. We are aware of a dirty lens, the wood we are using is particularly dirty and produces lots of smoke, resin etc. Now that we have a longer focus the lens isn't getting anywhere near as dirty, we are now cleaning it every hour or so instead of every sheet. We have found air assist with the cone on only made matters worse so we are in the middle of doing an air assist mod such as Rodney has posted here (many thanks again to Rodney).
We have spent quite a while playing with speed and power, currently at 5% speed and 100% power. Any slower and the charring / debris from the cuts almost makes the job unusable.
As it is just the holes that don't cut properly, I'm wondering if it could possibly be a software issue - ie the holes in particular groups are cutting to fast? Why does one row not cut but the row 6" underneath cuts perfectly? Is there any way to vary the speed of different vector points in a print job ie have a line cut faster but holes cut slower?
ULS calls it dpi and we have fiddled with this till the cows come home.
I might get the service tech around and give the problem to him, not sure I want the answer if he says our laser unit might be in trouble.....

Rodne Gold
08-25-2011, 9:56 AM
Why not just mark the hole centres and drill em with a drill press.

Dee Gallo
08-25-2011, 10:46 AM
I agree with Rodney. I have a similar thing where I have to make holes in small bamboo items and I tried using the laser while it was already doing the engraving. What I got was not the nice clean hole my drill press makes, but a charred little black hole which I don't like much. I don't have thousands to make, so for forty holes, the drill press is a better option for me. Once you make a simple jig, the lining up is nothing and it goes quickly. It does help to raster the hole position.

cheers, dee

Scott Shepherd
08-25-2011, 11:08 AM
What version driver are you using?

Also, what are you image density settings? What quality level is your vector quality set on, and in the vector settings, are you using "Enhance and Sort", "Sort", or "None"?

Michael Kowalczyk
08-25-2011, 1:09 PM
Allan,
Not familiar with a Chinese laser, if that is what you have, but since you are using Corel Draw, you can map your vectors by color. For me, I almost always use Blue for all interior vector cuts and Desert Blue for final exterior cuts. You almost always want to cut your interior vectors first just in case your material moves after the exterior vector is cut. This way you can adjust your speed and power to the color instead of the sheet. You may need to slow the interior cuts down a little because they are doing cross grain cuts.

I used "almost always" because there are exceptions to this rule. Just haven't found one yet.:rolleyes:

Please add your laser info and location to you signature and profile, so we might be able better assist you. (See example below;))

Hope this helps and ...

Richard Rumancik
08-25-2011, 1:26 PM
Is there any way to vary the speed of different vector points in a print job ie have a line cut faster but holes cut slower? . . .

From your description this sounds like a really odd problem where every second row will not cut properly. I can't think of a possible reason offhand. Levelling is a good idea but out-of-level can't cause this kind of problem.

When you say the problem is "intermittent" what do you mean? Does the problem come and go randomly? If it is repeatable (always the same rows don't cut) then you have a chance of solving it but if it is truly intermittent/random then finding the answer will be difficult.

Maybe you need to time the cutting of rows with a stopwatch to see if the elapsed time is actually different. With a single color it shouldn't be.

If the problem is repeatable, then as a temporary work-around you can color-code the vector objects so row 1, 3, 5 etc cut at one power/speed level and holes in row 2, 4, 6 cut at another power/speed level. The straight lines could be a third color. (By the way, make sure you are using RGB colors in CorelDraw and you are using a proper RGB palette to map to. Is there any chance that there is some corruption in the file i.e. the "bad" rows are an invalid vector color? Check the color of good rows vs. bad rows.)

To answer another quastion - there are three main ways a laser driver can organize cutting order - by layer, color, and by "order" on the layer (i.e. front to back position). If everything is on one layer/one color then it is just controlled by the "order". So on a specific layer, if you pick an object, and send it "to back", then select another object -> to back etc then eventually they will be in an ordered sequence such that the LAST object sent "to back" will cut first (as it is furthest back; the first one send to the back will be pushed to the front.)

At least this is how GCC works. Others might be reversed - perhaps someone can help here with Universal mode of operation. You can also use object manager tools as Rodne suggested but I usually find that confusing if there are a lot of shapes.

I suppose grouping can also have a factor in the sequence of cutting. If you group 3 holes and duplicate the group, then it will cut the three in sequence as a group instead of hopping around. You need to experiment with your driver.

You can drag a whole layer down/up the list in the object manager to change the sequence that the layer cuts. eg if one layer was "holes" and another was "outline" you can control whether "holes" or "outline" cuts first by where it appears in the object manager list.

Craig Matheny
08-25-2011, 6:38 PM
I have never cut it but isn't MDF a tough board to cut in the first place due to the glue, now add a glued veneer? If this is random it can easily be a glue issue being one area is denser then the other and the laser needs to slow down for the curved cuts. I cut straight 3mm birch at 30 sp but if I have curves down to 16 sp. As Richard said color Map your curves to a higher power. I know there is a Light Density board that has been talked about on the forums maybe get your stuff laid up using that instead of MDF.

Allan Longson
08-25-2011, 6:56 PM
thanks to all your replies so far.
I've added details of the unit to my sig. Image density is 5, Vector quality is standard and we are using enhance and sort.
I've added an image to show the problem. Here you see the holes, the first 5 cut fine and then the following 5 didn't, like it got half way thru the job and ran out of puff.... Sometimes the cut is only just short of making it thru the wood and other times it isn't even close to making it thru. I could understand if it was the density or the cross grain and we were getting entire sections of the wood not cutting but as you can see here, some holes cut and some didn't and the edge of the cover cut fine which is only 10mm from the holes that didn't cut.
206051

Can I also add that as the day wore on the issue got worse. Prior to lunch time everything was going ok but after lunch we started to get intermittent failures which gradually led to sections all across the sheet of wood not cutting thru properly. There is no rhyme or reason that we can tell as to why a line will cut yet a hole that is 10mm away will not.

Allan Longson
08-25-2011, 7:11 PM
You raise a good point and it is something we are mulling over all the time. However we can go for hours merrily cutting away at this stuff having no problems at all and then things slowly start to go wrong. If it was an mdf / glue issue I'd expect to see problems in nearly every sheet we cut all the time but this is not the case.

Craig Matheny
08-25-2011, 7:47 PM
How is the temperature in the area of the machine?

Allan Longson
08-25-2011, 8:10 PM
Beautiful sunny almost spring time day down here in good old New Zealand, around 16 degrees and the past week has been like this.

Allan Longson
08-25-2011, 9:31 PM
An update which explains a lot of what is happening but not why. We loaded the various graphic files we have been printing and started them off with the cover open. We made note of what vectors it each print job started on first and then checked these with our faulty cuts. At this stage, we have determined that all of the first vector cuts in each print job are not cutting thru properly. It's as though the laser has to vector cut for about 2 minutes before it reaches full power. We proved this by doing a cut on the bed, noting which vectors cut first (a row of holes). After the job was finished we confirmed the first lot of holes did not cut through, on lifting the sheet off the bed you could see this clearly because of the resin left behind. Where the hole did not cut thru there was just a dot of resin and as you move along the holes this dot slowly changed into a complete circle, but it took around 40 holes before it got there.
So can anyone shed a light as to why the laser needs to "warm up" at the start of each print job?

Allan Longson
08-26-2011, 5:42 PM
Also etching before vectoring does not help, the laser must vector for this initial time before it starts to cut fully thru the material.
Is our laser unit on its way out?

Mike Mackenzie
08-26-2011, 6:39 PM
Get the updated software 5.31.54.24

I believe this is what the problem is

Resolved problem for certain materials in cut power algorithm, which was giving the wrong power for the thickness less than or equal the shallow cut depth in database.

Also your PPI setting should be set between 200 and 300 for best results. Go into the vector tab and try the three setting they offer. Also make sure that the color management is off in your CorelDraw.

Allan Longson
08-26-2011, 6:49 PM
Thanks Mike, will try this and see how it goes.

Craig Matheny
08-27-2011, 1:53 PM
Allan how often do you clean the lens and mirrors??

Allan Longson
08-27-2011, 7:23 PM
Mirrors are cleaned at the start of the day (and the cotton bud tips are always clean after cleaning so we are not getting any dirt on the mirrors), lens is now cleaned after every 3 sheets we cut and the cotton bud tip is clear after cleaning. We used to clean the lens after every sheet we cut but since we installed a chinese replacement lens that has a longer focal length, as the lens is 1" further away from the wood it now hardly gets dirty at all.