A strange problem??

[Tom Bull]

My epilog legend (30 watt) does just fine vector cutting along the top ruler guide and down about 6 in. from there. Closer to the bottom it will not cut all the way through (1/8 oak plywood). I checked the focus and it seems to be within a 64th all around the main perimeter of the work area and the table is just slightly bowed up in the middle. I am taping the ply down tightly to the vector table so it is not moving. Now here is what is strange to me...when I do a small test in the four corners of the same size work piece it cuts all the way through with no problem. The project I am doing constist of a lot of the same item over the entire sheet (18 x 12). Any ideas? Thanks in advance.

[Richard Rumancik]

When you do your test in the four corners, make sure it is a representative test and done in both axis; i.e. don't just cut a straight line but cut a square out. You don't need to waste a large sheet for testing, just place four rectangles of scrap in the corners and vector cut a test shape in each.

If you just cut a short test line it may appear to be cutting fine but then you may find with an actual shape it won't cut as well. At least, that is my observation with my Mercury. So I suggest you repeat the test if necessary with a represenative shape.

Normally, the beam is attenuated the more it travels through air so the worst location in most laser systems is the lower right corner, since the beam enters in the upper left. I can't really think of a reason for why the beam would be appear to be strong in the corners and weak in the center.

Also when doing power testing I would use acrylic as it is homogeneous while plywood can be quite variable. If you want to test the laser uniformity it is probably better to use a material that is known to be uniform.

[Tom Bull]

I did indeed use both squares and circles to do the testing. As I lay awake thinking about this I considered the fact that there was a greater distance involved, but could not see that as having that great of an effect. I believe the temporary solution will be to just modify the project to cut from smaller sheets and have more of them, but will continue to try to figure out the real solution rather than just a work around.
Thank you for your input.

["Terry Pless"]

Hi, I have a Legend 24EX 35watt and it does the same exact thing. I've measured the table as well also done test cuts at the four corners with shapes as well and the trouble persist. I've made sure the windows and mirrors are all clean thinking distance as well. On a few jobs it was the material warping so I place tape and or weights to hold it down but it still does have a problem cutting larger peices. Any more Ideas ? Terry

[Joe Pelonio]

When the honeycomb wears you will have a dip on both sides of the center vertical brace, so the material will be higher there than on the sides and therefore is out of focus. Sometimes you can take it off of the frame and turn it over and use the other side to again be level, otherwise it's time to replace it. Last time I bought a 12x24 it was under $40. You can also try this to verify the problem and get around it. Place pieces of 1/4" acrylic, say 3"x12" on the left and right ends of the honeycomb, vertically. Then place a sacrificial piece of 1/4" acrylic on them, and place your material to be
cut on that, and it should be more evenly spaced for cutting well on
all areas.

[Richard Rumancik]

Tom and Terry

If I understand correctly you are both seeing poor cutting at the lower middle, and it gets better at the lower right.

I would not have expected this, as distance does indeed attenuate the beam. High humidity will make it worse. There would have to be some counteracting effect going on which would account for this behaviour you are seeing. I can only guess that maybe the beam is diverging more in the lower right (its divergence will certainly be greater with distance) and because of this it is resulting in a larger input beam to the laser lens. A larger input beam will result in a smaller final beam size after the focusing optics. This will mean that the energy is concentrated and could result in better cutting, as long as you are in-focus there. So as a guess, maybe these two effects are non-linear and are being played off against each other in some way. But if so, I would also expect poor cutting in the right middle, as the distance through air would be the same as for the lower middle, and due to symmetry it should result in a similar condition. If this is not evident, then I can't guess any further as to what might be happening . . .

Using smaller pieces may be a "solution" but I find that it is better to use table-size sheets (say 18 x 24 or so, depending on your machine and stock material size). I would cut a group of parts, then flip or rotate the sheet till there was an inadequate amount left. Overall I find less waste this way and less time to prep the material.

Alternatively, I might vector a few rows of parts, do a cutoff with the laser, and then index the sheet back up to the top of the table.

Another trick is to figure out the areas of the table that don't vector well, (for me it is the lower right) then color code these shapes with a different color. Then set a different speed/power for these selected items. It works well if you have a larger job to run and only a few colors are used.

Tom, I admit that these are all work-arounds and are not necessarily convenient to do. It would be good if you can find a permanent solution as you were hoping for, but I have not had success in doing so. Let us know what you find out . . .

If you can borrow a power meter, you might want to try to map the table so you can see if what you think is happening is reflected in the actual measured numbers.

Here is another one of my ideas for the laser manufacturers: Allow the user to map the table in terms of energy delivered (or factory-map the table); then allow the user to set an option whereby the laser would automatically adjust the laser energy from the set-point depending on the actual x,y location of the carriage. (Generally it would do this by reducing the speed of the cut.) Then it would compensate automatically for beam energy differences over the table regardless of the physics behind it.

[Tom Bull]

Joe, I am using plastic honeycomb as in light fixtures (an idea found here at the creek) which works out well as I can have several and prep them by taping down the work piece around the edges and when one has run just toss in the next one and good to go. Also makes registration a snap because my project is 2 sided. It is all pretty darn new, and I checked even-ness across the table with the honeycomb in place so don't think that is the issue.
Richard, thanks for the ideas. I am maximizing my material, though I do loose about 1/2 inch in doing it twice.
Will definately keep you all posted on my progress.

[AL Ursich]

My 20 Watt would loose power 4 inches down the table and it ended up being a burnt mirror lower right. I have the Mirror and the Laser Triggering device, just need to time to do it.... SO busy..... Mostly V Carving Signs and Plaques.

AL

[Tom Bull]

Perhaps a silly question, but how does one diagnose "burnt mirror"? Is it obvious or subtle? Also my focusing lens looks a bit funky upon close inspection, maybe that is the problem. Would it work well in one area but not in another area if it were the lens?
Thanks again,
Tom

[Darren Null]

It might do if it were manky in the middle AND your beam is a little bit out of alignment...the beam would drift from one side of the lens to the other as you went across/down the table. You'd then get a stripe of poor results, horizontal or vertical, depending on your mirror setup/how your beam was out of alignment.

That would only work if your lens is manky in the middle and relatively clean around the edges.

Burned mirrors are normally fairly easy to spot...usually it's stuff sticking to them and then burning; thus killing the mirror or a small piece thereof. You might have to remove the mirrors to look properly (and clean them while they're out & it's easy).

[Larry Bratton]

Checked your alignment lately? I was having a similar problem of cutting through the material except in the bottom left. Alignment fixed it. Good luck.

[Tom Bull]

OK, maybe another dumb question, but alignment of what and how does one accomplish said check? Are we talking lens alignment?
Once again, thank you all.

[Darren Null]

Mirror alignment. When it's all good, the beam passes straight through the centre of the lens, no matter what the position of the head on your table. When it's a little bit out of alignment, the beam 'drifts' around the lens, depending upon the position of the head on the table; and in extreme cases doesn't leave the head assembly at all.

To get it right, you have to twonk about with *every single mirror* from your laser to the head, and make sure they're all perfectly positioned. I do it by burning holes in post-it notes over the mirrors, but there's probably a better way. A red guide beam, if you have one, helps tremendously, but it isn't in exactly the same place as your actual beam.
Quick & dirty: do the mirror on the head and the one before that first...they're easier to get to and -due to movement and proximity to dust etc.- they're the most likely culprits. Otherwise, to do it properly, start at the laser and do 'em all.

If your problem was OK in the centre and not burning so well at the edges, I'd guess beam alignment. As your iffy burning is in the centre (with both sides being OK), a little bit of misalignment AND gunk on the centre of the lens might be it, but I think it'd have to be both.

the table is just slightly bowed up in the middle

Why's that then?

[Rob Bosworth]

Tom, you should contact Epilog Tech support about an alignment procedure for your Epilog. They have a very nice write up on how to do it. Everyone who owns a laser should make themselves learn how to do an alignment. It is very important, and it will cost you a lot of money when the system does go out of alignment. Do not be afraid of trying to learn how to do an alignment. If you lose the beam at any particular point, put a bigger target (tape) on and see if you can't find the beam again. Then just start walking it back to being aligned.

You can check the quality of your optics by running the machine at full power for 10 minutes or so. Then, stop the machine and being careful, feel the backs of all of your optics. Any heat build up on the optic holder either means your beam is out of alignment, or the coatings on your mirror(s) and/ or lenses are starting to break down.

Good luck.

[Larry Bratton]

OK, maybe another dumb question, but alignment of what and how does one accomplish said check? Are we talking lens alignment?
Once again, thank you all.

Tom:
Check this thread. http://www.sawmillcreek.org/showthread.php?t=86543
However, Rob is right. Epilog tech support is the place to start. Good luck with it.