Need help with "burr" at end of cut

[Al Stewart]

I have a Versalaser, 40W with air assist and I cut 3/16" acrylic - extruded and cast.

If I cut a circle, there is a burr or rough point in the cut right where the cut starts and ends. If I cut a rectangle with filleted corners, the cut always starts at the beginning of a fillet and that is where the burr is left.

I get it even with the work sitting on the vector table (I thought maybe it was the cut piece falling away when elevated to prevent reflections)

Any ideas? What causes it? Can it be prevented?

Is it possible to force the machine to start/end the cut where the burr wouldn't matter so much? I use CorelDraw X3 on Windows Vista.

Thanks!

Al

[Scott Shepherd]

Only tip I can give right now is make sure you are using the latest driver. I've been in touch with ULS for a while now tweaking some driver issues and they have made a lot of changes that will have very subtle results.

A couple of questions for you aside from that- what power, speed, ppi are you vectoring at. Also, what is your image density set at? One more- what is your "Vector Quality" set at?

To get the best cut possible, you'll want 1000ppi, Image Density at 6, and Vector Quality set to the highest quality.

Try those if you can and see if it helps. If it does not, make sure you have the latest driver, and then try all those things again.

Let us know if any of that works.

[Mike Christen]

One thing you can do in corel is to break the node apart, this will be the start point of the vector cut. You can also drag the node that you break apart and create a lead in and lead out so that the start and end points of cut are not on the finished piece. Hope this makes sense. I have a post not to long ago where this was discussed.

[Tom Bull]

Do you detect any sort of slack/looseness etc in your belts or pulleys? Any catching or jumpiness? Sounds like something has a hitch in it.

[Al Stewart]

Thanks for the ideas, everyone.

Scott: I haven't been able to change the power-speed-ppi for this problem because I finally got a set of settings that allows me to cut my sandwich of clear masking-5 mil laminating film-photo print-adhesive-acyclic-masking without damaging the edge of the photo. I don't find a "Vector quality" setting in my driver, and isn't "image density" only for raster engraving? I find that setting only under raster. I have written to ULS for the latest driver. I wonder why they don't post latest drivers like regular companies do?

Mike: Breaking apart the node will allow me to place the start of cut in the least harmful position. Good idea! For a circle or ellipse cut I will have to use the lead in lead out modification, but I'm afraid I don't understand how to do that. I tried to drag the the node to extend the line, but the node is free to go in every direction so I screw up the original line position. What am I missing?

Tom: I don't detect any slack or bind. I noticed the problem when I first got the Versalaser new but haven't had to worry about it until now. It just seems to me like it's a problem in the driver. Just not completing the cut by about .015". Maybe they'll send a fix in the newest driver.

UPDATE: Just got this reply from Universal - "
This is the Start/Stop point and can be a problem the only way to eliminate it is to use a lead in lead out on the image so that the laser starts outside the part then leads into the part and then at the line leads out giving a seamless cut, most mechanical cutters have to do this but on the laser it may be necessary depending on the material and the thickness (Needed more the thicker the materials is). Software's like AutoCAD have a lead in lead out feature that can be automatically turned on."

[Dan Hintz]

Al,

If it's a strict horizontal/vertical line, holding down the <ctrl> key while moving the endpoint will constrain movement along one axis.

[Scott Shepherd]

Al, you'd think since Image Density is on the "raster" tab, it would only impact raster engraving. It does not. Trust me!

I've had a number of conversations with ULS folks and I am 100% certain, at this point in time, that Image Density does have an impact on vector cutting.

As for the drivers not being online, the newest drivers have an "update" button on them, so it will go out and look for the latest driver from the ULS servers when you hit that. BUT....that's in the latest drivers, so you'll have to get the latest drivers before you'll even have that capability.

Also, if you'd like to post that file or any file that you are having an issue with, I'll be glad to cut it myself and see if we have the same issue. Just let me know all your speed/power/ppi settings.

[Al Stewart]

For my jobs it's not a problem if the start/stop is on a corner, only ellipses. But I figured out how to add the lead in and lead out lines:
After converting to curve, break apart with shape tool, then using freehand tool click on the node and again where you want the line to start or end.

Thanks, Dan!

[Al Stewart]

Scott, thanks for your kind offer of making a cut for me. I don't think it will be necessary because by breaking the node apart I can put the start/stop where it won't hurt anything, or in the case of an ellipse, I can add the lead in and lead out lines.

But if you wanted to play a little, use the Materials Database driver and simply cut a circle in 1/8" or 1/4" acrylic. It should give you the burr I'm describing.

Now that I have a workaround I'm smiling again!

That is really weird about the Image Density effecting vector cuts. I'll have to play around with that.

Al

[Lee DeRaud]

That is really weird about the Image Density effecting vector cuts.(Warning: random zero-data speculation follows.)

The only reason I can think of is if the driver is cutting all curves as sequences of (very short) straight segments, and that setting affects the length of the vectors.

[George Brown]

I've cut 1/4 inch acrylic and have never seen a burr where the laser starts. Does it only happen on curves? What happens if you cut a square with the starting point in the middle of a side?

[Al Stewart]

It happens where a fillet meets the straight side of a rectangle or at the start of an ellipse. I have never tried moving the starting point until I learned of the technique in this thread, so I can't yet tell you if starting in the middle of a straight cut would help.

According to the comments from the Universal rep., it sounds like it is a normal occurrence and requires lead in lead out lines.

I recently made an award of .241" cast clear acrylic: 4x6" with a fillet at the two top corners. I had to sand the burr off and yet I still had a divot below the surface of the cut that looked like it had been brushed with a hack saw blade. If I recall correctly, I used the Materials Database setting for acrylic. The engraving and the rest of the cut were fantastic.

[George Brown]

According to the comments from the Universal rep., it sounds like it is a normal occurrence and requires lead in lead out lines.



That is a way of saying that it is a bug in the software that they don't want to fix. I will look more closely next time I use the laser, but I have not (as far as I can recall) seen it on mine. I'll post the result.

[Al Stewart]

I tend to agree, George. It sure seems the driver should know where the cut started and be able to at least go there again and perhaps overlap the start point a little to assure a complete cut.

[Dan Hintz]

While I find ULS's solution to bugs more like a hunt and peck method, it doesn't necessarily mean this is a bug. When you cut acrylic, you need to eject the dross away from the cut. When first starting a new cut in the middle of a sheet, there's no where for the dross to go except up and to the sides. This can lead to an odd-shaped spot right where the laser first begins cutting, but once it has drilled through to the bottom the rest of the cut looks better.

Another way to test it would be to start a cut juuuuust off the edge of a sheet... if you don't get the burr, you know it's an ejection issue.

[Scott Shepherd]

(Warning: random zero-data speculation follows.)

The only reason I can think of is if the driver is cutting all curves as sequences of (very short) straight segments, and that setting affects the length of the vectors.

I only retain a very small part of what I'm told by the people at ULS that are trying to educate me in my quest to perfect the vector cutting side of the driver, so here's what I think I understood (which could be completely inaccurate).

Image Density is set when you send the job to the job control software. Image density is essentially "resolution". Corel can only send one resolution image over. You have to pick one. If you pick 4, then you have sent a lower resolution image to the control panel. If you pick 6, you have sent the highest resolution to the control panel. Rastering AND vectoring can only be as good as the resolution of the image you send over. So sending the highest resolution over will allow for a better, smoother cut.

Also, turning "Enhance" off in the vector control panel can improve quality in specific instances as well.

I cut 1,000's of objects a month that have tight tolerances, so I've been dealing with issues and working through them with ULS for some time now. I have seen some very good improvements made in vector cutting recently. That's why I say you need to be on the latest driver before you start troubleshooting.

[Rodne Gold]

Corel will send a vector to the driver - which is essentially perfect in resolution. What the driver does to interpolate (IE to translate the vector into non linear movement in this case ) is another story. Quality of cut depends on the motion system and way the motors are controlled when interpolating curves.
A square , no matter what, should have no issuees with misaligned cuts as the instuctions the motors get is essentially straight lines. So if you get nibs when cutting squares , something is not right.
There has been some comment about the fact that corels vectors are not as good as other packages - I havent found this to be the case , but you could try sending the same file from illustrator or Acad - if your driver supports these.
Other issues could be that there is some expansion of the item due to heat generated and start and end point dont align , some slack in one of the axes , some misregistration in one axis , a faulty motor or encoder or some setting thats not good.

A laser cuts in most cases by trepanning , IE cuts are a lot of series of overlapped drilled holes , The first hole and the last should be identical , there is no dwell times like on a cnc machine and the only reason to use lead in on CnC's is the fact that when a cutter plunges , it can bend and the biting and rotation aspect can cause distorted cuts , this is not the case with a laser. If this nib/burr was a general condition , then all of us would be having the same issues - and it seems we arent.
I can tell you , I would be very upset if I had to add lead ins and lead outs in my vector cutting , maybe it's a workaround but its a big hassle.

[Scott Shepherd]

Corel will send a vector to the driver - which is essentially perfect in resolution.

Rodney, maybe you can help me understand this. Corel can't send a "vector" because printers don't understand anything but a bitmap. My printers don't know what a vector is, I print something from Illustrator and it's sent to the printer and whatever resolution I picked. Same with Corel, isn't it?

You pick a resolution to send it at and it sends it. No "vector" information reaches the printer, it's just lines and shapes.

That's what I understand was the issue- when you print, you have to pick a resolution. You do that and even though you send a vector over, it's still broken into a bitmap, more or less. I could be completely wrong, but that's how I was understanding it. Calling anything a "vector" object is for our purposes only, when it's sent to the printer, it's all about DPI. The printers don't recognize anything as being a "vector object", to my understanding. Am I wrong?

[Rodne Gold]

A laser is a printer , but its also a plotter - when you enter vector mode , the laser driver doesnt see a raster (pixel/dot) image but it recieves a set of instructions to convert that vector into x and y motion. For example with a 1" square , the laser should see an instruction set like this
go to top left - travel x 1" , travel -y 1" , travel -x 1" and then travel y 1".
If you ENGRAVED the square it would see the square lines as dots
Some plotters/lasers cannot interpolate on a continous basis , IE they cannot infinitely vary X and Y on a continuous basis - so they "interpret" curves as a series of straight lines , the more straight lines , the smoother the curves , albeit I am not familiar with your driver , it may be that image density on your laser/driver is a way of controlling how many straight lines are used to plot curves.

[Dan Hintz]

HPGL is a vector-based protocol started by HP... most printers support it. It's up to the graphics engine within the printer (or in the case of dumb printers, it's up to the driver) to translate the vector into raster points. I would like to know what protocol(s) the ULS driver uses, but I'm willing to bet it supports both vector- and raster-based protocols.

PostScript is another vector-based protocol... TrueType fonts are sent as vector-based files.

[Dan Hintz]

Rodney,

Is the new avatar a pic off of the newly finished/painted vette?

[Rodne Gold]

No , its me taking a pic of myself in the bumper of an old Citroen - just a change.
I sold my C3 vette accident damaged and bought a C4 - white
My "stable" is an 86 C4 , a 96 Camaro Z28 and a 74 454 el Camino (actually a Holden ute - called El Camino here)
Vettes and Camaros are quite rare here - I love driving em , LhD and V8 rumble with soom Vooma

[Dan Hintz]

Briefly "owned" a '67 Camaro SuperSport convertible in Metallic Gold (the 396-cid "big-block" Turbo-Jet V8 version, I believe) my dad purchased during college. He hitchhiked to the Chevy factory and drove it right off of the line.

Early in the 80's he had minor body rust damage repaired (many years driving in winter salt) and the whole thing repainted, as well as all new upholstery (everything matched the original). He installed custom gauges in a panel on the transmission tunnel, AM/FM radio, etc. I "owned" it for a grand total of 6 weeks until he sold it so we could afford a new roof (money was a bit tight back then).

Here's a very similar '68:
http://www.minimusclecars.com/image.php?type=T&id=17159

[Mike Chance in Iowa]

Vettes and Camaros are quite rare here - I love driving em , LhD and V8 rumble with soom Vooma

Nothing beats the sound and rumble of a good V8.

Gotta love the late great Paul Newman when asked by James Lipton during an interview what his favorite sound was .... a V8. :D