Vector cutting and stair steps on curves

[Tim Goldstein]

Trying to get up to speed and learn the ins and outs of lasering. Am cutting airfoil ribs on 1/32" balsa wood. I am getting random spots on the curve of the airfoils where the cut is jagged or stair stepped instead of a smooth curve. There are multiple ribs on the same sheet. They were all created in Corel by duplicating the first one we drew so in the Corel file they are all identical. The jagged area is not always in the same spot on any given sheet.

Talked to my rep and what he is telling me is that to get smooth curves in vector cuts you have to decrease the speed until the curve is smooth and then adjust the power to match the speed. A paraphrase of his statement is that the machine can only vector cut smoothly at below about 20% speed. This just strikes me as odd that the machine is not capable of maintaining true paths at anything beyond a 1/5 of the speed you can set it for. Because this is such thin balsa there is enough power to cut at any speed up to and including 100% speed.

Am I getting an honest answer or an I getting smoke up my b*tt?

[Mitchell Andrus]

Smells like smoke. I'd check the tension on your belt. Sounds like your getting belt whip.

[Robert Alexander]

Tim, I had the same problem vector cutting mat board. I did some trail and error cuts, and I found out that for my machine turning down the power and speed gave me better vector cutting. So right now I do not run over 25 inches per minute and a power setting of about 17. And if it is a very intricate cut I turn down the speed to 20.

[Mike Null]

Your rep is telling you the straight of it.

[Dennis Perry]

Tim, I have the same machine as you, Set the image density to 6 the highest setting if you haven't already. This setting is not just for rastering, also has an effect on the smoothness of vectoring curves.

Dennis

[Gary Hair]

I had a similar problem with my machine trying to vector cut some large text. The dealer sent me a new x motor and had me adjust the belt and finally gave me the answer you got. Different brand, same answer. I thought it was crazy to have an 80 ips machine (40ips vector) and have to cut small curves at 5-10% speed. There is no reason for this to happen, the computer can certainly control the motors to make this a non-issue, yet it is the way they work.
Someday they will figure out how to give us full speed vector cuts around a curve... I hope.

Gary

[Dave Jones]

I just went through the same thing cutting very thin veneer. Annoying, but I also had to turn my speed down to around 20% to get smooth cuts. (Epilog Mini-24)

[Mike Null]

I read somewhere, not professing this to be fact, that CorelDraw doesn't makes true curves but rather segments of curves. If this is true that could explain some of the reason for the necessity to slow the vector speeds down.

[Tim Goldstein]

I read somewhere, not professing this to be fact, that CorelDraw doesn't makes true curves but rather segments of curves. If this is true that could explain some of the reason for the necessity to slow the vector speeds down.

Mike,

If it was identical on all the ribs I would agree. But it varies from rib to rib even though they are duplicated in Corel to create them.

[Tim Goldstein]

Tim, I have the same machine as you, Set the image density to 6 the highest setting if you haven't already. This setting is not just for rastering, also has an effect on the smoothness of vectoring curves.

Dennis

Dennis,

Gave your suggestion a try and it definitely improved, but did not eliminate the problem. Improvement is noticeably.

Thanks.

[Tim Goldstein]

I played with lowering the speed and power. With the image density setting maxed out at 5% speed I get perfect paths. At 10% speed I see some raggedness. Did not have the chance to find exactly where it starts in. Absolutely crazy that you have to run at a fraction of the speed and power the machine has to get acceptable output.

[Mark Winlund]

Welcome to the club. To do really precise work, 3% speed is my limit. The machine has mechanical resonances built into it because of bad design. Nothing can be done... ULS is very aware of this, and quietly ignores it. Higher tension in the belts can sometimes help, but this just moves the resonant frequency up. Adding damping (weight on your lens assembly) also can help, but at the risk of lost steps and increased wear.

Mark

[Tim Goldstein]

Mark,

Appreciate the feedback. Based on the responses to this post it would seem that ULS is not the only one with issues in this regard. I don't mean to say it is correct or acceptable by that, but that it is a common problem.

I see from your tag line that you are also a Haas owner. We have a VF2 and an SL20 with live tooling. Have to say that with Haas the machine has performed exactly as we expected and as the company and sales rep said it would. Can not say the same with the laser.

[Michael Kowalczyk]

Hey Tim,
We have a Trotec Speedy II 60 watt and it goes 140 IPS but I would never vector cut at that speed. Being in the CNC business also we know how inertia works but it usually more tooling dependant, that said a laser has no tooling issues but I do not think they were designed to go all out on vector cutting and I think some of them actually have different speed limits for vector and rastering. If I go over 1-2 % speed/velocity, depending on material, for vector cutting it turns a circle into an egg. So what I have done in the past is make around a 1-2" circle and keep testing it with raising and lowering the power and speed settings accordingly until I get satisfactory results.

When I try to push the limits it sometimes looks like this .............. as it goes around even if I pump the PPI (pulses per inch) to 10K.

I think you just have to play with the settings until you get what you want and charge accordingly.

Speaking of playing, have you had a chance to play with the 3mm birch yet?

Have a great day,

[Tim Goldstein]

Michael,

We have the HS machining option on our Haas. It will maintain perfect tool paths by looking ahead 50 blocks and calculating the acceleration reqired to overcome inertia and then automatically reducing the feed as needed to maintain the path. Lets you do complex 3D surfacing at high feeds so you get good cycle time, but slows it down as needed to you get accurate parts.

On a top end laser I would expect the same. But instead I have to run all the part at the lowest denominator speed and accept the poor productivity. This same part has probably 70% straight line cuts. So either I redo the drawings with high speeds and power on the straights and low speed and power on the curves or live with poor cycle times.

The 3mm birch ply is great. Have not used a lot of it yet, but love the results on what I have run so far. Even better the pieces are perfect sized so I don't have to mess around with cutting up bigger sheets.

[Mark Winlund]

Tim... I would agree that for the money, ULS could have come up with something better. Or at least acknowledge the problem. Still, at the time I bought it (4 years ago) the fact that it worked at all was nothing short of miraculous. Sort of like the 3D printers for making patterns and prototypes.

I am looking forward to the company that can come up with a good servo driven laser. That would eliminate many of the problems with the ULS machines.

Regarding the Haas, I have also had very good luck with mine, with only minor problems with the tool changer. Their manual is one of the best I have seen for such a complex machine... oriented towards the average machinist. (which describes me!) With the look forward and HS machining, there is very little that I can't do with it. I also have the C axis table for it.


Mark

[Mike Mackenzie]

I will hesitantly reply to this issue and hopefully explain a little on how and why the vector speeds are what they are.

First off I would like to put a scenario to all of you If you have a Ferrari that can go 200 mph in a straight line do you think you would have to slow down to make a 90 degree turn? I would hope so.

The laser systems are the same way the difference being to many different materials, size of the system, cost of the system, and the laser power.

All of these things make a difference in how the system will vector cut and raster engrave. Personally I only know of one laser system that can even come close to performing both in speed of vectoring and rastering with acceptable quality and that system costs 100k for a 50 watt!!

I am not saying that corners were cut to produce a cost effective system but some things had to be sacrificed in order to please everyone and all markets that the laser systems are sold into.

Please keep in mind that this is my opinion only I have no idea what the laser mfg's do with there R&D and production of this equipment.

I did a test on our system to see the time difference between different speeds. Here are the results cutting a 2" circle at 100% speed the time was 6 seconds, at 90,80,70,60,50,40,30,20,15% speed the time was 6 seconds the actual cutting time did not change until I got down to 10% speed and then it took 8 seconds to cut the same circle.

So what are we talking about here 2 seconds difference between jagged edges or smooth edges and this was a very basic test. The material you are cutting will have a significant difference in the actual speed you are cutting with. We have to remember we are using a beam of light not an end mill. The simple fact that any vibrations can effect the beam of light and the quality of the cut.

With all of this said I do believe they can be improved, I also believe that they do a very good job for what most of us use them for and they do have some limitations.

I am a firm believer in educating the customer up front so they no beyond a shadow of a doubt what and how the systems work before they purchase. Then these situations would be avoided.

There are some things that can occur with systems that would cause more than normal edge quality. (Belts, bearings,motors, etc.) which can all be corrected.

All in all these lasers systems do the job and do it very well and I am talking about all brands.

Tim,
I would ask your rep to come over and look at the issue with your system it might need some adjustments. It also sounds like he should spend some time with you on settings.

[Ray Palleschi]

I had a similar problem with my Epilog Mini 18 about a year ago, I had the problem since we bought the machine. When vectoring the cutout the X-axis would behave very erratically. How bad it behaved was in direct porportion to the speed, i.e, the higher the speed the worse it was.

After months of working with Epilog trying to solve the problem, my partner who seldom does work on the laser but has an electronic background came up with a theory that the problem was not mechanical or in the machine, but electrical noise on the power line feeding the laser. We shut off power and unplugged anything unnecessary from the area of the laser. Lo and behold, the stairstepping completely stopped. We one-by-one replugged the other things on the circuit and eventully found it was a combination of our exhaust blower and the air assist pump that caused the problem. We plugged them into different outlets (I believe they were on different circuits) and moved all the electrical cords as far away from the laser as possible. I also added a Uninteruptable Power Supply on the laser (only) for both power backup and the line filtering that it supplies.

So far the problem has not come back. I don't know if this is the same problem for you but you might want to try it out.

Ray Palleschi

[Mike Null]

Just 2 cents more. I basically agree with Mike MacKenzie's position. Machines are sold on the basis of raster speed and not on vector speed so when one is expecting a drag racer to run a sports car course they're going to be disappointed.

I came across the following somewhere--I can't remember where--and I haven't tried it but it's harmless and can be changed quickly if it doesn't help.

Details
When printing a CorelDRAW® document to a non-postscript printer, rounded curves print as if they are made up of flat line segments. What can be done to correct this issue?


Answer
To resolve this issue, follow these steps:

1. Click File | Print Preview.

2. Click Settings| Printing Preferences.

3. Select Driver Compatibility.

4. Select the printer in the Printer drop-down list.

5. Enable Send beziers and paths to driver and click OK.

6. The curves in the document should now print as curves.

[Jerry Allen]

There a a number of things that don't get said regarding Draw and printer drivers. I have previously found that setting "Software clipping for fills" by just making an educated guess based on experiences with HPCL drivers.
I just found the following from a readme file from a Canon PCL printer.
So it looks like a few things should be set.
Note that this is slightly different than Mike's instruction and is accessed though the Tools/Options menu, but either method is okay and the settings will stick.

************************************************** *************************
Copyright (c) 2004 Canon, Inc.
Windows(R) 98/Me/NT4.0/2000/XP/Server 2003 PCL5e/5c Printer Driver
- Version 6.41
Windows(R) 98/Me/NT4.0/2000/XP/Server 2003 PCL6 Printer Driver
- Version 4.40
************************************************** ************************
This README file contains supplemental information to help you install and
use your PCL5c, PCL5e or PCL6 printer driver software with Microsoft(R)
Windows(R) 98, Windows Me, Windows NT(R) 4.0, Windows 2000,
Windows XP and Windows Server 2003.
As with most software and hardware products, some information is made
available after the development of the manual. Updated information
regarding this driver software is provided in this README file. If you
require additional assistance, please contact Canon authorized dealer
or Canon authorized service provider.
````````````````````````
23. If it takes long time to print a document from CorelDraw, the following
settings may shorten the printing time.
1) From the Tools menu, select Options.
2) In the Options dialog box, select Global->Printing->Driver Compatibility
from the tree view in the left side of the dialog box.
3) In the Driver Compatibility sheet, select Canon PCL printer driver from
the Printer drop-down list, and then select the following check boxes.
-Use software clipping for fills,
-Output bitmaps in 64k chunks, and
-Send beziers and paths to driver
4) Click the OK button to close the dialog box.

Note that you will be looking for your laser's driver, not a Canon PCL...

[Tim Goldstein]

I had a similar problem with my Epilog Mini 18 about a year ago, I had the problem since we bought the machine. When vectoring the cutout the X-axis would behave very erratically. How bad it behaved was in direct porportion to the speed, i.e, the higher the speed the worse it was.

After months of working with Epilog trying to solve the problem, my partner who seldom does work on the laser but has an electronic background came up with a theory that the problem was not mechanical or in the machine, but electrical noise on the power line feeding the laser. We shut off power and unplugged anything unnecessary from the area of the laser. Lo and behold, the stairstepping completely stopped. We one-by-one replugged the other things on the circuit and eventully found it was a combination of our exhaust blower and the air assist pump that caused the problem. We plugged them into different outlets (I believe they were on different circuits) and moved all the electrical cords as far away from the laser as possible. I also added a Uninteruptable Power Supply on the laser (only) for both power backup and the line filtering that it supplies.

So far the problem has not come back. I don't know if this is the same problem for you but you might want to try it out.

Ray Palleschi

Ray,

Thanks for the ideas. Don't know if it is the same issue as I already have the laser on a dedicated circuit. I can't easily use a UPS as my laser it 20 amps 220V. I am sure them make them, but cost for a 5KW UPS would be off the wall.

[Rob Bosworth]

Let's take a look at what you are really seeing when you are "limited" by the "poor design of your machine. If you have a machine than can move at what the marketing departments tell you it can move, let's say it is a 80 inches per second machine. IF you try to vector cut at full speed, you aree actually cutting at 4800 inches per minute. (That's flying on anyone's machine.) So if the manufacture tells you that you can only vector cut at 10% speed, you are limited to having to suffer through 480 inches per minute cutting speed. If you are getting nice smooth cut edges, that isn't too bad. If you have to slow the machine down to 5% speed, you are still cutting at 240 inches per minute. I would guess none of your other machines, purchased for less than $25,000 will cut through a material at anywhere close to those speeds.

Another thing to consider. CorelDRAW lays out their vector cutting lines as a series of pixels. IF you look at the nodes on an arc, it is actually made up of a series of dots. These machines are made to be affordable to most of us. They are not structurally built as heavy as a machine that is made to cut faster and smoother, but probably can't do diddly for raster engraving. The machine is actually trying to run dot, run dot, run dot, so it is really starting and stopping to create a curve. IF you reduce the number of nodes on your curve, your laser engraving machine will run faster and smoother. IF you run a software that actually lays out a true curve, you can run your machine faster andf get the desired effects. IF you use something like AutoCAD to lay out your graphic, then run your machine as in a HPGL driver, you will see much improved speeds and smoothness on your cuts.

[Tim Goldstein]

Mike,

Appreciate your input and advise as always.

The problem with your Ferrari analogy is that with the Ferarri I can hit the go pedal when I get out of the turn. With the laser I have to drive the whole course at the turn speed and may as well be driving a Yugo. On my Haas it acts like a car with a driver and accelerates and decelerates as the path changes.

I also noted what you are saying on the cut time vs the speed setting. Until I got under 10% speed the setting appears to do nothing. So we definitely have an adjustment that is with non-linear or just plain does nothing until 10%. In the case of the one pattern I am experimenting on going to 6% (where all the jaggedness disappears) increases the cut time from 1:45 to 2:50. That is a major change in productivity when I start filling the table instead of cutting just a 3"x12" sheet.

All in all I am happy with the machine. What I find disappointing is that the entire laser manufacturer industry seems to be less then forth right with what the product will and will not do.

[Mark Winlund]

Tim... I have been following this closely, as I have had this problem for some time. First, let me say that I have been engraving for a long time... since 1975. I got my first CNC engraver in 1981... a Dahlgren that was booted with a cassette tape. When we moved up to disks (5") we thought we had died and gone to heaven!

At any rate, I am very familiar with stepper driven equipment. The speeds and positional accuracy was very good in the 1980's.... better than ULS's current offerings. When I say "bad design", I mean just that. Today's modern software and drivers are remarkable in what they can do.... anyone that has seen what a Xenetech Viper machine can do will agree with me. The weight of a typical cutting spindle is far heavier than one of the flying optics head, yet they outperform ULS by a wide margin. Even my old Dahlgren tables, where the steppers are also moving a heavy motor in addition to the spindle, can outperform ULS's system.

Also, any modern software can cope with circular interpolation, and the latest can handle bezier curves as well. The fact that ULS converts these curves to straight line segments internally is more of an indictment of their design practices than anything else.

I'm not sure that I followed Mr. Bosworths line of reasoning regarding cutting speeds:

" let's say it is a 80 inches per second machine. IF you try to vector cut at full speed, you aree actually cutting at 4800 inches per minute"

The above statement is not very clear to me.

In any event, for the price they get, it would seem that they could provide performance that was widely available 20 years ago with stepper driven servo systems.

Regards, Mark

[Tim Goldstein]

I tried the "Send beziers and paths to driver" setting. Interesting. It does improve the path. Unfortunately the driver seems to be tripped up by it and the laser fires in a totally different manner than in the default setting. Some segments on my pattern cut perfectly, some segments became lightly vector engraved. You could seem the laser pulsing in an entirely different manner. Even at 100% power (120 watt machine, 1/32" balsa) it would not cut all segments with this setting turned on. Changed to the default and suddenly the laser goes back to looking like it is on for the entire vector segment and cut is all the way through.

Looks like another instance of the print driver being a black box interface. You have a bunch of wiggets to change and they effect far more then is explained.

[Rodne Gold]

I can cut vector at 100% on my machine (laserpro) with perfect results and we often do so for thin fabrics , paper etc.
There is a setting called ramping (or should be on most machines) that takes care of the linear vs curve power/speed issues.
Corel does not extrapolate curves as a series of lines , they are true curves , its the way the machine handles the corel output that does the extrapolation. No stepper machine can possibly extrapolate true curves as a it uses steps. the determination of smooth curves on a stepper machine depends on a lot of things , size of step , the inertia and play in the motion system , hysterisis etc , similar concerns are for feedback servo systems.
The laser does not stop to fire a pulse , it fires pulses while in motion , the motion system and the firing are actually "seperate" systems in this respect , however thay are linked cos of ramping , IE the ppi setting should dynamically change as the speed of the motion system does , ie have less PPI as the aser gets to corners and rounds curves and the actual linear speed slows to avoid overburning these areas. What the laser does is cut with pulses , ie it trepans the material it doesn't really "join the dots"
On servo systems there are also problems in regard to motion systems , bearing systems and feedack , for example on our big overhead routers we have to seriously throttle back speed when doing fine curve engraving as the inertia in the spindle assembly makes it "overshoot" and the servo system tries to correct this leading to extremely poor curve quality at speeds the machine is capable of engraving at. The weight of a flying optic system as well as the drive technology and bearing construction will also limit the above on a laser based servo feedback machine. No bearing system is completely friction free. The advertised max IPS of any of these machines would be based on linear x or y travel with no accel/decel/curves involved.
At the end of it all , all that REALLY counts on a laser is cycle times with acceptable results , and if cycle times do not drop really significantly linearly with decreased speed (IE 10% speed is not a 10x longer cycle time than 100% speed) and the results are acceptable , there is no real harm done.
Should this NOT be the case , then I would take it up with the manufacturer if they have indeed promised the capability of vector cutting at a particular speed. At any rate , when evaluating machines , the advice to take some of the materials you wish to process and see for yourself at what speeds and quality this can be done is paramount. XY raster/vector type lasers are a compromise in that you are asking the same machine to do perfect dot matrix printing and be a plotter at the same time. No other CnC machines really work this way.

[Abdul Baseer Hai]

Rodney,

A question for you regarding GCC print driver 3.55.02

On the raster screen, the first function is "contrast".
How and when is it used?

Thanks
Abdul

[Rodne Gold]

I don't know , it's probably to do with lasering photos and the like and I use photograv for that , I dont find the GCC driver gives the same or as predictable results.
However form my photography , essentially the contrast adjustement , to put it simply ,will darken dark shades and make whites whiter and remove some shades of grey , so for example would remove the "muddyness" associated with various colours when converting to greyscale.
For example a royal blue ball on a green lawn would not stand out when converting to greyscale but adjusting the contrast would probably make the ball "blacker" and then the green of the lawn "whiter" so it would stand out more.

[Roy Brewer]

...XY raster/vector type lasers are a compromise in that you are asking the same machine to do perfect dot matrix printing and be a plotter at the same time. No other CnC machines really work this way.
Rodney,

Very well done!

[Jerry Allen]

I
tried the "Send beziers and paths to driver" setting. Interesting. It does improve the path. Unfortunately the driver seems to be tripped up by it and the laser fires in a totally different manner than in the default setting. Some segments on my pattern cut perfectly, some segments became lightly vector engraved. You could seem the laser pulsing in an entirely different manner. Even at 100% power (120 watt machine, 1/32" balsa) it would not cut all segments with this setting turned on. Changed to the default and suddenly the laser goes back to looking like it is on for the entire vector segment and cut is all the way through.



Tim,
I cut acrylic and some wood yesterday using the settings I mentioned above. Primarily, the plots were up significantly quicker at the laser. However, I noticed no difference in the vector cuts although it seemed like a little less power was in order.
Based on your results, I'd think your machine is malfunctioning. However I am using a Mercury, and I don't know if your machine is HPCL compatable, although I suspect that it is.

[Abdul Baseer Hai]

Rodne,

Thanks. If you do find find out more about this function, please post it here.
abdul