Sloooow the printer speed down

[heathenx]

Hey folks

So some of you know that I have a 2w laser diode attachment mounted to my Rostock Max. The laser works fine but I'm struggling with printer speed. This printer was designed to go fast. I want it to go slow...really slow. I've been trying to slow it down to 2mm/s so I can cut acrylic but it doesn't want to go that slow. I can pass the laser through 1/8" and 3/16" thick acrylic sheet if I turn the laser on and manually feed the sheet by hand. I just can't get the printer to do that for me. It almost appears like there is a minimum feed/travel rate locked into the printer somewhere, either in the firmware or in Repetier software. Is that a possibility?

Here's what I've cut today. 1/4" balsa. 10 passes to get through it. I'm guessing it took 3-4 minutes to cut (wasn't paying attention to time).

[Generic Default]

There are constants defined in the firmware and in the slicing program to limit the minimum speed. Just search for them.


How are you getting the slicing program to only draw an outline around the object?
By the way, a 2 watt laser diode is at the high end of what laser diodes can do. Too bad you can't put a giant CO2 glass tube laser on the end effector!

[Glacian22]

If you can't slow it down any further, just do a couple of passes.

[heathenx]

There are constants defined in the firmware and in the slicing program to limit the minimum speed. Just search for them.


How are you getting the slicing program to only draw an outline around the object?
By the way, a 2 watt laser diode is at the high end of what laser diodes can do. Too bad you can't put a giant CO2 glass tube laser on the end effector!

If I use Repetier/Slic3r to do the slicing then I tell it to not print the top and bottom and turn my infill off. That gets just the perimeter of the shape (along with any holes or cutouts if I have those). My stl file will have the same thickness as the material I'm cutting. I might set my layer height to .05 or .1mm. Nozzle size .1mm. There are a few other settings too but that's the basic stuff. I actually do not prefer using a slicer for laser cutting. There are a few things that do not work very well. Namely, I haven't figured out how to step the Z down with each pass. Also, the laser wants to stay on all of the time, engraving a path where it travels.

My preferred method is Inkscape. I draw the shape, center it on 0,0, convert the shape to a path, flatten beziers, export the gcode. I manually change the Z0 in the code to equal my material thickness. In the case of my 1/4" thick balsa above, I set Z0 to Z6.55. This ensures that the laser has the sharpest focus dot on top of my material. With each pass, the code steps the Z down about .1mm. It should only take about 7 passes to get through 6.6mm stock but since I can't slow the printer down enough I run a few more passes. I plop that gcode into Repetier and print over USB. Very simple process. I intend to make a YouTube video of my workflow but I haven't had a chance to record it yet.

If I can't slow the printer down then my alternative is to add more passes. I don't know what else to do. So far the only thing that helps is moving the feedrate slider from 100% down to 25% in Repetier.

[Eaglezsoar]

Heathenx, could you provide a source for the 2 watt laser diode that you used?

[teoman]

Towards the end of this thread he reveals ithttp://forum.seemecnc.com/viewtopic.php?f=59&t=6001&p=45609&hilit=laser#p45609

on a stupid monile phone and my fingers do not have enough precision to just copy the link.

[RegB]

Wild guess alert;

Could you LIE to it in the EEPROM somewhere, e.g. in the X & Y steps per mm ?
It would SEEM that a 10x lie about the number of steps would either slow things down by a factor of 10, or cause 10x as many step pulses to be sent... so probably not.

[heathenx]

Heathenx, could you provide a source for the 2 watt laser diode that you used?

https://www.indiegogo.com/projects/l-ch ... attachment

http://robots-everywhere.com/re_wiki/in ... in.LCheapo

[heathenx]

I was able to cut 3mm thick acrylic today but it took 60 passes. I can't seem to run the printer any slower than I've managed to run it. It took 19 minutes to cut this and it didn't cut cleanly. I had to use an xacto knife on the backside to cut the slivers. Also, my laser path was too thin. I thickened the cut by cutting two paths, one that was offset by a stroke thickness. That doubled the cutting time but increased but help with the rebonding issue.

[Polygonhell]

There's nothing mechanical limiting the minimum speed, the firmware has to pick something to avoid accumulating too much error.
This is the code that sets it

minimumSpeed = accel*sqrt(2.0f/(axisStepsPerMM[X_AXIS]*accel));

So you can reduce the minimum speed by reducing the acceleration in the firmware but it only changes with the sqrt of the acceleration.

[heathenx]

There's nothing mechanical limiting the minimum speed, the firmware has to pick something to avoid accumulating too much error.
This is the code that sets it

minimumSpeed = accel*sqrt(2.0f/(axisStepsPerMM[X_AXIS]*accel));

So you can reduce the minimum speed by reducing the acceleration in the firmware but it only changes with the sqrt of the acceleration.

Interesting. Thank-you for that. Although, I've been wondering about something. I wonder if I could just add an M201 line to my gcode instead of messing with the firmware. M201 sets maximum acceleration. Does that sound crazy?

[Polygonhell]

There's nothing mechanical limiting the minimum speed, the firmware has to pick something to avoid accumulating too much error.
This is the code that sets it

minimumSpeed = accel*sqrt(2.0f/(axisStepsPerMM[X_AXIS]*accel));

So you can reduce the minimum speed by reducing the acceleration in the firmware but it only changes with the sqrt of the acceleration.

Interesting. Thank-you for that. Although, I've been wondering about something. I wonder if I could just add an M201 line to my gcode instead of messing with the firmware. M201 sets maximum acceleration. Does that sound crazy?

The code uses a cached value, so I wouldn't bet M201 will work, it might.
It's easy enough to change the value in the EEPROM settings, you might have to reset the board after the change. You can probably set it very low, since you'll always be running slower than the Jerk setting when cutting, 0 might even work, but I wouldn't bet on it.

[heathenx]

Polygonhell, you're a genius!

I just tried changing the Acceleration and Travel Acceleration values in the eeprom and I have a buttery smooth slow speed. Problem solved! Thanks a bunch.

Update: I jut cut the star shape out of 3mm acrylic again with these new acceleration settings. Running the bot this slow makes it nearly inaudible. One can barely hear the stepper motors. Anyway, I was able to drop the passes down to 10 from 60 and it cut cleanly through. This works much much better.

[bubbasnow]

which goggles are you using?

[heathenx]

Goggles? Who needs those? I stare right into the beam. No laser's gonna beat me.

When you buy the L-Cheapo kit he'll send you a pair of safety glasses that are rated for 445nm and now I understand that you'll get two pair once the Indiegogo orders are fulfilled. I also bought some protective plexiglass from JTechPhotonics and built a safety enclosure to protect myself and my co-workers. Here's a link to both the goggles and protective sheilding: http://jtechphotonics.com/?product_cat=accessories

Here's a 10 pass cut after I slowed the acceleration down. The gear cut pretty cleanly.

[mhackney]

I know you are joking but for everyone else - please where goggles! A friend of mine in graduate school worked with "low power" lasers. Enough power to burn paper. He was a little lax in his lab safety. One day he got a stray beam reflected into his eye that left a black spot right in dead center. It has been 30 years and it has caused him lots of problems. He doesn't have words to describe the effect it has on his vision, sometimes things in clear focus simply disappear. Which is very dangerous. He wears an eye patch to drive because of that.

Cheers,
Michael

[geneb]

[img]http://kategreene.net/blog/wp-content/u ... 00x200.png[/img]

[heathenx]

Yes, not only should you protect your own eyes but make doubly sure you protect your environment if you have co-workers or other people that can walk into your room. I highly recommend an enclosure. Mine just consists of a cardboard wrap around with a cutout for my safety panel. Even with that panel in place, if I want to watch the laser path I'll put on my goggles. Don't take chances people.

[jesse]

I received my kit in the mail. Where did you buy the #6-32 x 6 inch machine screws?

Can you post info on how you're doing the cutting? http://forum.seemecnc.com/viewtopic.php ... 081#p47081

[heathenx]

I received my kit in the mail. Where did you buy the #6-32 x 6 inch machine screws?

Can you post info on how you're doing the cutting? http://forum.seemecnc.com/viewtopic.php ... 081#p47081

I ordered the 6" screws from McMaster and then cut them down to size with my wire strippers/crimpers. (http://www.mcmaster.com/#machine-screws/=tdo4z6) Pan head zinc coated should suffice and they are easy to cut. I think you get 5 of them. You'll need 4 with my mount. The rest of my fasteners I get next door at Fastenal. They're like 75 yards away from my office. Any hardware should have these though.

I'd be glad to share everything that I know regarding lasering. However, I've discovered a big problem with scale. Whether it's Inkscape or Repetier my laser cut parts aren't true to size. I have been working on this problem on and off for two days now. I've tried scaling things in Inkscape first but it's not consistent. Gcode appear spot on. I'll be glad to work with you on it. Maybe between the both of us we can figure it out. I'll post over on your new thread.

[critical_limit]

Hi,

for your on/off Problem of the Laser. Isnt it possible to connect the laser to the layerfan wires instead to the Hotend wires? So you can switch on/off via gcode and/or in repetier.

cheers
Dirk

[heathenx]

You can do it a couple different ways. Either connect it to a fan input or a hotend input. I opted for the hotend approach. Oly gave me a couple thermistor connector pigtails which I want to try using on the fan2 import someday.

[critical_limit]

I ordered a Kit tonight also.

After finishing my magnetic Ball ends Mod, I will give it a try.
Want to cut acrylics with it only. Maybe some engravings. But we will see.

Do you have something special to protect your glas of the heated bed? Or just a plate of aluminum? What do you use?

cheers
dirk

[heathenx]

Any number of things will work. I had cut a piece of cardboard and 1/2" thick wood long ago to protect my glass bed when I was working on my hotend. I also leave it on there from time-to-time to keep the dust off of it when not in use. On top of that I slide a piece of 1/4" luan (cheap) as my safety surface. The laser burns into it but doesn't cut...very deep (if you leave your laser on it will eventually get through it). The main thing you want is the surface to be flat. If the wood or other material is warped then you will get uneven cuts. Stay away from the warped stuff. The wood and cardboard is freely available at my workplace and that's why I used it. One day, I'd like to get a 11" round aluminum plate made or something equivalent.