Lightobject.com Support Forum

I currently have my K40 conversion running what seems fairly well with a DSP 2012 board. I thought I'd post here so other people can see the settings and if other have recommendations to change let me know.

I used the original steppers which came with the machine they are designated as follows with the JMC 2M415 settings:
Y Axis: TYPE42BYGH48910-39A
Y Stepper Driver: JMC 2M415
Y Driver Settings: 8 Micro Steps, 1.06A
Y Driver Switches: Off On Off On On Off

X Axis: TYPE42BYGH34907-102
X Stepper Driver: JMC 2M415
X Driver Settings: 8 Micro Steps, 0.42A
X Driver Switches: Off Off On On On Off

Based on math with MXL belt, 20 tooth pinion on the stepper these motor are actually 400 steps per revolution not the 200 I originally thought. While initial testing indicated micro stepping set at 4 would work better, I experience extreme problems with registration on complex jobs. Moving back to 8 micro steps (2000 steps per inch) has solved this nicely. I can now make the exact same part several times in a row.Update: Micro-stepping was not the cause, the X shuttle was loose on the gantry causing the higher torque larger steps to cause wobble.

Currently I have the following settings setup inside the DSP.
X Pulse Unit: 12.672206
X Pulse Edge: Falling Edge
X Datum: Negative
X Key Direction: Negative
X Start Speed: 10
X Max Acceleration: 8000
X Max Speed: 300

Y Pulse Unit: 12.708269
Y Pulse Edge: Falling Edge
Y Datum: Negative
Y Key Direction: Positive
Y Start Speed: 10
Y Max Acceleration: 1000
Y Max Speed: 150

User Parameters
Space Speed: 100
Start Speed: 10
Speed Factor: 2
Space Jerk: 10000
Engrave Jerk: 10000
Min Acc: 100
Cut Acc: 1000
Space Acc: 1000
Eng Acc: 8000

12-1-2012: Updated properties based off switch to 16 micro steps instead of 8.
12-1-2012: Updated properties to 4 micro steps to fix missed steps in X direction on complex curves
12-2-2012: Updated back to 8 micro steps. 4 Caused severe registration problems on jobs with many circles. 8 does the same cuts dead on every time.
12-4-2012: Increased acceleration and max speed after fixing mechanical wobble
4-26-2012: Updated stepper settings based on Marco's findings of the stepper parameters.

Questions for those who have treaded before me.
1) What micro-stepping are you using? How much is to much and how much was not enough?
2) What do you have your acceleration set to?
3) How did you test to make sure your max speed and acceleration where ok?

There isn't much benefit in going over 8-10 micro steps with a stepper motor. All you do is chew up more processing power for little gain in resolution.
Mariss explains much about Steppers in his documents over at http://www.geckodrive.com

Acceleration is usually set to around 10,000 to 30,000 and you need these large settings or you will get a "slop over" fault when engraving if set smaller.

To test you just have to do some test runs at different speeds and see how it goes. Start at 400 then go to 800 then out to 1200 and keep going until the steppers fault. You won't hurt them by losing steps or stalling them but you have to do it in the middle of the table when testing to make sure you don't get slop errors (just means the laser head has to travel too far off the work piece to be able to get up to the acceleration speeds before it will lase the work/job and it will go past the software limit settings causing the fault).

Once the top end is found then you can set your Max speed to about 75% of that figure for a more reliable set up. I can push my laser head out to about 1500mm/sec but it needs about 250mm either side of the job to get up to speed. I haven't tried to adjust the start off settings to reduce that amount of slop over yet as I am quite comfortable engraving at 300mm/sec for most jobs. It's a lot less strain on the mechanics and belts, which really isn't much anyway, but that's just how I like it.

I hope this clears a few things up for you. When you get it all working properly you will love what you can do with it and you will always be searching for things to cut with it.
Just one word of WARNING ********** NEVER cut vinyl (PVC) sheet stock as the chloride in it reacts with moisture in the air and creates hydrochloric acid which is bad not just for you but for your machine as well. I cut some sheets for a friend about 1 year ago and used a carbon activated filter and full face mask but I left the shed while it was cutting and used it when I returned to do the pick off. After cutting about 20 sheets 4 at a time there was a brown coating all over my brand new linear guide rails and exposed steel work. It had started rusting straight away and has never recovered. It's just not worth doing it.

Rich.

I have updated my stepper drivers to run at 16 micro steps which seems to have made the machine run a little smoother even if there is not increased resolution. According to my calculations this means i'm running at 4000 steps per inch. I also reduced the engrave acceleration to 8000 which seems to have helped keep the engravings straight at higher speeds. I will do some more testing on this later this weekend on acceleration settings.

If I try to cut at anything over 30 mm/s I get "wobble" when the head makes a 90 turn where the vertical (Y) axis lines have wobble right after the turn from a full speed horizontal (x) cut. I assume this is because of slight play in the X shuttle and the way it's attached. That will probably not go away until I upgrade to a full 2.x laser build (probably not till mid next year).

Here are some pictures of my upgrades.


Here is a shot of my current cutting bed and make shift air assist. I just received the egg crate today and so far i'm loving it. I used some aluminum angle and used threaded rod to create a ledge for the egg crate to site on. What you see in the cutting bed is the "shims" i place under the egg crate to adjust focus height. I have 2 1/8th shims and 2 1/16th shims for each side. My air assist is a set of surgical tubing and some parts off an old airbrush to restrict airflow and increase pressure. It hangs off the focus head assembly with some stiff wire. I fashioned a hanger from the wire to keep it from folding under the laser head itself as well. This works well for makeshift until I can order a real air assist nozzle from here or buildlog.


These two shots show the faceplate I cut to hold the DSP control panel and the digital amp meter. This was cut out of 1/8th black cast acrylic.


This last shot shows the electronics. Thankfully my K40 came with a 24v power supply and a PWM capable laser power supply so the conversion to DSP was painless. I reused the flat ribbon cable to run the Y stepper and X axis limit switch I just solder leads on the end. I will replace these with proper cables once I order some cable chains.

I'll get some pictures of the air exhaust plate I modified as well.

Gadroc wrote:
If I try to cut at anything over 30 mm/s I get "wobble" when the head makes a 90 turn where the vertical (Y) axis lines have wobble right after the turn from a full speed horizontal (x) cut. I assume this is because of slight play in the X shuttle and the way it's attached. That will probably not go away until I upgrade to a full 2.x laser build (probably not till mid next year).

Sounds like looseness in you X axis ("spongy" till it settles down after a turn). Try tightening the X axis belt. There is an adjustment on the right end of the gantry.

Overall, your setup is looking really great.

Thanks Tim.

I'll try adjusting the x belt tension tonight. Do you have any good "accuracy test" patterns?

Gadroc wrote:Thanks Tim.

I'll try adjusting the x belt tension tonight. Do you have any good "accuracy test" patterns?

Sorry, I don't. For this, probably about anything like a classical Southwest design (square notches). You just want to see if you can get square corners and straight lines.

Well I found a few items. First it wasn't the belt tension it was the cut acceleration that was to fast. Setting the max Y acceleration to 800 removed the wobble and I can do cuts up to 200mm/s on paper with out the wobble. I actually had to loosen the X belt a little.

Second I noticed I was missing a few steps in the X direction on complex shapes with curves. The only way I could fix this was by setting my steppers to 4x micro stepping which set the machine back to it's default 1000 steps per inch. After tweaking that I started testing different speed engravings. After I set max X acceleration to 5000 I was able to engrave at up to 300mm/s with out misalignment. I also moved back to falling edge on the X/Y axis settings.

I'll try these settings for a while and see what it runs like.

I have gone back to 8 micro steps after having really bad problems with accuracy when running at 4 micro steps. After a couple test cuts on paper all seems back to normal.

Found the other cause for the "wobble" one of the rollers was a little loose. I went through tonight and realigned the laser shuttle by loosing all the set screws and adjusting the tension on the rollers so it was solid but not tight and made sure it was square with the X rail then retightened the set screws. This let me get the right tension on the belt a well.

I also lowered the laser tube so the laser was in the middle of the mirrors and did a full alignment again this time getting it spot on everywhere... YEA! Who knew tinkering with the machine would be almost as fun as making stuff with it.

Very very happy with results after the mechanical fixes. I was able to re-increase the acceleration and speed settings. I am successfully engraving at 300mm/s on paper with .09 step size and everything is straight and true. I've cut several pieces with differing thickness materials with exact registration, I can lay the pieces on top of each other and not notice a difference in hole alignment.

Original post updated with current settings and added user parameters as well.

Just wanted to say thanks for the settings and the pictures. Just got my DSP/K40 running and it ran right out of the box.

Glad it was helpful!