Setting Up the Correct Bed Size Questions

Can you please confirm my understanding of this. Here are my current assumptions.

Beta max is the offset from the homing location to the desired y origin. Beta max is used since the homing direction for beta is positive in the ccs.

Alpha min is the offset from the homing location to the desired x origin. Alpha min is used since the homing direction for Alpha is negative in the ccs.

What I did for setup was jogged the machine in lightburn to some positive coordinate that was on the work area but close to the origin. I used 20, 20. I manually burned a small spot on the workpiece that was positioned at the origin and I used a caliper to measure the location of the dot from the origin of the work piece. I calculated the difference between the programmed value of 20,20 to the actual burn position and adjusted beta max and alpha min to put my origin exactly at 0,0

I’m not sure how this relates to the work area setup in lightburn. I see many people saying that the bed size has to match in lightburn and the config.txt file but the way I am understanding is that the bed size setup in lightburn is from the established origin by smoothie and the end stop alpha min and beta max are what define the origin in terms of offsets from the machine home position

Please clarify for me


The instructional article here clearly states what to do for Beta (the Y axis) which homes to max: Setting Up the Correct Bed Size

Alpha (the X axis) is completely different and homes to min. You do not need to change anything in the config file for X to be able to travel past 300mm, you just need to set it up in LightBurn device setup as the new size for X - whether that’s 310 or 320mm of actual usable X travel for your K40…

So what if x =0 is to the left of your usable origin? How do you move it to the right?

Please provide me a very clear real life example of where and how that would happen.

I replaced the bed on my k40 with a home brewed version for the time being. I used aluminum angle and aluminum flat strip to create a border to sandwich some expanded metal. Since the angle is sandwiching the plate, the aluminum sits about 1/8” above the expanded metal which is actually kind of handy since it gives me a raised corner at the lower left of my machine that I can butt my work up against for a 0,0 reference for the workpiece position. After I did this however, I found that due to the frame border x=0 on the machine was actually in the neighborhood of 10mm to the left of my new mechanical “bed origin”.

I know that was kind of wordy but I hope I made it clear enough to understand

Actually it’s only a couple of mm off but I would still like to tell the machine to go to 0,0 that is exactly at the corner of my homemade bed

Ah, yes, I have had a similar case in 3D Printing where I had the nozzle home a few mm off the side of the bed to purge, but I wanted the printing to happen on the bed itself.

In this case, I think I set the alpha_min 0 line to be -3 or whatever the offset value was.

Since the board is homing to min for X, it is now at negative 3 when it homes,

So, before you do this, home it, and jog to the right by 1mm at a time, until you find the correct amount of offset to reach the actual bed, count how many that was, and set that as the negative offset value explained above.

Ok, so if I measure the width of my usable bed area in x(the distance between my frames, that would be the bed size input into Lightburn correct?

So in my case anyway, alpha min and beta max are offsets from the homing position to the 0,0 on my bed and the actual bed length and width between my frame members is what you would set in Lightburn, correct??

And if that is true, there is a great way to get your alpha min and beta max set perfectly as follows:

  1. Put a scrap rectangular workpiece in the laser up against the bottom corner.

  2. Move the laser to an arbitrary position on the workpiece close to the lower left corner, I.e. 10, 10 or 15,15 and manually lase a dot using the test fire button.

  3. Measure the distance from the left edge of the workpiece to the dot and calculate the difference between the intended location, 10, or 15, and adjust the current alpha min number to compensate for the error. Do the same with y and beta max.

Measure the working bed size in x and y and input into Lightburn.

Your thoughts?

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