Size of objects in lightburn double the size when i laser them, any advice

k4 extended bed openbuilds v slot

Board: 3d mini, running the cluster update firmware i believe

Firmware: _Smoothie

Problem/ Question: _Hello laser people, i extended my bed a while ago but i didnt like how that went due to being very hard to align so ive ripped all that out and started again with a v slot openbuilds approach.

Ive got rid of the old k40 belts an steppers and replaced with gt2 6mm setup and nema17 1703hs168a.

there are two steppers driving the y axis and they are wire in series i believe.

first of i wired the steppers incorrectly and the y axis wouldnt home, when i figured that out and got the laser homing correctly, i did a simple square and its double the size and nearly went past my limits, when its quite near where the head homes, any ideas guys? is there something in the firmware i can look into?

I’ve read through the origin page done the M119 check, adjusted my acceleration and y axis limit to 220mm with the x axis set at 590 in lightburn, i can not find find where to set the x axis in the config (I’m very green when it comes to the config file)

lightburn 0.9. 06

Wiring that got me homed correctly

Wiring that I thought was correct for the steppers in series but the y just juddered and didn’t move fast at all.

left y axis stepper

X axis stepper

config.txt (25.2 KB)

my config file, i believe ive altered the acceleration/size of bed on the y (couldnt find the x axis or how to do it?) and i believe to amp of for my steppers

maybe i should download the lastest update for the 3d mini?

I swapped the y axis around (turned it 180) as it was coming towards me and to the right when I first powered it up.

My machine homes to the back left, where both my limit switches are placed.

Wow - thanks for the flood of information here :slight_smile: makes it easy to see how things are connected. This is the model post for how to provide detailed information!

K40s usually come with 0.9° steppers and the ones you replaced them with are 1.8° steppers. If things are twice the size they should be, that’s likely why.

With a custom machine build like this it’ll take some tweaking to find the right value, but look at this section in the config file:

# Arm solution configuration : Cartesian robot. Translates mm positions into stepper positions
alpha_steps_per_mm                           157.575          # Steps per mm for alpha stepper
beta_steps_per_mm                            157.575          # Steps per mm for beta stepper
gamma_steps_per_mm                           157.575          # Steps per mm for gamma stepper

Cut whatever values you have there in half and retry the cut operation. Try it with something easy to measure, say, a 20x20mm square, then grab a caliper and measure what it actually comes out to be. You’ll need to tweak those values until a 20mm cut actually measures 20mm :slight_smile:

That said, be wary of running two steppers on the same axis on a CO2 machine. If, for whatever reason, one starts losing steps you could end up with a very dangerous situation on your hands. If you can rework the machine to use a single high-torque dual shaft motor and drive linkage for both sides of the gantry, that’d be a way safer option.

Good luck!

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Thanks loather, this is what I thought it may be as I did see in the config the steps were different, I was just not sure enough to do it off my own back.

I’ve been quite rightly put in my place before when I’ve had problems with my laser for not providing enough information and being frankly quite vague so I now know what to do,lol.

Thanks for the heads up on the use of duel steppers, I shall run it like this for a bit an swap over in the new year.

Thanks for your help loather, much appreciated. :grinning:

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