K40 and LightObject Z table with end stops

Hi Everyone,
I just wanted to put a place holder here to cover a potential gap in the documentation that has taken me a while to figure out.
Z table will not jog up or down, other axis also locked. Remove the z end stops by # the line in the config and everything works fine. Homing Z will not work, it tries but crashes into the end stops.
I may have the stepper wired wrong but I could not get this working till the jog movement was up when entering negative values. So go from 0 to -1 the table should move up.
Everything fell right into place when I made this change and I tried every combination of things outside of this prior…for several hours.
I changed gamma_dir_pin 0.020! to 0.020 this changes the direction of the stepper on the z axis.
I ended up on a totally different forum looking up smoothy issues to find this little nugget.
I wired mechanical stops to normally closed (normally open will lock all axis when the end stops are enabled), I put the top switch in the z min connection on the board. If you set the switch to normally open which is what I expected as default the board thinks something is hitting the sensor and this locks everything out.
Changed the gamma_steps_per_mm to 3169 (this is going to need a slight adjustment as a step is not 1mm but its close), gamma_homing_direction to home_to_min, gamma_min to 0, and gamma_max to the travel distance displayed when jogging from the top to bottom stops meaning the total distance. I have not started working in lightburn yet so I am not sure if this translates to a working system.

Other observations on my K40.
I needed to extend the x and y stepper cables
Had to modify the back rail so the z stepper could fit in snug and still be in range of the y end stop
Needed to ben the end stop so it could contact the carriage before the laser head hit the z table
Needed to use a washer to lift the front of the z table so it sat level
Needed to remove the front top bezel covering the stepper to get the z table in without removing the gantry
I had an AC leak to the frame of the K40, this went away with soldering the connection on the ground cable coming off the laser tube or by replacing the board
Cloudray mirror set required me to lift the laser tube and create a new mount for the laser head. The Air assist nozzle needs to point to the right so that the x axis end stop can still function
Lastly the cohesion 3d add on screen is worth it so you can easily test everything

I hope this saves others some time,

Thank you for posting this! I just assembled my LightObject Z table and am in the process of setting it up. This will save me quite a bit of frustration I am sure! One thing I noted right off the bat… I have an OMT K40 with an anodized aluminum air assist head. Could not get the Z table in without first removing the nozzle and tilting my side mounted red dot up. It fits then with just a hair clearance! Once in, you can replace all the nozzles and put the pointer back down.

Yes that’s an issue too. And you have to take off the panel that covers the rail to get it out. I removed the locking collar to move the air nozzle up as far as possible but that did not allow me to aim the input in a position where I could keep it out the way. Can’t tell you how much I have had that nozzle on and off.
Drop me a PM if you need any help. I made my own end stop bracket. I also used a caliper to set the x y z steps per mm. They were all off slightly. I think the best move would be to drop the table through the bottom of the unit. Add longer legs. Add honeycomb to the platform. Set this to 1mm at the bottom of the air nozzle. Use brackets to mount the z table lower. Cut and splice the y rails to increase the usable room. Make a new belt. But first I need to have some fun after all the modding.

Are you using the stepper driver built in to the board, or an external stepper driver for your Z Table?

I am using the driver on the board set to 1.2amps. And I have reduced the speed considerably as I was finding the mechanism would slip a little when it first moves. Reducing the speed remove all issues.
Again it’s the direction it moves in that seemed to be the key so everything else would line up.

I’m looking at cutting the bottom out as well. As for the z-bed itself, it is now a solid piece of hardware but man, I had to make a few mods! First of all, had to drop a washer into each of the bearing holes on the bottom to lift the bearings up just above the rails as the sprokets rubbed on the bottom. Added some thicker washers to the top rail posts and longer screws. It’s now moving very smoothly with no binding at all. Did all the step calibration outside the laser first using calipers like you did. Finally!

Right it’s a bit of a mess. I need to check the bearings as mine is binding also. Honestly I am a little tired of how much work this thing was just to get semi functional. Ended up with a bed size of 150x256mm. Bothers me as there is tons of room left over. Got some honeycomb metal coming as the birch I have is making a mess on the stock metal on the bed. Not sure if there will be room to add it in yet. My flow meter from banggood is lost. So still waiting on that. Also I noticed a lot of jittering when cutting diagonals. So I had to reduce the speed a lot. Not checked the belt tension yet as slowing down the speed worked. Could be the bed moving. I had to use washers under the bed on the front side to level it. I used a large and a small and some stick holes in the case. Large washer goes under. Small washer holds the side of the bed. The way it sits means it’s up on a piece of sheet metal close to the laser tube and on the base in the front. Honestly wished I would have just dropped the bottom out, extended the size of the bed, and made a new belt.

Extending the bed and making a new belt is dangerously close to just scrapping the whole thing and making a custom machine. Beware the rabbit holes! :slight_smile:

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Lol that’s why I am avoiding it! This has already been a much larger voyage than expected.
Still need to check on the potential binding issue but I am a little tired of working on it.
I am wondering how much it would cost to have someone mill out some aluminum so it’s a straight drop in modification to extend the bed in the y direction. I have fairly handy with illustrator and fusion 360.

Here’s an update on my LightObject Z table. Finally have it functioning as it should but had to make a few adjustments. Now it’s smooth as silk. Here’s what I did:

  • Dropped a thin washer under the bottom bearings to lift them just a hair above the bottom rail. The pulleys were dragging and this fixed it.
  • Bought longer screws for the top and dropped and extra washer on the top posts to increase clearance and make up for the raised bearings on the bottom. This fixed the binding.
  • Increased the current in the config file on the board from the default 0.6 to 0.8 to match, but not exceed, my stepper’s max current or the boards capability.
  • Tuned the stepping parameters using the excellent documentation on the C3D site (thanks!)

Now for the additional issues I need to conquer and I think it will be perfect… Because of the shallow case of my K40, the top rails of the z-table interfere with head travel if I have my air assist nozzle on, AND it is in the total way of my new American Photonics adjustable lens, even without the air assist. Short term fix was to just program the head in Lightburn to stay within the frame and not home on start. Long term fix will be to drop the bottom about 3" and add some standoffs to the z-table bed so I can hold larger items above the z-table top rail. Seems like a lot of work eh? You would be right!

Hey Allen,
We have all came to exactly the same conclusions. Been toying with the idea of dropping it lower extending the legs on the case, angle a fan in there, but leaving it open front and back. This way I can slide in longer materials if I can get the focal point right. The clearance of the top rail is a big problem when you add another laser head with air assist and a laser to see where it’s going to cut. Called a local machine shop to see what the hourly rate and material costs are. Maybe get someone else to do the heavy lifting for a change. Been thinking an s bracket would work well. Also my 3d printed laser head holder has some flex to it. So if I go above a certain speed like when engraving it produces some wobble. The more distance between things the more risk of introducing this into these cheap boxes. Dreading the idea of replacing it and trying to align it again.

Glad to see I’m not the only one! LOL!. On the red dot. Mine came with a fairly heavy-duty aluminum machined bracket. Quite by accident, I decided to flip it around and mount it on the top of the head bracket and it works great! Not only does it fix the clearance issue on side rails, in case you want to pinch a few more mm out of the bed size, but also gave me a better focused dot. The little laser module was focused for a longer focal length I think and when I switched to a 1.5 FL, it was a little fat.

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