Hi all, I need to build a huge "CNC" like machine to cut shipping containers. It does not have to be super accurate, we are shooting for 1 mm. Additional challenge is that the machine must me mobile to be moved from construction site to the next. So far the idea is to create two "sledges". A horizontal running on tracks secured on the floor with concrete footers and the same concept vertical secured on the horizontal sledge. The floor rails would be 12 feet sections, so can be unmounted and transported. The sledge with the vertical rail would also be 12 feet, so also transportable. So far we are working on the base tracks. We are thinking of 1x3 x 0.12 square tubes with 3x3 (we have those left over) sleepers. Same would go for the vertical. Challenge currently is what wheels to use to run on the tracks ? It should be "cheap". Metal Casters seem not to work, not exact enough. Bearings are to expensive for something big enough and at least 1 inch wide. The idea is to have 12 wheels on each sledge, 4 on top, 4 on the sides and 4 on the bottom so the sledges run fully locked on the track. Any thoughts ? Anybody build a big machine yet ?
When you say "cut" what do you have in mind? Torch? Grinder? What... And to what extent are you cutting the containers? Just openings? Full section cutaways? In half? All of this makes a big difference in the type of suggestions.
I did some try cuts with grinder, saw and plasma. The saw was the fastest with the cleanest (then weldable) cut, but plasma might work with the machine. With the hand its just not accurate enough. We need to cut some containers in full, but it's an overkill to build a machine for it. We will just put it at one side and cut openings and then turn the container to cut the other side.
Is this for like, architected shipping container homes or something? Still not quite visualizing these cuts. Define "in full". Through-cuts, miters, partial v-cuts, windows...? +/-1mm, while kinda necessary for MIGing back together, is also ambitious for such a large-scale, relatively inexpensive, modular-type project. I'd spend more time worrying about calibration upon setup and less about how the thing is actually constructed, you've got the cart a little before the horse here. The former should probably inform the latter. My guess would be some kind of autocollimator rig that mounts onto each section of track, so that you can laser-align the whole thing in relatively short order. A plasma head would keep the gantry lightweight, and thus the track easily movable, during alignment. Could you do it a different way, perhaps with a machine-vision line-follower bot? Might be easier to elevate the container off the ground, draw the cut lines on all the way around, and let it rip, than carefully align a precision track, tram the container into parallel with it, cut, turn the container, re-tram and reset "z" height, cut, etc. You'll need to leave tabs to turn the container with, too, or you'll have cut three sides and suddenly realise it's a lot harder to turn now... It's not unlike a portable sawmill, and they're not particularly convenient to use, either. In any direction, it's a hell of a project. Few ways to do it, but none of them "nice". I'd consider buying a really big bandsaw.
Rob, thanks for the great info. I found a pic which is close to how the machine should look like. The vertical sledge will be smaller and have a linear z-axis movable tool holder (multiple tools, plasma, grinder etc). I see your point with the accuracy. I think with that size it is better to install a feedback system. I.e. accept that the machine is inaccurate and instead of moving by controlling steppers to a position, move until the sensors confirm the position. The z axis I think we will do with stepper, its just max 50cm move, so for the 40+ feet horizontal and the 9+ feet vertical, the idea is to install laser distances sensors. On machine start one move to a position which is considered the 0,0,0 point on the container and subtract the sensor reading. This is all software which is my expertise domain So maybe best to start a new thread for the sensors ? Preferable they should have less than 1 mm accuracy. I do not see any in the store, for sure something not used to often.
Makes sense. "Long" distance (more than long enough for your needs) +/-1mm laser rangefinders exist: https://www.amazon.com/dp/B008ZCS278/ref=emc_b_5_t I'd build the system around something like that. A portable, possibly even flexible/rollable track, a laser rangefinder that gets the carriage into position, a pair of cheaper rangefinders that bring the carriage into square with the container (imagine an Edge Pro Tram, but with lasers instead of dial indicators), and then you lock down and roll in 2.5D from there, like a WorkBee tilted up on its side to face the work (y is vertical, z is still z, and x is like the sideshifter on a forklift). Can probably get pretty close to what you want with a semi-manual system like that. There may even be rangefinders with serial outputs like some digital calipers have, for either further automation, or a de-skilling of the operation, depending on how much I/O control it gives.
