I've started to build a machine I plan to use to print aluminium structures. It will use a welder and feeder to print Aluminium. Then after the Aluminium is cold it will mill away any errors/excess the welder has made.

It's going to be used to print aluminium structures 2.2m x 2.2 x 15m

I think I am going to need a lot of help especially on selection of components.

Here is the design criteria;

1. Accuracy only needs to be about 1mm but over the full 15m.

2. It could take a year to print each structure. So weeks to setup is acceptable.

3. It will be OUTSIDE because the y axis is going up 15m vertically. The Y axis HAS to go up vertically because molten metal and gravity.

5. I will build the y axis as it prints. Like the top of a crane or building form work climbs the structure it is making.

6. I will set 4 aluminium posts into the ground with helical gear rails attached to the sides. This will be the y axis which the rest of the printer will climb, I will weld the structure that is being printed to the posts as the height increases. I am printing ridiculously rigid structures which will be far more rigid than the CNC printer itself, so the height will not be a problem as the structure being built is welded at intervals to the climbing posts. Even when the gantry is at full 15m height it will only be a meter from being physically attached to the structure being printed.

7. There will be no physical machining contact between the welding head and the object being printed. The only physical machining contact with the printer will be the spindle used for milling what the welder laid down.

8. The milling spindle is only there to follow the welder around and clean up any excess, shaving off a few millimeters. No deep cutting/milling required. Same grade of aluminium every time behind the welder.

9. Both the welding/printing head and milling spindle will be located close to each other. It will either be printing or milling never both together.

10. I plan to use AI and a camera to make measurements from a reference(not on the machine) and adjust the welding/milling as required.

11. If the machine distorts/bends/vibrates while in operation then I will cut it, straighten it then reweld it.


From my design requirements I believe the smallest motor spindle is all I require. Am I wrong? missing anything? The welder has to be water cooled so cooling water is going to be on the gantry may as well get a water cooled one and avoid the noise. If am only going to be removing a few mm from the just printed aluminium then a 400W motor should do? Yes/No? Is the quality of the aluminium finish going to be reliant on the quality of the motor? Will a good cutting tool and small cuts give me as good a finish as a high quality motor taking chunks off?

I also decided to use Helical gear rails throughout for linear movement because of the long lengths involved and the possibility to add extra rail when needed. Are there any better solutions, cheaper? I can just afford the helical gears solution so unless there is a better and cheaper option then I think I am just going to bite the bullet and go for helical gears.

I am trying to find the cheapest rail solution. I think linear bearings are too expensive(15m x 2,5m x 2,5m) and the accuracy way more than I actually need. I am thinking of using the aluminum beams that I am going to build my gantry on as the rails and use regular bearings as wheels. Will I have problems with the helical gears if the gantry is not on linear bearings? I see this is how most cheap 3D printers do it, but they use belts for motion and not helical gears. I never bothered considering a belt setup because my belt lengths would be 10m long. I could not find anyone that was using these type of belt lengths for CNC or 3D printing. And the 25mm belt cost $12 per meter. Can belts be used successfully at those sort of lengths? Saw a Youtube video where the stretch on a 500mm belt was visible.

Anyway I am going to visit the scrap yards and Aluminium suppliers this week and find 12.5m of the biggest aluminium box sections I can afford and weld them up into a 2.5m x 2.5m square for my frame and then another 2.5m beam that will traverse them. First build my x and z axis without servos, connect a cheap motor and measure how much vibration and deflection I get when taking off a few mm of aluminium weld, then strengthen/dampen as required. Weigh the beam I end up with and then get the servos/motors to shift that.

I would be very grateful for any information/opinions on rails and motion solutions that would suit my application.