[awerby]

Have you made a picture of this thing? I'm trying to visualize it - especially the part about it building its own Y axis as it goes - but not having much success.

I'd suggest using steel beams rather than aluminum ones. Steel is much stiffer, and it's also cheaper. I have seen 3D printers based on MIG welders, so that's not hard to picture, but I'm not seeing how this could possibly be rigid enough over that huge span to carve away at the weldment without chattering madly, especially since you're using wheels on your beams instead of real linear rails.

[joeavaerage]

Hi,
great sounding project.

I agree with Andrew, use steel in the construction, it is way cheaper to build a structure of given rigidity out of steel than aluminum.

To be honest I think a 400w spindle is a bit of a joke. This project will cost many thousands, what matter if you up the ante in the spindle power to 2.2kW, they are only a few hundred
dollars?.

I am rather dubious that the bearing arrangement you have described will be sufficiently accurate to ensure optimal mesh of the helical gear and pinion. I would have thought that the mesh
needs be +-0.02mm or there abouts....and that would probably exceed the bearing idea.

The only other idea to a rack and pinion is a rotating nut ballscrew. They are used on very large machines and I suspect prohibitively expensive for your project....could be wrong of course.
Even transporting a 15m long ballscrew will give you grief.

Craig

[G-Spot]

Hi,
great sounding project....

Thanks Craig

Yes I usually look at the most expensive option then the cheapest and try to get something in the middle.
I also hate noise. I recently switched from electrically produced air to petrol because I have a residential electricity supply, now I am always looking for electric tools and not the air ones because I can't stand to work with the racket the petrol compressor makes. So I am definitely going to go water cooled.

I also hate gearbox problems. When they go wrong its hard to tell why when all you are left with is pieces. So I am going to take yours and Peter's advice and go with linear rails of some sort.

I already started this project before COVID hit but had to shelve it until now. But I did spend a couple of months researching balls screws and as you pointed out getting long ones delivered without damage is the biggest problem. Half the stuff I get delivered to me here in South Africa comes with physical damage. And shipping is criminally expensive because of how bad the Customs and Duty clearance is. Anything more than 700mm in dimension is usually $250 for shipping.

Paul

[G-Spot]

Have you made a picture of this thing?

I only know how to use ACAD 3D-Studio and it's the Johnny Depp version which I need to rehack onto my PC. So that will take at least a week to get working again.
I am keen as this is probably going to be a commercial project, eventually, if I am lucky..lol.., to use something a lot simpler and cheaper. What do you use?

Imagine a 4 post car lift. Going to attach a square frame which prints the x and z axis. Standard 3D printer design but moving the top of the printer up and down and not the bed.

I live within 50 miles of the biggest Aluminium smelter and mill in the country so I am not getting much difference between the price of Aluminium and steel for the same dimensions, like only 15% more for the Aluminium.

From my experience in sailing I am not convinced that a steel structure is more rigid than aluminium. In sailing the more rigid boat wins. If your mast or boat flexes you spill the wind. But there isn't a single modern racing boat with a steel mast, the trick is they use steel stays to brace the Aluminium mast. They use a little bit of steel where it works best, in tension, to make the aluminium structure more rigid than steel would be. Of course Carbon fiber is what is used now but before that came along it was all aluminium masts.

I also happen to be working on my own DIY construction project where I am making a pre-stressed concrete beam 20m long x 1.5m x 0.2m. I spent the last 2 years sinking 15 6m deep reinforced concrete piles into the ground with about 50 tons of concrete on top. I now have the ability to prestress large objects up to 20m in length to 100s of tons. Had to design and make a machine capable of digging 6m deep holes only 30cm x 30cm through stone or soil that could be operated by 1 person. Been there done that got the t-shirt. Only cost me $100 for the steel and 3 months from start to first hole finished. In case you are wondering why I didn't just hire a pile digger, there was a massive flood here 18 months back and for 3 months you could not hire any. Anyway my machine can go through stone and concrete while the ones you hire are augers and cant. Also my machine could do undercut piles which only piling machines costs hundreds of thousands can do which cost thousands to hire.

Was thinking of using large Aluminium box sections only 5mm thick. Fill them with concrete with dozens of high tensile steel rebars running down the length then pull them between my end posts leave for 30 days then cut the rebar away from my end posts, thread the ends and then use them for my machine.

Not sure why so many DIY builds go for the post stressing option on their concrete interiors. The amazing thing about prestressed concrete is after the cement is dry you no longer have to carry around the machine that did all the stressing. The energy it exerted is now locked in your cement. So if you now encase the prestressed concrete in your machine you are adding the energy stored inside to resist flexing to your machine. If you use the post stressing method then your machines tensile strength is being used to stress the concrete. And because the rods running through your concrete are not attached to the cement they provide a pathway for vibrations to travel directly through the concrete bypassing any dampening properties your cement may have.

If you try to insulate a house exterior wall from vibrations if you have anything rigid between the 2 walls like bolts etc then it bypasses whatever insulating material you put in the middle. Same with submarines, no use filling a layer between the outer and inner hull with vibration absorbing material if you then attach the inner hull to the outer hull with hundreds of bolts.